The Project Gutenberg EBook of Concrete Construction, by
Halbert P. Gillette and Charles S. Hill
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Title: Concrete Construction
Methods and Costs
Author: Halbert P. Gillette
Charles S. Hill
Release Date: March 16, 2008 [EBook #24855]
Language: English
*** START OF THIS PROJECT GUTENBERG EBOOK CONCRETE CONSTRUCTION ***
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CONCRETE CONSTRUCTION
METHODS AND COST
BY
HALBERT P. GILLETTE
_M. Am. Soc. C. E.; M. Am. Inst. M. E._
_Managing Editor, Engineering-Contracting_
AND
CHARLES S. HILL, C. E.
_Associate Editor, Engineering-Contracting_
NEW YORK AND CHICAGO
THE MYRON C. CLARK PUBLISHING CO.
1908
COPYRIGHT. 1908
BY
THE MYRON C. CLARK PUBLISHING CO.
Transcriber's note:
For Text: A word surrounded by a cedilla such as ~this~ signifies that
the word is bolded in the text. A word surrounded by underscores like
_this_ signifies the word is italics in the text. The italic and bold
markup for single italized letters (such as variables in equations) and
"foreign" abbreviations are deleted for easier reading.
For numbers and equations: Parentheses have been added to clarify
fractions. Underscores before bracketed numbers in equations denote a
subscript. Superscripts are designated with a caret and brackets, e.g.
11.1^{3} is 11.1 to the third power. Greek letters in equations are
translated to their English version.
Minor typos have been corrected.
PREFACE.
How best to perform construction work and what it will cost for
materials, labor, plant and general expenses are matters of vital
interest to engineers and contractors. This book is a treatise on the
methods and cost of concrete construction. No attempt has been made to
present the subject of cement testing which is already covered by Mr. W.
Purves Taylor's excellent book, nor to discuss the physical properties
of cements and concrete, as they are discussed by Falk and by Sabin, nor
to consider reinforced concrete design as do Turneaure and Maurer or
Buel and Hill, nor to present a general treatise on cements, mortars and
concrete construction like that of Reid or of Taylor and Thompson. On
the contrary, the authors have handled the subject of concrete
construction solely from the viewpoint of the builder of concrete
structures. By doing this they have been able to crowd a great amount of
detailed information on methods and costs of concrete construction into
a volume of moderate size.
Though the special information contained in the book is of most
particular assistance to the contractor or engineer engaged in the
actual work of making and placing concrete, it is believed that it will
also prove highly useful to the designing engineer and to the architect.
It seems plain that no designer of concrete structures can be a really
good designer without having a profound knowledge of methods of
construction and of detailed costs. This book, it is believed, gives
these methods and cost data in greater number and more thoroughly
analyzed than they can be found elsewhere in engineering literature.
The costs and other facts contained in the book have been collected from
a multitude of sources, from the engineering journals, from the
transactions of the engineering societies, from Government Reports and
from the personal records of the authors and of other engineers and
contractors. It is but fair to say that the great bulk of the matter
contained in the book, though portions of it have appeared previously
in other forms in the authors' contributions to the technical press, was
collected and worked up originally by the authors. Where this has not
been the case the original data have been added to and re-analyzed by
the authors. Under these circumstances it has been impracticable to give
specific credit in the pages of the book to every source from which the
authors have drawn aid. They wish here to acknowledge, therefore, the
help secured from many engineers and contractors, from the volumes of
Engineering News, Engineering Record and Engineering-Contracting, and
from the Transactions of the American Society of Civil Engineers and the
proceedings and papers of various other civil engineering societies and
organizations of concrete workers. The work done by these journals and
societies in gathering and publishing information on concrete
construction is of great and enduring value and deserves full
acknowledgment.
In answer to any possible inquiry as to the relative parts of the work
done by the two authors in preparing this book, they will answer that it
has been truly the labor of both in every part.
H. P. G.
C. S. H.
Chicago, Ill., April 15, 1908.
TABLE OF CONTENTS.
PAGE
CHAPTER I.--METHODS AND COST OF SELECTING AND PREPARING
MATERIALS FOR CONCRETE. 1
~Cement:~ Portland Cement--Natural Cement--Slag Cement--Size and Weight of
Barrels of Cement--Specifications and Testing. ~Sand:~ Properties of Good
Sand--Cost of Sand--Washing Sand; Washing with Hose; Washing with Sand
Ejectors; Washing with Tank Washers. ~Aggregates:~ Broken
Stone--Gravel--Slag and Cinders--Balanced Aggregate--Size of
Aggregate--Cost of Aggregate--Screened and Crusher Run Stone for
Concrete--Quarrying and Crushing Stone--Screening and Washing Gravel.
CHAPTER II.--THEORY AND PRACTICE OF PROPORTIONING CONCRETE. 25
~Voids:~ Voids in Sand; Effect of Mixture--Effect of Size of Grains--Voids
in Broken Stone and Gravel; Effect of Method of Loading; Test
Determinations; Specific Gravity; Effect of Hauling--Theory of the
Quantity of Cement in Mortar; Tables of Quantities in Mortar--Tables of
Quantities in Concrete--Percentage of Water in Concrete--Methods of
Measuring and Weighing; Automatic Measuring Devices.
CHAPTER III.--METHODS AND COSTS OF MAKING AND PLACING
CONCRETE BY HAND. 45
Loading into Stock Piles--Loading from Stock Piles--Transporting
Materials to Mixing Boards--Mixing--Loading and Hauling Mixed
Concrete--Dumping, Spreading and Ramming--Cost of
Superintendence--Summary of Costs.
CHAPTER IV.--METHODS AND COST OF MAKING AND PLACING
CONCRETE BY MACHINE. 61
Introduction--Conveying and Hoisting Devices--Unloading with Grab
Buckets--Inclines--Trestle and Car Plants--Cableways--Belt
Conveyors--Chutes--Methods of Charging Mixers--Charging by Gravity from
Overhead Bins; Charging with Wheelbarrows; Charging with Cars; Charging
by Shoveling; Charging with Derricks--Types of Mixers; Batch Mixers;
Chicago Improved Cube Tilting Mixer, Ransome Non-Tilting Mixer, Smith
Tilting Mixer; Continuous Mixers; Eureka Automatic Feed Mixer; Gravity
Mixers; Gilbreth Trough Mixer, Hains Gravity Mixer--Output of
Mixers--Mixer Efficiency.
CHAPTER V.--METHODS AND COST OF DEPOSITING CONCRETE
UNDER WATER AND OF SUBAQUEOUS GROUTING. 86
Introduction--Depositing in Closed Buckets; O'Rourke Bucket; Cyclopean
Bucket; Steubner Bucket--Depositing in Bags--Depositing Through a
Tremie; Charlestown Bridge; Arch Bridge Piers, France; Nussdorf Lock,
Vienna--Grouting Submerged Stone; Tests of H. F. White; Hermitage
Breakwater.
CHAPTER VI.--METHODS AND COST OF MAKING AND USING RUBBLE
AND ASPHALTIC CONCRETE. 98
Introduction--Rubble Concrete: Chattahoochee River Dam; Barossa
Dam, South Australia; other Rubble Concrete Dams, Boonton Dam,
Spier Falls Dam, Hemet Dam, Small Reservoir Dam, Boyd's Corner
Dam; Abutment for Railway Bridge; English Data, Tharsis & Calamas
Ry., Bridge Piers, Nova Scotia--Asphalt Concrete; Slope Paving for
Earth Dam; Base for Mill Floor.
CHAPTER VII.--METHODS AND COST OF LAYING CONCRETE IN
FREEZING WEATHER. 112
Introduction--Lowering the Freezing Point of the Mixing Water; Common
Salt (Sodium Chloride):--Freezing Temperature Chart--Heating Concrete
Materials; Portable Heaters; Heating in Stationary Bins; Other Examples
of Heating Methods, Power Plant, Billings, Mont., Wachusett Dam,
Huronian Power Co. Dam, Arch Bridge, Piano, Ill., Chicago, Burlington &
Quincy R. R. Work, Heating in Water Tank--Covering and Housing the Work;
Method of Housing in Dam, Chaudiere Falls, Quebec; Method of Housing in
Building Work.
CHAPTER VIII.--METHODS AND COST OF FINISHING CONCRETE
SURFACES 124
Imperfectly Made Forms--Imperfect Mixing and
Placing--Efflorescence--Spaded and Troweled Finishes--Plaster and Stucco
Finish--Mortar and Cement Facing--Special Facing Mixtures for Minimizing
Form Marks--Washes--Finishing by Scrubbing and Washing--Finishing by
Etching with Acid--Tooling Concrete Surfaces--Gravel or Pebble Surface
Finish--Colored Facing.
CHAPTER IX.--METHODS AND COST OF FORM CONSTRUCTION 136
Introduction--Effect of Design on Form Work--Kind of Lumber--Finish and
Dimensions of Lumber--Computation of Forms--Design and
Construction--Unit Construction of Forms--Lubrication of
Forms--Falsework and Bracing--Time for and Method of Removing
Forms--Estimating and Cost of Form Work.
CHAPTER X.--METHODS AND COST OF CONCRETE PILE AND PIER
CONSTRUCTION 151
Introduction--Molding Piles in Place; Method of Constructing Raymond
Piles; Method of Constructing Simplex Piles; Method of Constructing
Piles with Enlarged Footings; Method of Constructing Piles
by the Compressol System; Method of Constructing Piers in Caissons--Molding
Piles for Driving--Driving Molded Piles: Method and Cost
of Molding and Jetting Piles for an Ocean Pier; Method of Molding
and Jetting Square Piles for a Building Foundation; Method of Molding
and Jetting Corrugated Piles for a Building Foundation; Method of
Molding and Driving Round Piles; Molding and Driving Square Piles
for a Building Foundation; Method of Molding and Driving Octagonal
Piles--Method and Cost of Making Reinforced Piles by Rolling.
CHAPTER XI.--METHODS AND COST OF HEAVY CONCRETE WORK
IN FORTIFICATIONS, LOCKS, DAMS, BREAKWATERS AND
PIERS 184
Introduction--Fortification Work: Gun Emplacement, Staten Island, N. Y.,
Mortar Battery Platform, Tampa Bay, Fla., Emplacement for Battery, Tampa
Bay, Fla.; U. S. Fortification Work--Lock Walls, Cascades Canal--Locks,
Coosa River, Alabama--Lock Walls, Illinois & Mississippi Canal--Hand
Mixing and Placing Canal Lock Foundations--Breakwater at Marquette,
Mich.--Breakwater, Buffalo, N. Y.--Breakwater, Port Colborne,
Ontario--Concrete Block Pier, Superior Entry, Wisconsin--Dam, Richmond,
Ind.--Dam at McCall Ferry, Pa.--Dam at Chaudiere Falls, Quebec.
CHAPTER XII.--METHODS AND COST OF CONSTRUCTING BRIDGE
PIERS AND ABUTMENTS 230
Introduction--Rectangular Pier for a Railway Bridge--Backing for
Bridge Piers and Abutments--Pneumatic Caissons, Williamsburg Bridge--Filling
Pier Cylinders--Piers, Calf Killer River Bridge--Constructing
21 Bridge Piers--Permanent Way Structures, Kansas City Outer Belt
& Electric Ry.--Plate Girder Bridge Abutments--Abutments and Piers,
Lonesome Valley Viaduct--Hand Mixing and Wheelbarrow Work for
Bridge Piers.
CHAPTER XIII.--METHODS AND COST OF CONSTRUCTING RETAINING
WALLS 259
Introduction--Comparative Economy of Plain and Reinforced Concrete
Walls--Form Construction--Mixing and Placing Concrete--Walls in
Trench--Chicago Drainage Canal--Grand Central Terminal, New
York, N. Y.--Wall for Railway Yard--Footing for Rubble Stone Retaining
Walls--Track Elevation, Allegheny, Pa.
CHAPTER XIV.--METHODS AND COST OF CONSTRUCTING CONCRETE
FOUNDATIONS FOR PAVEMENT 288
Introduction--Mixtures Employed--Distribution of Stock Piles--Hints on
Hand Mixing--Methods of Machine Mixing--Foundation for Stone Block
Pavement, New York, N. Y.--Foundation for Pavement, New Orleans,
La.--Foundation for Pavement, Toronto, Canada--Miscellaneous Examples of
Pavement Foundation Work--Foundation for Brick Pavement, Champaign,
Ill.--Foundation Construction using Continuous Mixers.--Foundation
Construction for Street Railway Track Using Continuous
Mixers--Foundation Construction Using Batch Mixers and Wagon
Haulage--Foundation Construction Using a Traction Mixer--Foundation
Construction Using a Continuous Mixer--Foundation Construction Using a
Portable Batch Mixer.
CHAPTER XV.--METHODS AND COST OF CONSTRUCTING SIDEWALKS,
PAVEMENTS, AND CURB AND GUTTER 307
Introduction--~Cement Sidewalks:~ General Method of Construction--Bonding
of Wearing Surface and Base--Protection of Work from Sun and
Frost--Cause and Prevention of Cracks--Cost of Cement Walks; Toronto,
Ont.; Quincy, Mass.; San Francisco, Cal.; Cost in Iowa. ~Concrete
Pavement:~ Windsor, Ontario--Richmond, Ind. ~Concrete Curb and Gutter:~
Form Construction--Concrete Mixtures and Concreting--Cost of Curb and
Gutter: Ottawa, Canada; Champaign, Ill.
CHAPTER XVI.--METHODS AND COST OF LINING TUNNELS AND
SUBWAYS 328
Introduction--Capitol Hill Tunnel, Pennsylvania R. R., Washington, D.
C.--Constructing Side Walls in Relining Mullan Tunnel--Lining a Short
Tunnel, Peekskill, N. Y.--Cascade Tunnel Great Northern Ry.--Relining
Hodges Pass Tunnel, Oregon Short Line Ry.--Lining a 4,000-ft.
Tunnel--Method of Mixing and Placing Concrete for a Tunnel
Lining--Gunnison Tunnel--New York Rapid Transit Subway--Traveling Forms
for Lining New York Rapid Transit Railway Tunnels--Subway Lining, Long
Island R. R., Brooklyn, N. Y.
CHAPTER XVII.--METHODS AND COST OF CONSTRUCTING ARCH
AND GIRDER BRIDGES 363
Introduction--Centers--Mixing and Transporting Concrete; Cableway
Plants; Car Plant for 4-Span Arch Bridge; Hoist and Car Plant for
21-Span Arch Viaduct; Traveling Derrick Plant for 4-Span Arch
Bridge--Concrete Highway Bridges Green County, Iowa--Highway Girder
Bridges--Molding Slabs for Girder Bridges--Connecticut Ave. Bridge,
Washington, D. C--Arch Bridges, Elkhart, Ind.--Arch Bridge, Plainwell,
Mich.--Five Span Arch Bridge--Arch Bridge, Grand Rapids, Mich.
CHAPTER XVIII.--METHODS AND COST OF CULVERT CONSTRUCTION 414
Introduction--Box Culvert Construction, C., B. & Q. R. R.--Arch Culvert
Costs, N. C. & St. L. Ry.; 18-ft. Arch Culvert; Six Arch Culverts 6 to
16-ft. Span; 14-3/4-ft. Arch Culvert--Culverts for New Construction,
Wabash Ry.--Small Arch Culvert Costs, Pennsylvania R. R.--26-ft. Span
Arch Culvert--12-ft. Culvert, Kalamazoo, Mich.--Method and Cost of
Molding Culvert Pipe.
CHAPTER XIX.--METHODS AND COST OF REINFORCED CONCRETE
BUILDING CONSTRUCTION 433
Introduction--Construction, Erection and Removal of Forms: Column Forms;
Rectangular Columns; Polygonal Columns; Circular Columns; Ornamental
Columns--Slab and Girder Forms; Slab and I-Beam Floors; Concrete Slab
and Girder Floors--Wall Forms--Erecting Forms--Removing Forms,
Fabrication and Placing Reinforcement; Fabrication; Placing--Mixing,
Transporting and Placing Concrete: Mixing; Transporting; Bucket Hoists;
Platform Hoists; Derricks--Placing and Ramming--Constructing Wall
Columns for a Brick Building--Floor and Column Construction for a
Six-Story Building--Wall and Roof Construction for One-Story Car
Barn--Constructing Wall Columns for a One-Story Machine
Shop--Constructing One-Story Walls with Movable Forms and Gallows
Frames--Floor and Roof Construction for Four-Story Garage.
CHAPTER XX.--METHOD AND COST OF BUILDING CONSTRUCTION
OF SEPARATELY MOLDED MEMBERS 515
Introduction--Column, Girder and Slab Construction: Warehouses,
Brooklyn, N. Y.; Factory, Reading, Pa.; Kilnhouse, New Village, N.
J.--Hollow Block Wall Construction: Factory Buildings, Grand Rapids,
Mich.; Residence, Quogue, N. Y., Two-Story Building, Albuquerque, N.
Mex.; General Cost Data.
CHAPTER XXI.--METHODS AND COST OF AQUEDUCT AND SEWER
CONSTRUCTION 532
Introduction--Forms and Centers--Concreting--Reinforced Conduit, Salt
River Irrigation Works, Arizona--Conduit, Torresdale Filters,
Philadelphia, Pa.--Conduit, Jersey City Water Supply, Twin Tube Water
Conduit at Newark, N. J.--66-in. Circular Sewer, South Bend, Ind.--Sewer
Invert Haverhill, Mass.--29-ft. Sewer, St. Louis, Mo.--Sewer,
Middlesborough, Ky.--Intercepting Sewer, Cleveland, Ohio--Reinforced
Concrete Sewer, Wilmington, Del.--Sewer with Monolithic Invert and Block
Arch--Cost of Block Manholes--Cement Pipe Constructed in Place--Pipe
Sewer, St. Joseph, Mo.--Cost of Molding Small Cement Pipe--Molded Pipe
Water Main, Swansea, England.
CHAPTER XXII.--METHODS AND COST OF CONSTRUCTING RESERVOIRS
AND TANKS 588
Introduction--Small Covered Reservoir--500,000 Gallon Covered Reservoir,
Ft. Meade, So. Dak.--Circular Reservoir, Bloomington, Ill.--Standpipe at
Attleborough, Mass.--Gas Holder Tank, Des Moines, Iowa--Gas Holder Tank,
New York City--Lining a Reservoir, Quincy, Mass.--Relining a Reservoir,
Chelsea, Mass.--Lining Jerome Park Reservoir--Reservoir Floor, Canton,
Ill.--Reservoir Floor, Pittsburg, Pa.--Constructing a Silo--Grained Arch
Reservoir Roof--Grain Elevator Bins.
CHAPTER XXIII.--METHODS AND COST OF CONSTRUCTING ORNAMENTAL
WORK 636
Introduction--Separately Molded Ornaments: Wooden Molds; Iron Molds;
Sand Molding; Plaster Molds--Ornaments Molded in Place: Big Muddy
Bridge; Forest Park Bridge; Miscellaneous Structures.
CHAPTER XXIV.--MISCELLANEOUS METHODS AND COSTS 653
Introduction--Drilling and Blasting Concrete--Bench Monuments, Chicago,
III.--Pole Base--Mile Post--Bonding New Concrete to Old--Dimensions and
Capacities of Mixers--Data for Estimating Weight of Steel in Reinforced
Concrete; Computing Weight from Percentage of Volume; Weights and
Dimensions of Plain and Special Reinforcing Metals--Recipes for Coloring
Mortars.
CHAPTER XXV.--METHODS AND COST OF WATERPROOFING CONCRETE
STRUCTURES 667
Impervious Concrete Mixtures--Star Stetten Cement--Medusa Waterproofing
Compound--Novoid Waterproofing Compound--Impermeable Coatings and
Washes: Bituminous Coatings; Szerelmey Stone Liquid Wash; Sylvester
Wash; Sylvester Mortars; Hydrolithic Coating; Cement Mortar Coatings;
Oil and Paraffine Washes--Impermeable Diaphragms; Long Island R. R.
Subway; New York Rapid Transit Subway.
Concrete Construction Methods and Cost
CHAPTER I.
METHODS AND COST OF SELECTING AND PREPARING MATERIALS FOR CONCRETE.
Concrete is an artificial stone produced by mixing cement mortar with
broken stone, gravel, broken slag, cinders or other similar fragmentary
materials. The component parts are therefore hydraulic cement, sand and
the broken stone or other coarse material commonly designated as the
aggregate.
CEMENT.
At least a score of varieties of hydraulic cement are listed in the
classifications of cement technologists. The constructing engineer and
contractor recognize only three varieties: Portland cement, natural
cement and slag or puzzolan cement. All concrete used in engineering
work is made of either Portland, natural or slag cement, and the great
bulk of all concrete is made of Portland cement. Only these three
varieties of cement are, therefore, considered here and they only in
their aspects having relation to the economics of construction work. For
a full discussion of the chemical and physical properties of hydraulic
cements and for the methods of determining these properties by tests,
the reader is referred to "Practical Cement Testing," by W. Purves
Taylor.
~PORTLAND CEMENT.~--Portland cement is the best of the hydraulic cements.
Being made from a rigidly controlled artificial mixture of lime, silica
and alumina the product of the best mills is a remarkably strong,
uniform and stable material. It is suitable for all classes of concrete
work and is the only variety of hydraulic cement allowable for
reinforced concrete or for plain concrete having to endure hard wear or
to be used where strength, density and durability of high degree are
demanded.
~NATURAL CEMENT.~--Natural cement differs from Portland cement in degree
only. It is made by calcining and grinding a limestone rock containing
naturally enough clayey matter (silica and alumina) to make a cement
that will harden under water. Owing to the imperfection and irregularity
of the natural rock mixture, natural cement is weaker and less uniform
than Portland cement. Natural cement concrete is suitable for work in
which great unit strength or uniformity of quality is not essential. It
is never used for reinforced work.
~SLAG CEMENT.~--Slag cement has a strength approaching very closely that
of Portland cement, but as it will not stand exposure to the air slag
cement concrete is suitable for use only under water. Slag cement is
made by grinding together slaked lime and granulated blast furnace slag.
~SIZE AND WEIGHT OF BARRELS OF CEMENT.~--The commercial unit of
measurement of cement is the barrel; the unit of shipment is the bag. A
barrel of Portland cement contains 380 lbs. of cement, and the barrel
itself weighs 20 lbs.; there are four bags (cloth or paper sacks) of
cement to the barrel, and the regulation cloth sack weighs 1½ lbs.
The size of cement barrels varies, due to the differences in weight of
cement and to differences in compacting the cement into the barrel. A
light burned Portland cement weighs 100 lbs. per struck bushel; a heavy
burned Portland cement weighs 118 to 125 lbs. per struck bushel. The
number of cubic feet of packed Portland cement in a barrel ranges from 3
to 3½. Natural cements are lighter than Portland cement. A barrel of
Louisville, Akron, Utica or other Western natural cement contains 265
lbs. of cement and weighs 15 lbs. itself; a barrel of Rosendale or other
Eastern cement contains 300 lbs. of cement and the barrel itself weighs
20 lbs. There are 3-¾ cu. ft. in a barrel of Louisville cement. Usually
there are three bags to a barrel of natural cement.
As stated above, the usual shipping unit for cement is the bag, but
cement is often bought in barrels or, for large works, in bulk. When
bought in cloth bags, a charge is made of 10 cts. each for the bags,
but on return of the bags a credit of 8 to 10 cts. each is allowed.
Cement bought in barrels costs 10 cts. more per barrel than in bulk, and
cement ordered in paper bags costs 5 cts. more per barrel than in bulk.
Cement is usually bought in cloth sacks which are returned, but to get
the advantage of this method of purchase the user must have an accurate
system for preserving, checking up and shipping the bags.
Where any considerable amount of cement is to be used the contractor
will find that it will pay to erect a small bag house or to close off a
room at the mixing plant. Provide the enclosure with a locked door and
with a small window into which the bags are required to be thrown as
fast as emptied. One trustworthy man is given the key and the task of
counting up the empty bags each day to see that they check with the bags
of cement used. The following rule for packing and shipping is given by
Gilbreth.[A]
[Footnote A: "Field System," Frank B. Gilbreth. Myron C. Clark
Publishing Co., New York and Chicago.]
"Pack cement bags laid flat, one on top of the other, in piles of 50.
They can then be counted easily. Freight must be prepaid when cement
bags are returned and bills of lading must be obtained in duplicate or
credit cannot be obtained on shipment."
The volumes given above are for cement compacted in the barrel. When the
cement is emptied and shoveled into boxes it measures from 20 to 30 per
cent more than when packed in the barrel. The following table compiled
from tests made for the Boston Transit Commission, Mr. Howard Carson,
Chief Engineer, in 1896, shows the variation in volume of cement
measured loose and packed in barrels:
Per cent
Brand Vol. Barrel Vol. Packed Vol. Loose Increase
Portland. cu. ft. cu. ft. cu. ft. in bulk
Giant 3.5 3.35 4.17 25
Atlas 3.45 3.21 3.75 18
Saylors 3.25 3.15 4.05 30
Alsen 3.22 3.16 4.19 33
Dyckerhoff 3.12 3.03 4.00 33
Mr. Clarence M. Foster is authority for the statement that Utica cement
barrels measure 16-1/4 ins. across at the heads, 19½ ins. across the
bilge, and 25-3/4 ins. in length under heads, and contain 3.77 cu. ft.
When 265 lbs. of Utica natural hydraulic cement are packed in a barrel
it fills it within 2½ ins. of the top and occupies 3.45 cu. ft., and
this is therefore the volume of a barrel of Utica hydraulic cement
packed tight.
In comparative tests made of the weights and volumes of various brands
of cements at Chicago in 1903, the following figures were secured:
Vol. per Weight per Weight per
bbl., cu. ft. bbl., lbs. cu. ft.
Brand. Loose. Gross. Net. Loose, lbs.
Dyckerhoff 4.47 395 369.5 83
Atlas 4.45 401 381 85.5
Alpha 4.37 400.5 381 86.5
Puzzolan 4.84 375 353.5 73.5
Steel 4.96 345 322.5 67.5
Hilton 4.64 393 370.5 79.5
~SPECIFICATIONS AND TESTING~--The great bulk of cement used in
construction work is bought on specification. The various government
bureaus, state and city works departments, railway companies, and most
public service corporations have their own specifications. Standard
specifications are also put forward by several of the national
engineering societies, and one of these or the personal specification of
the engineer is used for individual works. Buying cement to
specification necessitates testing to determine that the material
purchased meets the specified requirements. For a complete discussion of
the methods of conducting such tests the reader is referred to
"Practical Cement Testing" by W. Purves Taylor.
According to this authority a field testing laboratory will cost for
equipment $250 to $350. Such a laboratory can be operated by two or
three men at a salary charge of from $100 to $200 per month. Two men
will test on an average four samples per day and each additional man
will test four more samples. The cost of testing will range from $3 to
$5 per sample, which is roughly equivalent to 3 cts. per barrel of
cement, or from 3 to 5 cts. per cubic yard of concrete. These figures
are for field laboratory work reasonably well conducted under ordinarily
favorable conditions. In large laboratories the cost per sample will run
somewhat lower.
SAND.
Sand constitutes from 1/3 to 1/2 of the volume of concrete; when a large
amount of concrete is to be made a contractor cannot, therefore, afford
to guess at his source of sand supply. A long haul over poor roads can
easily make the sand cost more than the stone per cubic yard of
concrete.
~PROPERTIES OF GOOD SAND.~--Engineers commonly specify that sand for
concrete shall be clean and sharp, and silicious in character. Neither
sharpness nor excessive cleanliness is worth seeking after if it
involves much expense. Tests show conclusively that sand with rounded
grains makes quite as strong a mortar, other things being equal, as does
sand with angular grains. The admixture with sand of a considerable
percentage of loam or clay is also not the unmixed evil it has been
supposed to be. Myron S. Falk records[B] a number of elaborate
experiments on this point. These experiments demonstrate conclusively
that loam and clay in sand to the amount of 10 to 15 per cent. result in
no material reduction in the strength of mortars made with this sand as
compared with mortars made with the same sand after washing. There can
be no doubt but that for much concrete work the expense entailed in
washing sand is an unnecessary one.
[Footnote B: "Cements, Mortars and Concretes" By Myron S. Falk. Myron C.
Clark Publishing Co., Chicago, Ill.]
The only substitute for natural sand for concrete, that need be
considered practically, is pulverized stone, either the dust and fine
screenings produced in crushing rock or an artificial sand made by
reducing suitable rocks to powder. As a conclusion from the records of
numerous tests, M. S. Falk says: "It may be concluded that rock
screenings may be substituted for sand, either in mortar or concrete,
without any loss of strength resulting. This is important commercially,
for it precludes the necessity of screening the dust from crushed rock
and avoids, at the same time, the cost of procuring a natural sand to
take its place."
The principal danger in using stone dust is failure to secure the proper
balance of different size grains. This is also an important matter in
the choice of natural sands. Sand composed of a mixture of grains
ranging from fine to coarse gives uniformly stronger mortars than does
sand with grains of nearly one size, and as between a coarse and a fine
sand of one size of grains the coarse sand gives the stronger mortar.
Further data on the effect of size of grains on the utility of sand for
concrete are given in Chapter II, in the section on Voids in Sand, and
for those who wish to study in detail, the test data on this and the
other matters referred to here, the authors recommend "Cements, Mortars
and Concretes; Their Physical Properties," by Myron S. Falk.
~COST OF SAND.~--A very common price for sand in cities is $1 per cu. yd.,
delivered at the work. It may be noted here that as sand is often sold
by the load instead of the cubic yard, it is wise to have a written
agreement defining the size of a load. Where the contractor gets his
sand from the pit its cost will be the cost of excavating and loading at
the pit, the cost of hauling in wagons, the cost of freight and
rehandling it if necessary, and the cost of washing, added together.
An energetic man working under a good foreman will load 20 cu. yds. of
sand into wagons per 10-hour day; with a poor foreman or when laborers
are scarce, it is not safe to count on more than 15 cu. yds. per day.
With wages at $1.50 per day this will make the cost of loading 10 cts.
per cubic yard. The cost of hauling will include the cost of lost team
time and dumping, which will average about 5 cts. per cubic yard. With 1
cu. yd. loads, wages of team 35 cts. per hour, and speed of travel 2½
miles per hour, the cost of hauling proper is ½ ct. per 100 ft., or 27
cts. per mile. Assuming a mile haul, the cost of sand delivered based on
the above figures will be 10 cts. + 5 cts. + ½ ct. per 100 ft. = 15 +
27 cts. = 42 cts. per cu. yd. Freight rates can always be secured and it
is usually safe to estimate the weight on a basis of 2,700 lbs. per
cubic yard. For a full discussion of the cost of excavating sand and
other earths the reader is referred to "Earth Excavation and
Embankments; Methods and Cost," by Halbert P. Gillette and Daniel J.
Hauer.
~METHODS AND COST OF WASHING SAND.~--When the available sand carries
considerable percentages of loam or clay and the specifications require
that clean sand shall be used, washing is necessary. The best and
cheapest method of performing this task will depend upon the local
conditions and the amount of sand to be washed.
~Washing With Hose.~--When the quantity of sand to be washed does not
exceed 15 to 30 cu. yds. per day the simplest method, perhaps, is to use
a hose. Build a wooden tank or box, 8 ft. wide and 15 ft. long, the
bottom having a slope of 8 ins. in the 15 ft. The sides should be about
8 ins. high at the lower end and rise gradually to 3 ft. in height at
the upper end. Close the lower end of the tank with a board gate about 6
ins. in height and sliding in grooves so that it can be removed. Dump
about 3 cu. yds. of sand into the upper end of the tank and play a
¾-in. hose stream of water on it, the hose man standing at the lower
end of the tank. The water and sand flow down the inclined bottom of the
tank where the sand remains and the dirt flows over the gate and off
with the water. It takes about an hour to wash a 3-cu. yd. batch, and by
building a pair of tanks so that the hose man can shift from one to the
other, washing can proceed continuously and one man will wash 30 cu.
yds. per 10-hour day at a cost, with wages at $1.50, of 5 cts. per cubic
yard. The sand, of course, has to be shoveled from the tank and this
will cost about 10 cts. per cubic yard, making 15 cts. per cubic yard
for washing and shoveling, and to this must be added any extra hauling
and, if the water is pumped, the cost of pumping which may amount to 10
cts. per cubic yard for coal and wages. Altogether a cost of from 15 to
30 cts. per cubic yard may be figured for washing sand with a hose.
[Illustration: Fig. 1.--Plan and Elevation of Two-Hopper Ejector Sand
Washing Plant.]
[Illustration: Fig. 2.--Plan and Elevation of Four-Hopper Ejector Sand
Washing-Plant.]
~Washing With Sand Ejectors.~--When large quantities of sand are to be
washed use may be made of the sand ejector system, commonly employed in
washing filter sand at large water filtration plants; water under
pressure is required. In this system the dirty sand is delivered into a
conical or pyramidal hopper, from the bottom of which it is drawn by an
ejector and delivered mixed with water into a second similar hopper;
here the water and dirt overflow the top of the hopper, while the sand
settles and is again ejected into a third hopper or to the stock pile or
bins. The system may consist of anywhere from two to six hoppers. Figure
1 shows a two-hopper lay-out and Fig. 2 shows a four-hopper lay-out. In
the first plant the washed sand is delivered into bins so arranged, as
will be seen, that the bins are virtually a third washing hopper. The
clean sand is chuted from these bins directly into cars or wagons. In
the second plant the clean sand is ejected into a trough which leads it
into buckets handled by a derrick. The details of one of the washing
hoppers for the plant shown by Fig. 1 are illustrated by Fig. 3.
[Illustration: Fig. 3.--Details of Washing Hopper and Ejector for Plant
Shown by Fig. 1.]
At filter plants the dirty sand is delivered mixed with water to the
first hopper by means of ejectors stationed in the filters and
discharging through pipes to the washers. When, as would usually be the
case in contract work, the sand is delivered comparatively dry to the
first hopper, this hopper must be provided with a sprinkler pipe to wet
the sand. In studying the ejector washing plants illustrated it should
be borne in mind that for concrete work they would not need to be of
such permanent construction as for filter plants, the washers would be
mounted on timber frames, underground piping would be done away with,
etc.; at best, however, such plants are expensive and will be warranted
only when the amount of sand to be washed is large.
The usual assumption of water-works engineers is that the volume of
water required for washing filter sand is 15 times the volume of the
sand washed. At the Albany, N. Y., filters the sand passes through five
ejectors at the rate of 3 to 5 cu. yds. per hour and takes 4,000
gallons of water per cubic yard. One man shovels sand into the washer
and two take it away. Based on an output of 32 cu. yds. in 10 hours, Mr.
Allen Hazen estimates the cost of washing as follows:
3 men, at $2 per day $6.00
110,000 gallons of water, at $0.05 5.50
------
Total, 32 cu. yds., at 36 cts. $11.50
~Washing With Tank Washers.~--Figure 4 shows a sand washer used in
constructing a concrete lock at Springdale, Pa., in the United States
government improvement work on the Allegheny river. The device consisted
of a circular tank 9 ft. in diameter and 7 ft. high, provided with a
sloping false bottom perforated with 1-in. holes, through which water
was forced as indicated. A 7½×5×6-in. pump with a 3-in. discharge pipe
was used to force water into the tank, and the rotating paddles were
operated by a 7 h.p. engine. This apparatus washed a batch of 14 cu.
yds. in from 1 to 2 hours at a cost of 7 cts. per cubic yard. The sand
contained much fine coal and silt. The above data are given by Mr. W. H.
Roper.
[Illustration: Fig. 4.--Details of Tank Washer Used at Springdale, Pa.]
[Illustration: Fig. 5.--Details of Tank Washer Used at Yonkers, N. Y.]
[Illustration: Fig. 6.--Details of Rotating Tank Sand Washer Used at
Hudson, N. Y.]
Another form of tank washer, designed by Mr. Allen Hazen, for washing
bank sand at Yonkers, N. Y., is shown by Fig. 5. This apparatus
consisted of a 10×2½×2½ ft. wooden box, with a 6-in. pipe entering one
end at the bottom and there branching into three 3-in. pipes, extending
along the bottom and capped at the ends. The undersides of the 3-in.
pipes were pierced with ½-in. holes 6 ins. apart, through which water
under pressure was discharged into the box. Sand was shoveled into the
box at one end and the upward currents of water raised the fine and
dirty particles until they escaped through the waste troughs. When the
box became filled with sand a sliding door at one end was opened and the
batch discharged. The operation was continuous as long as sand was
shoveled into the box; by manipulating the door the sand could be made
to run out with a very small percentage of water. Sand containing 7 per
cent of dirt was thus washed so that it contained only 0.6 per cent
dirt. The washer handled 200 cu. yds. of sand in 10 hours. The above
data are given by F. H. Stephenson.
A somewhat more elaborate form of tank washer than either of those
described is shown by Fig. 6. This apparatus was used by Mr. Geo. A.
Soper for washing filter sand at Hudson, N. Y. The dirty sand was
shoveled into a sort of hopper, from which it was fed by a hose stream
into an inclined cylinder, along which it traveled and was discharged
into a wooden trough provided with a screw conveyor and closed at both
ends. The water overflowing the sides of the trough carried away the
dirt and the clean sand was delivered by the screw to the bucket
elevator which hoisted it to a platform, from which it was taken by
barrows to the stock pile. A 4-h.p. engine with a 5-h.p. boiler operated
the cylinder, screw, elevator and pump. Four men operated the washer and
handled 32 cu. yds. of sand per day; with wages at $1.50 the cost of
washing was 20 cts. per cubic yard.
[Illustration: Fig. 7.--Arrangement of Sand Washing Plant at Lynchburg,
Va.]
In constructing a concrete block dam at Lynchburg, Va., sand containing
from 15 to 30 per cent. of loam, clay and vegetable matter was washed
to a cleanliness of 2 to 5 per cent of such matter by the device shown
by Fig. 7. A small creek was diverted, as shown, into a wooden flume
terminating in two sand tanks; by means of the swinging gate the flow
was passed through either tank as desired. The sand was hauled by wagon
and shoveled into the upper end of the flume; the current carried it
down into one of the tanks washing the dirt loose and carrying it off
with the overflow over the end of the tank while the sand settled in the
tank. When one tank was full the flow was diverted into the other tank
and the sand in the first tank was shoveled out, loaded into wagons, and
hauled to the stock pile. As built this washer handled about 30 cu. yds.
of sand per 10-hour day, but the tanks were built too small for the
flume, which could readily handle 75 cu. yds. per day with no larger
working force. This force consisted of three men at $1.50 per day,
making the cost, for a 30 cu. yd. output, 15 cts. per cu. yd. for
washing.
None of the figures given above includes the cost of handling the sand
to and from the washer. When this involves much extra loading and
hauling, it amounts to a considerable expense, and in any plan for
washing sand the contractor should figure, with exceeding care, the
extra handling due to the necessity of washing.
AGGREGATES.
The aggregates commonly used in making concrete are broken or crushed
stone, gravel, slag and cinders. Slag and cinders make a concrete that
weighs considerably less than stone or gravel mixtures, and being the
products of combustion are commonly supposed to make a specially fire
resisting concrete; their use is, therefore, confined very closely to
fireproof building work and, in fact, to floor construction for such
buildings. Slag and cinder concretes are for this reason given minor
consideration in this volume.
~BROKEN STONE.~--Stone produced by crushing any of the harder and tougher
varieties of rock is suitable for concrete. Perhaps the best stone is
produced by crushing trap rock. Crushed trap besides being hard and
tough is angular and has an excellent fracture surface for holding
cement; it also withstands heat better than most stone. Next to trap
the hard, tough, crystalline limestones make perhaps the best all around
concrete material; cement adheres to limestone better than to any other
rock. Limestone, however, calcines when subjected to fire and is,
therefore, objected to by many engineers for building construction. The
harder and denser sandstones, mica-schists, granites and syanites make
good stone for concrete and occasionally shale and slate may be used.
~GRAVEL.~--Gravel makes one of the best possible aggregates for concrete.
The conditions under which gravel is produced by nature make it
reasonably certain that only the tougher and harder rocks enter into its
composition; the rounded shapes of the component particles permit gravel
to be more closely tamped than broken stone and give less danger of
voids from bridging; the mixture is also generally a fairly well
balanced composition of fine and coarse particles. The surfaces of the
particles being generally smooth give perhaps a poorer bond with the
cement than most broken stone. In the matter of strength the most recent
tests show that there is very little choice between gravel and broken
stone concrete.
~SLAG AND CINDERS.~--The slag used for concrete aggregate is iron blast
furnace slag crushed to proper size. Cinders for aggregate are steam
boiler cinders; they are best with the fine ashes screened out and
should not contain more than 15 per cent. of unburned coal.
~BALANCED AGGREGATE.~--With the aggregate, as with the sand for concrete,
the best results, other things being equal, will be secured by using a
well-balanced mixture of coarse and fine particles. Usually the product
of a rock crusher is fairly well balanced except for the very fine
material. There is nearly always a deficiency of this, which, as
explained in a succeeding section, has to be supplied by adding sand.
Usually, also, the engineer accepts the crusher product coarser than
screenings as being well enough balanced for concrete work, but this is
not always the case. Engineers occasionally demand an artificial mixture
of varying proportions of different size stones and may even go so far
as to require gravel to be screened and reproportioned. This artificial
grading of the aggregate adds to the cost of the concrete in some
proportion which must be determined for each individual case.
~SIZE OF AGGREGATE.~--The size of aggregate to be used depends upon the
massiveness of the structure, its purpose, and whether or not it is
reinforced. It is seldom that aggregate larger than will pass a 3-in.
ring is used and this only in very massive work. The more usual size is
2½ ins. For reinforced concrete 1¼ ins. is about the maximum size
allowed and in building work 1-in. aggregate is most commonly used. Same
constructors use no aggregate larger than ¾ in. in reinforced building
work, and others require that for that portion of the concrete coming
directly in contact with the reinforcement the aggregate shall not
exceed ¼ to ½ in. The great bulk of concrete work is done with aggregate
smaller than 2 ins., and as a general thing where the massiveness of the
structure will allow of much larger sizes it will be more economic to
use rubble concrete. (See Chapter VI.)
~COST OF AGGREGATE.~--The locality in which the work is done determines
the cost of the aggregate. Concerns producing broken stone or screened
and washed gravel for concrete are to be found within shipping distance
in most sections of the country so that these materials may be purchased
in any amount desired. The cost will then be the market price of the
material f. o. b. cars at plant plus the freight rates and the cost of
unloading and haulage to the stock piles. If the contractor uses a local
stone or gravel the aggregate cost will be, for stone the costs of
quarrying and crushing and transportation, and, for gravel, the cost of
excavation, screening, washing and transportation.
~SCREENED OR CRUSHER-RUN STONE FOR CONCRETE.~--Formerly engineers almost
universally demanded that broken stone for concrete should have all the
finer particles screened out. This practice has been modified to some
considerable extent in recent years by using all the crusher product
both coarse and fine, or, as it is commonly expressed, by using
run-of-crusher stone. The comparative merits of screened and crusher-run
stone for concrete work are questions of comparative economy and
convenience. The fine stone dust and chips produced in crushing stone
are not, as was once thought, deleterious; they simply take the place of
so much of the sand which would, were the stone screened, be required to
balance the sand and stone mixture. It is seldom that the proportion of
chips and dust produced in crushing stone is large enough to replace the
sand constituent entirely; some sand has nearly always to be added to
run-of-crusher stone and it is in determining the amount of this
addition that uncertainty lies. The proportions of dust and chips in
crushed stone vary with the kind of stone and with the kind of crusher
used. Furthermore, when run-of-crusher stone is chuted from the crusher
into a bin or pile the screenings and the coarse stones segregate.
Examination of a crusher-run stone pile will show a cone-shaped heart of
fine material enclosed by a shell of coarser stone, consequently when
this pile of stone is taken from to make concrete a uniform mixture of
fine and coarse particles is not secured, the material taken from the
outside of the pile will be mostly coarse and that from the inside
mostly fine. This segregation combined with the natural variation in the
crusher product makes the task of adding sand and producing a balanced
sand and stone mixture one of extreme uncertainty and some difficulty
unless considerable expenditure is made in testing and reproportioning.
When the product of the crusher is screened the task of proportioning
the sand to the stone is a straightforward operation, and the screened
out chips and dust can be used as a portion of the sand if desired. The
only saving, then, in using crusher-run stone direct is the very small
one of not having to screen out the fine material. The conclusion must
be that the economy of unscreened stone for concrete is a very doubtful
quantity, and that the risk of irregularity in unscreened stone mixtures
is a serious one. The engineer's specifications will generally determine
for the contractor whether he is to use screened or crusher-run stone,
but these same specifications will not guarantee the regularity of the
resulting concrete mixture; this will be the contractor's burden and if
the engineer's inspection is rigid and the crusher-run product runs
uneven for the reasons given above it will be a burden of considerable
expense. The contractor will do well to know his product or to know his
man before bidding less or even as little on crusher-run as on screened
stone concrete.
~COST OF QUARRYING AND CRUSHING STONE.~--The following examples of the
cost of quarrying and crushing stone are fairly representative of the
conditions which would prevail on ordinary contract work. In quarrying
and crushing New Jersey trap rock with gyratory crushers the following
was the cost of producing 200 cu. yds. per day:
Per day. Per cu. yd.
3 drillers at $2.75 $ 8.25 $0.041
3 helpers at $1.75 5.25 0.026
10 men barring out and sledging 15.00 0.075
14 men loading carts 21.00 0.105
4 cart horses 6.00 0.030
2 cart drivers 3.00 0.015
2 men dumping carts and feeding crusher 3.00 0.015
1 fireman for drill boiler 2.50 0.013
1 engineman for crusher 3.00 0.015
1 blacksmith 3.00 0.015
1 blacksmith helper 2.00 0.010
1 foreman 5.00 0.025
2 tons coal at $3.50 7.00 0.035
150 lbs. 40% dynamite at 15 cts. 22.50 0.113
------ -------
Total $106.50 $0.533
The quarry face worked was 12 to 18 ft., and the stone was crushed to
2-in. size. Owing to the seamy character of the rock it was broken by
blasting into comparatively small pieces requiring very little sledging.
The stone was loaded into one-horse dump carts, the driver taking one
cart to the crusher while the other was being loaded. The haul was 100
ft. The carts were dumped into an inclined chute leading to a No. 5
Gates crusher. The stone was elevated by a bucket elevator and screened.
All stone larger than 2 ins. was returned through a chute to a No. 3
Gates crusher for recrushing. The cost given above does not include
interest, depreciation, and repairs; these items would add about $8 to
$10 more per day or 4 to 5 cts. per cubic yard.
In quarrying limestone, where the face of the quarry was only 5 to 6 ft.
high, and where the amount of stripping was small, one steam drill was
used. This drill received its steam from the same boiler that supplied
the crusher engine. The drill averaged 60 ft. of hole drilled per 10-hr.
day, but was poorly handled and frequently laid off for repairs. The
cost of quarrying and crushing was as follows:
Quarry.
1 driller $ 2.50
1 helper 1.50
1 man stripping 1.50
4 men quarrying 6.00
1 blacksmith 2.50
1/8 ton coal at $3 1.00
Repairs to drill .60
Hose, drill steel and interest on plant .90
24 lbs. dynamite 3.60
------
Total $20.10
Crusher.
1 engineman $ 2.50
2 men feeding crusher 3.50
6 men wheeling 9.00
1 bin man 1.50
1 general foreman 3.00
1/3 ton coal at $3 1.00
1 gallon oil .25
Repairs to crusher 1.00
Repairs to engine and boiler 1.00
Interest on plant 1.00
------
Total $23.75
Summary:
Per day. Per. cu. yd.
Quarrying $20.10 $0.37
Crushing 23.75 0.39
------ -----
Total for 60 cu. yds. $43.85 $0.76
The "4 men quarrying" barred out and sledged the stone to sizes that
would enter a 9×16-in. jaw crusher. The "6 men wheeling" delivered the
stone in wheelbarrows to the crusher platform, the run plank being never
longer than 150 ft. Two men fed the stone into the crusher, and a
bin-man helped load the wagons from the bin, and kept tally of the
loads. The stone was measured loose in the wagons, and it was found that
the average load was 1½ cu. yds., weighing 2,400 lbs. per cu. yd. There
were 40 wagon loads, or 60 cu. yds. crushed per 10-hr. day, although on
some days as high as 75 cu. yds. were crushed. The stone was screened
through a rotary screen, 9 ft. long, having three sizes of openings,
½-in., 1¼-in. and 2¼-in. The output was 16% of the smallest size, 24% of
the middle size, and 60% of the large size. All tailings over 2½ ins. in
size were recrushed.
It will be noticed that the interest on the plant is quite an important
item. This is due to the fact that, year in and year out, a quarrying
and crushing plant seldom averages more than 100 days actually worked
per year, and the total charge for interest must be distributed over
these 100 days, and not over 300 days as is so commonly and erroneously
done. The cost of stripping the earth off the rock is often considerably
in excess of the above given cost, and each case must be estimated
separately. Quarry rental or royalty is usually not in excess of 5 cts.
per cu. yd., and frequently much less. The dynamite used was 40%, and
the cost of electric exploders is included in the cost given. Where a
higher quarry face is used the cost of drilling and the cost of
explosives per cu. yd. is less. Exclusive of quarry rent and heavy
stripping costs, a contractor should be able to quarry and crush
limestone or sandstone for not more than 75 cts. per cu. yd., or 62 cts.
per ton of 2,000 lbs., wages and conditions being as above given.
The labor cost of erecting bins and installing a 9×16 jaw crusher,
elevator, etc., averages about $75, including hauling the plant two or
three miles, and dismantling the plant when work is finished.
The following is a record of the cost of crushing stone and cobbles on
four jobs at Newton, Mass., in 1891. On jobs A and B the stone was
quarried and crushed; on jobs C and D cobblestones were crushed. A
9×15-in. Farrel-Marsondon crusher was used, stone being fed in by two
laborers. A rotary screen having ½, 1 and 2½-in. openings delivered the
stone into bins having four compartments, the last receiving the
"tailings" which had failed to pass through the screen. The broken stone
was measured in carts as they left the bin, but several cart loads were
weighed, giving the following weights per cubic foot of broken stone:
-----------Size.--------------
½-in. 1-in. 2½-ins. Tailings.
lbs. lbs. lbs. lbs.
Greenish trap rock, "A" 95.8 84.3 88.3 91.0
Conglomerate, "B" 101.0 87.7 94.4 ....
Cobblestones, "C" and "D" 102.5 98.0 99.6 ....
A one-horse cart held 26 to 28 cu. ft. (average 1 cu. yd.) of broken
stone; a two-horse cart, 40 to 42 cu. ft., at the crusher.
---------------------Job.-------------
A. B. C. D.
Hours run 412 144 101 198
Short tons per hour 9.0 11.2 15.7 12.1
Cu. yds. per hour 7.7 8.9 11.8 9.0
Per cent of tailings 31.8 29.3 17.5 20.5
Per cent of 2½-in. stone 51.3 51.9 57.0 55.1
Per cent of 1-in. stone 10.2 .... .... ....
Per cent of ½-in. stone or dust 6.7 18.8 25.5 23.4
---------------------Job.-------------
A. B. C. D.
Explosives, coal for drill and repairs $0.084 $0.018 .... ....
Labor steam drilling 0.092 .... .... ....
Labor hand drilling .... 0.249 .... ....
Sharpening tools 0.069 0.023 .... ....
Sledging stone for crusher 0.279 0.420 .... ....
Loading carts 0.098 0.127 .... $0.144
Carting to crusher 0.072 0.062 $0.314 0.098
Feeding crusher 0.053 0.053 0.033 0.065
Engineer of crusher 0.031 0.038 0.029 0.036
Coal for crusher 0.079 0.050 0.047 0.044
Repairs to crusher 0.041 .... .... 0.011
Moving portable crusher .... 0.023 .... 0.019
Watchman ($1.75 a day) .... 0.053 0.022 0.030
------ ------ ------ ------
Total cost per cu. yd. $0.898 $1.116 $0.445 $0.447
Total cost per short ton 0.745 0.885 0.330 0.372
Note.--"A" was trap rock; "B" was conglomerate rock; "C" and
"D" were trap and granite cobblestones. Common laborers on jobs
"A" and "D" were paid $1.75 per 9-hr. day; on jobs "B" and "C,"
$1.50 per 9-hr. day; two-horse cart and driver, $5 per day;
blacksmith, $2.50; engineer on crusher, $2 on job "A," $2.25 on
"B," $2.00 on "C," $2.50 on "D"; steam driller received $3, and
helper $1.75 a day; foreman, $3 a day. Coal was $5.25 per short
ton. Forcite powder, 11-1/3 cts. per lb.
For a full discussion of quarrying and crushing methods and costs and
for descriptions of crushing machinery and plants the reader is referred
to "Rock Excavation; Methods and Cost," by Halbert P. Gillette.
~SCREENING AND WASHING GRAVEL.~--Handwork is resorted to in screening
gravel only when the amount to be screened is small and when it is
simply required to separate the fine sand without sorting the coarser
material into sizes. The gravel is shoveled against a portable inclined
screen through which the sand drops while the pebbles slide down and
accumulate at the bottom. The cost of screening by hand is the cost of
shoveling the gravel against the screen divided by the number of cubic
yards of saved material. In screening gravel for sand the richer the
gravel is in fine material the cheaper will be the cost per cubic yard
for screening; on the contrary in screening gravel for the pebbles the
less sand there is in the gravel the cheaper will be the cost per cubic
yard for screening. The cost of shoveling divided by the number of cubic
yards shoveled is the cost of screening only when both the sand and the
coarser material are saved. Tests made in the pit will enable the
contractor to estimate how many cubic yards of gravel must be shoveled
to get a cubic yard of sand or pebbles. An energetic man will shovel
about 25 cu. yds. of gravel against a screen per 10-hour day and keep
the screened material cleared away, providing no carrying is necessary.
A mechanical arrangement capable of handling a considerably larger
yardage of material is shown by Fig. 8. Two men and a team are required.
The team is attached to the scraper by means of the rope passing through
the pulley at the top of the incline. The scraper is loaded in the usual
manner, hauled up the incline until its wheels are stopped by blocks and
then the team is backed up to slacken the rope and permit the scraper to
tip and dump its load. The trip holding the scraper while dumping is
operated from the ground. The scraper load falls onto an inclined
screen which takes out the sand and delivers the pebbles into the wagon.
By erecting bins to catch the sand and pebbles this same arrangement
could be made continuous in operation.
[Illustration: Fig. 8.--Device for Excavating and Screening Gravel and
Loading Wagons.]
[Illustration: Fig. 9.--Gravel Washing Plant of 120 to 130 Cu. Yds., Per
Hour Capacity.]
In commercial gravel mining, the gravel is usually sorted into several
sizes and generally it is washed as well as screened. Where the pebbles
run into larger sizes a crushing plant is also usually installed to
reduce the large stones. Works producing several hundred cubic yards of
screened and washed gravel per day require a plant of larger size and
greater cost than even a very large piece of concrete work will warrant,
so that only general mention will be made here of such plants. The
commercial sizes of gravel are usually 2-in., 1-in., ½-in. and ¼-in.,
down to sand. No very detailed costs of producing gravel by these
commercial plants are available. At the plant of the Lake Shore &
Michigan Southern Ry., where gravel is screened and washed for ballast,
the gravel is passed over a 2-in., a ¾-in., a ¼-in. and a 1/8-in. screen
in turn and the fine sand is saved. About 2,000 tons are handled per
day; the washed gravel, 2-in. to 1/8-in. sizes, represents from 40 to 65
per cent. of the raw gravel and costs from 23 to 30 cts. per cu. yd.,
for excavation, screening and washing. The drawings of Fig. 9 show a
gravel washing plant having a capacity of 120 to 130 cu. yds. per hour,
operated by the Stewart-Peck Sand Co., of Kansas City, Mo. Where washing
alone is necessary a plant of one or two washer units like those here
shown could be installed without excessive cost by a contractor at any
point where water is available. Each washer unit consists of two
hexagonal troughs 18 ins. in diameter and 18 ft. long. A shaft carrying
blades set spirally is rotated in each trough to agitate the gravel and
force it along; each trough also has a fall of 6 ins. toward its
receiving end. The two troughs are inclosed in a tank or box and above
and between them is a 5-in. pipe having ¾-in. holes 3 ins. apart so
arranged that the streams are directed into the troughs. The water and
dirt pass off at the lower end of the troughs while the gravel is fed by
the screws into a chute discharging into a bucket elevator, which in
turn feeds into a storage bin. The gravel to be washed runs from 2 ins.
to 1/8-in. in size; it is excavated by steam shovel and loaded into 1½
cu. yd. dump cars, three of which are hauled by a mule to the washers,
where the load is dumped into the troughs. The plant having a capacity
of 120 to 130 cu. yds. per hour cost $25,000, including pump and an
8-in. pipe line a mile long. A 100-hp. engine operates the plant, and 20
men are needed for all purposes. This plant produces washed gravel at a
profit for 40 cts. per cu. yd.
CHAPTER II.
THEORY AND PRACTICE OF PROPORTIONING CONCRETE.
American engineers proportion concrete mixtures by measure, thus a 1-3-5
concrete is one composed of 1 volume of cement, 3 volumes of sand and 5
volumes of aggregate. In Continental Europe concrete is commonly
proportioned by weight and there have been prominent advocates of this
practice among American engineers. It is not evident how such a change
in prevailing American practice would be of practical advantage. Aside
from the fact that it is seldom convenient to weigh the ingredients of
each batch, sand, stone and gravel are by no means constant in specific
gravity, so that the greater exactness of proportioning by weight is not
apparent. In this volume only incidental attention is given to
gravimetric methods of proportioning concrete.
~VOIDS.~--Both the sand and the aggregates employed for concrete contain
voids. The amount of this void space depends upon a number of
conditions. As the task of proportioning concrete consists in so
proportioning the several materials that all void spaces are filled with
finer material the conditions influencing the proportion of voids in
sand and aggregates must be known.
~Voids in Sand.~--The two conditions exerting the greatest influence on
the proportion of voids in sand are the presence of moisture and the
size of the grains of which the sand is composed.
TABLE I.--SHOWING EFFECT OF ADDITIONS OF DIFFERENT PERCENTAGES OF
MOISTURE ON VOLUME OF SAND.
Per cent of water in sand 0 0.5 1 2 3 5 10
Weight per cu. yd. of fine Lbs. Lbs. Lbs. Lbs. Lbs. Lbs. Lbs.
sand and water 3,457 2,206 2,085 2,044 2,037 2,035 2,133
Weight per cu. yd. of coarse
sand and water 2,551 2,466 2,380 2,122 2,058 2,070 2,200
The volume of sand is greatly affected by the presence of varying
percentages of moisture in the sand. A dry loose sand that has 45 per
cent. voids if mixed with 5 per cent. by weight of water will swell,
unless tamped, to such an extent that its voids may be 57 per cent. The
same sand if saturated with water until it becomes a thin paste may show
only 37½ per cent. voids after the sand has settled. Table I shows the
results of tests made by Feret, the French experimenter. Two kinds of
sand were used, a very fine sand and a coarse sand. They were measured
in a box that held 2 cu. ft. and was 8 ins. deep, the sand being
shoveled into the box but not tamped or shaken. After measuring and
weighing the dry sand 0.5 per cent. by weight of water was added and the
sand was mixed and shoveled back into the box again and then weighed.
These operations were repeated with varying percentages of water up to
10 per cent. It will be noted that the weight of mixed water and sand is
given; to ascertain the exact weight of dry sand in any mixture, divide
the weight given in the table by 100 per cent. plus the given tabular
per cent.; thus the weight of dry, fine sand in a 5 per cent. mixture is
2,035 ÷ 1.5 = 1,98 lbs. per cu. yd. The voids in the dry sand were 45
per cent. and in the sand with 5 per cent. moisture they were 56.7 per
cent. Pouring water onto loose, dry sand compacts it. By mixing fine
sand and water to a thin paste and allowing it to settle, it was found
that the sand occupied 11 per cent. less space than when measured dry.
The voids in fine sand, having a specific gravity of 2.65, were
determined by measurement in a quart measure and found to be as follows:
Sand not packed, per cent. voids 44½
Sand shaken to refusal, per cent. voids 35
Sand saturated with water, per cent. voids 37½
Another series of tests made by Mr. H. P. Boardman, using Chicago sand
having 34 to 40 per cent. voids, showed the following results:
Water added, per cent. 2 4 6 8 10
Resulting per cent. increase 17.6 22 19.5 16.6 15.6
Mr. Wm. B. Fuller found by tests that a dry sand, having 34 per cent.
voids, shrunk 9.6 per cent. in volume upon thorough tamping until it had
27 per cent. voids. The same sand moistened with 6 per cent. water and
loose had 44 per cent. voids, which was reduced to 31 per cent. by
ramming. The same sand saturated with water had 33 per cent. voids and
by thorough ramming its volume was reduced 8½ per cent. until the sand
had only 26¼ per cent. voids. Further experiments might be quoted and
will be found recorded in several general treatises on concrete, but
these are enough to demonstrate conclusively that any theory of the
quantity of cement in mortar to be correct must take into account the
effect of moisture on the voids in sand.
The effect of the size and the shape of the component grains on the
amount of voids in sand is considerable. Feret's experiments are
conclusive on these points, and they alone will be followed here. Taking
for convenience three sizes of sand Feret mixed them in all the varying
proportions possible with a total of 10 parts; there were 66 mixtures.
The sizes used were: Large (L), sand composed of grains passing a
sieve of 5 meshes per linear inch and retained on a sieve of 15 meshes
per linear inch; medium (M>), sand passing a sieve of 15 meshes and
retained on a sieve of 50 meshes per linear inch, and fine (F), sand
passing a 50-mesh sieve. With a dry sand whose grains have a specific
gravity of 2.65, the weight of a cubic yard of either the fine, or the
medium, or the large size, was 2,190 lbs., which is equivalent to 51 per
cent. voids. The greatest weight of mixture, 2,840 lbs. per cu. yd., was
an L_{6}M_{0}F_{4} mixture, that is, one composed of six parts
large, no parts medium and 4 parts fine; this mixture was the densest of
the 66 mixtures made, having 36 per cent. voids. It will be noted that
the common opinion that the densest mixture is obtained by a mixture of
gradually increasing sizes of grains is incorrect; there must be enough
difference in the size of the grains to provide voids so large that the
smaller grains will enter them and not wedge the larger grains apart.
Turning now to the shape of the grains, the tests showed that rounded
grains give less voids than angular grains. Using sand having a
composition of L_{5}M_{3}F_{2} Feret got the following results:
--Per cent. Voids--
Kind of Grains. Shaken. Unshaken.
Natural sand, rounded grains 25.6 35.9
Crushed quartzite, angular grains 27.4 42.1
Crushed shells, flat grains 31.8 44.3
Residue of quartzite, flat grains 34.6 47.5
The sand was shaken until no further settlement occurred. It is plain
from these data on the effect of size and shape of grains on voids why
it is that discrepancies exist in the published data on voids in dry
sand. An idea of the wide variation in the granulometric composition of
different sands is given by Table II. Table III shows the voids as
determined for sands from different localities in the United States.
TABLE II.--SHOWING GRANULOMETRIC COMPOSITIONS OF DIFFERENT SANDS.
Held by a Sieve. A B C E
No. 10 35.3%
No. 20 32.1 12.8% 4.2% 11%
No. 30 14.6 49.0 12.5 14
No. 40 ... ... 44.4 ...
No. 50 9.6 29.3 ... 53
No. 100 4.9 5.7 ... ...
No. 200 2.0 2.3 ... ...
----- ----- ----- -----
Voids 33% 39% 41.7% 31%
NOTE.--A, is a "fine gravel" (containing 8% clay) used at
Philadelphia. B, Delaware River sand. C, St. Mary's River sand.
D, Green River, Ky., sand, "clean and sharp."
TABLE III.--SHOWING MEASURED VOIDS IN SAND FROM DIFFERENT LOCALITIES.
Percent
Locality. Authority. Voids. Remarks.
Ohio River W. M. Hall 31 Washed
Sandusky, O. C. E. Sherman 40 Lake
Franklin Co., O. C. E. Sherman 40 Bank
Sandusky Bay, O. S. B. Newberry 32.3 ......
St. Louis, Mo. H. H. Henby 34.3 Miss. River
Sault Ste. Marie H. von Schon 41.7 River
Chicago, Ill. H. P. Broadman 34 to 40 ......
Philadelphia, Pa 39 Del. River
Mass. Coast 31 to 34 ......
Boston, Mass Geo. Kimball 33 Clean
Cow Bay, L. I. Myron S. Falk 40½ ......
Little Falls, N. J. W. B. Fuller 45.6 ......
Canton, Ill. G. W. Chandler 30 Clean
~Voids in Broken Stone and Gravel.~--The percentage of voids in broken
stone varies with the nature of the stone: whether it is broken by hand
or by crushers; with the kind of crusher used, and upon whether it is
screened or crusher-run product. The voids in broken stone seldom
exceed 52 per cent. even when the fragments are of uniform size and the
stone is shoveled loose into the measuring box. The following records of
actual determinations of voids in broken stone cover a sufficiently wide
range of conditions to show about the limits of variation.
The following are results of tests made by Mr. A. N. Johnson, State
Engineer of Illinois, to determine the variation in voids in crushed
stone due to variation in size and to method of loading into the
measuring box. The percentage of voids was determined by weighing the
amount of water added to fill the box:
Method of Per cent.
Size. Loading. of Voids.
3 in. 20-ft. drop 41.8
3 in. 15-ft drop 46.8
3 in. 15-ft. drop 47.2
3 in. Shovels 48.7
1½ in. 20-ft. drop 42.5
1½ in. 15-ft. drop 46.8
1½ in. 15-ft. drop 46.8
1½ in. Shovels 50.5
¾ in. 20-ft. drop 39.4
¾ in. 15-ft. drop 42.7
¾ in. 15-ft. drop 41.5
¾ in. 15-ft. drop 41.8
¾ in. Shovels 45.2
¾ in. Shovels 44.6
3/8 in. Shovels 41.0
3/8 in. Shovels 40.6
3/8 in. Shovels 41.0
The table shows clearly the effect on voids of compacting the stone by
dropping it; it also shows for the ¾-in. and the 3/8-in. stone loaded by
shovels how uniformly the percentages of voids run for stone of one size
only. Dropping the stone 20 ft. reduced the voids some 12 to 15 per
cent. as compared with shoveling.
TABLE IV.--SHOWING DETERMINED PERCENTAGES OF VOIDS IN BROKEN STONE FROM
VARIOUS COMMON ROCKS.
--------------------+--------+------------------------------------------------
| Percent|
Authority. | Voids.| Remarks.
--------------------+--------+------------------------------------------------
Sabin | 49.0 | Limestone, crusher run after screening out
| | 1/8-in. and under.
" | 44.0 | Limsetone (1 part screenings mixed with
| | 6 parts broken stone).
Wm. M. Black | 46.5 | Screened and washed, 2-ins. and under.
J. J. R. Croes | 47.5 | Gneiss, after screening out ¼-in. and under.
S. B. Newberry | 47.0 | Chiefly about egg size.
H. P. Broadman |39 to 42| Chicago limestone, crusher run.
" |48 to 52| " " screened into sizes.
Wm. M. Hall | 48.0 | Green River limestone, 2½-ins. and smaller
| | dust screened out.
" | 50.0 | Hudson River trap, 2½-ins. and smaller,
| | dust screened out.
Wm. B. Fuller | 47.6 | New Jersey trap, crusher run, 1/6 to 2.1 in.
Geo. A. Kimball | 49.5 | Roxbury conglomerate, ½ to 2½ ins.
Myron S. Falk | 48.0 | Limestone, ½ to 3 ins.
W. H. Henby | 43.0 | " 2-in size.
" | 46.0 | " 1½-in size
Feret | 53.4 | Stone, 1.6 to 2.4 ins.
" | 51.7 | " 0.8 to 1.6 in.
" | 52.1 | " 0.4 to 0.8 in.
A. W. Dow | 45.3 | Bluestone, 89% being 1½ to 2½ ins.
" | 45.3 | " 90% being 1/6 to 1½ in.
Taylor and Thompson | 54.5 | Trap, hard, 1 to 2½ ins.
" | 54.5 | " " ½ to 1 in.
" | 45.0 | " " 0 to 2½ in.
" | 51.2 | " soft, ¾ to 2 ins.
G. W. Chandler | 40.0 | Canton, Ill.
Emile Low | 39.0 | Buffalo limestone, crusher run, dust in.
C. M. Saville | 46.0 | Crushed cobblestone, screened into sizes.
--------------------+--------+-----------------------------------------------
TABLE V.--SHOWING PERCENTAGES OF VOIDS IN GRAVEL AND BROKEN STONE OF
DIFFERENT GRANULOMETRIC COMPOSITIONS.
/--Per cent Voids in--\
Passing a ring of 2.4" 1.6" 0.8" Round Broken
Held by a ring 1.6" 0.8" 0.4" Pebbles. Stone.
Parts 1 0 0 40.0 53.4
" 0 1 0 38.8 51.7
" 0 0 1 41.7 52.1
" 1 1 0 35.8 50.5
" 1 0 1 35.6 47.1
" 0 1 1 37.9 40.5
" 1 1 1 35.5 47.8
" 4 1 1 34.5 49.2
" 1 4 1 36.6 49.4
" 1 1 4 38.1 48.6
" 8 0 2 34.1 ....
Table IV gives the voids in broken stone as determined by various
engineers; it requires no explanation. Table V, taken from Feret's
tests, shows the effect of changes in granulometric composition on the
amount of voids in both broken stone and gravel. Considering the column
giving voids in stone it is to be noted first how nearly equal the voids
are for stone of uniform size whatever that size be. As was the case
with sand a mixture of coarse and fine particles gives the fewest voids;
for stone an L_{1}M_{0}F_{1} mixture and for gravel an L_{8}M_{0}F_{2}
mixture. Tamping reduces the voids in broken stone. Mr. Geo. W. Rafter
gives the voids in clean, hand-broken limestone passing a 2½-in. ring as
43 per cent. after being lightly shaken and 37½ per cent. after being
rammed. Generally speaking heavy ramming will reduce the voids in loose
stone about 20 per cent.
It is rare that gravel has less than 30 per cent. or more than 45 per
cent. voids. If the pebbles vary considerably in size so that the small
fit in between the large, the voids may be as low as 30 per cent. but if
the pebbles are tolerably uniform in size the voids will approach 45 per
cent. Table V shows the effect of granulometric composition on the voids
in gravel as determined by Feret. Mr. H. Von Schon gives the following
granulometric analysis of a gravel having 34.1 per cent. voids:
Retained on 1-in. ring, per cent. 10.70
Retained on 3/8-in. ring, per cent. 23.65
Retained on No. 4 sieve, per cent. 8.70
Retained on No. 10 sieve, per cent. 17.14
Retained on No. 20 sieve, per cent. 21.76
Retained on No. 30 sieve, per cent. 6.49
Retained on No. 40 sieve, per cent. 5.96
Passed a No. 40 sieve, per cent. 5.59
Passed a 1½-in ring, per cent. 100.00
As mixtures of broken stone and gravel are often used the following
determinations of voids in such mixtures are given. The following
determinations were made by Mr. Wm. M. Hall for mixtures of blue
limestone and Ohio River washed gravel:
Per cent. Per cent. Per cent.
Stone. Gravel. Voids in Mix
100 with 0 48
80 " 20 44
70 " 30 41
60 " 40 38½
50 " 50 36
0 " 100 35
The dust was screened from the stone all of which passed a 2½-in. ring;
the gravel all passed a 1½-in. screen. Using the same sizes of gravel
and Hudson River trap rock, the results were:
Per cent. Per cent. Per cent.
Trap. Gravel. Voids in Mix.
100 with 0 50
60 " 40 38½
50 " 50 36
0 " 100 35
The weight of a cubic foot of loose gravel or stone is not an accurate
index of the percentage of voids unless the specific gravity is known.
Pure quartz weighs 165 lbs., per cu. ft., hence broken quartz having 40
per cent. voids weighs 165 × .60 = 99 lbs. per cu. ft. Few gravels are
entirely quartz, and many contain stone having a greater specific
gravity like some traps or a less specific gravity like some shales and
sandstone. Tables VI and VII give the specific gravities of common
stones and minerals and Table VIII gives the weights corresponding to
different percentages of voids for different specific gravities.
TABLE VI.--SPECIFIC GRAVITY OF STONE. (Condensed from Merrill's "Stones
for Building.")
Trap, Boston, Mass. 2.78
" Duluth, Minn. 2.8 to 3.0
" Jersey City, N. J. 3.03
" Staten Island, N. Y. 2.86
Gneiss, Madison Ave., N. Y. 2.92
Granite, New London, Conn. 2.66
" Greenwich, Conn. 2.84
" Vinalhaven, Me. 2.66
" Quincy, Mass. 2.66
" Barre, Vt. 2.65
Limestone, Joliet, Ill. 2.56
" Quincy, Ill. 2.51 to 2.57
Limestone, (oolitic) Bedford, Ind. 2.25 to 2.45
" Marquette, Mich. 2.34
" Glens Falls, N.Y. 2.70
" Lake Champlain, N. Y. 2.75
Sandstone, Portland, Conn. 2.64
" Haverstraw, N. Y. 2.13
" Medina, N. Y. 2.41
" Potsdam, N. Y. 2.60
" (grit) Berea, O. 2.12
TABLE VII.--SPECIFIC GRAVITY OF COMMON MINERALS AND ROCKS.
Apatite 2.92-3.25
Basalt 3.01
Calcite, CaCO_{3} 2.5-2.73
Cassiterite, SnO_{2} 6.4-7.1
Cerrusite, PbCO_{3} 6.46-6.48
Chalcopyrite, CuFeS_{2} 4.1-4.3
Coal, anthracite 1.3-1.84
Coal, bituminous 1.2-1.5
Diabase 2.6-3.03
Diorite 2.92
Dolomite, CaMg (CO_{3})² 2.8-2.9
Felspar 2.44-2.78
Felsite 2.65
Galena, Pbs 7.25-7.77
Garnet 3.15-4.31
Gneiss 2.62-2.92
Granite 2.55-2.86
Gypsum 2.3-3.28
Halite (salt) NaCl 2.1-2.56
Hematite, Fe_{2}O_{3} 4.5-5.3
Hornblende 3.05-3.47
Limonite, Fe_{3}O_{4} (OH)^{6} 3.6-4.0
Limestone 2.35-2.87
Magnetite, Fe_{3}O_{4} 4.9-5.2
Marble 2.08-2.85
Mica 2.75-3.1
Mica Schist 2.5-2.9
Olivine 3.33-3.5
Porphyry 2.5-2.6
Pyrite, FeS_{2} 4.83-5.2
Quartz, SiO_{2} 2.5-2.8
Quartzite 2.6-2.7
Sandstone 2.0-2.78
" Medina 2.4
" Ohio 2.2
" Slaty 1.82
Shale 2.4-2.8
Slate 2.5-2.8
Sphalerite, ZnS 3.9-4.2
Stibnite, Sb_{2}S_{3} 4.5-4.6
Syenite 2.27-2.65
Talc 2.56-2.8
Trap 2.6-3.0
TABLE VIII.--SHOWING WEIGHT OF STONE WITH DIFFERENT PERCENTAGES OF VOIDS
FOR DIFFERENT SPECIFIC GRAVITIES.
Weight Weight
in Lbs. in Lbs. Weight in Lbs. per cu. yd.
Specific per per when Voids are
Gravity. cu. ft. cu. yd. 30% 35% 40% 45% 50%
1.0 62.355 1,684 1,178 1,094 1,010 926 842
2.0 124.7 3,367 2,357 2,187 2,020 1,852 1,684
2.1 130.9 3,536 2,475 2,298 2,121 1,945 1,768
2.2 137.2 3,704 2,593 2,408 2,222 2,037 1,852
2.3 143.4 3,872 2,711 2,517 2,323 2,130 1,936
2.4 149.7 4,041 2,828 2,626 2,424 2,222 2,020
2.5 155.9 4,209 2,946 2,736 2,525 2,315 2,105
2.6 162.1 4,377 3,064 2,845 2,626 2,408 2,189
2.7 168.4 4,546 3,182 2,955 2,727 2,500 2,273
2.8 174.6 4,714 3,300 3,064 2,828 2,593 2,357
2.9 180.9 4,882 3,418 3,174 2,929 2,685 2,441
3.0 187.1 5,051 3,536 3,283 3,030 2,778 2,526
3.1 193.3 5,219 3,653 3,392 3,131 2,871 2,609
3.2 199.5 5,388 3,771 3,502 3,232 2,963 2,694
3.3 205.8 5,556 3,889 3,611 3,333 3,056 2,778
3.4 212.0 5,724 4,007 3,721 3,434 3,148 2,862
3.5 218.3 5,893 4,125 3,830 3,535 3,241 2,947
In buying broken stone by the cubic yard it should be remembered that
hauling in a wagon compacts the stone by shaking it down and reduces the
volume. Table IX shows the results of tests made by the Illinois Highway
Commission to determine the settlement of crushed stone in wagon loads
for different lengths of haul. The road over which the tests were made
was a macadam road, not particularly smooth, but might be considered as
an average road surface. The wagon used was one with a dump bottom
supported by chains, which were drawn as tight as possible, so as to
reduce the sag to a minimum. It will be noticed that about 50 per cent.
of the settlement occurs within the first 100 ft., and 75 per cent. of
the settlement in the first 200 ft. Almost all of the settlement occurs
during the first half mile, as the tests showed practically no
additional settlement for distances beyond. Some of the wagons were
loaded from the ground with shovels, others were loaded from bins, the
stone having a 15-ft. drop, which compacted the stone a little more than
where loaded with shovels, so that there was somewhat less settlement.
But at the end of a half mile the density was practically the same,
whatever the method of loading. The density at the beginning and at the
end of the haul can be compared by the weight of a given volume of
crushed stone. For convenience, the weight of a cubic yard of the
material at the beginning of the haul and at the end was computed from
the known contents of a wagon.
TABLE IX.--SHOWING SETTLEMENT OF BROKEN STONE DUE TO DIFFERENT LENGTHS
OF HAUL ON ORDINARILY GOOD ROAD IN WAGONS.
[Transcriber's Note: Table split]
-----------+------------+---------------------------------------------------+
Size. | Method of | |
| Loading. | Per cent Settlement for Hauling. |
| +---------------------------------------------------+
| |100'|200'|300'|400'|500'|600'|700'|½ Mile|1 Mile |
-----------+------------+----+----+----+----+----+----+----+------+---------+
Screenings |15 ft. drop |....| ...|....|....|....|....|....| 11.5 | 11.5 |
Screenings |15 ft. drop |....| ...|....|....|....|....|....| 12.6 | 12.6 |
Screenings |15 ft. drop | 7.3| 8.3| 8.9| 9.2| 9.5|10.1|10.1| 11.2 | .... |
Screenings |15 ft. drop | 5.0| 9.6|10.2|10.2|10.4|10.4|10.4| 12.4 | .... |
| | | | | | | | | | |
===========+============+====+====+====+====+====+====+====+======+=========+
1½ inch |15 ft. drop | ...|....|....|....|....|....|....| 11.5 | 11.5[C] |
1½ inch |15 ft. drop | 5.3| 6.2| 7.1| 7.7| 7.9| 8.0| 8.3| 9.2 | .... |
1½ inch |15 ft. drop | 2.6| 3.7| 4.9| 5.3| 5.3| 5.3| 5.4| 5.4 | .... |
1½ inch |Shovels | 3.5| 4.1| 4.8| 5.3| 5.3| 5.7| 6.5| 7.25| .... |
1½ inch |Shovels | ...|....|....|....|....|....|....| 12.6 | 12.6 |
===========+============+====+====+====+====+====+====+====+======+=========+
3 inch |15 ft. drop | ...|....|....|....|....|....|....| 10.1 | 10.1 |
3 inch |15 ft. drop | 3.5| 4.2| 4.5| 4.8| 5.0| 5.0| 5.0| 6.0 | .... |
3 inch |15 ft. drop | 0.5| 2.5| 2.5| 4.1| 4.3| 4.3| 4.3| 4.9 | .... |
3 inch |Shovels | ...|....|....|....|....|....|....| 12.6 | 12.6 |
3 inch |Shovels | 5.0| 5.6| 6.5| 6.5| 6.8| 6.8| 6.8| 7.1 | .... |
------------------------+----+----+----+----+----+----+----+------+---------+
[Footnote C: Same per cent of settlement for two-mile haul.]
-----------+------------+-----------------
Size. | Method of | Weight per
| Loading. | Cu. Yd. in Lbs.
| +-----------------
| | At | At
| | start.| finish.
-----------+------------+-------+-------
Screenings |15 ft. drop | 2,518 | 2,840
Screenings |15 ft. drop | 2,518 | 2,886
Screenings |15 ft. drop | 2,450 | 2,770
Screenings |15 ft. drop | 2,425 | 2,780
===========+============+=======+========
| | |
1½ inch |15 ft. drop | 2,305 | 2,600
1½ inch |15 ft. drop | 2,380 | 2,625
1½ inch |15 ft. drop | 2,450 | 2,600
1½ inch |Shovels | 2,270 | 2,445
1½ inch |Shovels | 2,305 | 2,642
===========+============+=======+========
3 inch |15 ft. drop | 2,376 | 2,638
3 inch |15 ft. drop | 2,360 | 2,505
3 inch |15 ft. drop | 2,470 | 2,595
3 inch |Shovels | 2,270 | 2,601
3 inch |Shovels | 2,335 | 2,510
------------------------+-------+--------
~THEORY OF THE QUANTITY OF CEMENT IN MORTAR AND CONCRETE.~--All sand
contains a large percentage of voids; in 1 cu. ft. of loose sand there
is 0.3 to 0.5 cu. ft. of voids, that is, 30 to 50 per cent. of the sand
is voids. In making mortar the cement is mixed with the sand and the
flour-like particles of the cement fit in between the grains of sand
occupying a part or all of the voids. The amount of cement required in a
mortar will naturally depend upon the amount of voids in the particular
sand with which it is mixed and since a correct estimate of the number
of barrels of cement per cubic yard of mortar is very important, and
since it is not always possible to make actual mixtures before bidding,
rules based on various theories have been formulated for determining
these quantities. In this volume the rule based on the theory outlined
by one of the authors in 1901 will be followed. The following is a
discussion of the authors' theory:
When loose sand is mixed with water, its volume or bulk is increased;
subsequent jarring will decrease its volume, but still leave a net gain
of about 10 per cent.; that is, 1 cu. ft. of dry sand becomes about 1.1
cu. ft. of damp sand. Not only does this increase in the volume of the
sand occur, but, instead of increasing the voids that can be filled with
cement, there is an absolute loss in the volume of available voids. This
is due to the space occupied by the water necessary to bring the sand to
the consistency of mortar; furthermore, there is seldom a perfect
mixture of the sand and cement in practice, thus reducing the available
voids. It is safe to call this reduction in available voids about 10 per
cent.
When loose, dry Portland cement is wetted, it shrinks about 15 per cent,
in volume, behaving differently from the sand, but it never shrinks back
to quite as small a volume as it occupies when packed tightly in a
barrel. Since barrels of different brands vary widely in size, the
careful engineer or contractor will test any brand he intends using in
large quantities, in order to ascertain exactly how much cement paste
can be made. He will find a range of from 3.2 cu. ft. to 3.8 cu. ft. per
barrel of Portland cement. Obviously the larger barrel may be cheaper
though its price is higher. Specifications often state the number of
cubic feet that will be allowed per barrel in mixing the concrete
ingredients, so that any rule or formula to be of practical value must
contain a factor to allow for the specified size of the barrel, and
another factor to allow for the actual number of cubic feet of paste
that a barrel will yield--the two being usually quite different.
The deduction of a rational, practical formula for computing the
quantity of cement required for a given mixture will now be given, based
upon the facts above outlined.
Let p = number of cu. ft. cement paste per bbl., as determined
by actual test.
n = number of cu. ft. of cement per bbl., as specified in
the specifications.
s = parts of sand (by volume) to one part of cement, as
specified.
g = parts of gravel or broken stone (by volume) to one
part of cement, as specified.
v = percentage of voids in the dry sand, as determined
by test.
V = percentage of voids in the gravel or stone, as determined
by test.
Then, in a mortar of 1 part cement to s parts sand, we have:
n s = cu. ft. of dry sand to 1 bbl. of cement.
n s v = " " " voids in the dry sand.
0.9 n s v = " " " available voids in the wet sand.
1.1 n s = " " " wet sand.
p - 0.9 n s v = " " " cement paste in excess of the voids.
Therefore:
1.1 n s + (p - 0.9 n s v) = cu. ft. of mortar per bbl.
Therefore:
27 27
N = ------------------------- = --------------------
1.1 n s + (p - 0.9 n s v) p + n s (1.1 - 0.9 v)
N being the number of barrels of cement per cu. yd. of mortar.
When the mortar is made so lean that there is not enough cement paste to
fill the voids in the sand, the formula becomes:
27
N = -------
1.1 n s
A similar line of reasoning will give us a rational formula for
determining the quantity of cement in concrete; but there is one point
of difference between sand and gravel (or broken stone), namely, that
the gravel does not swell materially in volume when mixed with water.
However, a certain amount of water is required to wet the surface of the
pebbles, and this water reduces the available voids, that is, the voids
that can be filled by the mortar. With this in mind, the following
deduction is clear, using the nomenclature and symbols above given:
ng = cu. ft. of dry gravel (or stone).
ng V = " " " voids in dry gravel.
0.9 ng V = " " " "available voids" in the wet gravel.
p + n s (1.1 - 0.9 v) - 0.9 ng V = excess of mortar over the available
voids in the wet gravel.
ng + p + n s (1.1 - 0.9 v) - 0.9 ng V = cu. ft. of concrete from
1 bbl. cement.
27
N = -----------------------------------------------
p + n s (1.1 - 0.9v) + ng (1 - 0.9V)
N being the number of barrels of cement required to make 1 cu. yd. of
concrete.
This formula is rational and perfectly general. Other experimenters may
find it desirable to use constants slightly different from the 1.1 and
the 0.9, for fine sands swell more than coarse sands, and hold more
water.
The reader must bear in mind that when the voids in the sand exceed the
cement paste, and when the available voids in the gravel (or stone)
exceed the mortar, the formula becomes:
27
N = ------
ng
These formulas give the amounts of cement in mortars and concretes
compacted in place. Tables X to XIII are based upon the foregoing
theory, and will be found to check satisfactorily with actual tests.
In using these tables remember that the proportion of cement to sand is
by volume, and not by weight. If the specifications state that a barrel
of cement shall be considered to hold 4 cu. ft., for example, and that
the mortar shall be 1 part cement to 2 parts sand, then 2 barrel of
cement is mixed with 8 cu. ft. of sand, regardless of what is the actual
size of the barrel, and regardless of how much cement paste can be made
with a barrel of cement. If the specifications fail to state what the
size of a barrel will be, then the contractor is left to guess.
TABLE X.--BARRELS OF PORTLAND CEMENT PER CUBIC YARD OF MORTAR.
(Voids in sand being 35%, and 1 bbl. cement yielding 3.65 cu. ft. of
cement paste.)
----------------------------------+------+-------+------+-------+------+------
Proportion of Cement to Sand |1 to 1|1 to 1½|1 to 2|1 to 2½|1 to 3|1 to 4
----------------------------------+------+-------+------+-------+------+------
| Bbls.| Bbls. | Bbls.| Bbls. | Bbls.| Bbls.
Barrel specified to be 3.5 cu. ft.| 4.22 | 3.49 | 2.97 | 2.57 | 2.28 | 1.76
" " " 3.8 | 4.09 | 3.33 | 2.81 | 2.45 | 2.16 | 1.62
" " " 4.0 | 4.00 | 3.24 | 2.73 | 2.36 | 2.08 | 1.54
" " " 4.4 | 3.81 | 3.07 | 2.57 | 2.27 | 2.00 | 1.40
+------+-------+------+-------+------+------
Cu. yds. sand per cu. yd. mortar | 0.6 | 0.7 | 0.8 | 0.9 | 1.0 | 1.0
----------------------------------+------+-------+------+-------+------+------
TABLE XI.--BARRELS OF PORTLAND CEMENT PER CUBIC YARD OF MORTAR.
(Voids in sand being 45%, and 1 bbl. cement yielding 3.4 cu. ft. of
cement paste.)
----------------------------------+------+-------+------+-------+------+------
Proportion of Cement to Sand |1 to 1|1 to 1½|1 to 2|1 to 2½|1 to 3|1 to 4
----------------------------------+------+-------+------+-------+------+------
| Bbls.| Bbls. | Bbls.| Bbls. | Bbls.| Bbls.
Barrel specified to be 3.5 cu. ft.| 4.62 | 3.80 | 3.25 | 2.84 | 2.35 | 1.76
" " " 3.8 " | 4.32 | 3.61 | 3.10 | 2.72 | 2.16 | 1.62
" " " 4.0 " | 4.19 | 3.46 | 3.00 | 2.64 | 2.05 | 1.54
" " " 4.4 " | 3.94 | 3.34 | 2.90 | 2.57 | 1.86 | 1.40
+------+-------+------+-------+------+------
Cu. yds. sand per cu. yd. mortar | 0.6 | 0.8 | 0.9 | 1.0 | 1.0 | 1.0
----------------------------------+------+-------+------+-------+------+------
If the specifications call for proportions by weight, assume a Portland
barrel to contain 380 lbs. of cement, and test the actual weight of a
cubic foot of the sand to be used. Sand varies extremely in weight, due
both to the variation in the per cent. of voids, and to the variation in
the kind of minerals of which the sand is composed. A quartz sand having
35 per cent. voids weighs 107 lbs. per cu. ft.; but a quartz sand
having 45 per cent. voids weighs only 91 lbs. per cu. ft. If the weight
of the sand must be guessed at, assume 100 lbs. per cu. ft. If the
specifications require a mixture of 1 cement to 2 of sand by weight, we
will have 380 lbs. (or 1 bbl.) of cement mixed with 2 × 380, or 760 lbs.
of sand; and if the sand weighs 90 lbs. per cu. ft., we shall have 760 ÷
90, or 8.44 cu. ft. of sand to every barrel of cement. In order to use
the tables above given, we may specify our own size of barrel; let us
say 4 cu. ft.; then 8.44 ÷ 4 gives 2.11 parts of sand by volume to 1
part of cement. Without material error we may call this a 1 to 2 mortar,
and use the tables, remembering that our barrel is now "specified to be"
4 cu. ft. If we have a brand of cement that yields 3.4 cu. ft. of paste
per bbl., and sand having 45 per cent. voids, we find that approximately
3 bbls. of cement per cu. yd. of mortar will be required.
TABLE XII.--INGREDIENTS IN 1 CUBIC YARD OF CONCRETE.
(Sand voids, 40%; stone voids, 45%; Portland cement barrel yielding 3.65
cu. ft. paste. Barrel specified to be 3.8 cu. ft.)
--------------------------------+-------+-------+-------+-------+-------+------
| 1:2:4 | 1:2:5 | 1:2:6 | 1:2½:5| 1:2½:6| 1:3:4
--------------------------------+-------+-------+-------+-------+-------+------
Bbls. cement per cu. yd. concr't| 1.46 | 1.30 | 1.18 | 1.13 | 1.00 | 1.25
Cu. yds. sand " " | 0.41 | 0.36 | 0.33 | 0.40 | 0.35 | 0.53
Cu. yds. stone " " | 0.82 | 0.90 | 1.00 | 0.80 | 0.84 | 0.71
--------------------------------+-------+-------+-------+-------+-------+------
Proportions by Volume. | 1:3:5 | 1:3:6 | 1:3:7 | 1:4:7 | 1:4:8 | 1:4:9
--------------------------------+-------+-------+-------+-------+-------+------
Bbls. cement per cu. yd. concr't| 1.13 | 1.05 | 0.96 | 0.82 | 0.77 | 0.73
Cu. yds. sand " " | 0.48 | 0.44 | 0.40 | 0.46 | 0.43 | 0.41
Cu. yds. stone " " | 0.80 | 0.88 | 0.93 | 0.80 | 0.86 | 0.92
--------------------------------+-------+-------+-------+-------+-------+------
NOTE.--This table is to be used where cement is measured packed
in the barrel, for the ordinary barrel holds 3.8 cu. ft.
It should be evident from the foregoing discussions that no table can be
made, and no rule can be formulated that will yield accurate results
unless the brand of cement is tested and the percentage of voids in the
sand determined. This being so the sensible plan is to use the tables
merely as a rough guide, and, where the quantity of cement to be used is
very large, to make a few batches of mortar using the available brands
of cement and sand in the proportions specified. Ten dollars spent in
this way may save a thousand, even on a comparatively small job, by
showing what cement and sand to select.
It will be seen that Tables XII and XIII can be condensed into the
following rule:
_Add together the number of parts and divide this sum into ten, the
quotient will be approximately the number of barrels of cement per cubic
yard._
TABLE XIII.--INGREDIENTS IN 1 CUBIC YARD OF CONCRETE.
(Sand voids, 40%; stone voids, 45%; Portland cement barrel yielding 3.65
cu. ft. of paste. Barrel specified to be 4.4 cu. ft.)
--------------------------------+------+------+------+------+------+-----
Proportions by Volume. |1:2:4 |1:2:5 |1:2:6 |1:2½:5|1:2½:6|1:3:4
--------------------------------+------+------+------+------+------+-----
Bbls. cement per cu. yd. concr't| 1.30 | 1.16 | 1.00 | 1.07 | 0.96 | 1.08
Cu. yds. sand " " | 0.42 | 0.38 | 0.33 | 0.44 | 0.40 | 0.53
Cu. yds. stone " " | 0.84 | 0.95 | 1.00 | 0.88 | 0.95 | 0.71
--------------------------------+------+------+------+------+------+-----
Proportions by Volume. |1:3:5 |1:3:6 |1:3:7 |1:4:7 |1:4:8 |1:4:9
--------------------------------+------+------+------+------+------+-----
Bbls. cement per cu. yd. concr't| 0.96 | 0.90 | 0.82 | 0.75 | 0.68 | 0.64
Cu. yds. sand " " | 0.47 | 0.44 | 0.40 | 0.49 | 0.44 | 0.42
Cu. yds. stone " " | 0.78 | 0.88 | 0.93 | 0.86 | 0.88 | 0.95
--------------------------------+------+------+------+------+------+-----
NOTE.--This table is to be used when the cement is measured
loose, after dumping it into a box, for under such conditions a
barrel of cement yields 4.4 cu. ft. of loose cement.
Thus for a 1:2:5 concrete, the sum of the parts is 1 + 2 + 5, which is
8; then 10 ÷ 8 is 1.25 bbls., which is approximately equal to the 1.30
bbls. given in the table. Neither is this rule nor are the tables
applicable if a different size of cement barrel is specified, or if the
voids in the sand or stone differ materially from 40 per cent. to 45 per
cent. respectively. There are such innumerable combinations of varying
voids, and varying sizes of barrel, that the authors do not deem it
worth while to give other tables. The following amounts of cement per
cubic yard of mortar were determined by test:
----------------+------+------+------+------+------+------+------+------+------
Authority | Neat.|1 to 1|1 to 2|1 to 3|1 to 4|1 to 5|1 to 6|1 to 7|1 to 8
----------------+-------------+------+------+------+------+------+------+------
| Bbls.| Bbls.| Bbls.| Bbls.| Bbls.| Bbls.| Bbls.| Bbls.| Bbls.
Sabin | 7.40 | 4.17 | 2.84 | 2.06 | 1.62 | 1.33 | 1.14 | .... | ....
W. B. Fuller | 8.02 | 4.58 | 3.09 | 2.30 | 1.80 | 1.48 | 1.23 | 1.11 | 1.00
H. P. Boardman. | 7.40 | 4.50 | 3.18 | 2.35 | .... | .... | .... | .... | ....
----------------+------+------+------+------+------+------+------+------+------
The proportions were by barrels of cement to barrels of sand, and Sabin
called a 380-lb. barrel 3.65 cu. ft., whereas Fuller called a 380-lb.
barrel 3.80 cu. ft.; and Boardman called a 380-lb. barrel 3.5 cu. ft.
Sabin used a sand having 38 per cent. voids; Fuller used a sand having
45 per cent. voids; and Boardman used a sand having 38 per cent. voids.
It will be seen that the cement used by Sabin yielded 3.65 cu. ft. of
cement paste per bbl. (i. e. 27 ÷ 7.4), whereas the (Atlas) cement used
by Fuller yielded 3.4 cu. ft. of cement paste per bbl. Sabin found that
a barrel of cement measured 4.37 cu. ft. when dumped and measured loose.
Mr. Boardman states a barrel (380 lbs., net) of Lehigh Portland cement
yields 3.65 cu. ft. of cement paste; and that a barrel (265 lbs., net)
of Louisville natural cement yields 3.0 cu. ft. of cement paste.
Mr. J. J. R. Croes, M. Am. Soc. C. E., states that 1 bbl. of Rosendale
cement and 2 bbl. of sand (8 cu. ft.) make 9.7 cu. ft. of mortar, the
extreme variations from this average being 7 per cent.
Frequently concrete is made by mixing one volume of cement with a given
number of volumes of pit gravel; no sand being used other than the sand
that is found naturally mixed with the gravel. In such cases the cement
rarely increases the bulk of the gravel, hence Table XIV will give the
approximate amount of cement, assuming 1 cu. yd. of gravel per cubic
yard of concrete.
TABLE XIV.--SHOWING BARRELS OF CEMENT PER CUBIC YARD OF VARIOUS MIXTURES
OF CEMENT AND PIT GRAVEL.
---------+------------------------------------------------------------
Spc. Vol.|Barrels of Cement per Cubic Yard of Concrete for Mixtures of
of bbl. +-------+-------+-------+-------+-------+-------+------------
cu. ft. | 1-5 | 1-6 | 1-7 | 1-8 | 1-9 | 1-10 | 1-12
---------+-------+-------+-------+-------+-------+-------+------------
3.8 | 1.41 | 1.18 | 1.01 | 0.874 | 0.789 | 0.71 | 0.59
4.4 | 1.25 | 1.02 | 0.875 | 0.766 | 0.681 | 0.61 | 0.51
---------+-------+-------+-------+-------+-------+-------+------------
~PERCENTAGE OF WATER IN CONCRETE.~--Tests show that dry mixtures when
carefully deposited and well tamped produce the stronger concrete. This
superiority of dry mixtures it must be observed presupposes careful
deposition and thorough tamping, and these are tasks which are difficult
to have accomplished properly in actual construction work and which, if
accomplished properly, require time and labor. Wet mixtures readily flow
into the corners and angles of the forms and between and around the
reinforcing bars with only a small amount of puddling and slicing and
are, therefore, nearly always used because of the time and labor saved
in depositing and tamping. The following rule by which to determine the
percentage of water by weight for any given mixture of mortar for wet
concrete will be found satisfactory:
_Multiply the parts of sand by 8, add 24 to the product, and divide the
total by the sum of the parts of sand and cement._
For example if the percentage of water is required for a 1-3 mortar:
(3 × 8) + 24
------------ = 12.
4
Hence the water should be 12 per cent. of the combined weight of cement
and sand. For a 1-1 mortar the rule gives 16 per cent.; for a 1-2 mortar
it gives 13½ per cent., and for a 1-6 mortar it gives 10.3 per cent.
To calculate the amount of water per cubic yard of 1-3-6 concrete for
example the procedure would be as follows: By the above rule a 1-3
mortar requires
(3 × 8) + 24
------------ = 12 per cent. water.
4
A 1-3-6 concrete, according to Table XII, contains 1.05 bbls. cement and
0.44 cu. yd. sand. Cement weighs 380 lbs. per barrel, hence 1.05 bbls.
would weigh 380 × 1.05 = 399 lbs. Sand weighs 2,700 lbs. per cu. yd.,
hence 0.44 cu. yd. of sand would weigh 2,700 × 0.44 = 1,188 lbs. The
combined weight of the cement and sand would thus be 399 + 1,188 = 1,587
lbs. and 12 per cent. of 1.587 lbs. is 190 lbs. of water. Water weighs
8.355 lbs. per gallon, hence 190 × 8.355 = 23 gallons of water per cubic
yard of 1-3-6 concrete.
~METHODS OF MEASURING AND WEIGHING.~--The cement, sand and aggregate for
concrete mixtures are usually measured by hand, the measuring being done
either in the charging buckets or in the barrows or other receptacles
used to handle the material to the charging buckets. The process is
simple in either case when once the units of measurement are definitely
stated. This is not always the case. Some engineers require the
contractor to measure the sand and stone in the same sized barrel that
the cement comes in, in which case 1 part of sand or aggregate usually
means 3.5 cu. ft. Other engineers permit both heads of the barrel to be
knocked out for convenience in measuring the sand and stone, in which
case a barrel means 3.75 cu. ft. Still other engineers permit the cement
to be measured loose in a box, then a barrel usually means from 4 to 4.5
cu. ft. Cement is shipped either in barrels or in bags and the engineer
should specify definitely the volume at which he will allow the original
package to be counted, and also, if cement barrels are to be used in
measuring the sand and stone, he should specify what a "barrel" is to
be. When the concrete is to be mixed by hand the better practice is to
measure the sand and stone in bottomless boxes of the general type shown
by Fig. 10 and of known volume, and then specify that a bag of cement
shall be called 1 cu. ft., 0.6 cu. ft., or such other fraction of a
cubic foot as the engineer may choose. The contractor then has a
definite basis on which to estimate the quantity of cement required for
any specified mixture. The same is true if the measuring of the sand and
stone be done in barrows or in the charging bucket. The volume of the
bag or barrel of cement being specified the contractor has a definite
and simple problem to solve in measuring his materials.
[Illustration: Fig. 10.--Bottomless Box for Measuring Materials in
Proportioning Concrete.]
To avoid uncertainty and labor in measuring the cement, sand and stone
or gravel various automatic measuring devices have been designed. A
continuous mixer with automatic measuring and charging mechanism is
described in Chapter XIV. Figure 11 shows the Trump automatic measuring
device. It consists of a series of revolving cylinders, each opening
onto a "table," which revolves with the cylinders, and of a set of fixed
"knives," which, as the "tables" revolve, scrape off portions of the
material discharged from each cylinder onto its "table." The
illustration shows a set of two cylinders; for concrete work a third
cylinder is added. The three tables are set one above the other, each
with its storage cylinder, and being attached to the same spindle all
revolve together. For each table there is a knife with its own
adjusting mechanism. These knives may be adjusted at will to vary the
percentage of material scraped off.
[Illustration: Fig. 11.--Sketch Showing Trump Automatic Measuring Device
for Materials in Proportioning Concrete.]
Automatic measuring devices are most used in connection with continuous
mixers, but they may be easily adapted to batch mixers if desired. One
point to be observed is that all of these automatic devices measure the
cement loose and this must be allowed for in proportioning the mixture.
CHAPTER III.
METHODS AND COST OF MAKING AND PLACING CONCRETE BY HAND.
The making and placing of concrete by hand is divided into the following
operations: (1) Loading the barrows, buckets, carts or cars used to
transport the cement, sand and stone to the mixing board; (2)
Transporting and dumping the material; (3) Mixing the material by
turning with shovels and hoes; (4) Loading the concrete by shovels into
barrows, buckets, carts or cars; (5) Transporting the concrete to place;
(6) Dumping and spreading; (7) Ramming.
~LOADING INTO STOCK PILES.~--Stock piles should always be provided unless
there is some very good reason to the contrary. They prevent stoppage of
work through irregularities in the delivery of the material, and they
save foreman's time in watching that the material is delivered as
promptly as needed for the work immediately in hand. The location of the
stock piles should be as close to the work as possible without being in
the way of construction; forethought both in locating the piles and in
proportioning their size to the work will save the contractor money.
The stone and sand will ordinarily be delivered in wagons or cars. If
delivered in cars, effort should be made to secure delivery in flat cars
when the unloading is to be done by shoveling; this is more particularly
necessary for the broken stone. Stone can be shoveled from hopper bottom
cars only with difficulty as compared with shoveling from flat bottom
cars; the ratio is about 14 cu. yds. per day per man from hopper bottom
cars as compared with 20 cu. yds. per day per man from flat bottom cars.
When the cars can be unloaded through a trestle, hopper bottom cars
should by all means be secured for delivering the stone. If the amount
of work will justify the expense, a trestle may be built; often there is
a railway embankment which can be dug away for a short distance and the
track carried on stringers to make a dumping place, from which the stone
can be shoveled.
Sand can be dumped directly on the ground, but broken stone unless it is
very small, ¾-in. or less, should always be dumped on a well made plank
floor. A good floor is made of 2-in. plank, nailed to 4×6-in. mud sills,
spaced 3 ft. apart, and well bedded in the ground. Loose plank laid
directly on the ground settle unevenly and thus the smooth shoveling
surface which is sought is not obtained; the object of the floor is to
provide an even surface, along which a square pointed shovel can be
pushed; it is very difficult to force such a shovel into broken stone
unless it is very fine. A spading fork is a better tool than a shovel,
with which to load broken stone from piles. A man can load from 18 to 20
cu. yds. of broken stone into wheelbarrows or carts in 10 hours when
shoveling from a good floor, but he can load only 12 to 14 cu. yds. per
day when shoveling from a pile without such a floor. It is a common
thing to see stone unloaded from cars directly onto the sloping side of
a railway embankment. This makes very difficult shoveling and results in
a waste of stone. Stone can usually be delivered by a steel lined chute
directly to a flooring located at the foot of the embankment; coarse
broken stone if given a start when cast from a shovel will slide on an
iron chute having a slope as flat as 3 or 4 to 1; sand will not slide on
a slope of 1½ to 1. When chuting is not practicable it will pay often to
shovel the stone into buckets handled by a stiff-leg derrick rather than
to unload it onto the bank. Stock piles of ample storage capacity are
essential when delivery is by rail, because of the uncertainty of rail
shipments. When the contractor is taking the sand and stone direct from
pit and quarry by wagon it is not necessary to have large stock piles.
~LOADING FROM STOCK PILES.~--In loading sand into wheelbarrows or carts
with shovels a man will load 20 cu. yds. per 10-hour day if he is
energetic and is working under a good foreman. Under opposite conditions
15 cu. yds. per man per day is all that it is safe to count on. A man
shoveling from a good floor will load 20 cu. yds. of stone per 10-hour
day; this is reduced to 15 cu. yds. per day if the stone is shoveled off
the ground and to 12 cu. yds. per day if in addition the management is
poor. There are ordinarily in a cubic yard of concrete about 1 cu. yd.
of stone and 0.4 cu. yd. of sand, so that the cost of loading the
materials into barrows or carts, with wages at 15 cts. per hour and
assuming 15 cu. yds. to be a day's work, would be:
1 cu. yd. stone loaded for 10 cts.
0.4 cu. yd. sand loaded for 4 cts.
-------
Total 14 cts.
To this is to be added the cost of loading the cement. This will cost
not over 2 cts. per cu. yd. of concrete; the total cost of loading
concrete materials into barrows or carts, therefore, does not often
exceed 16 cts. per cu. yd. of concrete.
~TRANSPORTING MATERIALS TO MIXING BOARDS~--Carrying the sand and stone
from stock piles to mixing board in shovels should never be practiced.
It takes from 100 to 150 shovelfuls of stone to make 1 cu. yd.; it,
therefore, costs 50 cts. per cu. yd. to carry it 100 ft. and return
empty handed, for in walking short distances the men travel very
slowly--about 150 ft. per minute. It costs more to walk a half dozen
paces with stone carried in shovels than to wheel it in barrows.
The most common method of transporting materials from stock piles to
mixing boards is in wheelbarrows. The usual wheelbarrow load on a level
plank runway is 3 bags of cement (300 lbs) or 3 cu. ft. of sand or
stone. If a steep rise must be overcome to reach the mixing platform the
load will be reduced to 2 bags (200 lbs.) of cement or 2 cu. ft. of sand
or stone. A man wheeling a barrow travels at a rate of 200 ft. per
minute, going and coming, and loses ¾ minute each trip dumping the load,
fixing run planks, etc. An active man will do 20 to 25 per cent. more
work than this, while a very lazy man may do 20 per cent. less. With
wages at 15 cts. per hour, the cost of wheeling materials for 1 cu. yd.
of concrete may be obtained by the following rule:
_To a fixed cost of 4 cts. (for lost time) add 1 ct. for every 20 ft. of
distance away from the stock pile if there is a steep rise in the
runway, but if the runway is level, add 1 ct. for every 30 ft. distance
of haul._
Since loading the barrows, as given above, was 16 cts. per cu. yd., the
total fixed cost is 16 + 4 = 20 cts. per cu. yd., to which is added 1
ct. for every 20 or 30 ft. haul depending on the grade of the runway.
The preceding figures assume the use of plank runways for the
wheelbarrows. These should never be omitted, and the barrows wheeled
over the ground. Even a hard packed earth path in dry weather is
inferior to a plank runway and when the ground is soft or muddy the loss
in efficiency of the men is serious. Where the runway must rise to the
mixing board, give it a slope or grade seldom steeper than 1 in 8, and
if possible flatter. Make a runway on a trestle at least 18 ins. wide,
so that men will be in no danger of falling. See to it, also, that the
planks are so well supported that they do not spring down when walked
over, for a springy plank makes hard wheeling. If the planks are so long
between the "horses" or "bents" used to support them, that they spring
badly, it is usually a simple matter to nail a cleat across the
underside of the planks and stand an upright strut underneath to support
and stiffen the plank.
When two-wheeled carts of the type shown by Fig. 12 are used the runway
requires two lines of planks.
Two-wheeled carts pushed by hand have been less used for handling
concrete materials than for handling concrete, but for distances from 50
to 150 ft. from stock pile to mixing board such carts are probably
cheaper for transporting materials than are wheelbarrows. These carts
hold generally three wheelbarrow loads and they are handled by one man
practically as rapidly and easily as is a wheelbarrow.
For all distances over 50 ft. from stock pile to mixing board, it is
cheaper to haul materials in one-horse dump carts than it is in
wheelbarrows. A cart should be loaded in 4 minutes and dumped in about 1
minute, making 5 minutes lost time each round trip. It should travel at
a speed of not less than 200 ft. per minute, although it is not unusual
to see variations of 15 or 20 per cent., one way or another, from this
average, depending upon the management of the work. A one-horse cart
will readily carry enough stone and sand to make ½ cu. yd. of concrete,
if the roads are fairly hard and level; and a horse can pull this load
up a 10 per cent. (rise of 1 ft. in 10 ft.) planked roadway provided
with cleats to give a foothold. If a horse, cart and driver can be hired
for 30 cts. per hour, the cost of hauling the materials for 1 cu. yd. of
concrete is given by the following rule:
_To a fixed cost of 5 cts. (for lost time at both ends of haul) add 1
ct. for every 100 ft. of distance from stock pile to mixing board._
[Illustration: Fig. 12.--Two-Wheeled Ransome Cart for Hauling Concrete.]
Where carts are used it is possible to locate the stock piles several
hundred feet from the mixing boards without adding materially to the
cost of the concrete. It is well, however, to have the stock piles in
sight of the foreman at the mixing board, so as to insure promptness of
delivery.
~METHODS AND COST OF MIXING.~--In mixing concrete by hand the materials
are spread in superimposed layers on a mixing board and mixed together
first dry and then with water by turning them with shovels or hoes. The
number of turns, the relative arrangement of the layers, and the
sequence of operations vary in practice with the notions of the
engineer controlling the work. No one mode of procedure in hand mixing
can, therefore, be specified for general application; the following are
representative examples of practice in hand mixing:
Measure the stone in a bottomless box and spread it until its thickness
in inches equals its parts by volume. Measure the sand in a bottomless
box set on the stone and spread the sand evenly over the stone layer.
Place the cement on the sand and spread evenly. Turn the material twice
with a square pointed shovel and then turn it a third time while water
is gently sprinkled on. A fourth turn is made to mix thoroughly the
water and the concrete is then shoveled into barrows, giving it a fifth
turn. Mr. Ernest McCullough, who gives this method, states that it is
the cheapest way to mix concrete by hand and still secure a good quality
of output.
In work done by Mr. H. P. Boardman the sand is measured in a bottomless
box and over it is spread the cement in an even layer. The cement and
sand are mixed dry with hoes, the water is added in pailfuls and the
whole mixed to a uniform porridge-like consistency. Into this thin
mortar all the stone for a batch is dumped, the measuring box is lifted
and the mixture turned by shovels. A pair of shovelers, one on each
side, is started at one end turning the material back and working toward
the opposite end. A second pair of shovelers takes the turned material
and turns it again. The concrete is then shoveled into the barrows by
the wheelers themselves as fast as it is turned the second time. By this
method a good gang of 20 to 25 men, using two boxes, will, Mr. Boardman
states, mix and place 45 to 60 cu. yds. of concrete in 10 hours,
depending on the wheelbarrow travel necessary. Assuming a gang of 25
men, this is a rate of 1.8 to 2.4 cu. yds. per man per 10-hour day,
concrete mixed and placed.
A method somewhat similar to the one just outlined is given by Mr. O. K.
Morgan. A mixing board made of 7/8-in. matched boards nailed to 2×3-in.
sills is used, with a mixing box about 8 ft. long, 4 ft. wide and 10 to
12 ins. deep. This box is set alongside the mixing board and in it the
cement and sand are mixed first dry and then wet; a fairly wet mortar is
made. Meanwhile the stone is spread in an even layer 6 ins. thick on
the mixing board and thoroughly drenched with water. The mortar from the
mixing box is cast by shovels in a fairly even layer over the stone and
the whole is turned two or three times with shovels, generally two turns
are enough. Six men are employed; two prepare the mortar, while four get
the stone in readiness, then all hands finish the operation.
The following method is given by Mr. E. Sherman Gould: Spread the sand
in a thin layer on the mixing board and over it spread the cement. Mix
dry with shovels, using four men, one at each corner, turning outward
and then working back again. Over the dry sand and cement mixture spread
the broken stone which has been previously wetted and on top of the
stone apply water evenly. The water will thus percolate through the
stone without splashing and evenly wet the sand and cement. Finally turn
the whole, using the same number of men and the same mode of procedure
as were used in dry mixing the sand and cement. Mr. Gould states that by
this method the contractor should average 2 cu. yds. of mixed concrete
per man per 10-hour day.
A novel method of hand mixing and an unusual record of output is
described by Maj. H. M. Chittenden, U. S. A., in connection with the
construction of a concrete arch bridge. The mixing was done by hand on a
single board 25 ft. long and sloping slightly from one end to the other.
The materials were dumped together on the upper end of the board.
Sixteen men were stationed along the board, eight on each side. The
first two men turned the mixture dry. Next to them stood a man who
applied the water after each shovelful. The next mixers kept turning the
material along and another waterman assisted in wetting it further down
the board. The men at the end of the board shoveled the concrete into
the carts which took it to the work. Each batch contained 18 cu. ft., or
0.644 cu. yd., and the rate of mixing was 10 cu. yds. per hour, or 6.25
cu. yds. per man per 10-hour day. The work of getting the materials
properly proportioned to the mixing board is not included in this
figure, but the loading of the mixed concrete is included.
It is plain from the foregoing, that specifications for hand mixing
should always state the method to be followed, and particularly the
number of turns necessary. If these matters are not specified the
contractor has to guess at the probable requirements of the engineer.
The authors have known of inspectors demanding from 6 to 9 turns of the
materials when specifications were ambiguous. It should also be made
clear whether or not the final shoveling into the barrows or carts
constitutes a turn, and whether any subsequent shoveling of the concrete
into place constitutes a turn. Inspectors and foremen have frequent
disputes over these questions.
Estimates of the cost of hand mixing may usually be figured upon the
number of times that the materials are to be turned by shovels. A
contractor is seldom required to turn the sand and cement more than
three times dry and three times wet, and then turn the mortar and stone
three times. A willing workman, under a good foreman, will turn over
mortar at the rate of 30 cu. yds. in 10 hours, lifting each shovelful
and casting it into a pile. With wages at $1.50 and six turns, this
means a cost of 5 cts. per cubic yard of mortar for each turn; as there
is seldom more than 0.4 cu. yd. of mortar in a cubic yard of concrete,
we have a cost of 2 cts. per cubic yard of concrete for each turn that
is given the mortar. So if the mortar is given six turns before the
stone is added and then the stone and mortar are mixed by three turns we
have: (2 cts. × 6) + (5 cts. × 3) = 12 + 15 = 27 cts. per cubic yard for
mixing concrete. In pavement foundation work two turns of the mortar
followed by two turns of the mortar and stone are considered sufficient.
The cost of mixing per cubic yard of concrete is then (2 cts. × 2) + (5
cts. × 2) = 4 + 10 = 14 cts. per cubic yard of concrete. One
specification known to the authors, requires six turns dry and three
turns wet for the mortar; under such specifications the cost of mixing
the mortar would be 50 per cent. higher than in the first example
assumed. On the other hand, they have seen concrete mixed for street
pavement foundation with only three turns before shoveling it into
place. These costs of mixing apply to work done by diligent men; easy
going men will make the cost 25 to 50 per cent greater.
~LOADING AND HAULING MIXED CONCRETE.~--Wheelbarrows and carts are employed
to haul the mixed concrete to the work. The loading of these with mixed
concrete by shoveling costs less than the loading of the materials
separately before mixing. While the weight is greater because of the
added water the volume of the concrete is much less than that of the
ingredients before mixing. Again the shoveling is done off a smooth
board with the added advantage of having the material lubricated and,
finally, the foreman is usually at this point to crowd the work. A good
worker will load 12½ cu. yds. of concrete per 10-hour day, and with
wages at $1.50 per day this would give a cost of 12 cts. per cu. yd. for
loading.
Practically the same principles govern the transporting of concrete in
barrows as govern the handling of the raw materials in them. The cost of
wheeling concrete is practically the same as for wheeling the dry
ingredients, so that the total cost of loading and wheeling may be
estimated by the following rule:
_To a fixed cost of 16 cts. for loading and lost time add 1 ct. for
every 30 ft. of level haul._
Within a few years wheelbarrows have been supplanted to a considerable
extent by hand carts of the general type shown by Fig. 12, which
illustrates one made by the Ransome Concrete Machinery Co. The bowl of
this cart has a capacity of 6 cu. ft. water measure. It is hung on a
1¼-in. steel axle; the wheels are 42 ins. in diameter with staggered
spokes and 2-in. half oval tires. The top of the bowl is 29½ ins. from
the ground. Owing to the large diameter of the wheels and the fact that
no weight comes on the wheeler, as with a wheelbarrow, this cart is
handled by one man about as rapidly and easily as is a wheelbarrow. It
will be noted that the two ends of the bowl differ in shape; the handle
is removable and can be attached to either end of the bowl. With the
handle attached as shown the bowl can be inverted for discharging onto a
pavement or floor; with the handle transferred to the opposite end the
bowl is fitted for dumping into narrow beam or wall forms. The maximum
load of wet concrete for a wheelbarrow is 2 cu. ft., and this is a heavy
load and one that is seldom averaged--1 to 1½ cu. ft. is more nearly the
general average. A cart of the above type will, therefore, carry from 3
to 5 wheelbarrow loads, and on good runways, which are essential, may be
pushed and dumped about as rapidly as a wheelbarrow. In succeeding pages
are given records of actual work with hand carts which should be studied
in this connection.
Portland cement concrete can be hauled a considerable distance in a dump
cart or wagon before it begins to harden; natural cement sets too
quickly to permit of its being hauled far. Portland cement does not
begin to set in less than 30 minutes. On a good road, with no long,
steep hills a team will haul a loaded wagon at a speed of about 200 ft.
per minute; it, therefore, takes 6½ minutes to travel a quarter of a
mile, 13 minutes to travel half a mile, and 26 minutes to travel a mile.
Portland cement concrete can, therefore, be hauled a mile before it
begins to set. The cost of hauling concrete in carts is about the same
as the cost of hauling the raw materials as given in a preceding
section.
When hand mixing is employed in building piers, abutments, walls, etc.,
the concrete often has to be hoisted as well as wheeled. A gallows frame
or a mast with a pulley block at the top and a team of horses can often
be used in such cases as described in Chapter XII for filling cylinder
piers, or in the same chapter for constructing a bridge abutment. It is
also possible often to locate the mixing board on high ground, perhaps
at some little distance from the forms. If this can be done, the use of
derricks may be avoided as above suggested or by building a light pole
trestle from the mixing board to the forms. The concrete can then be
wheeled in barrows and dumped into the forms. If the mixing board can be
located on ground as high as the top of the concrete structure is to be,
obviously a trestle will enable the men to wheel on a level runway. Such
a trestle can be built very cheaply, especially where second-hand
lumber, or lumber that can be used subsequently for forms is available.
A pole trestle whose bents are made entirely of round sticks cut from
the forest is a very cheap structure, if a foreman knows how to throw it
together and up-end the bents after they are made. One of the authors
has put up such trestles for 25 cts. per lineal foot of trestle,
including all labor of cutting the round timber, erecting it, and
placing a plank flooring 4 ft. wide on top. The stringers and flooring
plank were used later for forms, and their cost is not included. A
trestle 100 ft. long can thus be built at less cost than hauling,
erecting and taking down a derrick; and once the trestle is up it saves
the cost of operating a derrick.
In conclusion, it should be remarked that the comparative economy for
concrete work of the different methods of haulage described, does not
depend wholly on the comparative transportation costs; the effect of the
method of haulage on the cost of dumping and spreading costs must be
considered. For example, if carts deliver the material in such form that
the cost of spreading is greatly increased over what it would be were
the concrete delivered in wheelbarrows, the gain made by cart haulage
may be easily wiped out or even turned into loss by the extra spreading
charges. These matters are considered more at length in the succeeding
section.
~DUMPING, SPREADING AND RAMMING.~--The cost of dumping wheelbarrows and
carts is included in the rules of cost already given, excepting that in
some cases it is necessary to add the wages of a man at the dump who
assists the cart drivers or the barrow men. Thus in dumping concrete
from barrows into a deep trench or pit, it is usually advisable to dump
into a galvanized iron hopper provided with an iron pipe chute. One man
can readily dump all the barrows that can be filled from a concrete
mixer in a day, say 150 cu. yds. At this rate of output the cost of
dumping would be only 1 ct. per cu. yd., but if one man were required to
dump the output of a small gang of men, say 25 cu. yds., the cost of
dumping would be 6 cts. per cu. yd.
Concrete dumped through a chute requires very little work to spread it
in 6-in. layers; and, in fact, concrete that can be dumped from
wheelbarrows, which do not all dump in one place, can be spread very
cheaply; for not more than half the pile dumped from the barrow needs to
be moved, and then moved merely by pushing with a shovel. Since the
spreader also rams the concrete, it is difficult to separate these two
items. As nearly as the authors have been able to estimate this item of
spreading "dry" concrete dumped from wheelbarrows in street paving
work, the cost is 5 cts. per cu. yd. If, on the other hand, nearly all
the concrete must be handled by the spreaders, as in spreading concrete
dumped from carts, the cost is fully double, or 10 cts. per cu. yd. And
if the spreader has to walk even 3 or 4 paces to place the concrete
after shoveling it up, the cost of spreading will be 15 cts. per cu. yd.
For this reason it is apparent that carts are not as economical as
wheelbarrows for hauling concrete up to about 200 ft., due to the added
cost of spreading material delivered by carts.
The preceding discussion of spreading is based upon the assumption that
the concrete is not so wet that it will run. Obviously where concrete is
made of small stones and contains an excess of water, it will run so
readily as to require little or no spreading.
The cost of ramming concrete depends almost entirely upon its dryness
and upon the number of cubic yards delivered to the rammers. Concrete
that is mixed with very little water requires long and hard ramming to
flush the water to the surface. The yardage delivered to the rammers is
another factor, because if only a few men are engaged in mixing they
will not be able to deliver enough concrete to keep the rammers properly
busy, yet the rammers by slow though continuous pounding may be keeping
up an appearance of working. Then, again, it has been noticed that the
slower the concrete is delivered the more particular the average
inspector becomes. Concrete made "sloppy" requires no ramming at all,
and very little spading. The authors have had men do very thorough
ramming of moderately dry concrete for 15 cts. per cu. yd., where the
rammers had no spreading to do, the material being delivered in shovels.
It is rare indeed that spreading and ramming can be made to cost more
than 40 cts. per cu. yd., under the most foolish inspection, yet one
instance is recorded which, because of its rarity, is worth noting: Mr.
Herman Conrow is the authority for the data: 1 foreman, 9 men mixing, 1
ramming, averaged 15 cu. yds. a day, or only 1½ cu. yds. per man per
day, when laying wet concrete. When laying dry concrete the same gang
averaged only 8 cu. yds. a day, there being 4 men ramming. With foreman
at $2 and laborers at $1.50 a day, the cost was $2.12 per cu. yd. for
labor on the dry concrete as against $1.13 per cu. yd. for the wet
concrete. Three turnings of the stone with a wet mortar effected a
better mixture than four turnings with a dry mortar. The ramming of the
wet concrete cost 10 cts. per cu. yd., whereas the ramming of the dry
concrete cost 75 cts. per cu. yd. The authors think this is the highest
cost on record for ramming. It is evident, however, that the men were
under a poor foreman, for an output of only 15 cu. yds. per day with 10
men is very low for ordinary conditions. Moreover, the expensive amount
of ramming indicates either poor management or the most foolish
inspection requirements.
In conclusion it may be noted that if engineers specify a dry concrete
and "thorough ramming," they would do well also to specify what the word
"thorough" is to mean, using language that can be expressed in cents per
cubic yard. It is a common thing, for example, to see a sewer trench
specification in which one tamper is required for each two men shoveling
the back-fill into the trench; and some such specific requirement should
be made in a concrete specification if close estimates from reliable
contractors are desired. Surely no engineer will claim that this is too
unimportant a matter for consideration when it is known that ramming can
easily be made to cost as high as 40 cts. per cu. yd., depending largely
upon the whim of the inspector.
~THE COST OF SUPERINTENDENCE.~--This item is obviously dependent upon the
yardage of concrete handled under one foreman and the daily wages of the
foreman. If a foreman receives $3 a day and is bossing a job where only
12 cu. yds. are placed daily, we have a cost of 25 cts. per cu. yd. for
superintendence. If the same foreman is handling a gang of 20 men whose
output is 50 cu. yds., the superintendence item is only 6 cts. per cu.
yd. If the same foreman is handling a concrete-mixing plant having a
daily output of 150 cu. yds., the cost of superintendence is but 2 cts.
per cu. yd. These elementary examples have been given simply because
figures are more impressive than generalities, and because it is so
common a sight to see money wasted by running too small a gang of men
under one foreman.
Of all classes of contract work, none is more readily estimated day by
day than concrete work, not only because it is usually built in regular
shapes whose volumes are easily ascertained at the end of each day, but
because a record of the bags, or barrels, or batches gives a ready
method of computing the output of each gang. For this reason small gangs
of concrete workers need no foreman at all, provided one of the workers
is given command and required to keep tally of the batches. If the
efficiency of a gang of 6 men were to fall off, say, 15 per cent., by
virtue of having no regular non-working foreman in charge, the loss
would be only $1.35 a day--a loss that would be more than
counterbalanced by the saving of a foreman's wages. Indeed, the
efficiency of a gang of 6 men would have to fall off 25 per cent., or
more, before it would pay to put a foreman in charge. In many cases the
efficiency will not fall off at all, provided the gang knows that its
daily progress is being recorded, and that prompt discharge will follow
laziness. Indeed, one of the authors has more than once had the
efficiency increased by leaving a small gang to themselves in command of
one of the workers who was required to punch a hole in a card for every
batch.
To reduce the cost of superintendence there is no surer method than to
work two gangs of 18 to 20 men, side by side, each gang under a separate
foreman who is striving to make a better showing than his competitor.
This is done with marked advantage in street paving, and could be done
elsewhere oftener than it is.
In addition to the cost of a foreman in direct charge of the laborers,
there is always a percentage of the cost of general superintendence and
office expenses to be added. In some cases a general superintendent is
put in charge of one or two foremen; and, if he is a high-salaried man,
the cost of superintendence becomes a very appreciable item.
~SUMMARY OF COSTS.~--Having thus analyzed the costs of making and placing
concrete, we can understand why it is that printed records of costs vary
so greatly. Moreover, we are enabled to estimate the labor cost with far
more accuracy than we can guess it; for by studying the requirements of
the specifications, and the local conditions governing the placing of
stock piles, mixing boards, etc., we can estimate each item with
considerable accuracy. The purpose, however, has not been solely to show
how to predict the labor cost, but also to indicate to contractors and
their foremen some of the many possibilities of reducing the cost of
work once the contract has been secured. An analysis of costs, such as
above given, is the most effective way of discovering unnecessary
"leaks," and of opening one's eyes to the possibilities of effecting
economies in any given case.
To indicate the method of summarizing the costs of making concrete by
hand, let us assume that the concrete is to be put into a deep
foundation requiring wheeling a distance of 30 ft.; that the stock piles
are on plank 60 ft. distant from the mixing board; that the
specifications call for 6 turns of gravel concrete thoroughly rammed in
6-in. layers; and that a good sized gang of, say, 16 men (at $1.50 a day
each), is to work under a foreman receiving $2.70 a day. We then have
the following summary by applying the rules already given:
Per cu. yd.
concrete.
Loading sand, stone and cement $ .17
Wheeling 60 ft. in barrows (4 + 2 cts.) .06
Mixing concrete, 6 turns at 5 cts. .30
Wheeling 30 ft. (4 + 1 ct.) .05
Dumping barrows (1 man helping barrowman) .05
Spreading and heavy ramming .15
------
Total cost of labor $.90
Foreman, at $2.70 a day .10
------
Grand total $1.00
To estimate the daily output of this gang of 16 laborers proceed thus:
Divide the daily wages of all the 16 men, expressed in cents, by the
labor cost of the concrete in cents, the quotient will be the cubic
yards output of the gang. Thus, 2,400 ÷ 90 is 27 cu. yds., in this case.
In street paving work where no man is needed to help dump the
wheelbarrows, and where it is usually possible to shovel concrete direct
from the mixing board into place, and where half as much ramming as
above assumed is usually satisfactory, we see that the last four labor
items instead of amounting to 12 + 5 + 5 + 15, or 37 cts., amount only
to one-half of the last item, one-half of 15 cts., or 7½ cts. This
makes the total labor cost only 60 cts. instead of 90 cts. If we divide
2,400 cts. (the total day's wages of 16 men) by 60 cts. (the labor cost
per cu. yd.), we have 40, which is the cubic yards output of the 16 men.
This greater output of the 16 men reduces the cost of superintendence to
7 cts. per cu. yd.
CHAPTER IV.
METHODS AND COST OF MAKING AND PLACING CONCRETE BY MACHINE.
The making and placing of concrete is virtually a manufacturing process.
This process as performed by manual labor is discussed in the preceding
chapter; it will be discussed here as it is performed by machinery. The
objects sought in using machinery for making and placing concrete are:
(1) The securing of a more perfectly mixed and uniform concrete, and (2)
the securing of a cheaper cost of concrete in place. As in every other
manufacturing process both objects cannot be obtained to the highest
degree without co-ordinate and universal efficiency throughout in plant
and methods. For example, the substitution of machine mixing for hand
mixing will not alone ensure cheaper concrete. If all materials are
delivered to the machine in wheelbarrows and if the concrete is conveyed
away in wheelbarrows, the cost of making concrete even with machine
mixers is high. On the other hand, where the materials are fed from bins
by gravity into the mixer and when the mixed concrete is hauled away in
cars, the cost of making the concrete may be very low. Making and
placing concrete by machinery involves not one but several mechanical
operations working in conjunction--in a word, a concrete making plant is
required.
The mechanical equipment of a concrete making plant has four duties to
perform. (1) It has to transport the raw materials from the cars or
boats or pits and place them in the stock piles or storage bins; (2) it
has to take the raw materials from stock and charge them to the mixer;
(3) it has to mix the raw materials into concrete and discharge the
mixture into transportable vehicles; and (4) it has to transport these
vehicles from the mixer to the work and discharge them. As all these
operations are interrelated component parts of one great process, it is
plain why one operation cannot lag without causing all the other
operations to slow up.
The mechanical devices which may be used for each of these operations
are various, and they may be combined in various ways to make the
complete train of machinery necessary to the complete process. In this
chapter we shall describe the character and qualities of each type of
devices separately. The practicable ways of combining them to form a
complete concrete making plant are best illustrated by descriptions and
records of work of actual plants, and such descriptions and records for
each class of structure considered in this book are given in the
following chapters and may be found by consulting the index. In
describing the various machines and devices we have made one
classification for those used in handling raw materials and mixed
concrete, for the reason that nearly all of them are suitable for either
purpose.
~UNLOADING WITH GRAB BUCKETS.~--The orange-peel or clam-shell bucket is an
excellent device for unloading sand or stone from cars or barges. The
cost of unloading, including cleaning up the portions not reached by the
bucket, is not more than from 2 to 5 cts. per cu. yd. A grab bucket of
either of these types can be applied to any derrick. In unloading broken
stone from barges at Ossining, N. Y., a Hayward clam-shell on a
stiff-leg derrick unloaded 100 cu. yds. of broken stone per day from
barge into wagons, with one engineman and one helper. In addition to the
bucket work there was 24 hours' labor cleaning on each 500-cu. yd. barge
load. The labor cost of unloading a 500-cu. yd. barge was as follows:
Per Cu. Yd.
One engineman, at $2.50 2.5 cts.
One helper, at $1.50 1.5 cts.
Labor cleaning, at $1.50 0.7 cts.
--------
Total cost per cubic yard 4.7 cts.
~INCLINES.~--Inclines to reach the tops of mixer and storage bins and the
level of concrete work can be operated on about the following grades:
For teams hauling wagons or cars, 2 per cent. maximum grade. A single
heavy team will haul a 5-cu. yd. car, with ordinary bearings, weighing
2½ tons empty and 12 tons loaded, with ease on a 1½ per cent. grade,
and with some difficulty on a 2 per cent. grade. A locomotive will
handle cars on a grade of from 4 to 5 per cent. For team haulage 20-lb.
rails may be used, and for locomotives 30-lb. rails. Grades steeper than
about 5 per cent. require cable haulage.
~TRESTLE AND CAR PLANTS.~--Trestle and car plants for handling both
concrete materials and mixed concrete have a wide range of application
and numerous examples of such plants are described in succeeding
chapters, and are noted in the index at the end of the book. The
following estimates of the cost of a trestle and car plant are given by
Mr. Wm. G. Fargo. The work is assumed to cover an area of 100×200 ft.
and to have three-fourths of its bulk below the economical elevation of
the mixer, which stands within 50 ft. of the near side of the work. If
the work is under 3,000 cu. yds. in bulk and there is a reasonable time
limit for completion one mixer of 200 cu. yds. capacity per 10-hour day
is assumed to be sufficient. The items of car plant cost will be about
as follows:
150 ft. trestle, at $1.50 $225
5 split switches with spring bridles, at $18 90
2 iron turntables, at $30 60
3-2/3 cu. yd. steel cars with roller bearings 190
------
Total $565
The trestle assumed is double 24-in. gage track, 6 ft. on centers;
stringers 6×8 ins.×22 to 24 ft.; ties 2×6 ins., 2½ ft. on centers;
running boards 2×12 ins. for each track, and 12-lb. rails; trestle legs,
average length 30 ft., of green poles at 5 cts. per foot. This outfit
with repairs and renewals amounting to 10 per cent., is considered good
for five season's work and the timber work for several jobs if not too
far apart. The yearly rental on the basis of five seasons' work would be
$124.30, or $1 per working day for a season of five months. Three cars
delivering ½ cu. yd. batches can deliver 200 cu. yds. of concrete, an
average of 100 ft. from the mixer in 10 hours. Five men, including a man
tending switches and turntable and one man to help dump, can operate the
plant. With wages at $1.75 per day the labor cost of handling 200 cu.
yds. of concrete would be 4-1/8 cts. per cu. yd.
~CABLEWAYS.~--Cableways arranged to span the work and if the area is wide
to travel across the work at right angles to the span will handle
concrete, concrete materials, forms, steel and supplies with great
economy. They are particularly suitable for bridge and dam work, filter
and reservoir work, building foundations and low buildings. The
arrangement of a cableway plant for bridge work is described in Chapter
XVII. A cableway of 800 ft. clear span on fixed towers 45 ft. high will
cost complete from $4,500 to $5,000, and will handle 200 cu. yds. of
concrete per 10-hour day. To put the cableway on traveling towers will
cost about $1,000 more. In constructing the Pittsburg filtration work
four traveling cableways from 250 to 600 ft. span were used. The towers
were from 50 to 60 ft. in height and each traveled on a 5-rail track.
The cableways were self-propelling. With conditions favorable each
cableway delivered 300 cu. yds. of concrete per day. A cableway plant
for heavy fortification work is described in Chapter XI.
~BELT CONVEYORS.~--Belt conveyors may be used successfully for handling
both concrete materials and mixed concrete. For handling wet concrete
the slope must be quite flat, and the belt must be provided with some
means of cleaning off the sticky mortar paste. In several cases rotating
brushes stationed at the end of the belt, where it turns over the tail
pulley, have worked successfully; these brushes sweep the belt clean.
Except for the cleaning device the ordinary arrangement of belt conveyor
for dry materials serves for concrete.
In constructing a large gas works at Astoria, Long Island, near New York
city, belt conveyors were used to handle both the sand, gravel and
cement bags and the mixed concrete. The belt for handling sand and
gravel is shown by Fig. 13. A derrick operating a clam-shell unloaded
the sand and gravel into a small hopper, discharging into dump cars
operated by a "dinky" up an incline, passing over sand and gravel
storage bins. A 20-in. belt conveyor ran horizontally 105 ft. under the
bins, then up an incline of 3.4 ft. in 125 ft. to feeding hoppers over
the mixers. This conveyor received alternately sand and gravel by chute
from the storage bins and bags of cement loaded by hand, and carried
them to the feeding bins and mixer platform. The speed of the belt was
350 ft. per minute, and it required 6 h.p. to operate it when carrying
100 tons per hour. The mixing was done in two Smith mixers, which turned
out 70 cu. yds. or 35 cu. yds. each per hour. The mixed concrete was
delivered onto a 50-ft. 24-in. belt conveyor traveling at a speed of 400
ft. per minute and dumping through a chute into cars. Only 1 h.p. was
required to run the concrete conveyor. A rotating brush was used to keep
the belt clean at the dumping end. It will be noted that only a small
amount of power is required for operation.
[Illustration: Fig. 13.--Belt Conveyor Transporting Sand and Gravel.]
~CHUTES.~--Chutes of wood or iron are among the simplest and most
efficient means of moving the cement, sand and stone and the mixed
concrete when the ground levels permit such devices.
Bags of cement if given a start in casting will slide down a steel or
very smooth wooden chute with a slope of 1 ft. in 5 or 6 ft. A wooden
trough 12 ins. deep and 24 ins. wide with boards dressed on the inside
may be used. When the inclination is steep and the fall is great, some
device is necessary to diminish the velocity of descent; the following
is an example of such a device which was successfully employed in a
chute of the above dimensions, 400 ft. long and having a drop of 110 ft.
This chute had a maximum inclination of 45° and its lower end curved to
a horizontal tangent, running into the storehouse. Near the bottom of
the chute a horizontal strip was nailed across the upper edges and to it
was nailed the upper end of a 20 ft., 1×12-in. board, the lower end of
which rested on the bottom of the chute. Several pieces of timber spiked
to the upper side loaded the lower end of this board. The cement bag in
descending wedged itself into the angle between the chute and the board
and lifted the latter, the spring of the board and the weight at the
lower end offering enough resistance to cut down the velocity. After the
chute had been in use for some time and had worn smooth it was found
necessary to add two more brakes to check the bags.
Broken stone will slide down a steel or steel lined chute with a slope
of 1 in 3 or 4 ft. if given a start in casting. Damp sand will not slide
down a chute with a slope of 1½ in 1.
A wet cement grout will flow down a smooth plank chute, with a slope of
1 in 4 ft., and wet concrete will move on the same slope; comparatively
dry concrete requires a slope of nearly 1 in 1, or 45°, to secure free
movement. Mr. W. J. Douglas gives the following examples of conveying
concrete by chute, prefaced by the statement that his experience
indicates that concrete can thus be conveyed considerable distances
without material injury if proper precautions are taken.
In the first case a semi-circular steel trough about 2 ft. wide and 1
ft. deep and 15 ft. long set on a slope of 45° was used. A lift gate of
sheet steel was set in the chute about 2 ft. from the upper end. The
concrete was allowed to accumulate behind this gate until a wheelbarrow
load was had, when the batch was let loose by lifting the gate and was
discharged into barrows at the bottom. In another case a vertical chute
15 ft. long, consisting of a 15-in. square box with a canvas end, was
used. The concrete was dumped into the chute in batches of about 8 cu.
ft.; two men at the bottom "cut down" the pile with hoes to keep it from
coning and causing separation of the stone. In a third case a continuous
mixer fed into a sheet iron lined rectangular chute about 2½ ft. wide
and 1 ft. deep, with a vertical drop of 60 ft. on a slope of 1 in 1, or
45°. A gate was fixed in the chute 2 ft. from the top and at the bottom
the chute fed into a pyramidal hopper 3 ft. square at the top, 1 ft.
square at the bottom and 4½ ft. deep. This hopper was provided with a
bottom gate and was set on legs so that its top was about 10 ft. above
ground. As the concrete filled in the hopper was raised and the chute
cut off. The hopper was kept full all the time and was discharged by
bottom gate and spout into wheelbarrows. In a fourth case the apparatus
shown by the sketch, Fig. 14, was used. The continuous mixer discharged
onto an 18-in. rubber conveyor belt on conical rollers and 18 ft. long.
The inner end of the conveyor frame was carried on the ground at the
edge of the pit and the outer end was supported by ropes from the top of
a gallows frame standing on the pit bottom. The belt discharged over end
into a vertical steel chute 12 ins. in diameter and 8 ft. long; this
chute was fastened to the conveyor frame. Encircling and overlapping the
12-in. chute was a second slightly larger chute suspended by means of
two ropes from the gallows frame. The bottom of this second chute was
kept about 6 ins. below the top edges of a pyramidal hopper like the one
described above. In operation the chutes and the hopper were kept filled
with concrete so that the only drop of the concrete was 3 ft. from the
conveyor belt into the topmost chute.
[Illustration: Fig. 14.--Belt Conveyor and Chute for Handling Concrete.]
Concrete may be handled in long flat chutes by stationing men along the
chute with shovels which they work like paddles to keep the mixture
moving. In one case concrete was so handled in a chute 200 ft. long
having a slope of 1 in 10 ft. The chute was a V-shaped trough made of
1×12-in. boards in sections 16 ft. long. The men paddling were stationed
10 ft. apart, so that with wages at $1.50 per day the cost would be 1½
cts. per cu. yd. for every 10 ft. the concrete was conveyed. In
connection with this particular work we are informed that a Eureka
continuous mixer was used. The gravel was dumped near the mixer and a
team hitched to a drag scraper delivered the gravel alongside the mixer.
Four men shoveled the gravel into the measuring hopper, but only two men
worked at a time, shoveling for a period of 15 minutes and then resting
for a corresponding period while the other two men worked. In this
manner the four men shoveled enough gravel to make 100 cu. yds. of
concrete per day. A fifth man opened the cement bags and kept the cement
hopper filled.
~METHODS OF CHARGING MIXERS.~--By charging is meant the process of
delivering raw materials from stock into the mixer. Several methods are
practiced and will be considered in the following order: (1) By gravity
from overhead bins; (2) by wheelbarrow or hand cart (a) to charging
chute and (b) to elevating charging hoppers; (3) by charging cars
operated by cable or other means; (4) by shoveling directly into mixer;
(5) by derricks or other hoists.
~Charging by Gravity from Overhead Bins.~--Chuting the sand and stone from
overhead bins to the charging hopper is a simple, rapid and economical
method of charging mixers. The bottoms of the bins should always be high
enough above the charging floor to give ample head room for men to move
about erect, and the length of chute may be anything reasonable more
than this that conditions such as the side hill delivery of material may
necessitate. When the mixer is located to one side of the bins the slope
of the chute will have to be watched. Broken stone or pebbles will move
on a comparatively flat slope but sand, particularly if damp, requires a
steep chute. The measuring hopper is best kept entirely independent of
the mixer so that it can be filled with a new charge while the mixer is
turning and discharging the preceding batch. One man can attend the sand
and cement chutes if they be conveniently arranged, and one man can open
and empty the cement bags if they be stacked close at hand. A third man
will level off the sand and stone in the measuring hopper and help in
the chuting. A gang of this size will easily measure up a charge every 2
minutes when no delays occur.
[Illustration: Fig. 15.--Side Hill Mixing Plant.]
A number of plants charging by gravity from overhead bins are described
in succeeding chapters and are referenced in the index. As a general
example a side hill plant of conventional construction is shown by Fig.
15. The trestle work was made of 12×12-in. timbers and was approximately
40 ft. in height. Three tracks occupy the top platform. Under each track
was a material bin; one on each side for gravel and a middle bin for
sand. The sand bin was divided by a partition into two compartments.
These bins discharged into two measuring hoppers one gravel bin and one
compartment of the sand bin into each hopper. Two cement chutes from the
top platform provided for the delivery of the cement to the mixers,
either directly from cars or from the cement storage house. The mixing
was done in two Smith No. 5 mixers, one under each measuring hopper, and
these mixers discharged by chutes into buckets on flat cars. Thus the
concrete materials brought directly from a siding in car load lots to
the top of the platform were handled entirely by gravity to the cars
delivering the mixed concrete to the work. The gang operating the mixing
plant, with the wages paid, was composed as follows: 1 foreman and
engineer at $3 per day, 1 fireman at $2 per day and 15 laborers at $1.50
per day. With this gang the two mixers turned out 400 cu. yds. of
concrete per day and, frequently, 800 cu. yds. in 24 hours. Taking these
figures the labor cost from raw materials in cars on the platform to
mixed concrete in cars on the delivery track was as follows:
1 foreman and engineer at $3 $ 3.00
1 fireman at $2 2.00
15 laborers at $1.50 22.50
-----
Total labor $27.50
Assuming 400 cu. yds. output, this gives a cost of $27.50 ÷ 400 = 6.875
cts. per cu. yd.
~Charging with Wheelbarrows.~--The economics of wheelbarrow haulage are
discussed in some detail in Chapter III. For machine mixer work the
problem of loading, transporting and dumping is complicated by the
greater rapidity with which the mixing is done and by the necessity,
usually, of using inclines to reach the charging hopper level. The
incline cuts down the output of the wheelers or in other words makes
necessary a larger gang to handle the same amount of material.
Conditions being the same, the height of the charging chute of the mixer
determines the height of incline and the size of the charging gang, so
that a mixer with a high charging level costs more to charge with
wheelbarrows than does one with a low charging level. Exact figures of
the increased cost of a few feet extra elevation of the wheelbarrow
incline are not available, but some idea may be had from a brief
calculation. The materials for a cubic yard of concrete will weigh about
3,700 lbs., so that to raise the materials for 100 cu. yds. of concrete,
including weight of barrows, 1 ft. calls for about 400,000 ft. lbs. of
work. A man will do about 800,000 ft. lbs. of useful work in a day, so
that each foot of additional height of incline means an additional
half-day's work for one man.
Wheeling to elevating charging hoppers obviates the use of inclines.
Figure 19 shows a mixer equipped with such a hopper, and the arrangement
provided for other makes of mixer is much similar. When the hopper is
lowered ready to receive its load its top edge over which the
wheelbarrows are dumped is from 12 to 14 ins. above ground level. The
wheeling is all done on the level. The elevating bucket is operated by
the mixer engine and is usually detachable. Where mixers have to be
moved frequently, requiring the erection and moving of the incline each
time, an elevating charging hopper is particularly useful; it can be
hoisted clear of the ground and moved with the mixer, so that it is
ready to use the moment that the mixer is set at its new station.
While the ordinary wheelbarrow is generally used for charging, better
work can be done under some conditions by using special charging barrows
of larger capacity and dumping from the end and ahead of the wheel. Two
forms of charging barrow are shown by Figs. 16 and 17. The Acme barrow
will hold 4 cu. ft. and the Ransome barrow is made in 3 to 6 cu. ft.
capacities. Where inclines are necessary these barrows can often be
hauled up the incline by power. A sprocket chain in the plane of the
incline and operated by the mixer engine is an excellent arrangement. A
prong riveted to the rear face of the barrow and projecting downward is
"caught into" the chain, which pulls the barrow to the top, the man
following to dump and return for another load.
[Illustration: Fig. 16.--Forward Dump Charging Barrow, Sterling
Wheelbarrow Co.]
[Illustration: Fig. 17.--Forward Dump Charging Barrow, Ransome Concrete
Machinery Co.]
~Charging with Cars.~--Cars moved by cable, team or hand are a
particularly economic charging device when the mixer is located a little
distance from the stock piles or bins. Either separate cars for cement,
sand and stone, each holding the proper amount of its material for a
batch, can be used, or a single car containing enough of all three
materials for a batch. The last arrangement is ordinarily more
economical in time and labor, and in plant required. In either case the
car serves as the measuring hopper, there being no further proportioning
of the materials after they have been loaded into the car, and it must
be arranged for measuring. Usually all that is necessary, where one car
is used, is to mark the levels on the sides to which it is to be filled
with sand and then stone; the car is run to the sand stock and filled to
the level marked for sand and then to the stone stock and filled to the
level marked for stone. The cement may be added to the charge either
before or after it is run to the mixer as convenience in storing the
cement stock dictates. Instead of having marks to show the proper
proportions of sand and stone, the car is sometimes divided into two
compartments, one for each material and each holding the proper
proportion of its material when level full. This arrangement makes
proper proportioning somewhat more certain, since the men charging the
car cannot over-run the marks. In case separate cars are used for each
material, they are simply filled level full or to mark, and dumped in
succession into the feeding hopper. Trestle and car plant construction
and costs are given in a preceding section.
~Charging by Shoveling.~--Charging by shoveling directly into the mixer is
seldom practiced except in street work with continuous mixers or in
charging gravity mixers of the trough type. Shoveling is not an economic
method of handling materials where the work involves carrying in
shovels, and it is only in a few classes of concrete work or in
isolated, exceptional cases that charging with shovels does not involve
carrying. The amount of material that men will load with shovels is
given in Chapter III, and the reader who wishes a full discussion of the
subject is referred to Gillette and Hauer, "Earth Excavation and
Embankments; Methods and Cost."
In charging continuous mixers with shovels the usual practice for mixers
without automatic feed devices is to work from a continuous stock pile
of sand, stone and cement spread in layers in the proper proportions.
The shoveling is done in such a manner that each shovelful contains a
mixture of cement, sand and stone, and so that the rate of delivery to
the mixer is as uniform as possible. In charging mixers having automatic
feed devices the sand and stone are simply shoveled into the sand and
stone hoppers, whence they are fed automatically to the mixer. In
charging gravity mixers by shoveling the method is essentially the same;
the cement, sand and stone properly proportioned are spread in layers on
the shoveling board at the head of the mixer and the mixture then
shoveled into the mixer. In both of these cases mixing is performed to a
certain extent by the shoveling, and in both the provision of the
combination stock pile from which the men work involves labor which
comes within the meaning of the term charging as we have used it here.
Examples of street work in which the mixers were charged by shoveling
are given in Chapter XIV.
~Charging with Derricks.~--When the stock piles are located close to the
mixer and the plant is fixed or is not frequently moved derricks can be
used economically for charging, particularly if the mixer be elevated so
that inclines become expensive. The following mode of operation will be
found to work well: Set the derrick so that its boom "covers" the sand
and stone piles and the mixer, and provide it with three buckets so that
there will always be one bucket at the stone pile and another at the
sand pile while the third is being handled. The derrick swinging from
the mixer, where it has discharged a bucket, drops the empty bucket at
the stone pile and picks up the bucket standing there, which has
received its proper charge of stone, and swings it to the sand pile and
drops it to get its charge of sand. Here it picks up the bucket standing
at the sand pile and which has its charges of both stone and sand, and
swings it to the mixer. By this arrangement the work of the derrick and
of the men filling the buckets is practically continuous. The buckets
can be provided with marks on the inside to show the proper points to
which to fill the stone and the sand or a partition may be riveted in
making a compartment for sand and another for stone. A special
charging-bucket that is arranged with a wheel and detachable handles
which permit it to be handled like a wheelbarrow is shown by Fig. 18.
This bucket can be used to advantage where the stock piles are too far
from the mixer for the derrick to reach both, the bucket being loaded
and wheeled to within reach of the derrick.
[Illustration: Fig. 18.--Charging Bucket With Wheel and Detachable
Handle.]
~TYPES OF MIXERS.~--There are two types of concrete mixing machines or
concrete mixers as they are more commonly called: (1) Batch mixers and
(2) continuous mixers. In mixers of the first type a charge of cement,
sand, aggregate and water is put into the machine which mixes and
discharges the batch before taking in another charge; charging, mixing
and discharging is done in batches. In continuous mixers the cement
sand, stone and water are charged into the machine in a continuous
stream and the mixed concrete is discharged in another continuous
stream. While all concrete mixers are either batch or continuous mixers,
it is common practice because of their distinctive character to separate
gravity mixers, whether batch or continuous, into a third type. In
gravity mixers the concrete materials are made to mingle by falling
through specially constructed troughs, or tubes, or hoppers. We shall
describe mixers in this chapter as (1) batch mixers, (2) continuous
mixers, and (3) gravity mixers. No attempt will be made, however, to
describe all or even all the leading mixers of each type; a
representative mixer or two of each type will be described, enough to
give an indication of the range of practice, and the reader referred to
manufacturers' literature for further information.
~Batch Mixers.~--Batch mixers are made in two principal forms which may be
designated as tilting and non-tilting mixers. In the first form the
mixer drum is tilted as one would tilt a bucket of water to discharge
the batch. In non-tilting mixers the mixer drum remains in one position,
the batch being discharged by special mechanism which dips it out a
portion at a time. In both forms the charge is put into the mixer as a
unit and kept confined as a unit during the time of mixing, which may be
any period wished by the operator.
[Illustration: Fig. 19.--Chicago Improved Cube Concrete Mixer with
Elevating Charging Hopper.]
_Chicago Improved Cube Tilting Mixer._--Figure 19 shows the improved
cube mixer made by the Municipal Engineering & Contracting Co., Chicago,
Ill. The drum consists of a cubical box with rounded corners and edges.
This box has hollow gudgeons at two diagonally opposite corners and
these gudgeons are open as shown to provide for charging and
discharging. The box is rotated by gears meshing with a circumferential
rack midway between gudgeons and another set of gears operate to tilt
the mixer. The inside of the box is smooth, there being no deflectors,
as its shape is such as to fold the batch repeatedly and thus accomplish
the mixing.
[Illustration: Fig. 20.--Ransome Concrete Mixer.]
_Ransome Non-Tilting Mixer._--Figure 20 shows a representative
non-tilting mixer made by the Ransome Concrete Machinery Co., Dunellen,
N. J. It consists of a cylindrical drum riding on rollers and rotated by
a train of gears meshing with circumferential racks on the drum. The
drum has a circular opening at each end; a charging chute enters one
opening and a tilting discharge chute may be thrown into or out of the
opposite opening. The cylindrical shell of the drum is provided inside
with steel plate deflectors, which plow through and pick up and drop the
concrete mixture as the drum revolves. The shape and arrangement of the
deflectors are such that the batch is shifted back and forth axially
across the mixer. To discharge the batch the discharge chute is tilted
so that its end projects into the mixer, in which position the material
picked up by the deflectors drops back onto the chute and runs out. The
discharge chute being independent of the mixing drum it can be thrown
into and out of discharge position at will without stopping the rotation
of the drum, and so can discharge any part or all of the batch at once.
The top edge of the charging chute ranges from 30½ to 38 ins. in height
above the top of the frame, varying with the size of the mixer.
[Illustration: Fig. 21.--Smith Concrete Mixer.]
_Smith Tilting Mixer._--Figure 21 shows a tilting mixer, known as the
Smith mixer, made by the Contractors' Supply & Equipment Co., Chicago,
Ill. The drum consists of two truncated cones with their large ends
fastened together and their small ends open for receiving the charge and
discharge of the batch. The drum is operated by a train of gears meshing
into a rack at mid-length where the cones join. In addition there is
another set of gears which tilt the drum to make the concrete flow out
of the discharge end. The inside of the drum is provided with steel
plate deflectors, which plow through and pick and drop the concrete
mixture shifting it back and forth axially in the process.
~Continuous Mixers.~--Continuous mixers are those in which the cement,
sand and stone are fed to the charging hopper in a continuous stream and
the mixed concrete is discharged in another continuous stream. They are
built in two principal forms. In one form the cement, sand and stone
properly proportioned are shoveled directly into the mixing drum. In the
other form these materials are dumped into separate charging hoppers and
are automatically fed into the mixing drum in any relative proportions
desired. One form of continuous mixer with automatic feed is described
in the succeeding paragraph and another form is described in Chapter
XIV. The continuous mixer without automatic feed consists simply of a
trough with a rotating paddle shaft and its driving mechanism. The
charging, the mixing and the discharging are done in what is virtually a
succession of very small batches.
[Illustration: Fig. 22.--Eureka Automatic Feed Continuous Mixer.]
_Eureka Automatic Feed Mixer._--Figure 22 shows the construction of the
continuous mixer built by the Eureka Machine Co., Lansing, Mich. The
cement bin and feeder is the small one in the foreground. There is a
pocketed cylinder revolving between concave plates, opening into the
hopper above, from which the pockets in the feeder are filled, and
discharging directly into the mixing trough below. Back of this is
shown the feeder for sand or gravel up to 2-in. screen size. This is a
pocketed cylinder similar to that used in the cement feeder, except that
it is larger, and instead of being provided on the discharge side with a
concave plate, is surmounted by a roller, held by springs. This serves
to cut off the excessive flow of material, but provides sufficient
flexibility to allow the rough coarse material to be fed through the
machine without its catching. The feeder for crushed stone is a similar
construction on larger lines, to handle material up to 3-in. size. These
several feeders can be set to give any desired mixture. On any material
fit to be used in concrete, they will measure with an error of less than
5 per cent., an agitator being provided in the sand bin to prevent damp
sand from bridging over the feeder, and preventing its action. The mixer
consists of a trough, with a square shaft, on which are mounted 37
mixing paddles, which are slipped on in rotation, so as to form
practically a continuous conveyor, but as each paddle is distinct, and
is shaped like the mold board of a plow, the material, as it passes from
one to the next, is turned over and stirred. Water is sprayed into the
mass at the center of the trough. The result is a dry mix, followed by a
wet mix. The mixing trough is made of heavy gage steel, well reinforced,
and practically indestructible. To take care of the discharge of
material while changing wheelbarrows, a hood is provided on the
discharge end of the machine, which can be lowered, and will hold about
a wheelbarrow load.
~Gravity Mixers.~--Gravity mixers are constructed in two general forms.
The first form is a trough whose bottom or sides or both are provided
with pegs, deflectors or other devices for giving the material a zig-zag
motion as it flows down the trough. The second form consists of a series
of hoppers set one above the other so that the batch is spilled from one
into the next and is thus mixed.
The chief advantage claimed for gravity mixers is that no power is
required to operate them. This is obviously so only in the sense that
gravity mixers have no power-operated moving mechanism, and the fact
should not be overestimated. The cost of power used in the actual
performance of mixing is a very small item. The distance between feed
and discharge levels is always greater for gravity mixers than for
machine mixers, and the power required to raise the concrete materials
the excess height may easily be greater than the power required to
operate a machine mixer. On the other hand the simplicity of the gravity
mixer insures low maintenance costs.
_Gilbreth Trough Mixer._--Figure 23 shows the construction of one of the
best known makes of gravity mixers of the trough form. In operation the
cement, sand and stone in the proper proportions are spread in
superimposed layers on a shoveling board at hopper level and are then
shoveled as evenly as possible into the hopper. From the hopper the
materials flow down the trough, receiving the water about half way down,
and are mixed by being cut and turned by the pins and deflectors. The
trough of the mixer is about 10 ft. long.
[Illustration: Fig. 23.--Gilbreth Gravity Mixer, Trough Form.]
[Illustration: Fig. 24.--Hains Gravity Mixer, Fixed Hopper Form.]
_Hains Gravity Mixer._--The form of gravity mixer made by the Hains
Concrete Mixer Co., Washington, D. C., is shown by Figs. 24 and 25. The
charge passes through the hoppers in succession. Considering first the
stationary plant, shown by Fig. 24, the four hoppers at the top have a
combined capacity of one of the lower hoppers. Each top hopper is
charged with cement, sand and stone in the order named and in the proper
proportions. Water is then dashed over the tops of the filled hoppers
and they are dumped simultaneously into the hopper next below. This
hopper is then discharged into the next and so on to the bottom.
Meanwhile the four top hoppers have been charged with materials for
another batch. It will be observed that (1) the concrete is mixed in
separate batches and (2) the ingredients making a batch are accurately
proportioned and begin to be mixed for the whole batch at once. The best
arrangement is to have the top of the hopper tower carry sand and stone
bins which chute directly into the top hoppers. In the telescopic mixer
shown by Fig. 25 the purpose has been to provide a mixer which, hung
from a derrick or cableway, will receive a charge of raw materials at
stock pile and deliver a batch of mixed concrete to the work, the
operation of mixing being performed during the hoist to the work. By
providing two mixers so that one can be charged while the other is being
hoisted continuous operation is secured. The following are records of
operation of stationary gravity mixers of this type.
[Illustration: Fig. 25.--Hains Gravity Mixer, Telescoping Hopper Form.]
In building a dock at Baltimore, Md., a plant consisting of two large
hoppers and four charging hoppers with sand and stone bins above was
used. One man at each large conical hopper tending the gates and two men
charging the four pyramidal hoppers composed the mixer gang. A scow load
of sand and another of stone were moored alongside the work and a
clam-shell bucket dredge loaded the material from these barges into the
mixer bins. Each batch was 25 cu. ft. of 1-2-5 concrete rammed in place.
The men at the upper hoppers would empty a sack of cement in each, and
then by opening gates in the bottom of the bins above, allow the
necessary amounts of sand and stone to flow in, marks having been
previously made on the sides of the hoppers to show the correct
proportion of each of the ingredients. The amount of water found by
experience to be necessary, would then be dashed into the hoppers, and
the charges allowed to run into the first cone hopper below. Refilling
would begin at the top while the men were caring for the first charge in
the lower hoppers. The process was thus continuous. The concrete was
chuted directly into place from the bottom hopper. The record of output
was 110 batches per 10-hour day. Wages of common labor were $1.50 per
day. The labor cost per cubic yard of concrete in place was 35 cts.
In constructing the Cedar Grove reservoir at Newark, N. J., a Hains
mixer made the following records of output:
Cu. yds.
Best output per 10-hour day 403
Average daily output for best month 302
Average daily output for whole job 225
The stone, sand and cement were all raised by bucket elevators to the
top of the high wooden tower that supported the bins and mixer. There
were 10 men operating the mixer so that (exclusive of power, interest
and depreciation) the labor cost of mixing averaged only 7 cts. per cu.
yd.; during one month it was as low as 5 cts. per cu. yd. This does not
include delivering the materials to the men at the mixer, nor does it
include conveying the concrete away and placing it. The work was done by
contract.
~OUTPUT OF MIXERS.~--With a good mixer the output depends upon the methods
of conveying the materials to and from the mixer. Most makers of mixers
publish capacities of their machines in batches or cubic yards output
per hour; these figures may generally be taken as stating nearly the
maximum output possible. Considering batch mixers, as being the type
most commonly used, it may be assumed that where the work is well
organized and no delay occurs in delivering the materials to the mixer
that a batch every 2 minutes, or 300 batches in 10 hours, will be
averaged, and there are a few records of a batch every 1½ minutes.
To illustrate to how great an extent the output of a mixer depends on
the methods adopted in handling the materials to and from the mixer we
compare two actual cases that came under the authors' observation. The
mixers used were of the same size and make. In one case the stone was
shoveled into the charging hopper by four men and the sand and cement
were delivered in barrows by four other men; six men took the concrete
away in wheelbarrows. The output of the mixer was one batch every 5
minutes, or 120 batches, or 60 cu. yds., in 10 hours. In the other case
the sand and the stone were chuted directly into the charging hopper
from overhead bins and the mixer discharged into one-batch buckets on
cars. The output of the mixer was one batch every 2 minutes, or 300
batches in 10 hours. In the first case the capacity of the mixer was
limited by the ability of a gang of workable size to get the raw
materials to and the mixed concrete away from the mixer. In the second
case the capacity was limited only by the amount of mixing deemed
necessary.
While the necessity of rapid charging of a mixer to secure its best
output is generally realized it is often forgotten that the rapidity of
discharge is also a factor of importance. The size of the conveyor by
which the concrete is removed affects the time of discharge. By timing a
string of wheelbarrows in line the authors have found that it takes
about 7 seconds to fill each barrow; as a rule slight delays will
increase this time to 10 seconds. With a load of 1 cu. ft. per barrow it
requires 13 barrow loads to take away a ½ cu. yd. batch. This makes the
time of discharging a batch 130 seconds, or say 2 minutes. The same
mixer discharging into a batch size bucket will discharge in 15 to 20
seconds, saving at least 1½ minutes in discharging each batch.
~MIXER EFFICIENCY.~--Various attempts have been made to rate the
efficiency of concrete mixers. In all cases a percentage basis of
comparison has been adopted; arbitrary values are assigned to the
several functions of a mixer, such as 40 per cent. for perfect mixing,
10 per cent. for time of mixing and 25 per cent. for control of water,
the total being 100 per cent., and each mixer analyzed and given a
rating according as it is considered to approach the full value of any
function. Such percentage ratings are unscientific and misleading; they
present definite figures for what are mere arbitrary determinations. The
values assigned to the several functions are purely arbitrary in the
first place, and in the second place the decision as to how near those
values any mixer approaches are matters of personal judgment.
_The most efficient mixer is the one that gives the maximum product of
standard quality at the least cost for production._
This rule recognizes the fact that in practical construction different
standards of quality are accepted for different kinds of work. No
engineer demands, for example, the same quality of mixture for a
pavement base that he does for a reinforced concrete girder. If mixer A
turns out concrete of a quality suitable for pavement base cheaper than
does mixer B, then it is the more efficient mixer for the purpose, even
though mixer B will make the superior quality of concrete required for a
reinforced girder while mixer A will not. This method of determining
efficiency holds accurate for any standard of quality that may be
demanded.
CHAPTER V.
METHODS AND COST OF DEPOSITING CONCRETE UNDER WATER AND OF SUBAQUEOUS
GROUTING.
Mixed concrete if emptied loose and allowed to sink through water is
destroyed; the cement paste is washed away and the sand and stone settle
onto the bottom more or less segregated and practically without
cementing value. In fact, if concrete is deposited with the utmost care
in closed buckets and there is any current to speak of a considerable
portion of cement is certain to wash out of the deposited mass. Even in
almost still water some of the cement will rise to the surface and
appear as a sort of milky scum, commonly called _laitance_. Placing
concrete under water, therefore, involves the distinctive task of
providing means to prevent the washing action of the water. It is also
distinguished from work done in air by the fact that it cannot be
compacted by ramming, but the main problem is that of preventing wash
during and after placing.
~DEPOSITING IN CLOSED BUCKETS.~--Special buckets for depositing concrete
under water are made by several manufacturers of concrete buckets. These
buckets vary in detail but are all similar in having doors to close the
concrete away from the water and, generally, in being bottom dumping.
The bucket shown by Fig. 26 was designed by Mr. John F. O'Rourke, and is
built by the Cockburn Barrow & Machine Co., of Jersey City, N. J. This
bucket was used in depositing the concrete for the City Island Bridge
foundations described in Chapter XII and also in a number of other
works. It consists of a nearly cubical shell of steel open at top and
bottom, and having heavy timbers rivetted around the bottom edges. The
open top has two flat flap doors. Two similar doors hinged about midway
of the sides close to form a V-shaped hopper bottom inside the shell and
serve when open, to close the openings in the sides of the shell. In
loading the bucket the bottom doors are drawn inward and upward by the
chains and held by a temporary key. The loaded bucket is then lifted by
the bail and the key removed, since when suspended the pull on the bail
holds the chains taut and the doors closed. As soon as the bucket rests
on the bottom the pull of the concrete on the doors slides the bail down
and the doors swing downward and back discharging the concrete. The
timbers around the bottom edges keep the bucket from sinking into the
deposited concrete, and the doors and shell exclude all water from the
batch until it is finally in place.
[Illustration: Fig. 26.--O'Rourke Bucket fur Depositing Concrete Under
Water.]
The subaqueous concrete bucket shown by Figs. 27 and 28 is made by the
Cyclopean Iron Works Co., Jersey City, N. J. Fig. 27 shows the bucket
suspended full ready for lowering; the cover is closed and latched and
the bail is held vertical by the tag line catch A. Other points to be
noted are the eccentric pivoting of the bail, the latch unlocking lever
and roller B and C, and the stop D. In the position shown the
bucket is lowered through the water and when at the proper depth just
above bottom the tag line is given a sharp pull, uncatching the bail.
The body of the bucket turns bottom side up, revolving on the bail
pivots, and just as the revolution is completed the bail engages the
roller C on the latch unlocking lever and swings the lever enough to
unlatch the top and allow it to swing down as shown by Fig. 28 and
release the concrete. The stop D keeps the body of the bucket from
swinging beyond the vertical in dumping.
[Illustration: Fig. 27.--Cyclopean Bucket for Depositing Concrete Under
Water (Closed Position).]
[Illustration: Fig. 28.--Cyclopean Bucket for Depositing Concrete Under
Water (Open Position).]
Figures 29 and 30 show the subaqueous concrete bucket made by the G. L.
Stuebner Iron Works, Long Island City, N. Y., essentially the same
bucket, omitting the cover and with a peaked bail, is used for work in
air. For subaqueous work the safety hooks A are lifted from the angles
B and wired to the bail in the position shown by the dotted lines, and
a tag line is attached to the handle bar C. The bucket being filled
and the cover placed is lowered through the water to the bottom and then
discharged by a pull on the tag line.
~DEPOSITING IN BAGS.~--Two methods of depositing concrete in bags are
available to the engineer; one method is to employ a bag of heavy tight
woven material, from which the concrete is emptied at the bottom, the
bag serving like the buckets previously described simply as means of
conveyance, and the other method is to use bags of paper or loose woven
gunnysack which are left in the work, the idea being that the paper will
soften or the cement will ooze out through the openings in the cloth
sufficiently to bond the separate bagfuls into a practically solid mass.
[Illustration: Fig. 29.--Stuebner Bucket for Depositing Concrete Under
Water (Closed Position).]
[Illustration: Fig. 30.--Stuebner Bucket for Depositing Concrete Under
Water (Open Position).]
[Illustration: Fig. 31.--Bag for Depositing Concrete Under Water.]
[Illustration: Fig. 32.--Form for Molding Footing for Block Concrete
Breakwater.]
The bag shown by Fig. 31 was used to deposit concrete for leveling up a
rough rock bottom and so provide a footing for a concrete block pier
constructed in 1902 at Peterhead, N. B., by Mr. William Shield, M. Inst.
C. E. Careful longitudinal profiles were taken of the rock bottom one at
each edge of the footing. Side forms were then made in 20-ft. sections
as shown by Fig. 32; the lagging boards being cut to fit the determined
profile and the top of the longitudinal piece being flush with the top
of the proposed footing. The concrete was filled in between the side
forms and leveled off by the T-rail straight-edge. In placing the side
forms the longitudinal pieces were placed by divers who were given the
proper elevations by level rods having 10 to 15-ft. extension pieces to
raise the targets above the water surface. When leveled the side pieces
were anchor-bolted as shown to the rock, the anchor-bolts being wedged
into the holes to permit future removal. The concrete was then lowered
in the bag shown by Fig. 31, the divers assisting in guiding the bag to
position. The mouth of the bag being tied by one turn of a line having
loops through which a wooden key is slipped to hold the line tight, a
sharp tug on the tripping rope loosens the key and empties the bag. The
bags used on this work had a capacity of 2¼ cu. ft. To permit the
removal of the side forms after the concrete had hardened, a strip of
jute sacking was spread against the lagging boards with a flap
extending 15 to 18 ins. under the concrete. The forms were removed by
divers who loosened the anchor bolt wedges.
In placing small amounts of concrete for bridge foundations in Nova
Scotia, bags, made of rough brown paper were used to hold the concrete.
Each bag held about 1 cu. ft. The bags were made up quickly and dropped
into the water one after the other so that the following one was
deposited before the cement escaped from the former one. The paper was
immediately destroyed by submersion and concrete remained. The bags cost
$1.35 per hundred or 35 cts. per cu. yd. of concrete. Concrete was thus
deposited in 18 ft. of water without a diver.
[Illustration: Fig. 33.--Steel Tremie for Depositing Concrete Under
Water.]
~DEPOSITING THROUGH A TREMIE.~--A tremie consists of a tube of wood or,
better, of sheet metal, which reaches from above the surface to the
bottom of the water; it is operated by filling the tube with concrete
and keeping it full by successive additions while allowing the concrete
to flow out gradually at the bottom by raising the tube slightly to
provide the necessary opening. A good example of a sheet steel tremie is
shown by Fig. 33. This tremie was used by Mr. Wm. H. Ward in
constructing the Harvard Bridge foundations and numerous other
subaqueous structures of concrete. In these works the tube was suspended
from a derrick. Wheelbarrows filled the tube and hopper with concrete
and kept them full; the derrick raised the tube a few inches and swung
it gently so as to move it slowly over the area to be filled. Care being
taken to keep the tube at one height, the concrete was readily deposited
in even layers. Concrete thus deposited in 18 ft. of water was found to
be level and solid on pumping the pit dry.
[Illustration: Fig. 34.--Tremie and Traveler Used at Charlestown, Mass.,
Bridge.]
Another method of handling a tremie was employed in constructing the
foundations for the Charlestown Bridge at Boston, Mass. Foundation piles
were driven and sawed off under water. A frame was built above water and
supported by a curbing attached to certain piles in the outer rows of
the foundation reserved for this purpose. In this frame the vertical
members were Wakefield sheet-piling plank, spaced 6 to 10 ft. apart, and
connected by three lines of double waling bolted to the verticals at
three different heights. This frame was lowered to the bottom so as to
enclose the bearing piles. The posts or verticals were then driven, one
by one, into the bottom, the frame being flexible enough to permit this.
The spaces between the posts or verticals were then filled by
sheet-piling and the frame was bolted to the curbing piles. This curbing
afterward supported the traveler used in laying the concrete. Thus a
coffer dam was formed to receive the concrete as shown in Fig. 34. The
1-2-5 concrete was deposited up to within 5½ ft. of the mean low water
level, the last foot being laid after water was pumped out. The tremie
used to deposit the concrete was a tube 14 ins. in diameter at the
bottom and 11 ins. at the neck, with a hopper at the top. It was made in
removable sections, with outside flanges, and was suspended by a
differential hoist from a truck moving laterally on a traveler, Fig. 34.
The foot of the chute rested on the bottom until filled with concrete;
then the chute was slowly raised and the concrete allowed to run but
into a conical heap, more concrete being dumped into the hopper. As the
truck moved across the traveler a ridge of concrete was made; then the
traveler was moved forward and another parallel ridge was made. The best
results were obtained when the layers were 2½ ft. thick, but layers up
to 6 ft. thick were laid. If the layer was too thick, or uneven, or if
the chute was moved or raised too quickly, the charge in the tube was
"lost." This was objectionable because the charging of the chute anew
resulted in "washing" the cement more or less out of the concrete until
the chute was again filled. To reduce this objection the contractor was
directed to dump some neat cement into the tube before filling with
concrete. A canvass piston was devised which could be pushed ahead of
the concrete when filling the chute. It consisted of two truncated cones
of canvass, one flaring downward to force the water ahead, and the other
flaring upward to hold the concrete. The canvass was stiffened and held
against the sides of the chute by longitudinal ribs of spring steel
wire; the waist was filled by a thick block of wood to which all the
springs were attached; and to this block were connected additional steel
guides to prevent overturning and a rope to regulate the descent. Very
little water forced its way past this piston and it was a success, but
as the cost was considerable and a piston was lost each time, its use
was abandoned as the evil to be avoided did not justify the outlay.
The chute worked best when the concrete was mixed not quite wet enough
to be plastic. If mixed too wet the charge was liable to be "lost," and
if dry it would choke the chute. An excess of gravel permitted water to
ascend in the tube; and an excess of sand tended to check the flow of
concrete.
In constructing the piers for a masonry arch bridge in France in 1888
much the same method was followed, except that a wooden tremie 16 ins.
square made in detachable sections was used. This tremie had a hopper
top and was also provided with a removable cap or cover for the bottom
end, the latter device being intended to keep the water out of the tube
and prevent "washing" the first charge of concrete. The piers were
constructed by first driving piles and sawing them off several feet
above the bottom but below water level, and then filling them nearly to
their tops with broken stone. An open box caisson was then sunk onto the
stone and embracing the pile tops and then filled around the outside
with more broken stone. The caisson was then filled with concrete
through the tremie which was handled by a traveling crane. The crane was
mounted and traveled transversely of the pier on a platform which in
turn moved along tracks laid lengthwise of the caisson. The tube was
gradually filled with concrete and lowered, the detachable bottom of the
tube was then removed, allowing the concrete to run out. The tube was
first moved across the caisson and then downstream and back across the
caisson, and this operation repeated until a 16-in. layer was completed.
The tube was then raised 16 ins. and the operations repeated to form
another layer. There was almost no _laitance_. From 90 to 100 cu. yds.
were deposited daily.
Still another example of tremie work is furnished by the task of
depositing a large mass of concrete under water in the construction of
the Nussdorf Lock at Vienna. This lock has a total width of 92 ft. over
all, and is 49.2 ft. clear inside. The excavation, which was carried to
a depth of 26.24 ft. below water level, was made full width, between
sheet piling, and the bottom was filled in with rammed sand and gravel,
forming a kind of invert with its upper surface horizontal in the middle
and sloping upwards a trifle at both sides. A mass of concrete having a
total thickness of 13.12 ft. was built on this foundation in the center
where the upper surfaces were 13.12 ft. below the water level. Concrete
walls were carried up at the sides of the lock to a height of 3.28 ft.;
these walls were 8.2 ft. thick. The methods used in placing the concrete
were as follows: Three longitudinal rows of piles were driven on each
side of the axis of the lock, these piles supporting a 6-rail track
about 7 ft. above the water level. Three carriages spanning the full
width of the lock transversely moved on this track. Each carriage had
three trolleys, one in each of the main panels of the transverse pile
bends. These trolleys each carried a vertical telescopic tube, by means
of which the concrete was deposited at the bottom of the lock. These
tubes or chutes were of different lengths in the three carriages; the
first ones deposited the concrete up to a level of 23 ft. below the
surface; the next set deposited the concrete between that level and 19.7
ft., and the last set completed the subaqueous work up to the final
height of 16.4 ft. below the surface. The tops of the tubes were level
with a transverse track extending the full length of the carriage. The
ends of these tracks just cleared the outside rows of piles, which, on
one side of the lock, supported a distribution track parallel to the
axis of the lock. Dump cars running on this distribution track delivered
the concrete to smaller dump cars on the carriage tracks, and in turn
these smaller cars dumped into either of these chutes on each carriage.
The carriages were moved from end to end of the lock, the whole area of
the lock coming under the nine chutes, inasmuch as each chute moved
one-third the length of the carriage. The concrete was deposited in
three horizontal layers 3.28 ft. thick, the layers being built in
comparatively narrow banks, so that the different layers would key
together and form a corrugated mass. The chutes were shortened as the
concrete was deposited, three layers being placed successively. The main
body of the bottom and the side walls were built by this method, and
then the water was pumped out and a 2.3 ft. layer of concrete rammed
over the bottom and completed with a finished surface 9 ft. thick.
~GROUTING SUBMERGED STONE.~--Masses of gravel, broken or rubble stone
deposited under water may be cemented into virtually a solid concrete by
charging the interstices with grout forced through pipes from the
surface. Mr. H. F. White gives the following records of grouting
submerged gravel:
In experiment No. 1 a reservoir 10 ft. square was filled to a depth of
18 ins. with clean gravel ballast (1½ to 2-in. size) submerged in water.
A 2-in. gas pipe rested on the gravel and was surmounted with a funnel.
A 1:1 Portland grout was poured in. After 21 days set the water was
drawn off, and it was found that the grout had permeated the ballast
for a space of 8 ft. square at the bottom and 6 ft. square at the top,
leaving a small pile of pure cement mortar 6 ins. high about the base of
the pipe; 16 cu. ft. of cement and 16 cu. ft. of sand concreted 100 cu.
yds. of ballast. In experiment No. 2, under the same conditions, a grout
made of 1 part lime, 1 part surki (puzzulana or trass) and 1 part sand,
was found to have spread over the entire bottom, 10 ft. square, rising 5
ins. on the sides, and making the concreted mass about 3½ ft. square at
the top; 25 cu. ft. of the dry materials concreted 100 cu. ft. of
ballast. In experiment No. 3 the ballast was 2½ ft. deep. A grout (using
8 cu. ft. of each ingredient) made as in experiment No. 2 covered the
bottom, rose 14 ins. on the sides and made a top surface 4½ ft. square;
32 cu. ft. of the dry materials grouted 100 cu. ft. of ballast. In
experiment No. 4 the ballast was of bats and pieces 3 or 4 ins. in size
laid 7 ft. deep. A grout made as in experiment No. 2 (using 88 cu. ft.
of each ingredient) concreted the whole mass to a depth of 6 ft. up the
sides, and 2½ ft. square at the pipe on the surface of the ballast. Mr.
White says that a grout containing more than 1 part of sand to 1 of
Portland cement will not run freely through a 2-in. pipe, as the sand
settles out and chokes the pipe. Even with 1:1 grout it must be
constantly stirred and a steady flow into the pipe maintained. The
lime-trass grout does not give the same trouble.
Mr. W. R. Knipple describes the work of grouting rubble stone and gravel
for the base of the Hermitage Breakwater. This breakwater is 525 ft.
long, 50 ft. wide at base and 42 ft. wide at top, and 68 ft. high, was
built on the island of Jersey. Where earth (from 0 to 8½ ft. deep)
overlaid the granite rock, it was dredged and the trench filled in with
rubble stones and gravel until a level foundation was secured. Cement
grout was then forced into this filling through pipe placed 8 to 10 ft.
apart. The grouting was done in sections 12½ ft. long, from 7 to 10 days
being taken to complete each. Upon this foundation concrete blocks,
4×4×9 to 12 ft., were laid in courses inclined at an angle of 68°. The
first four courses were laid by divers, the blocks being stacked dry two
courses high at a time. The joints below water were calked by divers and
above water by masons, and a section was then grouted. When two courses
had been laid and grouted, two more courses were laid and grouted in
turn, and so on. In places, grouting was done in 50 ft. of water. The
grout should be a thick paste; a 30-ft. column of grout will balance a
60-ft. column of water.
CHAPTER VI.
METHODS AND COST OF MAKING AND USING RUBBLE AND ASPHALTIC CONCRETE.
Two kinds of concrete which vary in composition and character from the
common standard mixtures of cement, sand and broken aggregate are
extensively employed in engineering construction. These are rubble
concrete and asphaltic concrete.
~RUBBLE CONCRETE.~--In constructing massive walls and slabs a reduction in
cost may often (not always) be obtained by introducing large stones into
the concrete. Concrete of this character is called rubble concrete, and
the percentage of rubble stone contained varies from a few per cent. to,
in some cases, over half of the volume. The saving effected comes partly
from the reduction in the cement required per cubic yard of concrete and
partly from the saving in crushing.
The saving in cement may be readily figured if the composition of the
concrete and the volume of the added rubble stones be known. A 1-2½-5
concrete requires according to Table X in Chapter II 1.13 bbls. of
cement per cubic yard. Assuming a barrel of cement to make 3.65 cu. ft.
of paste, we have 3.65 × 1.13 = 4.12 cu. ft. of cement paste per cubic
yard of 1-2½-5 concrete. This means that about 15 per cent. of the
volume of the concrete structure is cement. If rubble stone be
introduced to 50 per cent. of the volume, then the structure has about
7½ per cent. of its volume of cement. It is of interest to note in this
connection that rubble masonry composed of 65 per cent. stone and 35 per
cent. of 1-2½ mortar would have some 11½ per cent. of its volume made up
of cement.
The saving in crushing is not so simple a determination. Generally
speaking, the fact that a considerable volume of the concrete is
composed of what, we will call uncrushed stone, means a saving in the
stone constituent of one structure amounting to what it would have cost
to break up and screen this volume of uncrushed stone, but there are
exceptions. For example, the anchorages of the Manhattan Bridge over the
East River at New York city were specified to be of rubble concrete,
doubtless because the designer believed rubble concrete to be cheaper
than plain concrete. In this case an economic mistake was made, for all
the rubble stone used had to be quarried up the Hudson River, loaded
onto and shipped by barges to the site and then unloaded and handled to
the work using derricks. Now this repeated handling of large, irregular
rubble stones is expensive. Crushed stone as we have shown in Chapter IV
can be unloaded from boats at a very low cost by means of clam shells.
It can be transported on a belt conveyor, elevated by bucket conveyer,
mixed with sand and cement and delivered to the work all with very
little manual labor when the installation of a very efficient plant is
justified by the magnitude of the job. Large rubble stones cannot be
handled so cheaply or with so great rapidity as crushed stone; the work
may be so expensive, due to repeated handlings, as to offset the cost of
crushing as well as the extra cost of cement in plain concrete. On the
other hand, the cost of quarrying rock suitable for rubble concrete is
no greater than the cost of quarrying it for crushing--it is generally
less because the stone does not have to be broken so small--so that when
the cost of getting the quarried rock to the crusher and the crushed
stone into the concrete comes about the same as getting the quarried
stone into the structure it is absurd practice to require crushing. To
go back then to our first thought, the question whether or not saving
results from the use of rubble concrete, is a separate problem in
engineering economics for each structure.
In planning rubble concrete work the form of the rubble stones as they
come from the quarry deserves consideration. Stones that have flat beds
like many sandstones and limestones can be laid upon layers of dry
concrete and have the vertical interstices filled with dry concrete by
tamping. It requires a sloppy concrete to thoroughly embed stones which
break out irregularly. In the following examples of rubble concrete work
the reader will find structures varying widely enough in character and
in the percentages of rubble used to cover most ordinary conditions of
such work.
Where the rubble stones are very large it is now customary to use the
term "cyclopean masonry" instead of rubble concrete. Many engineers who
have not studied the economics of the subject believe that the use of
massive blocks of stone bedded in concrete necessarily gives the
cheapest form of masonry. We have already indicated conditions where
ordinary concrete is cheaper than rubble concrete. We may add that if
the quarry yields a rock that breaks up naturally into small sized
blocks, it is the height of economic folly to specify large sized
cyclopean blocks. Nevertheless this blunder has been frequently made in
the recent past.
[Illustration: Fig. 35.--Diagram Cross-Section of Rubble Concrete Dam,
Chattahoochee River.]
~Chattahoochee River Dam.~--The roll-way portion, 680 ft. long, of the dam
for the Atlanta Water & Electric Power Co., shown in section by Fig. 35,
was built of a hearting of rubble concrete with a fine concrete facing
and a rubble rear wall. The facing, 12 ins. thick of 1-2-4 concrete,
gave a smooth surface for the top and face of the dam, while the rubble
rear wall enabled back forms to be dispensed with and, it was
considered, made a more impervious masonry. The concrete matrix for the
core was a 1-2-5 stone mixture made very wet. The rubble stones, some as
large as 4 cu. yds., were bedded in the concrete by dropping them a few
yards from a derrick and "working" them with bars; a well formed stone
was readily settled 6 ins. into a 10-in. bed of concrete. The volume of
rubble was from 33 to 45 per cent. of the total volume of the masonry.
The 1-2-4 concrete facing was brought up together with the rubble core,
using face forms and templates to get the proper profile. The work was
done by contract and the average was 5,500 cu. yds. of concrete placed
per month.
[Illustration: Fig. 36.--Cross-Section of Barossa Dam of Rubble
Concrete.]
~Barossa Dam, South Australia.~--The Barossa Dam for the water-works for
Gawler, South Australia, is an arch with a radius of 200 ft., and an arc
length on top of 422 ft.; its height above the bed of the stream is 95
ft. Figure 36 is a cross-section of the dam at the center. The dam
contains 17,975 cu. yds. of rubble concrete in the proportions of 2,215
cu. yds. of rubble stone to 15,760 cu. yds. of concrete; thus about 12.3
per cent. of the dam was of rubble. The concrete was mixed by weight of
1 part cement, 1½ parts sand, and a varying proportion of aggregate
composed of 4½ parts 1¼ to 2-in. stone, 2 parts ½ to 1¼-in. stone and 1
part 1/8 to ½-in. stone or screenings. The sand was one-half river sand
and one-half crusher sand. The following shows the amounts by weight of
the several materials for each of the several classes of concrete per
cubic yard:
-------------Stone----------
Class. Excess Mortar. 1¼-2. ½-1¼. 1/8-½. Sand. Cement.
A 7.5% 1,500 661½ 333¼ 804 434
B 12.5 1,433-1/3 637 318 858½ 463
C 12.5 1,434 637 318½ 859 474
D 15 1,402 623 312 884 484
[Illustration: Fig. 37.--Apparatus Used for Weighing Concrete Materials
at Barossa Dam.]
The average composition of the concrete was 1-1½-3½. Its cost per cubic
yard in place including rubble was 38s 9d per cu. yd. or about $9.30. In
proportioning the mixture on the work use was made of the device shown
by Fig. 37 to weigh the aggregate. The measuring car is pushed back
under the stone hopper chute until the wheels drop into shallow notches
in the balanced track rails; stone is then admitted until the lead
weight begins to rise, when the car is pushed forward and dumps
automatically as indicated.
~Other Rubble Concrete Dams.~--Rubble concrete containing from 55 to 60
per cent. rubble was used in constructing the Boonton Dam at Boonton, N.
J. The stones used measured from 1 to 2½ cu. yds. each; the concrete was
made so wet that when the stones were dropped into it, it flowed into
every crevice. The materials were all delivered on cars, from which they
were delivered to the dam by derricks provided with bull-wheels. On the
dam there were 4 laborers and 1 mason to each derrick, and this gang
dumped the concrete and joggled the rubble stones into it. Records of
125 cu. yds. per 10 hours, with one derrick, were made. With 35
derricks, 20 of which were laying masonry and 15 either passing
materials or being moved, as much as 21,000 cu. yds. of masonry were
laid in one month. The amount of cement per cubic yard of masonry is
variously stated to have been 0.6 to 0.75 bbl. The stone was granite.
The Spier Falls Dam on the upper Hudson River was built of rubble
concrete containing about 33 per cent. rubble stone. The concrete was a
1-2½-5 mixture, and the engineer states that about 1 bbl. of cement was
used per cubic yard of rubble concrete. This high percentage of cement
may be accounted for by the fact that there was a considerable amount of
rubble masonry in cement mortar included in the total. The stones and
concrete were delivered along the dam by cableways and stiff-leg
derricks set on the downstream sloping face of the dam delivered them
from the cableways into place. There were two laborers to each mason
employed in placing the materials, wages being 15 and 35 cts. per hour,
respectively. The labor cost of placing the materials was 60 cts. per
cubic yard of masonry. The stone was granite.
Granite rubble laid in layers on beds of concrete and filled between
with concrete was used in constructing the Hemet Dam in California. The
concrete was a 1-3-6 mixture, and was thoroughly tamped under and
between the stones. For face work the stones were roughly scabbled to
shape and laid in mortar. The stone was taken from the quarry 400 ft.
away and delivered directly on the dam by cableways; here two derricks
handled the stone into place, the dam being only 246 ft. arc length on
top, though it was 122½ ft. high. The cableways would take a 10-ton
load; stones could be taken from the quarry, hoisted 150 ft. and
delivered to the work in 40 to 60 seconds. Common labor at $1.75 per day
was used for all masonry except facing, where masons at $3.50 were
employed. Cement cost delivered $5 per barrel, of which from $1 to $1.50
per barrel was the cost of hauling 23 miles by team over roads having 18
per cent. grades in places. Sand was taken from the stream bed and
delivered to the work by bucket conveyor. "Under favorable conditions
some of the masonry was put in for as low as $4 per cu. yd." There were
31,100 cu. yds. of masonry in the dam, which required 20,000 bbls. of
cement, or 0.64 bbl. per cubic yard.
The following novel method of making rubble concrete was employed in
enlarging two old dams and in constructing two new dams for a small
water-works. The available time was short, the amount of work was too
small and too scattered to justify the installation of a stone crusher,
and suitable gravel was not at hand. Sufficient small boulders in old
walls, and borrow pits and on surface of fields were available, and were
used with thin Portland cement mortar. One part of Alpha or Lehigh
cement and three parts sand were mixed dry at first and then wet with
just enough water to make the resulting mortar flow by gravity. This
mortar was shoveled into the forms continuously by one set of men while
other men were throwing into the mortar in the forms the boulders which
were cleaned and broken so as not to be more than 7 ins. long. In
general the performance was continuous. Three mortar beds were placed
parallel with, and against, one side of the forms, with spaces of about
4 ft. between the ends of the beds. The boulders were dumped on the
opposite side of the forms. Two men shoveled in all the mortar and did
nothing else. While they were emptying one bed the mortar was being
mixed in the preceding bed by two other men and the materials placed in
the third bed by still others. Another gang was continually throwing in
the boulders and small stones and still another was breaking stone. One
man should keep the mortar well stirred while the bed is being emptied.
About 20 men were necessary to do all parts of the work. The forms were
of 2-in. planed plank tongued and grooved. Especial pains were taken to
make the forms tight, and all leaks that appeared were quickly stopped
with dry cement. Some pains were taken to prevent a flat side of large
stones from coming in direct contact with the forms, but round boulders
and small stones needed no care to prevent their showing in the finished
work.
[Illustration: Fig. 38.--Bridge Abutment of Rubble Concrete.]
In conclusion it is interesting to note, perhaps, the earliest use of
rubble concrete for dam construction in this country in constructing the
Boyd's Corner Dam on the Croton River near New York. This dam was begun
in 1867 and for a time rubble concrete was used, but was finally
discontinued, due to the impression that it might not be watertight. The
specifications called for dry concrete to be thoroughly rammed in
between the rubble stones, and to give room for this ramming the
contractor was not permitted to lay any two stones closer together than
12 ins. As a result not more than 33 per cent. of the concrete was
rubble.
~Abutment for Railway Bridge.~--Figure 38 shows a bridge abutment built of
rubble concrete at a cost of about $4.50 per cu. yd. The concrete was a
1-2½-4½ mixture laid in 4-in. layers. On each layer were laid large
rubble stones bedded flat and spaced to give 6-in. vertical joints; the
vertical joints were filled with concrete by ramming and then another
layer of concrete placed and so on. A force of 28 men and a foreman
averaged 40 cu. yds. of rubble concrete per day. The following is the
itemized cost per cubic yard, not including forms, for 278 cu. yds:
Item. Per Cu. Yd.
0.82 bbls. cement, at $2.60 $2.14
0.22 cu. yd. sand, at $1.00 0.22
0.52 cu. yd. broken stone, at $0.94 0.49
0.38 cu. yd. rubble stone, at $0.63 0.24
Water 0.07
Labor, at 15 cts. per hour 1.19
Foreman 0.09
-------
Total $4.44
~Some English Data on Rubble Concrete.~--Railway work, under Mr. John
Strain, in Scotland and Spain, involved the building of abutments, piers
and arches of rubble concrete. The concrete was made of 1 part cement to
5 parts of ballast, the ballast consisting of broken stone or slag and
sand mixed in proportions determined by experiment. The materials were
mixed by turning with shovels 4 times dry, then 4 times more during the
addition of water through a rose nozzle. A bed of concrete 6 ins. thick
was first laid, and on this a layer of rubble stones, no two stones
being nearer together than 3 ins., nor nearer the forms than 3 ins. The
stones were rammed and probed around with a trowel to leave no spaces.
Over each layer of rubble, concrete was spread to a depth of 6 ins. The
forms or molds for piers for a viaduct were simply large open boxes, the
four sides of which could be taken apart. The depth of the boxes was
uniform, and they were numbered from the top down, so, that, knowing the
height of a given pier, the proper box for the base could be selected.
As each box was filled, the next one smaller in size was swung into
place with a derrick. The following bridge piers for the Tharsis &
Calanas Railway were built:
Length Height No. Cu. Yds. Weeks
of of of in to
Name. Bridge. Piers. Spans. Piers. Build.
Ft. Ft.
Tamujoso River 435 28 12 1,737 14½
Oraque 423 31 11 1,590 15
Cascabelero 480 30 to 80 10 2,680 21
No. 16 294 28 to 50 7 1,046 16½
Tiesa 165 16 to 23 8 420 4
It is stated that the construction of some of these piers in ordinary
masonry would have taken four times as long. The rock available for
rubble did not yield large blocks, consequently the percentage of pure
concrete in the piers was large, averaging 70 per cent. In one case,
where the stones were smaller than usual, the percentage of concrete was
76½ per cent. In other work the percentage has been as low as 55 per
cent., and in still other work where a rubble face work was used the
percentage of concrete has been 40 per cent.
In these piers the average quantities of materials per cubic yard of
rubble concrete were:
448 lbs. (0.178 cu. yd.) cement.
0.36 cu. yd. sand.
0.68 cu. yd. broken stone (measured loose in piles).
0.30 cu. yd. rubble (measured solid).
Several railway bridge piers and abutments in Scotland are cited. In one
of these, large rubble stones of irregular size and weighing 2 tons each
were set inside the forms, 3 ins. away from the plank and 3 ins. from
one another. The gang to each derrick was: 1 derrick man and 1 boy, 1
mason and 10 laborers, and about one-quarter of the time of 1 carpenter
and his helper raising the forms. For bridges of 400 cu. yds., the
progress was 12 to 15 cu. yds. a day. The forms were left in place 10
days.
To chip off a few inches from the face of a concrete abutment that was
too far out, required the work of 1 quarryman 5 days per cu. yd. of
solid concrete chipped off.
Concrete was used for a skew arch over the River Dochart, on the Killin
Railway, Scotland. There were 5 arches, each of 30 ft. span on the
square or 42 ft. on the skew, the skew being 45°. The piers were of
rubble concrete. The concrete in the arch was wheeled 300 ft. on a
trestle, and dumped onto the centers. It was rammed in 6-in. layers,
which were laid corresponding to the courses of arch stones. As the
layers approached the crown of the arch, some difficulty was experienced
in keeping the surfaces perpendicular. Each arch was completed in a day.
In a paper by John W. Steven, in Proc. Inst. C. E., the following is
given:
Rubble Per Cent.
Concrete Concrete of Rubble
Per Per in Rubble
Cu. Yd. Cu. Yd. Concrete.
Ardrossan Harbor $6.00 $5.00 20.0
Irvine Branch 7.00 3.68 63.6
Calanas & Tharsis Ry 7.08 3.43 30.3
Mr. Martin Murphy describes some bridge foundations in Nova Scotia.
Rubble concrete was used in some of the piers. The rubble concrete
consisted of 1 part cement, 2 parts sand, 1 part clean gravel, and 5
parts of large stones weighing 20 lbs. each and upwards. The sand,
cement and gravel were turned three times dry and three times wet, and
put into the forms. The rubble stones were bedded in the concrete by
hand, being set on end, 2 or 3 ins. apart. No rubble stones were placed
within 6 ins. of the forms, thus leaving a face of plain concrete; and
the rubble stones were not carried higher than 18 ins. below the top of
the pier. One cubic yard of this rubble concrete required 0.8 to 0.9
bbl. of cement.
~ASPHALT CONCRETE.~--Asphalt or tar concrete in which steam cinders or
broken stone or gravel and sand are mixed with asphaltum or tar instead
of cement paste are used to some extent in lining reservoirs,
constructing mill floors, etc. Such mixtures differ in degree only from
the mixtures used for asphalt street paving, for discussion of which the
various books on paving and asphalts should be consulted. The two
examples of asphalt concrete work given here are fairly representative
of the mixtures and methods employed for concrete work as distinguished
from asphalt work.
~Slope Paving for Earth Dam.~--Mr. Robert B. Stanton describes a small log
dam faced upstream with earth, upon which was laid an asphalt concrete
lining to make it water tight. The stone was broken to 2-in. pieces,
all the fines being left in and sufficient fine material added to fill
the voids. The stone was heated and mixed in pans or kettles from a
street paving outfit; and the asphaltum paste, composed of 4 parts
California refined asphaltum and 1 part crude petroleum, was boiled in
another kettle. The boiling hot paste was poured with ladles over the
hot stone, and the whole mixed over the fire with shovels and hoes. The
asphalt concrete was taken away in hot iron wheelbarrows, placed in a
4-in. layer rammed and ironed with hot irons. The concrete was laid in
strips 4 to 6 ft. wide, the edges being coated with hot paste. After the
whole reservoir was lined, it was painted with the asphalt paste, boiled
much longer, until when cold it was hard and stone was broken to 2-in.
pieces, all the fines being left in and sufficient fine material added
to fill the voids. The stone was heated and mixed in pans or kettles
from a street paving outfit; and the asphaltum paste, composed of 4
parts California refined asphaltum and 1 part crude petroleum, was
boiled in another kettle. The boiling hot paste was poured with ladles
over the hot stone, and the whole mixed over the fire with shovels and
hoes. The asphalt concrete was taken away in hot iron wheelbarrows,
placed in a 4-in. layer rammed and ironed with hot irons. The concrete
was laid in strips 4 to 6 ft. wide, the edges being coated with hot
paste. After the whole reservoir was lined, it was painted with the
asphalt paste, boiled much longer, until when cold it was hard and
brittle, breaking like glass under the hammer. This paste was put on
very hot and ironed down. It should not be more than {1/8}-in. thick or
it will "creep" on slopes of 1½ to 1. After two hot summers and one cold
winter there was not a single crack anywhere in the lining. A mixture of
sand and asphalt will creep on slopes of 1½ to 1, but asphalt concrete
will not. With asphalt at $20 a ton, and labor at $2 a day, the cost was
15 cts. a sq. ft. for 4-in. asphalt concrete. On a high slope Mr.
Stanton recommends making slight berms every 6 ft. to support the
concrete and prevent creeping. Asphalt concrete resists the wear of wind
and water that cuts away granite and iron.
~Base for Mill Floor.~--In constructing 17,784 sq. ft. of tar concrete
base for a mill floor, Mr. C. H. Chadsey used a sand, broken stone and
tar mixture mixed in a mechanical mixer. The apparatus used and the mode
of procedure followed were as follows:
Two parallel 8-in. brick walls 26 ft. long were built 4 ft. apart and 2½
ft. high to form a furnace. On these walls at one end was set a 4×6×2
ft. steel plate tar heating tank. Next to this tank for a space of 4×8
ft. the walls were spanned between with steel plates. This area was used
for heating sand. Another space of 4×8 ft. was covered with 1½ in. steel
rods arranged to form a grid; this space was used for heating the broken
stones. The grid proved especially efficient, as it permitted the hot
air to pass up through the stones, while a small cleaning door at the
ground allowed the screenings which dropped through the grid to be
raked out and added to the mixture. A fire from barrel staves and refuse
wood built under the tank end was sufficient to heat the tar, sand and
stone.
For mixing the materials a Ransome mixer was selected for the reason
that heat could be supplied to the exterior of the drum by building a
wood fire underneath. This fire was maintained to prevent the mixture
from adhering to the mixing blades, and it proved quite effective,
though occasionally they would have to be cleaned with a chisel bar,
particularly when the aggregate was not sufficiently heated before being
admitted to the mixer. A little "dead oil" applied to the discharge
chute and to the shovels, wheelbarrows and other tools effectually
prevented the concrete from adhering to them.
The method of depositing the concrete was practically the same as that
used in laying cement sidewalks. Wood strips attached to stakes driven
into the ground provided templates for gaging the thickness of the base
and for leveling off the surface. The wood covering consisted of a layer
of 2-in. planks, covered by matched hardwood flooring. In placing the
planking, the base was covered with a ¼-in. layer of hot pitch, into
which the planks were pressed immediately, the last plank laid being
toe-nailed to the preceding plank just enough to keep the joint tight.
After a few minutes the planks adhered so firmly to the base that they
could be removed only with difficulty. The hardwood surface was put on
in the usual manner. The prices of materials and wages for the work were
as follows:
Pitch, bulk, per lb. $ 0.0075
Gravel, per cu. yd. 1.50
Spruce sub-floor, per M. ft. B. M. 15.00
Hardwood surface, per M. ft. B. M. 33.00
Laborers, per 10-hour day. 1.50
Foreman, per 10-hour day. 4.00
Carpenters, per 10-hour day. 2.00
At these prices and not including a small administration cost or the
cost of tools and plant, the cost of the floor consisting of 4½ ins. of
concrete, 2 ins. of spruce sub-flooring and 7/8-in. hardwood finish was
as follows per square foot:
Pitch $0.04
Gravel 0.02
Spruce, for sub-floor 0.03
Hardwood for surfacing 0.035
Labor, mixing 0.03
Labor, laying 0.015
Carpenter work 0.025
------
Total per square foot $0.195
CHAPTER VII.
METHODS AND COST OF LAYING CONCRETE IN FREEZING WEATHER.
Reinforced concrete work may be done in freezing weather if the end to
be gained warrants the extra cost. Laboratory experiments show beyond
much doubt that Portland cement concrete which does not undergo freezing
temperatures until final set has taken place, or which, if frozen before
it has set, is allowed to complete the setting process after thawing
without a second interruption by freezing, does not suffer loss of
ultimate strength or durability. These requirements for safety may be
satisfied by so treating the materials or compounding the mixture that
freezing will not occur at normal freezing temperature or else will be
delayed until the concrete has set, by so housing in the work and
artificially treating the inclosed space that its temperature never
falls as low as the freezing point, or, by letting the concrete freeze
if it will and then by suitable protection and by artificial heating
produce and maintain a thawing temperature until set has taken place.
~LOWERING THE FREEZING POINT OF THE MIXING WATER.~--Lowering the freezing
point of the mixing water is the simplest and cheapest method by which
concrete can be mixed and deposited in freezing weather. The method
consists simply in adding some substance to the water which will produce
a brine or emulsion that freezes at some temperature below 32° F.
determined by the substance added and the richness of the admixture. A
great variety of substances may be added to water to produce low
freezing brines, but in concrete work only those may be used that do
little or no injury to the strength and durability of the concrete.
Practice has definitely determined only one of these, namely, sodium
chloride or common salt, though some others have been used successfully
in isolated cases. A point to be borne in mind is that cold retards the
setting of cement and that the use of anti-freezing mixtures emphasizes
this phenomenon and its attendant disadvantages in practical
construction. The accompanying diagram, Fig. 39, based on the
experiments of Tetmajer, show the effect on the freezing point of water
by the admixtures of various substances that have been suggested for
reducing the freezing point of mortar and concrete mixtures.
[Illustration: Fig. 39.--Diagram Showing Effect on Freezing Point of
Water by Admixture of Various Substances.]
~Common Salt (Sodium Chloride).~--The substance most usually employed to
lower the freezing point of water used in concrete is common salt.
Laboratory experiments show that the addition of salt retards the
setting and probably lowers the strength of cement at short periods, but
does not, when not used to excess, injure the ultimate strength. The
amount beyond which the addition of salt begins to affect injuriously
the strength of cement is stated variously by various authorities.
Sutcliffe states that it is not safe to go beyond 7 or 8 per cent. by
weight of the water; Sabin places the safe figures at 10 per cent., and
the same figure is given by a number of other American experimenters. A
number of rules have been formulated for varying the percentage of salt
with the temperature of the atmosphere. Prof. Tetmajer's rule as stated
by Prof. J. B. Johnson, is to add 1 per cent. of salt by weight of the
water for each degree Fahrenheit below 32°. A rule quoted by many
writers is "1 lb. of salt to 18 gallons of water for a temperature of
32° F., and an increase of 1 oz. for each degree lower temperature."
This rule gives entirely inadequate amounts to be effective, the
percentage by weight of the water being about 1 per cent. The familiar
rules of enough salt to make a brine that will "float an egg" or "float
a potato" are likewise untrustworthy; they call respectively, according
to actual tests made by Mr. Sanford E. Thompson, for 15 per cent. and 11
per cent. of salt which is too much, according to the authorities quoted
above, to be used safely. In practice an arbitrary quantity of salt per
barrel of cement or per 100 lbs. of water is usually chosen. Preferably
the amount should be stated in terms of its percentage by weight of the
water, since if stated in terms of pounds per barrel of cement the
richness of the brine will vary with the richness of the concrete
mixture, its composition, etc. As examples of the percentages used in
practice, the following works may be quoted: New York Rapid Transit
Railway, 9 per cent. by weight of the water; Foster-Armstrong Piano
Works, 6 per cent. by weight of the water. In summary, it would seem
that if a rule for the use of salt is to be adopted that of Tetmajer,
which is to add 1 per cent. by weight of the water for each degree
Fahrenheit below 32°, is as logical and accurate as any. It should,
however, be accompanied by the proviso that no more than 10 per cent. by
weight of salt should be considered safe practice, and that if the frost
is too keen for this to avail some other method should be adopted or the
work stopped. It may be taken that each unit per cent. of salt added to
water reduces the freezing temperature of the brine about 1.08° F.; a 10
per cent. salt brine will therefore freeze at 32° - 11° = 21° F. The
range of efficiency of salt as a preventative of frost in mixing and
laying concrete is, obviously, quite limited.
~HEATING CONCRETE MATERIALS.~--Heating the sand, stone and mixing water
acts both to hasten the setting and to lengthen the time before the
mixture becomes cold enough to freeze. At temperatures not greatly below
freezing the combined effects are sufficient to ensure the setting of
the concrete before it can freeze. More specific data of efficiency are
difficult to arrive at. There are no test data that show how long it
takes a concrete mixture at a certain temperature to lose its heat and
become cold enough to freeze at any specific temperature of the
surrounding air, and a theoretical calculation of this period is so
beset with difficulties as to be impracticable. Strength tests of
concrete made with heated materials have shown clearly enough that the
heating has no effect worth mentioning on either strength or
durability. Either the water, the sand, the aggregate or all three may
be heated; usually the cement is not heated but it may be if desired.
~Portable Heaters.~--An ordinary half cylinder of sheet steel set on the
ground like an arch is the simplest form of sand heater. A wood fire is
built under the arch and the sand to be heated is heaped on the top and
sides. The efficiency of this device may be improved by closing one end
of the arch and adding a short chimney stack, but even the very crude
arrangement of sheets of corrugated iron bent to an arc will do good
service where the quantities handled are small. This form of heater may
be used for stone or gravel in the same manner as for sand. It is
inexpensive, simple to operate and requires only waste wood for fuel,
but unless it is fired with exceeding care the sand in contact with the
metal will be burned. The drawings of Fig. 40 show the construction of a
portable heater for sand, stone and water used in constructing concrete
culverts on the New York Central & Hudson River Railroad. This device
weighs 1,200 lbs., and costs about $50.
[Illustration: Fig. 40.--Portable Sand, Stone and Water Heater.]
~Heating in Stationary Bins.~--The following arrangement for heating sand
and gravel in large quantities in bins was employed in constructing the
Foster-Armstrong Piano Works at Rochester, N. Y. The daily consumption
of sand and gravel on this work was about 50 cu. yds. and 100 cu. yds.,
respectively. To provide storage for the sand and gravel, a bin 16 ft.
square in projected plan was constructed with vertical sides and a
sloping bottom as illustrated in Fig. 41. This bin was divided by a
vertical partition into a large compartment for gravel and a small
compartment for sand and was provided with two grates of boiler tubes
arranged as shown. These grates caused V-shaped cavities to be formed
beneath in the gravel and sand. Into these cavities penetrated through
one end of the bin 6-in. pipes from a hot air furnace and 1-in. pipes
from a steam boiler. The hot air pipes merely pass through the wall but
the steam pipes continue nearly to the opposite side of the bin and are
provided with open crosses at intervals along their length. In addition
to the conduits described there is a small pipe for steam located below
and near the bottom of the bin. The hot air pipes connected with a small
furnace and air was forced through them by a Sturtevant No. 6 blower.
The steam pipes connected with the boiler of a steam heating system
installed to keep the buildings warm during construction.
[Illustration: Fig. 41.--Bin Arrangement for Heating Sand and Stone.]
~Other Examples of Heating Materials.~--In the construction of the power
plant of the Billings (Mont.) Water Power Co., practically all of the
concrete work above the main floor level was put in during weather so
cold that it was necessary to heat both the gravel and water used. A
sand heater was constructed of four 15-ft. lengths of 15-in. cast iron
pipe, two in series and the two sets placed side by side. This gave a
total length of 30 ft. for heating, making it possible to use the gravel
from alternate ends and rendering the heating process continuous. The
gravel was dumped directly on the heater, thus avoiding the additional
expense of handling it a second time. The heater pipes were laid
somewhat slanting, the fire being built in the lower end. A 10-ft. flue
furnished sufficient draft for all occasions. With this arrangement it
was possible to heat the gravel to a temperature of 80° or 90° F. even
during the coldest weather. Steam for heating the water was available
from the plant. The temperature at which the concrete was placed in the
forms was kept between 65° and 75° F. This was regulated by the man on
the mixer platform by varying the temperature of the water to suit the
conditions of the gravel. When the ingredients were heated in this
manner it was found advisable to mix the concrete "sloppy," using even
more water than would be commonly used in the so-called "sloppy"
concrete. No difficulty was experienced with temperature cracks if the
concrete, when placed, was not above 75° F. All cracks of this nature
which did appear were of no consequence, as they never extended more
than ½ in. below the surface. The concrete was placed in as large masses
as possible. It was covered nights with sacks and canvas and, when the
walls were less than 3 ft. in width, the outside of the forms was lagged
with tar paper. An air space was always left between the surface of the
concrete and the covering. Under these conditions there was sufficient
heat in the mass to prevent its freezing for several days, which was
ample time for permanent setting.
During the construction in 1902 of the Wachusett Dam at Clinton, Mass.,
for the Metropolitan Water Works Commission the following procedures
were followed in laying concrete in freezing weather: After November 15
all masonry was laid in Portland cement, and after November 28 the sand
and water were heated and salt added in the proportion of 4 lbs. per
barrel of cement. The sand was heated in a bin, 16½×15½×10 ft. deep,
provided with about 20 coils of 2-in. pipe, passing around the inside of
the bin. The sand, which was dumped in the top of the bin and drawn from
the bottom, remained there long enough to become warm. The salt for each
batch of mortar was dissolved in the water which was heated by steam;
steam was also used to thaw ice from the stone masonry. The laying of
masonry was not started on mornings when the temperature was lower than
18° F. above zero, and not even with this temperature unless the day was
clear and higher temperature expected. At the close of each day the
masonry built was covered with canvas.
In the construction of dams for Huronian Company's power development in
Canada a large part of the concrete work in dams, and also in power
house foundations, was done in winter, with the temperature varying from
a few degrees of frost to 15 degrees below zero, and on several
occasions much lower. No difficulty was found in securing good concrete
work, the only precaution taken being to heat the mixing water by
turning a ¾-in. steam pipe into the water barrel supplying the mixer,
and, during the process of mixing, to use a jet of live steam in the
mixer, keeping the cylinder closed by wooden coverings during the
process of mixing. No attempt was made to heat sand or stone. In all the
winter work care was taken to use only cement which would attain its
initial set in not more than 65 minutes.
In constructing a concrete arch bridge at Plano, Ill., the sand and
gravel were heated previous to mixing and the mixed concrete after
placing was kept from freezing by playing a steam jet from a hose
connected with the boiler of the mixer on the surface of the concrete
until it was certain that initial set had taken place. Readings taken
with thermometers showed that in no instance did the temperature of the
concrete fall below 32° F. within a period of 10 or 12 hours after
placing.
From experience gained in doing miscellaneous railway work in cold
weather Mr. L. J. Hotchkiss gives the following:
"For thin reinforced walls, it is not safe to rely on heating the water
alone or even the water and sand, but the stone also must be heated and
the concrete when it goes into the forms should be steaming hot. For
mass walls the stone need not be heated except in very cold weather.
Where concrete is mixed in small quantities the water can be heated by a
wood fire, and if a wood fire be kept burning over night on top of the
piles of stone and sand a considerable quantity can be heated. The fire
can be kept going during the day and moved back on the pile as the
heated material is used. This plan requires a quantity of fuel which in
most cases is prohibitive and is not sufficient to supply a power mixer.
For general use steam is far better.
"A convenient method is to build a long wooden box 8 or 10 in. square
with numerous holes bored in its sides. This is laid on the ground,
connected with a steam pipe and covered with sand, stone or gravel. The
steam escaping through the holes in the box will heat over night a pile
of sand, or sand and gravel, 8 or 10 ft. high. Perforated pipes can be
substituted for boxes. Material can be heated more rapidly if the steam
be allowed to escape in the pile than if it is confined in pipes which
are not perforated. Crushed stone requires much more heat than sand or
sand and gravel mixed because of the greater volume of air spaces. In
many cases material which has already been unloaded must be heated. The
expense of putting steam boxes or pipes under it is considerable. To
avoid this one or more steam jets may be used, the end of the jet pipe
being pushed several feet into the pile of material. If the jets are
connected up with steam hose they are easily moved from place to place.
It is difficult to heat stone in this way except in moderate weather.
"On mass work and at such temperatures as are met with in this latitude
(Chicago, Ill.) it is not usually necessary to protect concrete which
has been placed hot except in the top of the form. This can be done by
covering the top of the form with canvas and running a jet of steam
under it. If canvas is not available boards and straw or manure answer
the purpose. If heat is kept on for 36 hours after completion, this is
sufficient, except in unusually cold weather. The above treatment is all
that is required for reinforced retaining walls of ordinary height. But
where box culverts or arches carrying heavy loads must be placed in
service as soon as possible, the only safe way is to keep the main part
of the structure warm until the concrete is thoroughly hardened. Forms
for these structures can be closed at the ends and stoves or salamanders
kept going inside, or steam heat may be used. The outside may be covered
with canvas or boards, and straw and steam jets run underneath. After
the concrete has set enough to permit the removal of the outer forms of
box culverts, fires may be built near the side walls and the concrete
seasoned rapidly. Where structures need not be loaded until after the
arrival of warm weather, heat may be applied for 36 hours, and the
centering left in place until the concrete has hardened. Careful
inspection of winter concrete should be made before loads are applied.
In this connection it may be noted that concrete which has been partly
seasoned and then frozen, closely resembles thoroughly seasoned
concrete. Pieces broken off with a smooth fracture through all the
stones and showing no frost marks, when thawed out, can be broken with
the hands."
In building Portland cement concrete foundations for the West End St.
Ry., Boston, and the Brooklyn Heights R. R., much of the work was done
in winter. A large watertight tank was constructed, of such size that
three skips or boxes of stone could be lowered into it. The tank was
filled with water, and a jet of steam kept the water hot in the coldest
weather. The broken stone was heated through to the temperature of the
water in a few minutes. One of the stone boxes was then hoisted out, and
dumped on one side of the mixing machine, and then run through the
machine with sand, cement and water. The concrete was wheeled to place
without delay and rammed in 12-in. layers. The heat was retained until
the cement was set. In severely cold weather the sand was heated and the
mixing water also. A covering of hay or gunnysacks may be used.
~COVERING AND HOUSING THE WORK.~--Methods of covering concrete to protect
it from light frosts such as may occur over night will suggest
themselves to all; sacking, shavings, straw, etc., may all be used.
Covering wall forms with tar paper nailed to the studding so as to form
with the lagging a cellular covering is an excellent device and will
serve in very cold weather if the sand and stone have been heated. From
these simple precautions the methods used may range to the elaborate
systems of housing described in the following paragraphs.
~Method of Housing in Dam, Chaudiere Falls, Quebec.~--In constructing a
dam for the water power plant at Chaudiere Falls, P. Q., the work was
housed in. The wing dam and its end piers aggregated about 250 ft. in
length by about 20 ft. in width. A house 100 ft. long and 24 ft. wide
was constructed in sections about 10 ft. square connected by cleats with
bolts and nuts. This house was put up over the wing dam. It was 20 ft.
high to the eaves, with a pitched roof, and the ends were closed up; in
the roof on the forebay side were hatchways with sliding doors along the
whole length. Small entrance doors for the workmen were provided in the
ends of the building. The house was heated by a number of cylindrical
sheet-iron stoves about 18 ins. in diameter by 24 ins. high, burning
coke; thermometers placed at different points in the shed gave warning
to stop work when the temperature fell below freezing, which, however,
rarely occurred. Mixing boards were located in the shed, and concrete,
sand and broken stone were supplied in skipfuls by guy derricks located
in the forebay, which passed the material through the hatchways in the
roof, the proper hatchway being opened for the purpose and quickly
closed. The mortar was first mixed on a board, and then a skip-load of
stone was dumped into the middle of the batch and the whole well mixed.
The water was made lukewarm by introducing a steam-jet into several
casks which were kept full. The sand was heated outside in the forebay
on an ordinary sand heater. The broken stone was heated in piles by a
steam-jet; a pipe line on the ground was made up of short lengths of
straight pipe alternating with T-sections--turned up. The stone was
piled 3 to 4 ft. deep over the pipe and a little steam turned into the
pipe. Several such piles kept going all the time supplied enough stone
for the work; the stone was never overheated, and was moist enough not
to dry out the mortar when mixed with it. In this manner the concreting
was successfully carried on and the wing dam built high enough to keep
high water out of the forebay.
Some danger from freezing was also encountered the next season, when the
last part of the wing dam was being constructed. This work was done when
the temperature was close to freezing, and it became necessary to keep
the freshly placed concrete warm over night. This was done by covering
the work loosely with canvas, under which the nozzle of a steam hose was
introduced. By keeping a little steam going all night the concrete was
easily kept above freezing temperature.
[Illustration: Fig. 42.--Canvas Curtain for Enclosing Open Walls.]
[Illustration: Fig. 43.--Sketch Showing Method of Applying Curtains to
Open Walls.]
~Method of Housing in Building Work.~--The following method of housing in
building work is used by Mr. E. L. Ransome. The feature of the system is
that the enclosing structure is made up of a combination of portable
units which can be used over and over again in different jobs. The
construction is best explained in connection with sketches.
Figure 43 shows a first floor wall column with the wall girder
surmounting it and the connecting floor system. It will be seen that the
open sides are enclosed by canvas curtains and the floor slab is covered
with wood shutters. The curtains are composed of separate pieces so
devised that they may be attached to each other by means of snaps and
eyes; one of these curtain units is shown by Fig. 42. Referring now to
Fig. 43, the curtain A is held by the tying-rings to a continuous
string piece B, the upper portion or flap D being held down by a
metal bar or other heavy object so as to lap over the floor covers E.
The lower edge of the curtain is attached to the string piece C. The
sketch has been made to show how the curtain adjusts itself to irregular
projections such as the supports for a wall girder form; to prevent the
curtain tearing on such projections it is well to cover or wrap the
rough edges with burlap, bagging or other convenient material. The
details of the wooden floor covers are shown by Fig. 44; they are
constructed so as to give a hollow space between them and the floor and
holes are left in the floor slab as at H, Fig. 43, to permit the warm
air from below to enter this hollow space. This warm air is provided by
heating the enclosed story of the building by any convenient adequate
means. In constructing factory buildings, 50×200 ft. in plan at
Rochester, N. Y., Mr. Ransome used a line of 3/4 to 3/8-in. steam pipe
located at floor level and running around all four sides and a similar
line running lengthwise of the building at the center, these pipes
discharging live steam through openings into the enclosed space. In
addition to the steam piping 10 braziers in which coke fires were kept
were scattered around the floor. This equipment kept the enclosed story,
50×100 ft.×13 ft. high, at a temperature of 80° F. and at temperature of
about 40° F. between the floor top and its board covering. The work was
not stopped at any time because of cold and the temperatures outside
ranged from zero to 10° above.
[Illustration: Fig. 44.--Portable Wooden Panels for Covering Floors.]
CHAPTER VIII.
METHODS AND COST OF FINISHING CONCRETE SURFACES.
Good design in concrete as well as in steel, masonry and wood, requires
that the structure shall be good to look at. This means that the
proportions must be good and that the surface finish must be pleasing.
Good proportions are a matter of design but a pleasing surface finish is
a matter of construction. Many, perhaps the majority of, concrete
structures do not have a pleasing surface finish; the surface is
irregular, uneven in texture, and stained or discolored or of lifeless
hue. The reasons for these faults and the possible means of remedying
them are matters that concern the construction engineer and the
contractor.
Imperfections in the surface of concrete are due to one or more of the
following causes: (1) Imperfectly made forms; (2) imperfectly mixed
concrete; (3) carelessly placed concrete; (4) use of forms with dirt or
cement adhering to the boards; (5) efflorescence and discoloration of
the surface after the forms are removed.
~IMPERFECTLY MADE FORMS.~--In well mixed and placed concrete the film of
cement paste which flushes to the surface will take the impress of every
flaw in the surface of the forms. It will even show the grain marks in
well dressed lumber. From this it will be seen how very difficult it is
so to mold concrete that the surface will not bear evidence of the mold
used. The task is impracticable of perfect accomplishment and the degree
of perfection to which it can be carried depends upon the workmanship
expended in form construction. Forms with a smooth and even surface are
difficult and expensive to secure. It is impracticable in the first
place to secure lagging boards dressed to exact thickness and in the
second place it is impracticable to secure perfect carpenter work;
joints cannot be got perfectly close and a nail omitted here or there
leaves a board free to warp. From this point on the use of imperfectly
sized lumber and careless carpentry can go to almost any degree of
roughness in the form work. Only approximately smooth and unmarked
concrete surfaces can be secured in plain wooden forms and this only
with the very best kind of form construction. So much for the
limitations of form work in the matter of securing surface finish. These
limitations may be reduced in various ways. Joint marks may be
eliminated wholly or partly by pointing the joints with clay or mortar
or by pasting strips of paper or cloth over them, or the whole surface
of the lagging can be papered; by the use of oiled paper there will be
little trouble from the paper sticking. Grain marks and surface
imperfections can be reduced by oiling the lumber so as to fill the
pores or by first oiling and then filling the coat of oil with fine sand
blown or cast against the boards.
The preceding remarks are of course based on the assumption that as
nearly as possible a smooth and even surface finish is desired. If
something less than this is sufficient, and in many cases it is, form
produced surface defects become negligible in the proportion that they
do not exceed the standards of roughness and irregularity considered
permissible by the engineer and these standards are individual with the
engineer; what one considers excessive roughness and irregularity
another may consider as amply even and smooth. The point to be kept in
mind is that beyond a certain state of evenness and regularity form
produced surfaces are impracticable to obtain, because to construct
forms of the necessary perfection to obtain them costs far more than it
does to employ special supplementary finishing processes.
Surface blemishes due to dirt or cement adhering to the form boards have
no excuse if the engineer or contractor cares to avoid them. It is a
simple matter to keep the lagging clean and free from such
accumulations.
~IMPERFECT MIXING AND PLACING.~--Imperfectly mixed and placed concrete
gives irregularly colored, pitted and honeycombed surfaces with here a
patch of smooth mortar and there a patch of exposed stone. Careful
mixing and placing will avoid this defect, or all chance of it may be
eliminated by using surface coatings of special mixtures. There is no
great difficulty, however, in obtaining a reasonably homogeneous surface
with concrete; the task merely requires that the mixing shall be
reasonably uniform and homogeneous and that in placing this mixture the
spading next to the lagging shall be done in such a way as to pull the
coarse stones back and flush the mortar to the surface. Spading forks
are excellent for this purpose. A better tool is a special spade made
with a perforated blade; this special spade costs $3.
~EFFLORESCENCE.~--Efflorescence is the term applied to the whitish or
yellowish accumulations which often appear on concrete surfaces.
"Whitewash" is another name given to these blotches. Efflorescence is
due to certain salts leaching out of the concrete and accumulating into
thin layers where the water evaporates on the surface. These salts are
most probably sulphates of calcium and magnesium, both of which are
contained in many cements and both of which are slightly soluble in
water. Efflorescence is very erratic in its appearance. Some concretes
never exhibit it; in some it may not appear for several years, and in
others it shows soon after construction and may appear in great
quantities. The most effective way to prevent efflorescence would
naturally be to use cements entirely free from sulphates, chlorides or
whatever other soluble salts are the cause of the phenomenon, but the
likelihood of engineers resorting to the trouble of such selection,
except in rare instances, is not great, even if they knew what cements
to select, so that other means must be sought. The most common place for
efflorescence to appear in walls is at the horizontal junction of two
days' work or where a coping is placed after the main body of the wall
has been completed. The reason of this seems to be that the salt
solutions seep down through the concrete until they strike the nearly
impervious film of cement that forms on the top surface of the old
concrete before the new is added, and then they follow along this
impervious film to the face of the wall. The authors have suggested that
this cause might be remedied by ending the day's work by a layer whose
top has a slight slope down toward the rear of the wall or perhaps by
placing all the concrete in similarly sloping layers. Mr. C. H.
Cartlidge is authority for the statement that this leaching at joints
can be largely done away with by the simple process of washing the top
surface of concrete which has been allowed to set over night by
scrubbing it with wire brushes in conjunction with thorough flushing
with a hose. But efflorescence frequently appears on the faces of walls
built without construction joints and in which a wet concrete is puddled
in and not tamped in layers, and here other means are obviously
essential. Waterproofing the surface of the wall should be effective so
long as the waterproofing lasts; indeed one of the claims made for some
of these waterproofing compounds is that efflorescence is prevented. The
various waterproofing mixtures capable of such use will be found
described in Chapter XXV. Failing in any or all of these methods of
preventing efflorescence the engineer must resort to remedial measures.
The saline coating must be scraped, or chipped, or better, washed away
with acids.
Efflorescence was removed from a concrete bridge at Washington, D. C, by
using hydrochloric (muriatic) acid and common scrubbing brushes; 30
gals. of acid and 36 scrubbing brushes were used to clean 250 sq. yds.
of concrete. The acid was diluted with 4 or 5 parts water to 1 of acid;
water was constantly played with a hose on the concrete while being
cleaned to prevent penetration of the acid. One house-front cleaner and
5 laborers were employed, and the total cost was $150, or 60 cts. per
sq. yd. This high cost was due to the difficulty of cleaning the
balustrades. It is thought that the cost of cleaning the spandrels and
wing walls did not exceed 20 cts. per sq. yd. The cleaning was perfectly
satisfactory. An experiment was made with wire brushes without acid, but
the cost was $2.40 per sq. yd. The flour removed by the wire brushes was
found by analysis to be silicate of lime. Acetic acid was tried in place
of muriatic, but required more scrubbing.
~SPADED AND TROWELED FINISHES.~--With wet-concrete and ordinarily good
form construction a reasonably good surface appearance can be obtained
by spading and troweling. For doing the spading a common gardener's hoe,
straightened out so that the blade is nearly in line with the handle
will do good work. The blade of the tool is pushed down next to the
lagging and the stone pulled back giving the grout opportunity to flush
to the face. Troweling, that is troweling without grout wash, requires,
of course, that the concrete be stripped before it has become too hard
to be worked. As troweling is seldom required except for tops of copings
and corners it is generally practicable to bare the concrete while it is
still fairly green. In this condition the edges of copings, etc., can be
rounded by edging tools such as cement sidewalk workers use.
~PLASTER AND STUCCO FINISH.~--The ordinary concrete surface with a
film-like cement covering will not hold plaster or stucco. To get proper
adhesion the concrete surface must be scrubbed, treated with acid or
tooled before the plaster or stucco is applied and this makes an
expensive finish since either of the preliminary treatments constitutes
a good finish by itself. When a coarse grained facing is made of very
dry mixtures, as described in a succeeding section, it has been made to
hold plaster very well on inside work. In general plaster and stucco
finishes can be classed as uncertain even when the concrete surface has
been prepared to take them, and when the concrete has not been so
prepared such finishes can be classed as absolutely unreliable.
~MORTAR AND CEMENT FACING.~--Where a surface finish of fine texture or of
some special color or composition is desired the concrete is often faced
with a coat of mortar or, sometimes, neat cement paste or grout. Mortar
facing is laid from 1 to 2 ins. thick, usually 1½-ins., the mortar being
a 1-1, 1-2 or 1-3 mixture and of cement and ordinary sand where no
special color or texture is sought. This facing often receives a future
special finish as described in succeeding sections, but it is more
usually used as left by the forms or at best with only a troweling or
brushing with grout. Engineers nearly always require that the mortar
facing and the concrete backing shall be constructed simultaneously.
This is accomplished by using facing forms, two kinds of which are shown
by Figs. 45 and 46. In use the sheet steel plates are placed on edge the
proper distance back of the lagging and the space between them and the
lagging is filled with the facing mortar. The concrete backing is then
filled in to the height of the plate, which is then lifted vertically
and the backing and facing thoroughly bonded by tamping them together.
The form shown by Fig. 46, though somewhat the more expensive, is the
preferable one, since the attached ribs keep the plate its exact
distance from the lagging without any watching by the men, while the
flare at the top facilitates filling. The facing mortar has to be rather
carefully mixed; it must be wet enough to work easily and completely
into the narrow space and yet not be so soft that in tamping the backing
the stones are easily forced through it. Also since the facing cannot
proceed faster than the backing the mortar has to be mixed in small
batches so that it is always fresh. A cubic yard of mortar will make 216
sq. ft. of 1½-in. facing. Cement facing is seldom made more than 1 in.
thick. If placed as a paste the process is essentially the same as for
placing mortar. When grout is used a form is not used; place and tamp
the concrete in 6 to 8-in layers, then shove a common gardener's spade
down between the concrete and the lagging and pull back the concrete
about an inch and pour the opening full of grout and withdraw the spade.
If this work is carefully done there will be very few stones showing
when the forms are removed. When stiff pastes or mortars are used the
contractor often places the facing by plastering the lagging just ahead
of the concreting; this process requires constant watching to see that
the plaster coat does not slough or peel off before it is backed up with
concrete.
[Illustration: Fig. 45.--Form for Applying Cement Facing (Massachusetts
Highway Commission).]
[Illustration: Fig. 46.--Form for Applying Cement Facing (Illinois
Central R. R.).]
~SPECIAL FACING MIXTURES FOR MINIMIZING FORM MARKS.~--The ordinary facing
mixture of mortar or cement is so fine grained and plastic that it
readily takes the impress of every irregularity in the form lagging;
where a particularly good finish is desired this makes necessary
subsequent finishing treatments. To avoid these subsequent treatments
and at the same time to reduce the form marks, special facing mixtures,
which will not take the imprint of and which will minimize rather than
exaggerate every imperfection in the forms, have been used with very
considerable success in the concrete work done for the various Chicago,
Ill., parks. The mixture used consists usually of 1 part cement, 3 parts
fine limestone screenings and 3 parts ¾-in. crushed limestone; these
materials are mixed quite dry so no mortar will flush to the surface
when rammed hard. With moderately good form work the imprint of the
joints is hardly noticeable and grain marks do not show at all. For thin
building walls the special mixture is used throughout the wall, but for
more massive structures it is used only for the facing.
~GROUT WASHES.~--Grout finishes serve only to fill the small pits and
pores in the surface coating; cavities or joint lines, if any exist,
must be removed by plastering or rubbing before the grout is applied or
else by applying the grout by rubbing. In ordinary work the grout is
applied with a brush after the holes have been plastered and the joint
marks rubbed down. The grout to be applied with a brush should be about
the consistency of whitewash; a 1 cement 2 sand mixture is a good one.
Where a more perfect finish of dark color is desired the grout of neat
cement and lampblack in equal parts may be applied as follows: Two coats
with a brush, the second coat after the first has dried, and one coat by
sweeping with a small broom. The broom marks give a slightly rough
surface. Instead of a liquid grout a stiff grout or semi-liquid mortar
applied with a trowel or float can be used. In this case the grout
should be applied in a very thin coat and troweled or floated so that
only the pores are filled and no body of mortar left on the surface or
else it will scale off. A more expensive but very superior grout finish
is obtained by rubbing and scouring the wet grout into the surface with
cement mortar bricks, carborundum bricks, or such like abrasive
materials. A 1 cement 1 sand mortar brick, with a handle molded into it,
and having about the dimensions of an ordinary building brick makes a
good tool for rubbing down joint marks as well as for applying grout.
[Illustration: Fig. 47.--Concrete Baluster Finished by Scrubbing and
Washing.]
~FINISHING BY SCRUBBING AND WASHING.~--A successful finish for concrete
structures consists in removing the forms while the concrete is green
and then scrubbing the surface with a brush and water until the film of
cement is removed and the clean sand or stone left exposed. This method
has been chiefly used in concrete work done by the city of Philadelphia,
Pa., Mr. Henry M. Quimby, Bridge Engineer. Figure 47 shows an example of
scrubbed finish, but of course the texture or color of the surface will
vary with the character of the face mixture and the hue of the sand or
chips used. Warm tones can be secured by the use of crushed brick or red
gravel; a dark colored stone with light sand gives a color much
resembling granite; fine gravel or coarse sand gives a texture like
sandstone. In much of this work done in Philadelphia a mixture composed
of 1 part cement, 2 parts bank sand and 3 parts crushed and cleaned
black, slaty shale from 3/8 to 1/4 in. in size, has been used with good
results both in appearance and in durability. The scrubbing is done
with an ordinary house scrubbing brush at the same time flushing the
concrete with water from a sponge or bucket or, preferably, from a hose.
In general the washing is done on the day following the placing of the
concrete but the proper time depends upon the rapidity with which the
concrete sets. In warm weather 24 hours after placing is generally about
right, but in cold weather 48 hours may be required, and in very cold
weather the concrete has been left to set a week and the scrubbing has
been successful. With the concrete in just the proper condition a few
turns of the brush with plenty of water will clean away the cement, but
if a little too hard wire brushes must be used and if still harder a
scouring brick or an ordinary brick with sand is necessary to cut the
cement film. The process requires that the forms shall be so constructed
that the lagging can be removed when the concrete has reached the proper
age for treatment. Mr. Quimby sets the studs 8 to 12 ins. from the face
and braces the lagging boards against them by cleats nailed so as to be
easily loosened. His practice is to use boards in one width the full
depth of the course and to nail a triangular bead strip to the face at
each edge. These bead strips mark the joints between courses as shown by
Fig. 48. When a "board" is taken off it is cleaned and oiled and reset
for a new course by inserting the bottom bead strip in the half
indentation left by the top bead in the concrete. This is, of course,
for work of such size that one course is a day's work of concreting. In
such work, two carpenters with perhaps one helper will remove a course
of "boards" say 100 ft. long in from 4 to 8 hours. While forms of the
kind described cost more to construct there is a saving by repeated
re-use of the lagging boards. The indentations or beads marking the
courses serve perfectly to conceal the construction joints. The cost of
scrubbing varies with the hardness of the concrete; when in just the
right condition for effective work one man can scrub 100 sq. ft. in an
hour; on the other hand it has taken one man a whole day to scrub and
scour the same area when the concrete was allowed to get hard.
[Illustration: Fig. 48.--Concrete Abutment with Scrubbed Finish and
Course Marks.]
~FINISHING BY ETCHING WITH ACID.~--The acid etched or acid wash process of
finishing concrete consists in first washing the surface with an acid
preparation to remove the surface cement and expose the sand and stone,
then with an alkaline solution to remove all free acid, and finally,
with clear water in sufficient volume to cleanse and flush the surface
thoroughly. The work can be done at any time after the forms are removed
and does not require skilled labor; any man with enough judgment to
determine when the etching has progressed far enough can do the work.
This process has been very extensively used in Chicago by the South Park
Commission, Mr. Linn White, Engineer. In this work the concrete is faced
with a mixture of cement, sand and stone chips, any stone being used
that is not affected by acid. Limestone is excluded. Where some color is
desired the facing can be mixed with mineral pigments or with colored
sand or stone chips. This acid wash process has been patented, the
patentees being represented by Mr. J. K. Irvine, Sioux City, Ia.
~TOOLING CONCRETE SURFACES.~--Concrete surfaces may be bush-hammered or
otherwise tool finished like natural stone, exactly the same methods and
tools being used. Tooling must wait, however, until the concrete has
become fairly hard. As the result of his experience in tooling some
43,000 sq. ft. of concrete, Mr. W. J. Douglas states that the concrete
should be at least 30 days old and, preferably, 60 days old, if
possible, when bush-hammered. There is a great variation in the costs
given for tooling concrete. Mr. C. R. Neher states that a concrete face
can be bush-hammered by an ordinary laborer at the rate of 100 sq. ft.
in 10 hours or at a cost of 1½ cts. per square foot with wages at 15
cts. per hour. Mr. E. L. Ransome states that bush-hammering costs from
1½ to 2½ cts. per square foot, wages of common laborers being 15 cts.
per hour. The walls of the Pacific Borax Co.'s factory at Bayonne, N.
J., were dressed by hand at the rate of 100 to 200 sq. ft. per man per
day; using pneumatic hammer one man was able to dress from 300 to 600
sq. ft. per day. In constructing the Harvard Stadium the walls were
dressed with pneumatic hammers fitted with a tool with a saw-tooth
cutting blade like an ice chopper. Men timed by one of the authors on a
visit to this work were dressing wall surface at the rate of 50 sq. ft.
per hour, but the contractor stated that the average work per man per
day was 200 sq. ft. Common laborers were employed. The average cost of
bush-hammering some 43,000 sq. ft. of plain and ornamental blocks for
the Connecticut Avenue Bridge at Washington, D. C, was 26 cts. per
square foot. Both pneumatic tools and hand tooling were employed and the
work of both is lumped in the above cost, but hand tooling cost about
twice as much as machine tooling. The work was done by high-priced men,
foremen stone cutters at $5 per day and stone cutters at $4 per day.
Moreover a grade of work equal to the best bush-hammered stone work was
demanded. Full details of the cost of this work are given in Chapter
XVII. Mr. H. M. Quimby states that the cost of tooling concrete runs
from 3 cts. to 12 cts. per square foot, according to the character and
extent of the work and the equipment.
~GRAVEL OR PEBBLE SURFACE FINISH.~--An effective variation of the ordinary
stone concrete surface is secured by using an aggregate of rounded
pebbles of nearly uniform size and by scrubbing or etching remove the
cement enough to leave the pebbles about half exposed at the surface. In
constructing a bridge at Washington, D. C, the concrete was a 1-2-5
gravel mixture of 1½ to 2-in. pebbles for the spandrels and arch ring
face and of 1-in. pebbles for the parapet walls. The forms were removed
while the concrete was still green and the cement scrubbed from around
the faces and sides of the pebbles using wire brushes and water. Tests
showed that at 12 hours age the concrete was not hard enough to prevent
the pebbles from being brushed loose and that at 36 hours age it was too
hard to permit the mortar to be scrubbed away without excessive labor;
the best results were obtained when the concrete was about 24 hours old.
~COLORED FACING.~--Where occasion calls for concrete of a color or tint
other than is obtained by the use of the ordinary materials either an
aggregate of a color suitable for the purpose may be used or the mixture
may be colored by the addition of some mineral pigment. The first method
is by all odds the preferable one; it gives a color which will endure
for all time and it in no way injures the strength or durability of the
concrete. Mineral pigments may be secured from any of several well-known
firms who make them for coloring concrete, and they may be had in almost
every shade. Directions for using these colors can be had from the
makers. All but a very few of these mineral colors injure the strength
and durability of the concrete if used in amounts sufficient to produce
the desired color and all of them fade in time. The best method of
producing a colored mortar or concrete facing is to mix the cement with
screenings produced by crushing a natural stone of the desired color.
CHAPTER IX.
METHODS AND COST OF FORM CONSTRUCTION.
Concrete being a plastic material when deposited requires molds or forms
to give it the shape required and to maintain it in that shape until it
has hardened to sufficient strength to require no exterior support. The
material used in constructing forms is wood. Beyond the use of metal
molds for building blocks for sewer construction and for ornamental and
a few architectural shapes, iron and steel are used in form construction
only as ties and clamps to hold parts of wood forms together--except in
rare instances. A discussion of form construction, therefore, is
essentially a discussion of wood forms.
Before taking up this discussion, however, attention deserves to be
called to the opportunities for the development of metal forms. Lumber
is costly and is growing more scarce and costly all the time. A
substitute which can be repeatedly used and whose durability and salvage
value are great presents itself in steel if only a system of form units
can be devised which is reasonably adjustable to varying conditions.
Cylindrical steel column molds have been used to some extent and are
discussed in Chapter XIX. In Chapter XVI we describe a steel form for
side walls of a tunnel lining. In some building work done in the
northwest corrugated steel panels or sheets have been used as lagging
for floor slab centers. A number of styles of metal forms or centers for
sewer and tunnel work have been devised and used and are discussed in
Chapter XXI. Despite this considerable use of metal for special forms
nothing approaching its general use like wood has been attempted, and
the field lies wide open for invention.
The economics of form construction deserve the most serious attention of
the engineer and contractor. It is seldom that form work, outside of
very massive foundation construction, costs less than 50 cts. per cubic
yard of concrete in place, and it is not unusual in the more complex
structures for it to cost $5 per cubic yard of concrete in place. These
costs include the cost of materials and of framing, handling and
removing the forms but they do not embrace extremely high or low costs.
It is evident without further demonstration that time spent in planning
economic form construction for any considerable job of concrete work is
time spent profitably.
In the following sections we review the general considerations which
enter into all form work. Specific details of construction and specific
costs of form work are given in succeeding chapters where each class of
concrete work is discussed separately. This chapter is intended
principally to familiarize the reader with general principles governing
form work.
~EFFECT OF DESIGN ON FORM WORK.~--The designing engineer can generally aid
largely in reducing the cost of form work if he will. This is
particularly true in building work in which, also, form costs run high.
By arranging his beam spacing and sizes with a little care he will
enable the contractor to use his forms over and over and thus greatly
reduce the expense for lumber. In the same way columns may be made of
dimensions which will avoid frequent remaking of column forms. Panel
recesses in walls may be made the thickness of a board or plank, instead
of some odd depth that will require a special thickness of lumber, or
beams may be made of such size that certain dimension widths of lumber
can be used without splitting. In general, carpenter work costs more
than concrete and where a little excess concrete may be contributed to
save carpenter work it pays to contribute it. The figures given in
Chapter XIX, showing the reduction in lumber cost coming from using the
same material over a second or third time, should be studied in this
connection. The leading firms of engineering-contractors which both
design and construct reinforced concrete buildings fully realize these
opportunities and take advantage of them, but the general practitioner,
particularly if he be an architect, does not do so. The authors have
personal knowledge of one building in which a slight change in spacing
and dimensions of beams--a change that would have been of no
architectural or structural significance--would have reduced the
successful contractor's bid for the work by $10,000. The designing
engineer should hold it as a cardinal point in design that form work,
and we will add here reinforcement also, should so far as possible be
made interchangeable from bay to bay and from floor to floor.
~KIND OF LUMBER.~--The local market and the character of the work
generally determine the kind of lumber to be used for forms. The
hardwoods are out of the question for form construction because they
cost too much and are too hard to work. Among the soft woods white pine
costs too much for general use and hemlock is unreliable when exposed to
the weather. This reduces the list generally available to spruce, Norway
pine and the southern pines. Neither green nor kiln-dried lumber is so
good as partially dry stuff, since the kiln-dried lumber swells and
crushes or bulges the joints and green lumber does not swell enough to
close the joints. Forms have to withstand, temporarily, very heavy
loads, therefore, knots, shakes and rot must be watched after. The
choosing of good lumber is a simple process and the contractor who wants
to be able to rely on his forms will look after it carefully, without
going to extremes which the work does not warrant.
~FINISH AND DIMENSIONS OF LUMBER.~--Dressing the lumber serves four
important purposes: It permits the forms to be constructed more nearly
true to line and surface; it permits tighter joint construction; it
gives a smoother surface finish to the concrete, and it facilitates the
removal and cleaning of the forms. Undressed lumber may be used for the
backs of walls and abutments, for work below ground and wherever a
smooth and true surface is unimportant; there are some contractors,
however, who prefer lumber dressed on one side even for these purposes
because of the smaller cost of cleaning. For floor and wall forms the
lumber should always be dressed on one side; where the work is very
particular both sides should be dressed, and in special cases the sides
of the joists or studs against which the lagging lies may be dressed.
For ordinary work a square edge finish does well enough but for fine
face work a tongue and groove or bevel edge finish is preferable. The
tongue and groove finish gives a somewhat tighter joint on first laying
but it does not take up swelling or resist wear so well as the bevel
edge finish.
When ordering new lumber for forms the contractor will save much future
work and waste if he does it from plans. Timber cut to length and width
to go directly into the forms reduces both mill and carpenter work on
the site, and in many cases it can be so ordered if ordered from plans.
Waste is another item that is reduced by ordering from plans; with
lumber costing its present prices crop ends run into money very rapidly.
When old lumber from a previous job is to be used the contractor can
only make the best of his stock, but even here form plans will result in
saving. Sort and pile the old lumber according to sizes and make a
schedule of the quantity of each size on hand; this schedule in the
hands of the man who designs the forms and of the head carpenter will
materially reduce waste and carpenter work. It is often possible
especially in making concrete foundations for frame buildings to use
lumber for forms which is subsequently used for floor beams, etc., in
the building.
Contractors differ greatly in their ideas of the proper thickness of
lumber to use for various parts of form work. Generally speaking 1¼ to
2-in. stuff is used for wall lagging held by studding and 1-in. stuff
when built into panels; for floor lagging 1-in stuff with joists spaced
up to 24 ins. or when built into panels; for column lagging 1¼ to 2-in.
stuff; for sides of girders 1, 1¼, 1½ and 2-in. stuff are all used; and
for bottoms of girders, 1½ and 2-in. stuff. These figures are by no
means invariable as a study of the numerous examples of actual form work
given throughout this book will show.
~COMPUTATION OF FORMS.~--If the minimum amount of lumber consistent with a
given deflection is to be used in form work the sizes and spacing of the
supporting members must be actually computed for the loading. As a
practical matter of fact the amount of material used and the arrangement
of the supports are often subject to requirements of unit construction,
clearance, staging, etc., which supersede the matter of economical
adaptation of material to loading. The designing of form work is at
best, therefore, a compromise between rules of thumb and scientific
calculation. In wall work empirical methods are nearly always followed.
In girder and floor slab work, on the other hand, design is commonly
based on computation.
In the matter of loads the general practice is to assume the weight of
concrete as a liquid at some amount which it is considered will also
cover the weight of men, barrows, runways and current construction
materials. The assumed weights vary. One prominent engineering firm
assumes the load to be the dead weight of concrete as a liquid and the
load due to placing and specifies that the forms shall be designed to
carry this load without deflection. Mr. W. J. Douglas, Engineer of
Bridges, Washington, D. C, assumes for lateral thrust on wall forms that
concrete is a liquid of half its own weight, or 75 lbs. per cu. ft. Mr.
Sanford E. Thompson, Consulting Engineer, Newton Highlands, Mass.,
assumes for dead load, weight of concrete including reinforcement as 154
lbs. per cu. ft., and for live load, 75 lbs. per sq. ft. on slabs and 50
lbs. per sq. ft. in figuring beam and girder forms and struts.
The assumed safe stresses in form work may be taken somewhat higher than
is usual in timber construction, because of the temporary character of
the load. In calculating beams the safe extreme fiber stress may be
assumed at 750 lbs. per sq. in. The safe stress in pounds per square
inch for struts or posts is shown by Table XV, compiled by Mr. Sanford
E. Thompson. The sizes of struts given are those most commonly used in
form work.
TABLE XV.--SAFE STRENGTH OF TIMBER STRUTS FOR FRAME WORK.
--Dimensions of Strut.--
Length Strut. 3×4-in. 4×4-in. 6×6-in. 8×8-in.
Feet. Lbs. Lbs. Lbs. Lbs.
14 ..... 700 900 1,100
12 600 800 1,000 1,200
10 700 900 1,100 1,200
8 850 1,050 1,200 1,200
6 1,000 1,200 1,200 1,200
In using this table it must be borne in mind that bracing both ways
reduces the length of a long strut. For example, if a strut 24 ft. long
be divided into three panels by bracing the length of strut so far as
the table is concerned is 8 ft.
As stated above wall forms are rarely computed. Experience has shown
that the maximum spans of various thicknesses of lagging between
supports are: 1-in. boards, 24 ins.; 1½-in. plank, 4 ft., and 2-in.
plank, 5 ft. Studding will vary in size from 2×4 to 4×6 ins., strutted
and braced horizontally to meet conditions. Column forms, like wall
forms, are rarely computed, yokes being spaced 2 ft. apart for 1¼-in.
lagging up to 3 to 3½ ft. apart for 2-in. lagging.
Floor forms, including girder and slab forms, are computed on the basis
of a maximum deflection and not on the basis of strength. Sagging forms
are liable to rupture the beam or slab. The amount of deflection
considered allowable varies from no deflection up to 3/8 to ½ in.
Assuming the deflection, permissible thickness of the timber necessary
to carry the load is determined by the formulas:
d = 5 W l³ ÷ 384 E I (1)
and
bh³
I = --- (2)
12
Formula (1) is the familiar one for computing deflection for a beam
supported (not fixed) at the ends. Mr. Sanford F. Thompson suggests
using the constant {3/384}, which is an approximate mean between {1/384}
that for beams with fixed ends and {5/384} that for beams with ends
supported. Formula (1) then becomes
d = 3 W l³ ÷ 384 E I,
in which as above:
d = maximum deflection in inches.
W = total load on plank or joist.
l = length between supports in inches.
E = modulus of elasticity of lumber.
I = moment of inertia of cross-section.
b = breadth of lumber.
h = depth of lumber.
The deflection, d, being assumed formula (1) is solved for I, moment
of inertia. Substituting the value of I in formula (2) we can readily
estimate the size of joist or thickness of plank to use.--For spruce,
yellow pine and the other woods commonly used in form work E may be
taken equal to 1,300,000 lbs. per sq. in.
~DESIGN AND CONSTRUCTION.~--The main points to be kept in mind in the
original design and construction of forms are: Economy in lumber,
economy in carpenter work, and economy in taking down, carrying and
re-erecting. Economy in lumber is not merely the matter of using the
least amount of lumber that will serve the purpose considering the form
as an isolated structure. It may be possible to build a column form, for
example, of very light material which will serve to mold a single
column, but it is evident that we could better afford to use twice this
amount of lumber if by doing so we obtained a form which could be used
over again to mold a second column; no more lumber per column would be
used while the cost of erecting a form already framed is less than the
cost of framing a new form. Economy in lumber in form construction
involves, therefore, recognition of the economies to be gained by
repeated use of the lumber. A certain amount of additional sturdiness is
required in the shape of heavier form lumber and stronger framing to
provide for the wear and tear of repeated use, and it is always economy
to provide it when repeated use is possible. The thing can be overdone,
however; there is an economical limit to repeated use, as we demonstrate
further on. In the matter of economy in carpenter work, a certain amount
of extra work put into framing the forms to withstand the stress of
repeated use is economically justifiable. Also carpenter work put into
framing which substitutes clamps and wedges for nails is sound economy;
generally speaking a skillful form carpenter is recognized by the
scarcity of nails he uses. The possibility of reducing carpenter work by
ordering lumber to length and width from plans has already been
mentioned. It is possible often to go a step further by having certain
standard panels, boxes, etc., made in regular shops. Piece work is often
possible and will frequently reduce framing costs. In designing for
economy in taking down, carrying and re-erecting forms a cardinal point
should be that the work be such that it can be executed by common
laborers. This result can be very nearly approached by careful design,
even for form work that is quite complex, if a special gang is devoted
to the work and trained a little in the various operations. Design the
forms so that they come apart in units by simply removing bolts, clamps
and wedges. They can then be taken down, carried and erected by common
laborers with a skilled man in charge to meet emergencies and to true
and line up the work.
In the matter of details the joints deserve particular attention. In
column and girder forms, generally, joints will be square or butt
joints, and to get them tight the lumber must be dressed true to edge.
Tight joints are considered essential by many not only to avoid joint
marks but for the more important reason that otherwise, with wet
mixtures, a honeycombed concrete is produced by leakage. Where tight
joints are desired tongue and groove stock or stock cut with one edge
beveled and the other square give the best results. The authors believe
that the best general satisfaction will be got from the bevel edge stock
placed so that the bevel edge of one board comes against the square edge
of the next board; undue swelling then results in the bevel edge cutting
into the adjacent square edge without bulging. Tongues and grooves
suffer badly from breakage. As a matter of fact square edged stock, if
well dressed and sized and well filled with moisture, can be used and is
used with entire success in nearly all kinds of work. The leakage will
be very slight with ordinarily good butt joints and so far as surface
appearance goes joint marks are more cheaply and more satisfactorily
eliminated by other means than attempting to get cabinet work in form
construction. Where girder forms join columns or beams connect with
girders and at the angles of floor slabs with beams the edges or corners
of the forms should be rounded. The edges of beams and column corners
will appear better if beveled; a triangular strip in the corners of the
forms will provide this bevel. Forms and mold construction for
ornamental work call for and are given special consideration in Chapter
XXIII. In conclusion, the reader should study the specific examples of
form construction for different purposes that are given throughout the
book for hints as to special practice and details.
~UNIT CONSTRUCTION OF FORMS.~--Unit construction has a somewhat variable
meaning in form work. In wall and tank work and in some other kinds of
work unit construction means the use of form units which are gradually
moved ahead or upward as the concreting progresses or of form units
which are used one after another in continuous succession as the
concreting progresses. In column, girder and floor work unit
construction means the division of the form work as a whole and also of
the individual forms into independent structural units; thus in forms
for a building the column forms may be independent of the girder forms
and also each column and girder form be made up of several separate
units. In all cases unit construction has for its purpose the use of the
same form or at least the same form lumber over and over for molding
purposes. Every time the use of the same form is repeated, the cost of
form work per cubic yard of concrete placed is reduced. The theoretical
limit of economical repetition is then the limit of endurance of the
form, the practical limit, however, is something quite different. Most
concrete work varies in form or dimensions often enough to prevent the
use of the same forms more than a few times, and even if these
variations did not exist the time element would enter to prevent the
same form or form lumber being used more than a certain number of times.
Unit construction to give repeated use of forming has, therefore, its
economic limits. The significance of this conclusion does not lie in any
novelty that it possesses but in the fact that for any piece of work it
determines the labor that may profitably be expended in working out and
constructing form units.
~LUBRICATION OF FORMS.~--All forms for concrete require a coating of some
lubricant to prevent the concrete from adhering to the wood with which
it comes in contact. Incidentally this coating tends to give a smoother
surface to the concrete and to preserve the wood against damage by its
alternate wetting and drying. The great value of lubrication is,
however, that it reduces the cost of removing forms. The requisite of a
good coating material is that it shall be thin enough to spread evenly
and to fill the pores and grain of the wood. Crude oil or petroline
makes one of the best coatings, but various other greasy substances will
serve. Where the forms are not to be removed until the concrete has set
hard a thorough wetting of the wood just before the concrete is placed
is all the coating necessary. Any concrete adhering to forms should be
thoroughly cleaned off before they are used again and the wood
underneath given a special heavy coating.
~FALSEWORKS AND BRACING.~--The falseworks which support the forms proper
and stagings for workmen, runways, material hoists, etc., do not call
for any striking differences in construction and arrangement from such
work elsewhere. For wall forms inclined props reaching from ground to
studding are used for walls of moderate height such as retaining walls,
wing walls, and abutments. For building walls of some height a gallows
frame arrangement or the common braced staging used by masons and
carpenters is used. In building construction, however, movable forms are
commonly employed for walls more than one story high and should always
be employed above one story to save staging timber. Column forms are
seldom braced unless erected without connecting girder or floor forms at
their tops, and then only by diagonal props to the floor or ground.
Girder and floor supports usually consist of uprights set under the
girder form at intervals and occasionally under floor slab forms. The
spacing of props and uprights will be regulated by the judgment of the
foreman and boss carpenter; no general rule is applicable, except that
enough lumber must be used to hold the forms rigid and true to line and
level. The various illustrations of actual formwork which follow are the
best guides to good practice.
~TIME FOR AND METHOD OF REMOVING FORMS.~--No exact time schedule for
removing forms is wise in concrete work. Concrete which is mixed wet
sets slower than dry concrete and concrete sets slower in cold weather
than it does in warm weather. Again the time of removal is influenced by
the risk taken by too early removal, and also by the nature of the
stresses in the member to be relieved of support. In all cases the forms
should be removed as soon as possible so that they can be used over
again and so that the concrete may be exposed to the air to hasten
hardening. The following suggestions as to time of removal are general
and must be followed with judgment.
Using dry concrete in warm weather the forms for retaining walls,
pedestals, isolated pillars, etc., can be removed in 12 hours; using wet
or sloppy concrete the time will be increased to 24 hours. In cold
weather the setting is further delayed and inspection is the only safe
guide to follow. Very cold weather delays setting indefinitely. Forms
for small arch work like sewers and culverts may be removed in 18 to 24
hours if dry concrete is used, and in 24 to 48 hours if wet concrete is
used. The time for removing large arch centers should not be less than
14 days for spans up to 50 ft. if the arch is back-filled at once; when
the center is not to be used again it is better to let it stand 28 days.
For very large arches the problem becomes a special one and is
considered in Chapter XVII. In building construction the following
schedule is a common one. Remove the column forms in 7 days and the
sides of the girder forms and the floor lagging in 14 days leaving the
bottom boards of the girder forms and their supports in place for 21
days.
As an example of individual practice the following requirements of a
large firm of concrete contractors are given:
Walls in mass work, 1 to 3 days, or until the concrete will bear
pressure of the thumb without indentation.
Thin walls, in summer, 2 days; in cold weather, 5 days.
Slabs up to 6-ft. span, in summer, 6 days; in cold weather, 2 weeks.
Beams and girders and long span slabs, in summer, 10 days or 2 weeks; in
cold weather, 3 weeks to 1 month. If shores are left without disturbing
them, the time of removal of the sheeting in summer may be reduced to 1
week.
Column forms, in summer, 2 days; in cold weather, 4 days, provided
girders are shored to prevent appreciable weight reaching columns.
Conduits, 2 or 3 days, provided there is not a heavy fill upon them.
Arches, of small size, 1 week; for large arches with heavy dead load, 1
month.
The method of removing forms will vary in detail with the character of
the structure. With proper design and lubrication of forms they will
ordinarily come away from the concrete with a moderate amount of sledge
and bar work. If the work will warrant it, have a special gang under a
competent foreman for removing forms. The organization of this gang and
the procedure it should follow will vary with the nature of the form
work, and they are considered in succeeding chapters for each kind of
work.
~ESTIMATING AND COST OF FORM WORK.~--It is common practice to record the
cost of forms in cents per cubic yard of concrete, giving separately the
cost of lumber and labor. This should be done, but the process of
analysis should be carried further. The records should be so kept as to
show the first cost per 1,000 ft. B. M. of lumber, the number of times
the lumber is used, the labor cost of framing, the labor cost of
erecting and the labor cost of taking down, all expressed in M. ft. B.
M. In this way only is it possible to compare the cost of forms on
different kinds of concrete work, and thus only can accurate predictions
be made of the cost of forms for concrete work having dimensions
differing from work previously done. It is well, also, to make a note of
the number of square feet of exposed concrete surface to which the forms
are applied.
Some of the items mentioned demand brief explanation. Framing and
erecting costs are kept separate for the reason that the framing is done
only once, whereas the erecting occurs two or more times. The lumber
cost, where the material is used more than once, can be computed in two
ways. An example will illustrate the two modes of procedure. In one of
the buildings described in Chapter XIX the lumber cost $30 per M. ft. B.
M. and was used three times. As 34,000 ft. B. M. were required to encase
the 200 cu. yds. of concrete in one floor, including columns, it would
have required 34,000 ÷ 200 = 170 ft. B. M. of lumber at $30 per M. per
cubic yard of concrete if it had been used only once. But since it was
used three times we may call it 170 ft. B. M. at $10 per M. per cubic
yard of concrete, or we may call it 170 ÷ 3 = 57 ft. B. M. at $30 per M.
per cubic yard of concrete. The authors prefer the first method, due to
the fact that it is 170 ft. B. M. that is handled and taken down each
time and it is more consistent to have the lumber cost on the same basis
thus:
170 ft. B. M. of lumber at $10 per M $1.70
170 ft. B. M. handled at $2 per M 0.34
170 ft. B. M. erected at $7 per M 1.19
-----
Total 170 ft. B. M. per cu. yd $3.23
Returning to our main thought, there are three ways of recording the
cost of form work: (1) In cents per cubic yard of concrete; (2) in cents
per square foot of concrete face to which forms are applied, and (3) in
dollars per 1,000 ft. B. M. of lumber used. In all cases the cost of
materials and of labor should be kept separate. It is well if it can be
done to attach a sketch of the forms to the record. So much for the
general method of recording costs in form work.
In estimating the probable cost of forms for any job the following
method will be found reliable: Having the total cubic yards of concrete
in the work and the time limit within which the work must be completed
determine the number of cubic yards that must be placed per day, making
liberal allowances for delays. Next estimate the number of thousands of
feet board measure of forms required to encase the concrete to be placed
in a day. This will give the minimum amount of lumber required, for it
is seldom permissible to remove the forms until the concrete has
hardened over night. Now we come to the very important and puzzling
question of the time element, particularly in work where it is possible
to use the same forms or the same form lumber two or more times.
It has already been pointed out that wet concrete sets more slowly than
dry concrete; that all concrete sets more slowly in cold than in warm
weather, and that the support of forms is necessary a longer time for
pieces subject to bending stress like arches and girders. General
suggestions as to specific times for removing forms have also been
given. Where the specifications state the time of removal the contractor
has a definite guide, but where they do not, as is most often the case,
he must depend very largely on judgment and previous experience. Another
matter which deserves consideration is the use of the forms as staging
for runways or tracks. Such use may result in forms having to stand on
work for sake of their service as trestles much longer than there is any
necessity so far as supporting the concrete is concerned. A derrick or
cableway may often prove cheaper than tieing up form lumber by trying to
make it serve the double purpose of a trestle.
The possibilities of repeated use of forms and of unit construction of
forms have already been noted. This is the next point to be considered
in estimating form lumber. At the expense of a little planning movable
forms can be used to materially reduce the amount of lumber required.
The reader is referred particularly to the chapters on retaining wall,
conduit and building work for specific data on movable form work.
Having estimated the amount of lumber required and the number of times
it can be used the labor cost of framing, erecting and taking down can
be figured. In ordinary retaining wall work forms will cost for framing
and erection from $6 to $7 per M. ft. B. M. To tear down such forms
carefully and to carry the lumber a short distance will cost some $1.50
to $2 per M. ft. B. M. We have then a cost of $7.50 to $9 per M. ft. B.
M. for each time the forms are erected and torn down. Where movable
panels are used and the forms not ripped apart and put together again
each time there is of course only the cost of moving, which may run as
low as 50 cts. per M. ft. B. M. Framing and erecting centers for piers
will run about the same as for retaining wall. At this point it may be
noted that in estimating the cost of forms for plain rectangular piers
the following method will give very accurate results. Ascertain the
surface area of the four sides of the pier. Multiply this area by 2, and
the product will be the number of feet board measure of 2-in. plank
required. Add 40 per cent. to this, and the total will be the number of
feet board measure of 2-in. plank and of upright studs (4×6), spaced 2½
ft. centers. Sometimes 3×6-in. studs are used, and spaced 2 ft. centers,
which requires practically the same percentage (40 per cent.) of timber
for the studs as where 4×6-in. studs are used and spaced 2½ ft. centers.
No allowance is made for timber to brace the studs, since, in pier work,
it is customary to hold the forms together either with bolts or with
ordinary No. 9 telegraph wire, which weighs 0.06 lb. per foot. The
foregoing data can be condensed into a rule that is easily remembered:
_Multiply the number of square feet surface area of the sides and ends
of a concrete pier by 2.8, and the product will be the number of feet
board measure required for sheet plank and studs for the forms._
If the form lumber can be used more than once, divide the number of feet
board measure by the number of times that it can be used, to ascertain
the amount to be charged to each pier. Forms can be erected and taken
down for $8 per M. carpenters being paid $2.50 and laborers $1.50 a day.
Since there are 2.8 ft. B. M. of forms per square foot of surface area
of concrete to be sheeted, it costs 2¼ cts. for the labor of carpenters
per square foot of surface area to be sheeted. If lumber is worth $24
per M., and is used three times, then the lumber itself also costs 2¼
cts. per sq. ft. of surface area of concrete. By dividing the total
number of cubic yards of concrete into the total number of square feet
of area of surface to be sheeted with forms, the area per cubic yard is
obtained. Multiply this area by 4½ cts., and the product is the cost per
cubic yard for material in the forms (assumed to be used three times)
and the labor of erecting it and taking it down.
The cost of framing and erection of forms for building work and of
centers for large arches is a special problem in each case and is
considered in the chapters devoted to those classes of work.
CHAPTER X.
METHODS AND COST OF CONCRETE PILE AND PIER CONSTRUCTION FOR FOUNDATIONS.
Two general methods of concrete pile construction are available for
engineering work. By one method a hole is formed in the ground by
driving a steel shell or by other special means and this hole is filled
with concrete. By the other method the pile is molded in suitable forms
and after becoming hard is driven as a wood or steel pile is driven.
Piles constructed by the first method may be either plain or reinforced,
but piles constructed by the second method are always reinforced to
strengthen them for handling and driving. Concrete piers for foundation
work are simply piles of enlarged diameter.
~MOLDING PILES IN PLACE.~--Molding piles in place requires the use of
special apparatus, and this apparatus is to a very large degree
controlled by patents. Pile work of this kind is thus generally done by
concerns which control the use of the apparatus employed and the general
contractor can undertake it only by permission of the proprietary
companies. The methods of work followed and the cost of work are thus of
direct interest only as general information.
~Method and Cost of Constructing Raymond Piles.~--The machinery and
processes employed in the construction of Raymond concrete piles are
patented and all piling work by this method is controlled by the Raymond
Concrete Pile Co. As detail costs of construction are not given out by
the company the following figures collected by the authors are subject
to revision. They are believed to be fairly approximate, having in one
case been obtained by personal watch on the work and in the other case
from authentic records of the engineers on the work.
The pile is made as follows: A collapsible steel core 30 ft. long, 20
ins. diameter at the top and 6 ins. diameter at the bottom, encased in
a thin sheet steel shell, is driven into the ground by an ordinary pile
driver. When it has reached the proper depth, a wedge is loosened,
permitting the two sections of the core to come closer together so that
the core can be pulled out of the hole, leaving the steel shell behind
as a casing to prevent the sides from caving in. The shell is made of
No. 20 gage steel, usually in four or more sections, which telescope one
over the other. A nest of sections is slipped over the lower end of the
core as it hangs in the leads, a rope is hitched around the outer
section and the engine hoists away until the sections are
"un-telescoped" and drawn snug onto the core. The rope is then
unfastened and the driving begins. Figure 49 shows the usual pile
driving rig used. The following are examples of pile construction in
actual work:
_Example I._--In this work, for a building foundation in New York City,
the pile driver was mounted on a turntable, the framework of the
turntable in turn resting on rollers traveling on timbers laid on the
ground. The driver was moved along and rotated when necessary by ropes
passing around the winch head of the engine. The driver had 50-ft. leads
and a 3,100-lb. hammer operated by an ordinary friction clutch hoisting
engine. The hammer blow was received by an oak block fitting into a
recess at the top of the steel core. This block was so battered by the
blows that it had to be renewed about every five or six piles driven. A
¾-in. wire rope passing over a 10-in. sheave lasted for the driving of
130 piles and then broke. When the work was first begun the crew
averaged 10 piles per 10-hour day, but the average for the job was 13
piles per day, and the best day's work was 17 piles. The cost of labor
and fuel per pile was as follows:
5 men on driver at $1.75 $ 8.75
2 men handling shells at $1.75 3.50
1 engineman 3.00
6 men mixing and placing concrete 10.50
1 foreman 5.00
Coal and oil 2.50
-------
Total, 13 piles, at $2.55 $33.25
[Illustration: Fig. 49.--Pile Driver Rigged for Constructing Raymond
Concrete Piles.]
Deducting the cost of placing the concrete we get a cost of $1.75 for
driving the cores. The pile, 25 ft. long, 6 ins. at the point and 18
ins. at the head, contains 21¼ cu. ft., or 0.8 cu. yd., of concrete, and
has a surface area of 77 ft. As No. 20 steel weighs 1.3 lbs. per sq.
ft., each shell weighed approximately 100 lbs. The cost per pile may
then be summarized as follows:
1.2 bbls. cement in 0.8 cu. yd., at $1.75 $2.10
0.8 cu. yd. stone at $1.25 1.00
1/3 cu. yd. sand at $1.05 0.35
100 lbs. steel in shell at 3½ cts. 3.50
Labor and fuel as above 2.55
-----
Total per pile (38 cts. per lin. ft.) $9.50
_This cost, it should be carefully noted, does not include cost of
moving plant to and from work or general expenses._
_Example II._--In constructing a building at Salem, Mass., 172
foundation piles, 14 to 37 ft. long, 6 ins. diameter at the point and 20
ins. diameter at the top, were constructed by the Raymond process. The
general contractor made the necessary excavations and provided clear and
level space for the pile driver, braced all trenches and pier holes, set
stakes for the piles and gave all lines and levels. The piles were
driven by a No. 2 Vulcan steam hammer with a 3,000-lb. plunger having a
drop of 3 ft., delivering 60 blows per minute. Figure 49 shows the
driver at work. Sixteen working days were occupied in driving the piles
after the driver was in position. The greatest number driven in one day
was 20, and the average was 11 piles per day. When in position for
driving, the average time required to complete driving was 12 minutes.
The total number of blows varied from about 310 to 360, the average
being about 350. The piles were driven until the penetration produced by
8 to 10 blows equaled 1 in. When in full operation, a crew of 5 men
operated the pile driver. Seven men were engaged in making the concrete
and 5 men working upon the metal shells.
Assuming the ordinary organization and the wages given below, we have
the following labor cost per day:
1 foreman at $5 $ 5.00
1 engineman at $3 3.00
4 laborers on driver at $1.75 7.00
6 laborers making concrete at $1.75 10.50
5 laborers handling shells at $1.75 8.75
------
Total $34.25
As 172 piles averaging 20 ft. in length were driven in 16 days, the
total labor cost of driving, given by the figures above, is 16 × $34.25
= $548, or practically 16 cts. per lineal foot of pile driven.
The concrete used in the piles was a 1-3-5 Portland cement, sand and
1½-in. broken stone mixture. A 20-ft. pile of the section described
above contains about 20 cu. ft. of concrete, or say 0.75 cu. yd. We can
then figure the cost of concrete materials per pile as follows:
0.85 bbl. cement at $1.60 $1.36
0.36 cu. yd. sand at $1 0.36
0.60 cu. yd. stone at $1.25 0.75
-----
Total per pile $2.47
The steel shell has an area of about 72 sq. ft., and as No. 20 gage
steel weighs 1.3 lbs. per sq. ft., its weight for each pile was about 94
lbs. Assuming the cost of coal, oil, etc., at $2.50 per day, we have the
following summary of costs:
Per lin. ft.
of pile.
Labor driving and concreting $0.16
Concrete materials 0.123
94 lbs. steel shell at 3 cts. 0.145
Coal, oil, etc. 0.011
------
Total $0.439
_The cost does not include interest on plant, cost of moving plant to
and from work and general expenses._
[Illustration: Fig. 50.--Sketch Showing Method of Constructing Simplex
Concrete Piles.]
~Method of Constructing Simplex Piles.~--The apparatus employed in driving
Simplex piles resembles closely the ordinary wooden pile driven, but it
is much heavier and is equipped to pull as well as to drive. A 3,300-lb.
hammer is used and it strikes on a hickory block set in a steel drive
head which rests on the driving form or shell. This form consists of a
¾-in. steel shell 16 ins. in diameter made in a single 40-ft. length.
Around the top of the shell a ½-in. thick collar or band 18 ins. deep is
riveted by 24 1-in. countersunk rivets. This band serves the double
purpose of preventing the shell being upset by the blows of the hammer
and of giving a grip for fastening the pulling tackle. The bottom of the
form or shell is provided with a point. Two styles of point are
employed. One style consists of two segments of a cylinder of the same
size as the form, so cut that they close together to form a sort of clam
shell point. In driving, the two jaws are held closed by the pressure of
the earth and in pulling they open apart of their own weight to permit
the concrete to pass them. This point, known as the alligator point, is
pulled with the shell. It is suitable only for driving in firm, compact
soil, in loose soil the pressure inward of the walls keeps the jaws
partly closed and so contracts the diameter of the finished pile. The
second style of point is a hollow cast iron point, 10 ins. deep and 16½
ins. in diameter, having a neck over which the driving form slips and an
annular shoulder outside the neck to receive the circular edge of the
shell. The projected sectional area of this point is 1.4 sq. ft. It is
left in the ground when the form is withdrawn. The form is withdrawn by
means of two 1-in. cables fastened to a steel collar which engages under
the band at the top of the form. The cables pass in the channel leads on
each side over the head of the driver and down in back to a pair of
fivefold steel blocks, the lead line from which passes to one of the
drums of the engine. In this manner the power of the drum is increased
ten times and it is not unusual to break the pulling cables when the
forms are in hard ground. The general method of construction is about as
shown by Fig. 50, being changed slightly to meet varying conditions. The
form resting on a cast iron point is driven to hard ground. A heavy
weight is then lowered into the form to make sure the point is loose.
While the weight is at the bottom of the form a target is placed on its
line at the top of the form, the purpose of which will be apparent
later. The weight is then withdrawn. Given the length of the pile and
sectional area, it is an easy matter to determine the volume of concrete
necessary to fill the hole.
This amount is put into the form by means of a specially designed bottom
dump bucket, which permits the concrete to leave it in one mass,
reaching its destination with practically no disintegration. It will be
noticed that when the full amount of concrete is in the form its surface
is considerably above the surface of the ground. This is due to the fact
that the thickness of the form occupies considerable space that is to be
occupied by the concrete. The weight is now placed on top of the
concrete and the form is pulled. The target previously mentioned now
becomes useful. As the form is withdrawn the concrete settles down to
occupy the space left by the walls of the form. Obviously this
settlement should proceed at a uniform rate, and as it is difficult to
watch the weight, the target on its line further up is of considerable
help. By watching this target in connection with a scale on the leads of
the driver, it can be readily told how the concrete in the form is
acting. As another check, the target, just as the bottom of the form is
leaving the ground should be level with the top of the form. This would
indicate that the necessary amount of concrete has gone into the ground
and that, other conditions being all right, the pile is a good one. In
some grounds where the head of concrete in the form exerts a greater
pressure than the back pressure or resistance of the earth, the concrete
will be forced out into the sides of the hole, making the pile of
increased diameter at that point and necessitating the use of more
concrete to bring the pile up to the required level.
~Method of Constructing Piles with Enlarged Footings.~--A pile with an
enlarged base or footing has been used in several places by Mr. Charles
R. Gow of Boston, Mass., who has patented the construction. A single
pipe or a succession of pipes connected as the work proceeds is driven
by hammer to the depths required. The material inside the shell is then
washed out by a water jet to the bottom of the shell and then for a
further distance below the shell bottom. An expanding cutter is then
lowered to the bottom of the hole and rotated horizontally so as to
excavate a conical chamber, the water jet washing the earth out as fast
as it is cut away. When the chamber has been excavated the water is
pumped out and the chamber and shell are filled with concrete. The
drawings of Fig. 51 show the method of construction clearly. The
chambering machine is used only in clay or other soil which does not
wash readily. In soil which is readily washed the chamber can be formed
by the jet alone. The practicability of this method of construction is
stated by Mr. Gow to be limited to pipe sizes up to about 14 ins. in
diameter.
[Illustration: Fig. 51.--Sketch Showing Method of Constructing Concrete
Piles with Enlarged Footings.]
~Method of Constructing Piles by the "Compressol" System.~--The compressol
system of concrete pile or pillar construction is a French invention
that has been widely used abroad and which is controlled in this country
by the Hennebique Construction Co., of New York, N. Y. The piles are
constructed by first ramming a hole in the ground by repeatedly
dropping a conical "perforator" weighing some two tons. This perforator
is raised and dropped by a machine resembling an ordinary pile driver.
The conical weight gradually sinks the hole deeper and deeper by
compacting the earth laterally; this lateral compression is depended
upon so to consolidate the walls of the hole that they do not cave
before the concrete can be placed. The concrete is deposited loose in
the hole and rammed solid by dropping a pear-shaped weight onto it as it
is placed. The view Fig. 52 shows the "perforator" and the tamping
apparatus at work. Very successful work has been done abroad by this
method.
[Illustration: Fig. 52.--View of Apparatus Used in Constructing
Compressol Piles.]
~Method of Constructing Piers in Caissons.~--For piles or pillars of
diameters larger than say 18 ins. the use of driving shells and cores
becomes increasingly impracticable. Concrete pillars of large size are
then used. They are constructed by excavating and curbing a well or
shaft and filling it with concrete. This construction has been most used
in Chicago, Ill., for the foundations for heavy buildings, but it is of
general application where the sub-soil conditions are suitable. The
method is not patented or controlled by patents in any particular,
except that certain tools and devices which may be used are proprietary.
_General Description._--The caisson method of construction is simple in
principle. A well is dug by successive excavations of about 5 ft. each.
After each excavation of 5 ft. is completed, wood lagging is placed
around the sides and supported by internal steel rings, so that the soft
ground around the excavation is maintained in its former position. The
methods of excavating and removing the soil and of constructing the
lagging are considered in detail further on. The caissons vary in
diameter according to the load; some as large as 12 ft. in diameter have
been sunk, but the usual diameter is 6 ft.; a caisson of 3 ft. in
diameter is as small as a man can get into and work. When the pier goes
to bed rock the caisson is made of uniform diameter from top to bottom,
but where the pier rests on hardpan the bottom portion of the well is
belled out to give greater bearing area. It is customary to load the
piers about 20 tons per square foot.
[Illustration: Fig. 53.--Curbing for Concrete Piers (Usual
Construction).]
_Caisson Construction._--The caisson construction, or more correctly the
form of curbing most commonly used, is that indicated by the sketch,
Fig. 53. The lagging is 2×6 in. or 3×6 in., stuff 5 ft. 4 ins. or 4 ft.
long set vertically around the well and held in place by interior
wrought iron rings. For a 6-ft. diameter caisson these hoops are ¾ by 3
ins.; they are made in two parts, which are bolted together as shown by
Fig. 53. Generally there are two rings for each length of lagging; for
5-ft. lagging they are placed about 9 ins. from each end. In some
cases, however, engineers have specified three rings for the upper
sections in soft clay and two rings for the sections in the hard ground
lower down. The lagging used is not cut with radial edges, but is rough,
square cut stuff; the rings, therefore, take the inward pressure
altogether.
[Illustration: Fig. 54.--Curbing for Concrete Piers (Jackson Patent).]
In some recent work done by the inventor use has been made of the
caisson construction shown by Fig. 54 and patented by Mr. Geo. W.
Jackson. In place of the plain rings a combination of T-beam ribs and
jacks is used; this construction is clearly shown by the drawing. The
advantages claimed for the construction are that it gives absolute
security to the workmen and the work, that the lagging can be jacked
tightly against the outer walls of the well, that the braces form a
ladder by which the workmen can enter and leave the well, and that the
possibility of shifting the bracing easily permits the concrete to be
placed to the best advantage. On the other hand the braces abstruct the
clear working space of the caissons.
[Illustration: Fig. 55.--Layout of Plant for Concrete Pier Construction.
Cook County Court House Foundations.]
_Excavating and Handling Material._--The excavation of the wells is done
by hand, using shovels and picks, and, in the hardpan, special grubs
made by A. J. Pement and George Racky, Chicago blacksmiths. The
excavated material is hoisted out of the well in buckets made by the
Variety Iron Works, of Chicago. For caissons which are not specified to
go to rock it is considered more economical to do the hoisting by
windlass derricks operated by hand. These derricks have four 6×6-in.
legs and a 3×6-in. top piece. When the caissons go to rock the hoisting
is done by power, so-called "cable set-ups" being used in most cases. To
illustrate this method the following account of the foundation work for
the Cook County Court House is given:
The Cook County Court House foundations consist of 126 caissons varying
from 4 ft. to 10½ ft. in diameter and averaging$ 7½ ft. in diameter.
They were sunk to rock at a depth of 115 ft. below street level. The
work involved 22,000 cu. yds. of excavation and the placing in the
caissons of 17,000 cu. yds. of concrete. Over 1,000 piles about 40 ft.
long, that had formed the foundation of the old Court House built in
1875, were removed. These piles were found to be in good condition. The
work was done by the George A. Fuller Co., of Chicago, Ill.,
Contractors, with Mr. Edgar S. Belden Superintendent in Charge. The
details which follow have been obtained from Mr. Belden.
[Illustration: Fig. 56.--Section Showing Arrangement of Hoist for
Concrete Pier Construction.]
The foundation area was 157×375 ft., and was excavated to a depth of 15
ft. below the street surface before the caissons were started. The
caissons, of which there were 126, were arranged in rows across the lot,
there being from six to eight caissons in a row. The arrangement of the
plant for the work is indicated by Fig. 55. One row of caissons formed a
unit. A platform or "stand" was erected over each caisson and carried in
its top a tripod fitted with a "nigger head" operated by a rope sheave.
This arrangement is shown by Fig. 56. An engine on the bank operated by
a rope drive all the tripod sheaves for a row of six or eight caissons.
The arrangement is indicated by Fig. 55. The clay hoisted from the pits
was dumped into 1 cu. yd. hoppers with which the stands were fitted, as
shown by Fig. 56; when a hopper was full it was dumped into a car
running on a 24-in. gage portable track. Side dump Koppel cars of 1 cu.
yd. capacity were used; they dumped their load into an opening connected
with the tracks of the Illinois Tunnel Co., where the material passed
into tunnel cars and was taken to the lake front about one mile away. As
soon as one row of caissons was completed the stands, tripods, etc.,
which were made portable, were shifted to another row. At times as many
as five units were in operation, sinking 40 caissons.
[Illustration: Fig. 57.--Details of Working Platform for Concrete Pier
Construction.
Side Elevation.
End Elevation.
Bottom Plan.
Section.]
Fig. 56 shows the arrangement in detail at one caisson. In this work the
lagging used was 3×6-in. maple, 5 ft. 4 ins. long, and was supported by
3×¾-in. steel hoops. The lagging was matched and dressed. The "nigger
head," as will be seen, is operated by a rope sheave on the same axle.
As stated above, an endless rope drive operated all the "nigger heads"
on a row of caissons. A 26-in. driving sheave was attached to an
ordinary hoisting engine equipped with a governor. The driving rope was
5/8-in. steel. It was wrapped twice around the driving sheave and once
around the "nigger head" sheaves. These latter were 18 ins. in diameter.
For the hoists 1-in. Manila rope was used. The other details, the
bucket, bucket hook, swivel block, etc., are made clear by the drawing.
The platforms, tripods, etc., were of the standard dimensions and
construction adopted by the contractors of the work. Detail drawings of
the standard platform are given by Fig. 57. One of these platforms
contains about 1,000 ft. B. M. of lumber. As will be seen, all
connections are bolted, no nails being used anywhere. A platform can
thus be taken down and stored or shipped and erected again on another
job with very little trouble.
The plant described handled some 22,000 cu. yds. of excavated material
on this work. Work was kept up night and day, working three 8-hour
shifts. It took an average of 35 shifts to excavate one row of caissons.
No figures of the working force or the cost of excavation of this work
are available.
_Mixing and Placing Concrete._--The placing of the concrete in the
excavated wells is done by means of tremies, or, which is more usual, by
simply dumping it in from the top, workmen going down to distribute it.
The manner of mixing the concrete and of handling it to the caisson
varies of course with almost every job. As an example of the better
arranged mixing and handling plants the one used on the Cook County
Court House work may be described. This plant is shown by the sketch,
Fig. 58.
Bins for the sand and stone were built at one side of the lot on the
sloping bank; their tops were level with the street surface and their
bottoms were just high enough to permit their contents to be delivered
by chutes into 1 cu. yd. cars. Wagons dumping through traps in the
platform over the bin delivered the sand and stone. The sketches
indicate the arrangement of the bins and mixer and the car tracks
connecting them. The raw material cars were first run under the stone
bin and charged with the required proportion of stone, and then to the
sand bin, where the required proportion of sand was chuted on top of the
stone. The loaded car was then hauled up the incline and dumped into the
hopper, where cement and water were added. A No. 2½ Smith mixer was used
and discharged into cars which delivered their loads on tracks leading
to the caissons. The same cars and portable tracks were used as had been
used to handle the excavated material. In operation a batch of raw
materials was being prepared in the hopper while the previous batch was
being mixed and while the concrete car was delivering the still previous
batch to the caissons. An average of 40 batches an hour mixed and put
into the caissons was maintained with a force of 25 men. In all some
17,000 cu. yds. of concrete were mixed and deposited.
[Illustration: Fig. 58.--Arrangement of Concrete Making Plant, Concrete
Pier Construction.]
_Cost of Caisson Work._--The following attempt to get at the cost of
caisson work is based largely upon information obtained from Mr. John M.
Ewen, John M. Ewen Co., Engineers and Builders, Chicago, Ill. Mr. Ewen
says:
"My experience has taught me that it is almost impossible to determine
any definite data of cost for this work. This is due to the fact that no
two caisson jobs will average the same cost, notwithstanding the fact
that the cost of material used and the labor conditions are exactly the
same. This condition is due to the great variety in texture of the soil
gone through. For instance, it has come under my experience that in
caissons of the same diameter on the same job it required but fifteen
8-hour shifts to reach bedrock in some of these, while it required as
many as 21 to 25 shifts to reach rock in the others, rock being at the
same elevation. In fact, the digging all the way to rock in some was the
best that could be wished for, while in the others boulders and
quicksand were encountered, and the progress was slower, and the cost
consequently greater.
"Again, we have known it to require eight hours for two men to dig 8
ins. in hardpan in one caisson, while on a job going on at the same time
and on the opposite corner of the street two men made progress of 2 ft.
in 8 hours through apparently the same stuff, the depth of hardpan from
grade being 61 ft. 6 ins. in both instances, and the quality of labor
exactly the same.
"There have been more heavy losses among contractors due to the
unexpected conditions arising in caisson digging than in any other item
of their work, and I predict a loss to some of them that will be serious
indeed if an attempt be made to base future bids for caisson work
entirely upon the data kept by them on past work. If a contractor is
fortunate enough to find the ordinary conditions existing in his caisson
work, and by ordinary conditions I mean few boulders, no quicksand,
ordinary hardpan and no gas, the following items may be considered safe
for figuring caisson work:
"Figure that it will require from 22 to 25 shifts of 8 hours each to
strike bedrock, bedrock being from 90 to 95 ft. below datum, and datum
being 15 ft. below street grade; figure 2 diggers to the shift in all
caissons over 5 ft. in diameter, 45 cts. per hour for each digger;
figure 1 top man at 40 cts. per hour, and 1 mucker or common laborer at
30 cts. per hour for all caissons in which there are two diggers, and 1
top man less if 1 digger is in the caisson, which condition exists
generally in caissons less than 5 ft. in diameter. Add the cost of
5/8-in. cable, tripods, sheaves, 1-in. Hauser laid line, nigger heads,
ball-bearing blocks, etc., for rigging of the job. Lagging, which is 2×6
ins. and 3×6 ins. hemlock or some hard wood, in length of 5 ft. 4 ins.
and 4 ft., is priced all the way from $20 to $22.50 and $21 to $24.50
per M. ft. B. M., respectively. The price of caisson rings is $2.40 per
100 lbs. The cost of specially made grubs for digging in hardpan is
about $26 per dozen. Shovels are furnished by the diggers themselves in
Chicago, Ill. The cost of temporary electric light is $10 per caisson.
This includes cost of cable, lamps, guards, etc. Add the cost of or
rental of engine or motors for power.
"Some engineers specify three rings to be used to each set of lagging
below the top set until hardpan is reached, then two rings for each of
the remaining sets from hardpan to rock. This is, of course, to insure
against disaster from great pressure of the swelling clay above the
hardpan strata, and may or may not be necessary. These rings are ¾×3
ins. wrought iron.
"For caissons which are not specified to go to rock, it is not
considered economical to rig up cable set-ups, but rather to use
windlass derricks. In this case 1-in. Hauser laid line is used as the
means of hoisting the buckets of clay out of the caisson, as is the case
in cable set-ups, hand power being used on the windlass derricks instead
of steam or electricity. The windlass derricks are made with four legs
out of 6×6-in. yellow pine lumber. The top piece is generally a piece of
3×6-in. lagging. The cost of windlass and boxes is about $35 per dozen.
Hooks for caisson buckets cost 45 cts. each. Caisson buckets cost $8
each.
"With the above approximate units as a basis, I have seen unit prices
given per lineal foot in caisson work which ranged all the way from $12
to $16.50 for 6-ft. diameter caissons, larger and smaller sized caissons
being graded in price according to their size. This unit price included
rings, lagging, concrete, power, light, labor, etc."
From the above data the following figures of cost can be arrived at,
assuming a 6-ft. caisson:
Labor. Per day.
2 diggers in caisson, at $3.60 $ 7.20
1 top man, at $3.20 3.20
1 mucker, at $2.40 2.40
------
$12.80
The depth sunk varies from 3½ to 8 ft. per 8-hour day, depending on the
material. Assuming an average of 4 ft., we have then 4 lin. ft. of
caisson, or 2.8 cu. yds. excavated at a labor cost of $12.80, which is
at the rate of $3.20 per lin. ft., or $4.57 per cu. yd. We now get the
following:
Per lin. ft.
Caisson.
40 ft. B. M. (2×6-in. lagging) at $25 $1.00
60 lbs. iron (¾×3-in. rings) at 2½ c. 1.50
0.7 cu. yd. excavation at $4.57 3.20
0.7 cu. yd. muck hauled away at $1 0.70
0.7 cu. yd. concrete at $5 3.50
Electric light 0.10
------
Total $10.00
If 3×6-in. lagging is used add 50 cts. per lin. ft. of caisson.
~MOLDING PILES FOR DRIVING.~--Piles for driving are molded like columns in
vertical forms or like beams in horizontal forms. European constructors
have a strong preference for vertical molding, believing that a pile
better able to withstand the strain of driving is so produced; such
lamination as results from tamping and settling is, in vertical molding,
in planes normal to the axis of the pile and the line of driving stress.
Vertical molding has been rarely employed in America and then only for
molding round piles. The common belief is that horizontal molding is the
cheaper method. In the ordinary run of work, where comparatively few
piles are to be made, it is probably cheaper to use horizontal molds,
but where a large number of piles is to be made, the vertical method has
certain economic advantages which are worth considering.
[Illustration: Fig. 59.--Plant for Vertical Molding of Concrete Piles.]
Vertical molding necessitates a tower or staging to support the forms
and for handling and placing the concrete; an example of such a staging
is shown by Fig. 59. To counterbalance this staging, horizontal molding
necessitates a molding platform of very solid and rigid construction if
it is to endure continued and repeated use. In the matter of space
occupied by molding plant, vertical molding has the advantage. A tower
40 ft. square will give ample space around its sides for 80 vertical
forms for 12-in. piles and leaves 1 ft. of clear working space between
each pair of forms. The ground area occupied by this tower and the forms
is 1,764 sq. ft. With the same spacing of molds a horizontal platform
at least 25 × 160 ft. = 4,000 sq. ft., would be required for the molds
for the same number of piles 25 ft. long. For round piles, vertical
molding permits the use of sectional steel forms; horizontal forms for
round piles are difficult to manage. For square piles vertical molding
requires forms with four sides; horizontal forms for square piles
consist of two side pieces only, the molding platform serving as the
bottom and no top form being necessary. Thus, for square piles
horizontal molding reduces the quantity of lumber per form by 50 per
cent. The side forms for piles molded on their sides can be removed much
sooner than can the forms for piles molded on end, so that the form
material is more often released for reuse. The labor of assembling and
removing forms is somewhat less in horizontal molding than in vertical
molding. Removing the piles from molding bed to storage yard for curing
requires derricks or locomotive cranes in either case and as a rule this
operation will be about as expensive in plant and labor in one case as
in the other. In the ease and certainty of work in placing the
reinforcement, horizontal molding presents certain advantages, the
placing and working of the concrete around the reinforcement is also
easier in horizontal molding. Mixing and transporting the concrete
materials and the concrete is quite as cheap in vertical molding as in
horizontal molding. If anything, it is cheaper with vertical molding,
since the mixer and material bins can be placed within the tower or
close to one side where a tower derrick can hoist and deposit the
concrete directly into the molds. Car tracks, cars, runways and
wheelbarrows are thus done away with in handling the concrete from mixer
to molds. Altogether, therefore, the choice of the method of molding is
not to be decided off-hand.
~DRIVING MOLDED PILES.~--Driving molded concrete piles with hammer drivers
is an uncertain operation. It has been done successfully even in quite
hard soils and it can be done if time is taken and the proper care is
exercised. The conditions of successful hammer driving are: Perfect
alignment of the pile with the line of stroke of the hammer; the use of
a cushion cap to prevent shattering of the pile-head, and a heavy hammer
with a short drop. The pile itself must have become well cured and
hardened. At best, hammer driving is uncertain, however; shattered piles
have frequently to be withdrawn and the builder is never sure that
fractures do not exist in the portion of the pile that is underground
and hidden. The actual records of concrete pile work given in succeeding
sections illustrate successful examples of hammer driving. The plant
required need not vary from that ordinarily used for driving wooden
piles, except that more power must be provided for handling the heavier
concrete pile and that means must be provided for holding the pile in
line and protecting its head.
Sinking concrete piles by means of water jets is in all respect a
process similar to that of jetting wooden piles. Examples of jetting are
given in succeeding section. In rare cases, driving shells, or sheaths
have been used for driving molded piles.
~Method and Cost of Molding and Jetting Piles for an Ocean Pier.~--In
reconstructing in reinforced concrete the old steel pier at Atlantic
City, N. J., some 116 reinforced concrete piles 12 ins. in diameter were
molded in air and sunk by jetting. The piles varied in length with the
depth of the water, the longest being 34½ ft. Their construction is
shown by Fig. 60, which also shows the floor girders carried by each
pair of piles and forming with them a bent, and the struts bracing the
bents together. In molding and driving the piles the old steel pier was
used as a working platform.
[Illustration: Fig. 60.--Concrete Pile for Pier at Atlantic City, N. J.]
The forms for the piles were set on end on small pile platforms located
close to the positions to be occupied by the piles and were braced to
the old pier. The forms were of wood and the bulb point, the shaft and
the knee braces were molded in one piece. Round iron rods were used for
reinforcement. The concrete was composed of 1 part Vulcanite Portland
cement, 2 parts of fine and coarse sand mixed and 4 parts of gravel 1
in. and under in size. The mixture was made wet and was puddled into the
forms with bamboo fishing rods, which proved very efficient in working
the mixture around the reinforcing rods and in getting a good mortar
surface. The concrete was placed in small quantities; it was mostly all
hand mixed. The forms were removed in from 5 to 7 days, depending on the
weather.
The piles were planned to be sunk by water jet and to this end had
molded in them a 2-in. jet pipe as shown. They were sunk to depths of
from 8 ft. to 14 ft. into the beach sand. Water from the city water
mains at a pressure of 65 lbs. per sq. in. was used for jetting; this
water was furnished under special ordinance at a price of $1 per pile,
and a record of the amount used per pile was not kept. The piles were
swung from the molding platforms and set by derricks and block and fall.
The progress of jetting varied greatly owing to obstructions in places
in the shape of logs, old iron pipes, etc. In some cases several days
were required to get rid of a single pipe. In clear sand, with no
obstruction, a 12-in. pile could be jetted down at the rate of about 8
ft. per hour, working 1 foreman and 6 men. The following is the itemized
actual cost of molding and sinking a 26-ft. pile with bulb point and
knee braces complete:
Cost per
Forms-- pile.
Lumber, 340 ft. B. M. @ $30 $10.20
Labor (carpenters @ $2.50 per day) 12.00
Oil, nails, oakum, bolts, clamps, etc. 1.20
-------
$23.40 $ 3.90
Times used 6
Reinforcement--
275 lbs. of plain ¾-in. steel rods @ 2 cts. per lb. $ 5.50
Preparing and setting, 4/10 ct. per lb. 1.10 6.60
Jet Pipe--
26½ ft. of 2-in. pipe @ 10 cts. per ft. in place. 2.65
Setting Forms--
6 men @ $2.50 per day = $15, set 4 piles 3.75
Material--
90/100 Cu. yds. gravel @ $1.50 per yd. 1.35
45/100 cu. yds. sand @ $1.50 per yd. .67
1.50 bbls. cement @ $1.60 2.40 4.42
Labor--
Concrete and labor foreman 3.00
6 laborers, mixing and placing by hand, $1.75
each 10.50
-------
$13.50 3.38
Average number of piles concreted per day 4
Removing Forms--
4 men @ $2.50 remove and clean in half day 4
columns 1.25
1 man @ $2.25 plastering column with cement
grout (4 per day) .56
Jetting 10 ft. into Sand--
Foreman $ 3.00
4 men, $2.25 each, handling hose and traveler 9.00
-------
$12.00 3.00
Average number of piles jetted per day 4
City water pressure used for jetting @ $1 per pile 1.00
Superintendence @ $5.00 per day 1.25
Caring for trestle, traveler, material, etc. 4.84
-------
Total cost per pile $36.60
The pile being 26 ft. long, the cost in place was $1.41 per foot.
Subtracting the cost of sinking amounting to $7.09 per pile, we have the
cost of a 26-ft. pile molded and ready to sink coming to about $1.10 per
foot. It should be noted that this is the cost for a pile of rather
complicated construction; a plain cylindrical pile should be less
expensive.
~Method of Molding and Jetting Square Piles for a Building
Foundation.~--The foundation covered about an acre. The soil was a
deposit of semi-fluid mud and quicksand overlying a very irregular rock
bottom and encircled by a ledge of rock. The maximum depth of the mud
pocket was 40 ft., and interspersed were floating masses of hard pan.
Soundings were made at the locations of all piles; a ½-in. gas pipe was
coupled to a hose fed by city pressure and jetted down to rock, the
depth was measured, the sounding was numbered and the pile was molded to
length and numbered like the sounding. In all 414 piles were required,
ranging in length from 1½ to 40 ft.; all piles up to 6 ft. were built
in place in wooden forms. The piles were 13 ins. square and were of
1-2½-4 concrete reinforced with welded wire fabric. A tin speaking tube
was molded into each pile at the center. This tube was stopped about 10
ins. from the head and by means of an elbow and threaded nipple
projected through the side of the pile to allow of attaching a pressure
hose. The piles were handled to the pile driver, the hose attached and
water supplied at 100 lbs. pressure by a pump. Churning the pile up and
down aided the driving. A hammer was used to force the piles through the
hard pan layers. A wooden follower was used to protect the pile head. A
2,800-lb. hammer falling 20 ft. did not injure the piles. One pile was
given 300 blows with a 2,800-lb. hammer falling 12 ft., and when pulled
was unbroken. It was found that 30 ft. piles and under could be picked
up safely by one end; longer piles cracked at the center when so
handled. These long piles were successfully handled by a long chain, one
end being wrapped around the pile at the center and the other end
similarly wrapped near the head; the hook of the hoisting fall was
hooked into the loop of the chain and as the pile was hoisted the hook
slipped along the chain toward the top gradually up ending the pile. The
piles weighed 175 lbs. per lin. ft. It was attempted to mold the piles
directly on the ground by leveling it off and covering it with tar
paper, but the ground settled and the method proved impracticable.
~Method of Molding and Jetting Piles for Building Foundations.~--In a
number of foundations Mr. Frank B. Gilbreth has used a polygonal pile,
either octagonal or hexagonal, with the sides corrugated or fluted as
indicated in Fig. 61. In longitudinal section these piles have a uniform
taper from butt to point and have flat points. Each pile is cored in the
center, the core being 4 ins. in diameter at the top and 2 ins. at the
bottom end. On each of the octagon or hexagon sides the pile has a
half-round flute usually from 2½ to 3 ins. in diameter. The principal
object of these flutes or "corrugations" is to give passage for the
escape to the surface of the water forced through the center core hole
in driving the pile. They are also for the purpose of increasing the
perimeter of the pile and thereby gaining greater surface for skin
friction.
The piles are reinforced longitudinally and transversely. On this
particular job the reinforcement was formed with Clinton Electrically
Welded Fabric, the meshes being 3 ins.×12 ins.; the longer dimension
being lengthwise with the pile and of No. 3 wire; the horizontal or
transverse reinforcement being of No. 10 wire. The meshes being
electrically welded together, the reinforcement was got out from a wide
sheet taking the form of a cone. No part of the reinforcement was closer
than 1 in. from the outside of the concrete. In general only sufficient
sectional area of material is put in the reinforcement to take the
tensile stresses caused by the bending action when handling the pile
preparatory to driving; more reinforcement than this only being
necessary when the piles are used for wharves, piers or other marine
structures, where a considerable length of pile is not supported
sidewise or when they are subjected to bending stresses.
[Illustration: Fig. 61.--Cross-Section of Corrugated Reinforced Concrete
Pile.]
_Molding._--The forms for molding the piles are made from 2-in. stuff,
gotten out to the required dimensions, the corrugations being formed by
nailing pieces on the inside whose section is the segment of a circle.
The sides of the octagon are fastened to the ends through which the core
projects some 6 or 8 ins. At times while the molding of the pile is in
progress, the central core is given a partial turn to prevent the
setting of the cement holding it fast and thereby preventing the final
removal.
The stripping of the forms from the piles is usually done from 24 to 48
hours after molding, and from this time on great care is taken that
there is a sufficient amount of moisture in the pile to permit of the
proper action for setting of the cement. This is usually accomplished by
covering the piles over with burlaps and saturating with water from a
hose; the operation of driving the pile not being attempted until the
concrete is at least ten days old.
_Driving._--The operation of driving corrugated concrete piles is
somewhat similar to that for driving ordinary wooden piles by water jet,
but a much heavier hammer with less drop is used. The jetting is
accomplished by inserting a 2-in. pipe within the pile. This pipe is
tapered at the bottom end to 1-in. diameter, forming a nozzle, and the
water pressure used is about 120 lbs. per sq. in. As a rule, this
pressure is obtained by the use of a steam pump which may be connected
with the boiler which operates the pile driver, or with a separate steam
supply. At the upper end of this 2-in. pipe an elbow is placed and a
short length of pipe is connected to this and to the hose from the water
supply.
[Illustration: Fig. 62.--Cushion Cap for Driving Gilbreth Corrugated
Pile.]
As it is not practicable to drop the hammer directly on the head of the
concrete piles, the driving is accomplished by the use of a special cap,
Fig. 62. This cap is about 3 ft. in height and the bottom end fits over
the head of the pile. In one side of this cap is a slot from the outside
to the center, which permits the 2-in. pipe, which supplies the water
jet for driving the pile, to project. The outside of this cap is formed
with a steel shell, the inside has a compartment filled with rubber
packing and the top has a wooden block which receives a blow from the
hammer. In this way the head of the pile is cushioned, which prevents
the blow of the hammer from bruising or breaking the concrete.
During the operation of driving, the water from the jet comes up on the
outside of the pile and carries with it the material which it displaces
in driving. This, with the assistance of the hammer, allows the pile to
be driven in place, and, contrary to what might be supposed, after the
operation of driving when the water has saturated into the ground or
been drained away, this operation puddles the earth around the pile, so
that after a few hours' time the skin friction is much more than it
would be with the pile driven into more compact soil without the use of
a jet.
[Illustration: Fig. 63.--View Showing Method of Fabricating
Reinforcement for a Round Pile with Flattened Sides.]
~Method of Molding and Driving Round Piles.~--In constructing a warehouse
at Bristol, England, some 600 spirally-reinforced piles of the Coignet
type were used. Coignet piles are in section circles with two
longitudinal flat faces to facilitate guiding during driving; this
section is the same as would be found by removing two thin slabs from
opposite sides of a timber pile. The reinforcement consists of
longitudinal bars set around the periphery and drawn together to a point
at one end and then inserted into a conical shoe; these longitudinal
bars are wound spirally with a ¼-in. rod wire tied to the bars at every
intersection. This spiral rod has a pitch of only a few inches, but to
bind it in place and give rigidity to the skeleton it is wound by a
second spiral with a reverse twist and a pitch of 4 or 5 ft. As thus
constructed, the reinforcing frame is sufficiently rigid to bear
handling as a unit. The piles used at Bristol were 14 to 15 ins. in
diameter and 52 ft. long, and weighed about 4 tons gross each. The
mixture used was cement, river sand and crushed granite.
_Molding._--In molding Coignet piles the reinforcement is assembled
complete as shown by Fig. 63 and then suspended as a unit in a
horizontal mold constructed as shown by the cross-section Fig. 64. The
concrete is deposited in the top opening and rammed and worked into
place around the steel after which the opening is closed by the piece
A. After 24 hours the curved side pieces B and C are removed and
the pile is left on the sill D until hard enough to be shifted; a pile
is considered strong enough for driving when about six weeks old.
[Illustration: Fig. 64.--Form for Molding Round Pile with Flattened
Sides.]
_Driving._--Coignet piles at the Bristol work were handled by a
traveling crane. The material penetrated was river mud and they were
driven with a hammer weighing 2 tons gross; in driving the pile head was
encircled by a metal cylinder into which fitted a wooden plunger or
false pile with a bed of shavings and sawdust between plunger and pile
head.
~Molding and Driving Square Piles for a Building Foundation.~--The Dittman
Factory Building at Cincinnati, O., is founded on reinforced concrete
piles varying from 8 to 22 ft. in length. The piles were square in
cross-section, with a 2-in. bevel on the edges; a 16-ft. pile was 10
ins. square at the point and 14 ins. square at the head, shorter or
longer piles had the same size of point, but their heads were
proportionally smaller or larger, since all piles were cast in the same
mold by simply inserting transverse partitions to get the various
lengths. Each pile was reinforced by four ¾-in. twisted bars, one in
each corner, bound together by ¼-in hoops every 12 ins.. The bars were
bent in at the point and inserted in a hollow pyramidal cast iron shoe
weighing about 50 lbs. The concrete was a 1-2-4 stone mixture and the
pile was allowed to harden four weeks before driving. They were cast
horizontally in wooden molds which were removed after 30 hours.
_Driving._--Both because of their greater weight and because of the care
that had to be taken not to shatter the head, it took longer to adjust
and drive one of these concrete piles than it would take with a wooden
pile. The arrangement for driving the piles was as follows: A metal cap
was set over the head of the pile, on this was set the guide cap having
the usual wood deadener and on this was placed a wood deadener about 1
ft. long. The metal cap was filled with wet sand to form a cushion, but
as the pile head shattered in driving the sand cushion was abandoned and
pieces of rubber hose were substituted. With this rubber cushion the
driving was accomplished without material damage to the pile head. The
hammer used weighed 4,000 lbs. and the drop was from 4 to 6 ft. The
blows per pile ranged from 60 up. The average being about 90. In some
cases where the driving was hard it took over 400 blows to drive a
14-ft. pile. An attempt to drive one pile with a 16-ft. drop resulted in
the fracture of the pile.
~Method of Molding and Driving Octagonal Piles.~--The piles were driven in
a sand fill 18 ft. deep to form a foundation for a track scales in a
railway yard. They were octagonal and 16 ins. across the top, 16 ft.
long, and tapered to a diameter of 12 ins. at the bottom. They were also
pointed for about a foot. The reinforcement consisted of four ½-in.
Johnson corrugated bars spaced equally around a circle concentric with
the center of the pile, the bars being kept 1½ ins. from the surface of
the concrete. A No. 11 wire wrapped around the outside of the bars
secured the properties of a hooped-concrete column. The piles were cast
in molds laid on the side. They were made of 1:4½ gravel concrete, and
were seasoned at least three weeks before being driven.
An ordinary derrick pile driver, with a 2,500-lb. hammer falling 18 ft.,
was used in sinking them. A timber follower 6 ft. long and banded with
iron straps at both ends was placed over the head of the pile to receive
directly the hammer blows. The band on the lower end was 10 ins. wide
and extended 6 ins. over the end of the follower. In this 6-in. space a
thick sheet of heavy rubber was placed, coming between the head of the
pile and the follower. Little difficulty was experienced in driving the
piles in this manner, although 250 to 300 blows of the hammer were
required to sink each pile. The driving being entirely through fine
river sand there is every probability that any kind of piles would have
been driven slowly. The heads of the first 4 or 5 piles were battered
somewhat, but after the pile driver crew became familiar with the method
of driving, no further battering resulted and the heads of most of the
piles were practically uninjured.
[Illustration: Fig. 65.--Cross-Section of Chenoweth Rolled Pile.]
[Illustration: Fig. 66.--Diagram Showing Method of Rolling Chenoweth
Pile.]
~Method and Cost of Making Reinforced Concrete Piles by Rolling.~--In
molding reinforced concrete piles exceeding 30 or 40 ft. in length, the
problem of molds or forms becomes a serious one. A pile mold 50 or 60
ft. long is not only expensive in first cost, but is costly to maintain,
because of the difficulty of keeping the long lagging boards from
warping. To overcome these difficulties a method of molding piles
without forms has been devised and worked out practically by Mr. A. C.
Chenoweth, of Brooklyn, N. Y. This method consists in rolling a sheet of
concrete and wire netting into a solid cylinder on a mandril, by means
of a special machine. Fig. 65 is a sketch showing a cross-section of a
finished pile, in which the dotted line shows the wire netting, the
hollow circle is the gas pipe mandril, and the solid circles are the
longitudinal reinforcing bars.
[Illustration: Fig. 67.--Machine for Rolling Chenoweth Piles.]
In making the pile the netting is spread flat, with the reinforcing bars
attached as shown at (a), Fig. 66, and is then covered with a layer of
concrete. One edge of the netting is fastened to the platform, the other
edge is attached to the winding mandril. The winding operation is
indicated by sketch (b), Fig. 66. Fig. 67 shows the machine for
rolling the pile. It consists of a platform and a roll. The platform is
mounted on wheels and is so connected up that it moves back under the
roll at exactly the circumferential speed of the roll; thus the forming
pile is under constant, heavy pressure between the roll and platform.
When the pile has been completely rolled it is bound at intervals by
wire ties; the wire for these ties is carried on spools arranged under
the edge of the platform at intervals of 4 ins. for the first 10 ft.
from the point and of 6 ins. for the remainder of the length. The
binding is done by giving the pile two or three extra revolutions and
then cutting and tying the wire; then by means of a long removable shelf
which contains the flushing mortar, as the pile revolves it becomes
coated on the outside with a covering that protects the ties and other
surface metal. Finally the pile is rolled onto a suitable table to
harden.
An exhibition pile rolled by the process described is 61 ft. long and 13
ins. in diameter. This pile was erected as a pole by hoisting with a
tackle attached near one end and dragging the opposite end along the
ground exactly as a timber pole would be erected. It was also suspended
free by a tackle attached at the center; in this position the ends
deflected 6 ins. Neither of these tests resulted in observable cracks in
the pile. The pile contains eight 1-in. diameter steel bars 61 ft. long,
one 2½-in. pipe also 61 ft. long, 366 sq. ft., or 40.6 sq. yds. ½-in.
mesh 14 B. & S. gage wire netting, and 2 cu. yds. loose concrete. Its
cost for materials and labor was as follows:
Materials--
Gravel, 28.8 cu. ft., at $1 per cu. yd. $ 1.05
Sand, 19.8 cu. ft., at $1 per cu. yd. .73
Cement, 3 bbls., at $1.60 per bbl. 4.80
Netting, 40.6 sq. yds., at 17½ cts. per sq. yd. 7.10
Rods, wire, etc., 1,826 lbs., at 2½ cts. per lb. 45.65
--------
Total $59.33
Mixing 2 cu. yds. concrete, four men one hour, at 15 cts.
per hour $ 0.60
Placing concrete and netting, four men 30 mins., at 15
cts. per hour .30
Winding pile, four men 20 mins., at 15 cts. per hour .20
Removing pile, four men 10 mins., at 15 cts. per hour .10
--------
$1.20
Grand total $60.53
This brings the cost of a pile of the dimensions given to about $1 per
lin. ft.
CHAPTER XI.
METHODS AND COST OF HEAVY CONCRETE WORK IN FORTIFICATIONS, LOCKS, DAMS,
BREAKWATERS AND PIERS.
The construction problem in building concrete structures of massive form
and volume is chiefly a problem of plant arrangement and organization of
plant operations. In most such work form construction is simple and of
such character that it offers no delay to placing the concrete as
rapidly as it can be produced. The same is true of the character of the
structure, it is seldom necessary for one part of the work to wait on
the setting and hardening of another part. As a rule, there is no
reinforcement to fabricate and place and where there is it is of such
simple character as not to influence the main task of mixing, handling,
and placing concrete. Stated broadly, the contractor in such work
generally has a certain large amount of concrete to manufacture,
transport and deposit in a certain space with nothing to limit the
rapidity of these operations, except the limitations of plant capacity
and management. Installation and operation of mixing and conveying
plant, then are matters to be considered carefully in heavy concrete
work.
In the following sections we have given one or more examples of nearly
every kind of heavy concrete work excepting bridge foundations and
retaining walls, which are considered in Chapters XII and XIII, and
except rubble concrete work, which is considered in Chapter VI. In each
case so far as the available records made it possible, we have given an
account of the plant used and of its operation.
~FORTIFICATION WORK.~--Concrete for fortification work consists very
largely of heavy platforms and walls for gun foundations and enclosures
and of heavily roofed galleries and chambers for machinery and
ammunition. The work is very massive and in the majority of cases of
simple form. A large number of data are to be found in the reports of
the Chief of Engineers, U. S. A., on all classes of fortification work,
but the manner in which they are recorded makes close analysis of
relative efficiencies of methods or of relative costs almost impossible.
The following data are given, therefore, as examples that may be
considered fairly representative of the costs obtained in fortification
work done under the direction of army engineers; these data are not
susceptible of close analysis because wages, working force, outputs,
etc., are nearly always lacking.
~Gun Emplacements, Staten Island, N. Y.~--The work comprised 5,609 cu.
yds. of concrete in two 12-in. gun emplacements, and 3,778 cu. yds. of
concrete in two 6-in. gun emplacements. Concrete was mixed in a
revolving cube mixer with the exception of 809 cu. yds. in the 6-in.
emplacements which were mixed by hand at a cost of 56 cts. more per
cubic yard than machine mixing cost. The body of the concrete was a
1-3-5 Portland cement, beach sand and broken trap rock mixture. The
floors and upper surface of the concrete had a pavement consisting of 6
ins. of 1-3-5 concrete surfaced with 2 ins. of 1-3 mortar. Wages are not
given, but for the time and place should have been about $1.50 per
8-hour day for common labor. The cost of materials was:
Alpha Portland cement, per bbl. $1.98
Broken trap rock, per cu. yd. 0.81
12-in. emplacement, hauling sand per cu. yd. 0.175
6-in. emplacement, hauling sand per cu. yd. 0.20
The cost of the concrete in place was as follows:
12-in., per 6-in., per
Body Concrete-- cu. yd. cu. yd.
Cement, at $1.98 per bbl. $2.546 $2.546
Broken stone, at 81 cts. per cu. yd. 1.041 1.041
Sand, at 17½ and 20 cts. per cu. yd. 0.225 0.257
Receiving and storing materials at 11.6 cts. per
cu. yd. and 8.4 cts. per bbl. 0.149 0.180
Mixing, placing and ramming 0.879 1.110
Forms, lumber and labor 0.477 0.950
Superintendence and miscellaneous 0.190 0.150
------ ------
Total $5.507 $6.234
Concrete Pavement--
Materials $2.97 $3.06
Labor 4.63 4.72
------ ------
Total $7.60 $7.78
[Illustration: Fig. 68.--Sketch Plans of Concrete Making Plant for
Mortar Battery Platform.]
~Mortar Battery Platform, Tampa Bay, Fla.~--The platform contained 8,994
cu. yds. of concrete composed of a mixture of Portland cement, sand,
shells and broken stone. The broken stone and cement were brought in by
vessel and the sand and shells were obtained from the beach near by. The
plant for the work was arranged as shown by the sketch, Fig. 68. Sand,
stone and shells were stored in separate compartments in the storage
bins. Box cars, divided into compartments of such size that when each
was filled with its proper material, the car would contain the proper
proportions for one batch of concrete, were pushed by hand under the
several compartments of the bin in succession until charged; then they
were hooked to a cable and hauled to the platform over the mixer and
dumped. The charge was then turned over with shovels and shoveled into
the hopper of a continuous mixer, located beneath. Two cars were used
for charging the mixer, running on separate tracks as shown. The mixer
discharged into buckets set on flat cars, which were hauled by mules
under the cableway, which then lifted and dumped the bucket and returned
it empty to the car. By using three bucket cars, one was always ready
to receive the mixer discharge as soon as the preceding one had been
filled, so that the mixer operated continuously. The cableway had a
working span of 270 ft., the cable being carried by traveling towers 69
ft. high; the cableway was very easily operated back and forth along the
work. The cableway complete, with 497 ft. of six-rail track for each
tower, cost $4,700. The cost of materials and labor for the 8,994 cu.
yds. of concrete was as follows:
Per cu. yd.
1 bbl. cement at $2.46 $2.46
0.89 cu. yd. stone, at $2.95 2.622
0.315 cu. yd. shells, at $0.45 0.142
0.51 cu. yd. sand, at $0.12 0.062
Mixing and placing 0.693
-------
Total $5.979
The above batch tamped in place to 30 cu. ft., or 1-1/9 cu. yds., which
gives the cost as follows:
Per cu. yd.
Cost of concrete tamped in place $5.381
Cost of form work 0.370
-------
Total cost $5.751
In the preceding prices of cement and stone, 59 cts. and 29 cts. per
cubic yard, respectively, are included for storage. The costs of sand
and shells are costs of screening and storing. Rough lumber for forms
cost $10.25, and dressed lumber $12.75 per M. ft. B. M.
~Emplacement for Battery, Tampa Bay, Fla.~--The emplacement contained
6,654 cu. yds. of Portland cement, sand, shells and broken stone
concrete. The plant arrangement is shown by Fig. 69. The sand and shells
were got near the site, using an inclined cableway running from a 40-ft.
mast near the mixer to a deadman at the shell bank. All the sand for the
fill around the emplacement was obtained in the same way. The other
materials were brought by vessel to a wharf, loaded by derrick onto cars
operated by an endless cable, and taken to the work. The storage bins
and mixing plant were operated much like those for the mortar battery
work, previously described. A cube mixer was used, and the concrete was
handled from it to the work by a crane derrick covering a circle of 100
ft. in diameter. The cost of materials and concrete was as follows:
Cement, plus 7 cts. for storage per bbl. $ 2.532
Stone, plus 38 cts. for storage per cu. yd. 3.047
Shells, excavating and storage. 0.481
Sand, excavating and storage. 0.250
Lumber, rough per M. ft. B. M. 10.25
Lumber, dressed per M. ft. B. M. 12.75
[Illustration: Fig. 69.--Sketch Plans of Concrete Making Plant for
Battery Emplacement.]
A batch made up as follows, tamped in place to a volume of 30 cu. ft. or
1-1/9 cu. yds.:
1 bbl. cement, at $2.532. $ 2.532
0.315 cu. yd. shells, at $0.481. 0.151
0.51 cu. yd. sand, at $0.25. 0.130
0.89 cu. yd. stone, at $3.047. 2.710
Mixing and placing. 0.761
--------
Total for 30 cu. ft. $ 6.284
This gives a cost per cubic yard of concrete in place as follows:
Concrete in place, per cu. yd. $ 5.655
Forms, per cu. yd. of concrete. 0.220
--------
Total cost of concrete per cu. yd. $ 5.875
~United States Fortification Work.~--The following methods and cost of
mixing and placing concrete by hand and by cubical mixers is given by
Mr. L. R. Grabill for U. S. Government fortification work done in 1899.
_Hand Mixing and Placing._--The work was done by contract, using a 1
cement, 2 sand, 2 pebbles and 3 stone mixture turned four times. A board
large enough for three batches at a time was used; one batch was being
placed, one being mixed and one being removed at the same time so that
the mixers moved without interval from one to the other. Two gangs were
worked, each mixing 64 batches of 0.75 cu. yd., or 48 cu. yds. of
concrete per day at the following cost:
Per Per
Hand Mixing 9,000 Cu. Yds.-- day. cu. yd.
6 men wheeling materials $ 7.50 $0.16
8 men mixing 10.00 0.21
8 men wheeling away 10.00 0.21
6 men placing and ramming 7.50 0.16
1 pump man 1.25 0.02
1 waterboy 1.00 0.02
1 foreman 2.00 0.04
------- -------
Totals $39.25 $0.82
The entire cost of plant for this work was about $500.
_Machine Mixing and Placing._--The concrete was mixed in a 4-ft. cubical
mixer operated by a 12 hp. engine which also hauled the material cars up
the incline to the mixer. These cars passed by double track under the
material bins where the compartments of the car body were filled through
trap doors; they then passed the cement house where the cement was
placed on the load, then up the incline to the mixer and dumped, and
then empty down an opposite incline. Seven turns of the mixer mixed the
charge which was discharged into iron tubs on cars hauled by horses to
two derricks whose booms covered the work. One gang by day labor mixed
and placed 168 batches of 0.7 cu. yd., or 117.6 cu. yds. per day at the
following cost:
Per Per
Machine Mixing 4,000 Cu. Yds.-- day. cu. yd.
32 men at $1.25 $40.00 $0.34
1 pumpman 1.25 0.01
1 teamster and horse 2.00 0.02
2 waterboys at $1 2.00 0.02
1 engineman 1.70 0.02
1 derrickman 1.50 0.01
1 fireman 1.50 0.01
1 foreman 2.88 0.03
Fuel (cement barrels largely) 1.25 0.01
------- -------
Totals $54.08 $0.47
The cost of the plant was about $5,000.
[Illustration: Fig. 70.--Concrete Making Plant for Constructing Lock
Walls, Cascades Canal.]
~LOCK WALLS, CASCADES CANAL.~--Four-fifths or 70,000 cu. yds. of lock
masonry was concrete, the bulk of which was mixed and deposited by the
plant shown by Fig. 70. The concrete was Portland cement, sand, gravel
and broken stone. Cement was brought in in barrels by railway, stored
and tested; from the store house the barrels were loaded onto cars and
taken 250 ft. to a platform onto which the barrels were emptied and from
which the cement was shoveled into the cement hopper and chuted to cars
which took it to the charging hopper of the mixer. The stone was crushed
from spalls and waste ends from the stone cutting yards, where stone for
wall lining and coping and other special parts was prepared. These
spalls and ends were brought in cars and dumped into the hopper of a
No. 5 Gates crusher, with a capacity of 30 tons per hour. From the
crusher the stone passed to a 2½-in. screen, the pieces passing going to
a bin below and the rejections going to a smaller Blake crusher and
thence to the bin. The dust and small particles were not screened out.
The sand and gravel were obtained by screening and washing pit gravel.
The gravel was excavated and brought in cars to the washer. This
consisted of a steel cylinder 2 ft. 6½ ins. in diameter and about 18 ft.
long, having an inclination of 1 in. per foot. An axial gudgeon
supported the cylinder at the lower end and it rested on rollers at the
other end and at an intermediate point. The gravel was fed by hopper and
chute into the upper end and into this same end a 3-in. perforated pipe
projected and extended to about mid-length of the cylinder. The cylinder
shell was solid and provided with internal fins for about half its
length from the feed end. For the remainder of its length nearly to the
end, the shell was perforated with 2½-in. holes. For a length of 4 ft.
beyond mid-point it was encircled by a concentric screen of 1/8-in.
holes, and this screen for 3 ft. of its length was encircled by another
screen of 30 meshes to the inch. The pit mixture fed into the cylinder
was gradually passed along by the combined inclination and rotation,
being washed and screened in the process. The sand fell into one bin and
the gravel into another, and the waste water was carried away by a
flume. The large stones passed out through openings at the lower end of
the shell and were chuted into cars. The cars came to the mixer as
clearly shown by Fig. 70.
The stone and gravel cars were side dump and the cement car was bottom
dump. The mixers were of the cube type 4 ft. on each edge and operated
by a 7×12-in. double cylinder engine at nine revolutions per minute. The
usual charge was 32 cu. ft. of the several ingredients, and it was found
that 15 revolutions requiring about 1½ minutes were sufficient for
mixing. The average work of one mixer was 17 batches or about 13 cu.
yds. per hour, but this could be speeded up to 20 batches per hour when
the materials were freely supplied and the output freely removed. Two
cars took the concrete from the mixer to the hopper, from which it was
fed to the work by chute. The hopper was mounted on a truck and the
chute was a wrought iron cylinder trussed on four sides and having a
45° elbow at the lower end to prevent scattering. The chute fed into a
car running along the wall and distributing the material. It was found
impracticable to move the chute readily enough to permit of feeding the
concrete directly into place. As the concreting progressed upward the
trestle was extended and the chute shortened. It was found that wear
would soon disable a steel chute so that the main trussed cylinder had a
smaller, cheaply made cylinder placed inside as a lining to take the
wear and be replaced when necessary.
The plant described worked very successfully. Records based on 9,614.4
cu. yds. of concrete laid, gave the following:
Cu. yds.
Concrete mixed by hand 1,777.0
Concrete mixed by machine 7,837.4
Total concrete laid 9,614.4
Concrete placed by derricks 2,372.0
Concrete placed by chute 7,242.4
Concrete 1-2-4 mixture 156.0
Concrete 1-3-6 mixture 1,564.0
Concrete 1-4-8 mixture 6,892.0
The average mixture was 1 cement, 3.7 sand, 4.8 gravel and 2.6 broken
stone. The average product was 1.241 cu. yds. concrete per barrel of
cement and 1.116 cu. yds. of concrete per cubic yard of stone and
gravel. The average materials for 1 cu. yd. of concrete were: Cement
0.805 bbl., sand 0.456 cu. yd., gravel 0.579 cu. yd., and stone 0.317
cu. yd.
The cost of these 9,614.4 cu. yds. of concrete in place was:
Hand Mixed and Placed by Derrick-- Per cu. yd.
Labor mixing 1,777 cu. yds $1,072
Repairs, fuel, etc 0.016
-------
Total cost mixing $1,088
Labor placing 2,372 cu. yds. 0.6025
Fuel, tramways, etc. 0.1958
-------
Total cost placing $0.7983
Machine Mixed and Placed by Chute--
Labor mixing 7,837 cu. yds. $0.388
Repairs, fuel, etc 0.046
------
Total cost mixing $0.434
Labor placing 7,242 cu. yds 0.414
Fuel, tramways, etc. 0.045
------
Total cost placing $0.459
Materials and Supplies 9,614 cu. yds.--
Timbering $0.145
Cement 3.289
Sand and gravel 1.073
Broken stone 0.536
Cement testing, repairs, etc. 0.223
------
Total $5,266
Plant and Superintendence, 9,614 Cu. Yds.--
Engineering, superintendence, repairs, etc. $1,508
20% cost of plant 0.165
------
Total $1,673
The comparative cost of hand and machine mixing and handling was thus:
Item-- Hand. Machine.
Mixing per cu. yd. $1.088 $0.434
Placing per cu. yd. 0.798 0.459
Materials, etc., per cu. yd. 5.466 5.466
Plant, etc., per cu. yd. 1.673 1.673
------ ------
Totals $9.025 $8.032
The average total costs of all the concrete placed were:
Mixing per cu. yd. $0.555
Placing per cu. yd. 0.543
Materials per cu. yd. 5.266
Plant, etc., per cu. yd. 1.673
------
Total $8.037
~LOCKS, COOSA RIVER, ALABAMA.~--The following methods and costs are given
by Mr. Charles Firth for constructing lock No. 31 for the Coosa River
canalization, Alabama. This lock is 420 ft. long over all, 322 ft.
between quoins, 52 ft. clear width, 14.7 ft. lift and 8 ft. depth of
water on sills; it contained 20,000 cu. yds. of concrete requiring
21,500 bbls. cement, half Alsen and half Atlas.
Figure 71 shows the concrete mixing plant, consisting of two 4×4 ft.
cube mixer, driven by a 10×16-in. engine. The top floor of the mixer
house stored the cement, 2,000 bbls. The concrete was a 1-3-5½ stone
mixture. Each mixer charge consisted of 3 cu. ft. cement, 9 cu. ft. sand
and 16.5 cu. ft. stone; the charge was turned over four times before and
six times after watering at a speed not exceeding eight revolutions per
minute. The average output of the plant was 200 cu. yds. per 8-hour day,
or 100 cu. yds. per mixer, but it was limited by the means for placing.
[Illustration: Fig. 71.--Concrete Mixing Plant for Lock Construction,
Coosa River, Alabama.]
The concrete was mixed dry, deposited in 6 to 8-in. layers, and rammed
with 30-lb. iron rammers with 6-in. square faces. For all exposed
surfaces a 6-in. facing of 1-3 mortar was placed by setting 2×12-in.
planks 4 ins. from the laggings, being kept to distance by 2×4-in.
spacers, placing and ramming the concrete behind them, then withdrawing
them, filling the 6-in. space with mortar and tamping it to bond with
the concrete. The walls were carried up in lifts, each lift being
completed entirely around the lock before beginning the next; the first
lift was 10.7 ft. high and the others 6 ft., except the last, which was
4.5 ft., exclusive of the 18-in. coping. The coping was constructed of
separately molded blocks 3 ft. long, made of 1-2-3 concrete faced with
1-1 mortar and having edges rounded to 3 ins. radius.
In constructing the forms a row of 6×8-in. posts 24 ft. long and 5 to 7
ft. apart was set up along the inside of each wall and a similar row of
posts 12 ft. long was set up along the outside. From the tops of the
short posts 6×8-in. caps reached across the wall and were bolted to the
long posts; these caps carried the stringers for the concrete car
tracks. The lagging consisted of 3×10-in. planks dressed on all sides.
The backs of the walls were stepped and as each step was completed the
rear 12-ft. posts were lifted to a footing on its top and carried in the
necessary distance. The front posts remained undisturbed until the wall
was completed. The lagging was moved up as the filling progressed. As no
tie bolts were permitted, these forms required elaborate bracing.
From the mixing plant, which was located on the bank above reach of
floods, the concrete cars were dropped by elevator to the level of the
track over the walls and then run along the wall and dumped onto
platforms inside the forms and just below the track. This arrangement
was adopted, because it was found that even a small drop separated the
stone from the mortar. The concrete was shoveled from the platforms to
place and rammed. The cars were bottom dumping with a single door hinged
at the side; this door when swinging back struck the track stringers and
jarred the form so that constant attention was necessary to keep it in
line. It would have been much better to have had double doors swinging
endwise of the car. Another point noted was that unless the track was
high enough to give good head room at the close of a lift the placing
and ramming were not well done.
The cost of 8,710 cu. yds. of concrete placed during 1895 by day labor
employing negroes at $1 per 8-hour day was as follows per cubic yard:
1 bbl. cement $2.48
0.88 cu. yd. stone at $0.76 0.67
0.36 cu. yd. sand at $0.34 0.12
Mixing, placing and ramming 0.88
Staging and forms 0.42
----
Total $4.57
~LOCK WALLS, ILLINOIS & MISSISSIPPI CANAL.~--The locks and practically all
other masonry for the Illinois & Mississippi Canal are of concrete. The
following account of the methods and cost of doing this concrete work is
taken from information published by Mr. J. W. Woermann in 1894 and
special information furnished by letter. The decision to use concrete
was induced by the fact that no suitable stone for masonry was readily
available (the local stone was a flinty limestone, usually without bed,
or, at best, in thin irregular strata, and cracked in all directions
with the cracks filled with fire clay) while good sand and gravel and
good stone for crushing were plentifully at hand. The concrete work done
in 1893-4 comprised dam abutments, piers for Taintor gates and locks.
_Dam Abutments._--Four dam abutments were constructed, three of which
were L-shaped, with sides next to the river 40 ft. long and sides
extending into the banks 20 ft. long; the top thickness was 3 ft., the
faces were vertical and the backs stepped with treads of 14 to 16 ins.,
and the width of base was 0.4 of the height. Each of these abutments was
built in four 30-cu. yd. sections, each section being a day's work. The
forms consisted of 2×8-in. planks, dressed on both sides, 2×8-in. studs
spaced 2 ft. on centers and 4×6-in. braces. For the first two of the
four abutments, the forms were erected in sections, the alternate
sections being first erected and filled. When these sections had
hardened the forms were shifted to the vacant sections and lined up to
and braced against the completed sections. This method did not give well
aligned walls, so in subsequent work the forms were erected all at once.
The concrete was mixed by hand. The sand and cement were mixed dry,
being turned four times and spread in a layer Pebbles and broken stone
previously wetted were spread over the sand and cement and the whole
turned four times, the last turn being into wheelbarrows; about five
common buckets of water were added during the mixing. The mixture sought
was one that would ram without quaking. Two forms of rammers were used;
for work next to forms a 4×6-in. rammer and for inside work 6-in
diameter circular rammer weighing 20 lbs. The gang mixing and placing
concrete consisted usually of:
Item. Per Day. Per Cu. Yd.
2 handling cement and sand $ 3.00 $0.10
3 filling barrows with aggregate 4.50 0.15
8 mixing concrete 12.00 0.40
2 shoveling concrete into barrows 3.00 0.10
5 wheeling concrete to forms 7.50 0.25
1 spreading concrete 1.50 0.05
5 tamping concrete 7.50 0.25
------ -----
Total, 26 men $39.00 $1.30
These cubic yard costs are based on 30 cu. yds. of wall completed per
8-hour day. The cost in detail of two abutments containing 254 cu. yds.
was per cubic yard as follows:
Item. Per Cu. Yd.
1.65 bbls. Portland (Germania) cement $ 5.60
0.5 cu. yd. crushed stone 2.07
0.24 cu. yd. gravel 0.59
0.53 cu. yd. sand 0.24
Lumber, forms, warehouses, platforms[D] 0.55
Carpenter work[E] ($9 per M.) 1.10
Mixing and placing 1.47
20 per cent. first cost of plant 0.31
Engineering and miscellanies 0.31
------
Total $12.24
[Footnote D: Charging ¼ of first cost of $18 per M. ft.]
[Footnote E: Carpenters $3.50, laborers $1.50 per day; there was one
laborer to two carpenters.]
The large amount of cement 1.65 bbls. per cubic yard was due to facing
the abutments with 8 ins. of 1-2 mortar. The concrete in the body of the
wall was 1 cement, 2 sand, 2 gravel and 2 broken stone mixture. A dry
mixture was used and this fact is reflected in the cost of ramming, 25
cts. per cu. yd. The cost of mixing was also high.
[Illustration: Fig. 72.--Concrete Mixing Plant for Lock Walls, Illinois
& Mississippi Canal.]
_Piers for Taintor Gates._--The masonry at this point consisted of three
piers 6×30 ft., and two abutments 30 ft. long, 6 ft. thick at base and 4
ft. thick at top, with wing walls; it amounted to 460 cu. yds. The feet
of the inclined braces were set into gains in the horizontal braces and
held by an 8-in. lag screw; after the posts were plumbed a block was
lag-screwed at the upper end of each brace. These forms proved entirely
satisfactory. The cost of the work per cubic yard was as follows:
Item. Per Cu. Yd.
1.45 bbls. Portland cement $4.330
0.55 cu. yd. crushed stone 0.604
0.252 cu. yd. pebbles 0.328
0.465 cu. yd. sand 0.419
40,000 ft. B. M. lumber (¼ cost of $16 per M.) 0.348
Carpenter work on forms 0.780
Mixing and placing concrete 1.909
20 per cent. cost of plant 0.090
Miscellaneous 0.182
-----
Total $8.99
_Mixing Plant._--The concrete for all the lock work of 1893-4 was mixed
by the plant shown by Figs. 72 and 73. The mixer plant proper consisted
of a king truss carried by two A-frames of unequal height; under the
higher end of the truss was a frame carrying a 4-ft. cubical mixer and
under the lower end a pit for a charging box holding 40 cu. ft. This
charging box was hoisted by ½-in. steel cable running through a pair of
double blocks as shown; the slope of the lower chord of the truss was
such that the cable hoisted the box and carried it forward without the
use of any latching devices. On two sides of the pit were tracks from
the sand and stone piles and on the other two sides were the cement
platform and water tank. The charging box dumped into the hopper above
the mixer and the mixer discharged into cars underneath. A 15-HP. engine
operated the hoist by one pulley and the mixer by the other pulley. Nine
revolutions of the mixer made a perfect mixture. The plant as
illustrated was slightly changed as the result of experience in
constructing the guard lock. The charging hopper was lowered 6 ins. and
the space between the mixer and lower platform reduced by 9 ins.;
diagonal braces were also inserted under the timbers carrying the mixer
axles. This plant cost for framing and erection $300 and for machinery
delivered $706. The crushing plant shown by Fig. 73 consisted of a No. 2
Gates crusher delivering to a bucket elevator.
[Illustration: Fig. 73.--Stone Crushing Plant for Lock Walls, Illinois &
Mississippi Canal.]
[Illustration: Fig. 74.--Forms for Guard Lock, Illinois & Mississippi
Canal.]
_Guard Lock._--The forms employed in constructing the guard lock are
shown by Fig. 74, and in this drawing the trestle and platform for the
concrete cars are to be noted. The walls were concreted in sections. A
batch of concrete consisted of 1 bbl. cement, 10 cu. ft. sand and 20 cu.
ft. crushed stone. The average run per 8-hour day was 40 batches of
facing and 60 batches concrete, representing 100 bbls. cement. The gang
worked was as follows:
Duty. No. Men. P. C. Cost.
Handling cement 3 5.26
Filling and pushing sand car 5 8.77
Filling and pushing stone car 9 15.79
Measuring water 1 1.75
Dumping bucket on top platform 3 5.26
Opening and closing door of mixer 1 1.75
Operating friction clutch 1 1.76
Attending concrete cars under mixer 1 1.76
Dumping cars at forms 2 3.51
Spreading concrete in forms 3 5.26
Tamping concrete in forms 10 17.54
Mixing mortar for facing 6 10.53
Finishing top of wall 2 3.51
Hauling concrete cars with 1 horse 1 3.51
Engineman operating hoist 1 3.51
Engineman operating engine 1 3.51
Foreman in charge of forms 1 3.51
General foreman 1 3.51
-- ------
Total 52 100.00
The percentages of cost in this statement have been calculated by the
authors upon the assumption that each laborer received one-half as much
wages as each engineman, foreman and horse and driver per 8 hours, which
would make the total daily wages equivalent to the wages of 57 men.
Wages of common labor were $1.50 per day. Considering the size of the
gang the output of 40 batches of mortar and 60 batches of concrete per
day was very small. The total yardage of concrete in the guard lock was
3,762 cu. yds., 2,212 cu. yds. in the walls and 1,550 cu. yds. in
foundations, culverts, etc. Its cost per cubic yard was made up as
follows:
Item. Total. Per Cu. Yd.
5,246 bbls. Portland cement $15,604}
} $4.170
152 bbls. natural cement 84}
2,910 cu. yds. stone 2,901 0.771
126 cu. yds. pebbles 113}
} 0.401
1,970 cu. yds. sand 1,398}
145,000 ft. B. M. lumber (¼th cost) 659 0.175
Iron for forms, trestles, etc. 90 0.024
Coal, oil, miscellaneous 327 0.087
Carpenter work 2,726 0.724
Mixing and placing concrete 6,693 1.780
Pumping, engineering, misc. 742 0.197
20 per cent of plant 550 0.146
------- ------
Total $31,887 $8.475
[Illustration: Fig. 75.--Forms for Regular Lock Walls, Illinois &
Mississippi Canal.]
_Lock No. 37._--The character of the forms used in constructing the lock
walls is shown by Fig. 75. The walls were built in sections and work was
continuous with three 8-hour shifts composed about as specified for the
guard lock work except that one or two men were added in several places
making the total number 58 men. The average output per shift was 65
batches of concrete and 31 batches of facing mortar. The cost of the
work, comprising 3,767 cu. yds., was as follows:
Item. Total. Per Cu. Yd.
4,564 bbls. Portland cement $14,181 $3.764
2,460 cu. yds. crushed stone 4,521 1.200
250 cu. yds. pebbles 325 0.086
1,750 cu. yds. gravel 2,335 0.619
450 cu. yds. sand 450 0.119
180,000 ft. B. M. lumber (¼th cost) 990 0.236
Fuel, light, repairs, etc. 1,171 0.311
Carpenter work 2,526 0.671
Pumping 270 0.071
Mixing and placing concrete 6,170 1.632
20% cost of plant 730 0.193
------- ------
Total $33,669 $8.902
_Lock No. 36._--The forms used were of the construction shown by Fig.
75. Three shifts were worked, each composed as specified for the guard
lock, except that the number of tampers and spreaders was doubled,
bringing the gang up to 65 men. The average output per gang per shift
was 76 batches of concrete and 35 batches of facing mortar. The cost of
2,141 cu. yds. of concrete in this lock was as follows:
Item. Total. Per Cu. Yd.
3,010 bbls. Portland cement $9,057 $4.23
1,377 cu. yds. broken stone 1,922 0.90
393 cu. yds. pebbles 354 0.17
459 cu. yds. gravel 310 0.15
500 cu. yds. sand 889 0.42
150,000 ft. B. M. lumber (¼th cost) 600 0.28
Fuel, light, repairs, etc. 253 0.68
Carpenter work 1,472 0.11
Mixing and placing concrete 3,897 1.82
20% cost of plant 650 0.30
------- -----
Total $19,404 $9.06
The preceding data, made public by Mr. Woermann in 1894, are
supplemented by the following information prepared for the authors:
"If any criticism was to be made of the concrete masonry erected in 1893
and 1894, it would probably be to the effect that it was too expensive.
The cost of the masonry erected during those two seasons was $8 to $9
per cu. yd. Our records showed that about 45 per cent. of this cost was
for Portland cement alone, and moreover, that 40 per cent. of the total
cement used at a lock was placed in the 8-in. facing and 5-in. coping.
So in the seven locks erected in 1895 on the eastern section, the facing
was reduced to 3 ins. and the proportions changed from 1-2 to 1-2½.
"In 1898 this cost received another severe cut, and Major Marshall's
instructions stated that the facing should not exceed 1½ ins. in
thickness nor be less than ¾-in., while the layer of fine material on
top of the coping was to be only sufficient to cover the stone and
gravel. The amount of sand was again increased so that the proportions
were 1-3.
"The cost of the Portland cement concrete was likewise cheapened by
increasing the amount of aggregates. On the earlier work the proportions
were 1-2-2-3, while on the work in 1898 the proportions were 1-4-4. The
cost of the walls was further cheapened by using Utica cement in the
lower steps of the wall, with 2 ft. of Portland cement concrete on the
face. The proportions used in the Utica cement concrete were 1-2½-2½.
This lower step is one-third of the height, or about 7 ft.
[Illustration: Fig. 76.--Sketch Showing Method of Attaching Lagging to
Studs, Illinois & Mississippi Canal.]
"The forms were of the same character as those used on the first locks,
except that for lining the inner face, 3×10-in. hard pine planks were
substituted for the 4×8-in. white pine. The hard pine was damaged less
by the continuous handling, and the cost was practically the same. There
was also an important change made in the manner of fastening the plank
to the 8×10-in. posts. A strip 1¾ ins. square was thoroughly nailed to
each post, once for all, with 20d. spikes, and the planking was then
nailed from the outside, as shown in Fig. 76. This kept the face of the
plank in a perfectly smooth condition, and prevented the formation of
the little knobs on the face of the concrete which represented all the
old nail holes. This style of forming was also easier to take apart
after the setting of the concrete. Rough pine planks, 2×12-in., were
used for the back of the form, the same as before.
"In order to keep ahead of the concrete force it was necessary to use
two gangs of carpenters, erecting the forms for the next two locks. Each
gang consisted of about 20 carpenters (at $2.25) and 10 helpers (at
$1.50); but men were transferred from one to the other, according to the
stage of completion of the two locks. In addition to these two gangs,
two carpenters were on duty with each concrete shift to put in the steps
in the back of the forms. Sufficient lumber was required for the forms
for three complete locks, and 14 locks (Nos. 8 to 21) were built.
"The same type of mixer has been used as on the earlier work at Milan,
namely, a 4-ft. cubical steel box mounted on corners diagonally
opposite. On account of the greater number of locks to be built on the
eastern section, however, two mixers were found necessary, so that while
the concrete force was at work at one lock, the carpenters and helpers
were erecting the mixer at the next lock. The facing was mixed by hand.
After turning over the dry cement and sand at least twice with shovels,
the mixture was then cast through a No. 5 sieve, after which the water
was incorporated slowly by the use of a sprinkling can so as to avoid
washing. The secret of good concrete, after the selection of good
materials, is thorough mixing and hard tamping. Each batch of concrete,
consisting of about 1.2 cu. yds. in place, was turned in the mixer for
not less than 2 mins. at the rate of 9 revolutions per minute. The
amount of tamping is indicated by the fact that about 16 men out of 72
on each shift did nothing but tamp. The rammers used were 6 ins. square
and weighed 33 lbs. The bottom of the rammer consisted of three ridges,
each 1-in. in height, so as to make more bond between the successive
layers.
"On the eastern section the top of the lock walls was higher above the
ground, as a rule, than at the Milan locks, and the cars were run up an
incline with a small hoisting engine. A 15-HP. portable engine and
boiler operated the bucket hoist from one pulley, the mixer from the
other pulley, and also furnished steam for the hoist which pulled the
cars up the incline. The incline made an angle of about 30° with the
ground. The practice of carrying on two sections at once was continued
the same as on the western section. Each main wall was systematically
divided into 11 sections, making each section about 20 ft. long. The
corners of the coping were dressed to a quadrant of about 3 ins. radius
with a round trowel like those used on cement walks. In fact, the whole
method of finishing the coping was the same as is used on concrete
walks. The mortar was put on rather wet and then allowed to stand for
about 20 mins. before finishing. This allowed the water to come to the
surface and prevented the formation of the fine water cracks which are
sometimes seen on concrete work. After its final set the coping was
covered with several inches of fine gravel which was kept wet for at
least a week.
"The last concrete laid during the season was in November, on Lock No.
21, and Aqueducts Nos. 2 and 3. Portions of these structures were built
when the temperature was below freezing. The water was warmed to about
60° or 70° F., by discharging exhaust steam into the tank. Salt was used
only in the facing, simply sufficient to make the water taste saline.
The maximum amount used on the coldest night when the temperature was
about 20° F. was 1½ per cent.
The concrete force on each shift was as follows:
Men.
Filling and pushing stone car 10
Filling and pushing gravel car 8
Measuring cement 3
Measuring water and cleaning bucket 2
Dumping bucket on top platform 2
Operating mixer 2
Loading concrete cars 1
Pushing and dumping cars on forms 3
Switchmen on forms 2
Spreading concrete in forms 12
Tamping concrete in forms 16
Mixing facing 3
Water boys 2
--
Total laborers 66
Operating hoists 2
Finishing coping 2
Fireman 1
Sub-overseers 2
Overseer 1
--
Total force 74
The cost of material and labor at Lock No. 15 (10-ft. lift), which
contains 2,559 cu. yds. of concrete, was as follows:
Materials. Per cu. yd.
0.56 bbl. Portland cement (0.96 per cu. yd.) $1.42
0.64 bbl. Utica cement (1.58 per cu. yd.) .30
0.58 cu. yd. stone 1.15
0.60 cu. yd. gravel .52
14 ft. B. M. lumber[F] at $15 per M. .21
0.6 lb. spikes .01
Coal (10 tons in all, at $1.70) .01
0.35 gal. kerosene .03
-----
Total materials $3.65
Labor.
Erecting forms ($7 per M.) .45
Removing forms ($2 per M.) .13
Erecting and removing mixer ($161) .06
Loading and unloading materials at yards and lock sites .23
Track laying ($86) .03
Train service (narrow gage road) .09
Delivering materials to mixer .28
Mixing concrete .11
Depositing concrete .21
Tamping concrete .21
Mixing, depositing and tamping, 69 cu. yds. face mortar
($160) .23
General construction ($553) .22
-----
Total labor $2.25
[Footnote F: The lumber was used nearly five times, which accounts for
its low cost per cu. yd.]
There were 1,430 cu. yds. of Portland cement concrete. 69 cu. yds. of
Portland cement mortar facing, and 1,059 cu. yds. of Utica cement
concrete. The Portland concrete cost $6.43 per cu. yd.; the Utica
concrete, $4.77 per cu. yd. The following is the cost of labor on Lock
No. 20 (11-ft. lift.; 2,750 cu. yds.):
Per cu. yd.
Erecting forms ($7 per M.) $.434
Removing forms ($1.70 per M.) .113
Erecting and removing mixer ($151) .058
Loading and unloading at yards, lock sites, etc. .614
Tracks .024
Train service (narrow gage) .016
Pumping .114
Delivering material to mixer .288
Mixing concrete .134
Depositing concrete .205
Tamping concrete .192
Mixing, depositing and tamping, 85 cu. yds. face
mortar .071
General construction .246
------
Total $2.509
~COST OF HAND MIXING AND PLACING, CANAL LOCK FOUNDATION.~--Mr. Geo. P.
Hawley gives the following record of mixing and placing 4,000 cu. yds.
of 1-4½ gravel concrete for the foundation of a lock constructed for the
Illinois and Mississippi Canal in 1897. The concrete was mixed on
14×16-ft. board platforms, from which it was shoveled directly into
place. The materials were brought to the board in wheelbarrows. Two
boards were used, the usual gang for each being 4 men wheeling gravel, 4
men mixing, 1 man sprinkling, 2 men depositing and leveling and 2 men
tamping. The two gangs were worked against each other. Ten hours
constituted a day's work, and the average time and cost per cubic yard
for mixing and placing were:
Cts.
Foreman, 0.21 hr., at 30 cts 6.30
Laborers, 3.339 hrs., at 15 cts 50.09
Pump runner, 0.129 hr., at 20 cts 3.58
Water boy, 0.087 hr., at 7½ cts 0.65
-----
Total labor per cu. yd., cents. 60.62
~BREAKWATER AT MARQUETTE, MICH.~--The breakwater extends out from the
shore and consists of a prism of concrete resting on timber cribs filled
with stone. Originally the cribs carried a timber superstructure; this
was removed to give place to the concrete work. A typical cross-section
of the concrete prism is shown by Fig. 77; the prism is 23 ft. wide on
the base. Farther in shore the base width was reduced to 20 ft., and in
the shore section the prism was changed to a triangular trapezoid by
continuing the first slope to the bottom cutting off the berm and second
slope. The wooden structure was removed to a level 1 ft. below mean low
water and on it a concrete footing approximately 2 ft. thick was
constructed for the prism proper. This footing reached the full width of
the crib and was constructed in various ways during the 5 years through
which the work continued. At first the footing concrete was deposited
loose under water by means of bottom dumping buckets; later the stone
filling of the cribs was simply leveled up by depositing concrete in
bags, and last toe and heel blocks were molded and set flush with the
sides of the crib and filled between. Methods of construction and
records of cost are reported for portions only of the work and these are
given here.
[Illustration: Fig. 77.--Cross Section of Marquette Breakwater.]
_Footing Placed under Water with Buckets._--Besides the material track
which was constructed along the old wooden structure the plant
consisted of a mixing scow and a derrick scow, which were moored
alongside the work. The sand, stone and cement were brought out in cars
between working hours and stored on the mixing scow, enough for one
day's work at a time. The derrick handled a 40-cu. ft. bottom dump
bucket, which sat in a well on the mixing scow with its top flush with
the deck. The concrete was mixed by hand on the deck and shoveled into
the bucket; the bucket was then handled by the derrick to the crib and
lowered and dumped under water. The gang consisted of 24 men, 1 foreman,
1 master laborer, 14 men shoveling and mixing, 3 men wheeling materials,
1 derrick man and 3 men placing and depositing concrete. No record of
output of this gang is available. The cost of the concrete in place with
wages $1.25 to $1.40 per day for common labor is given as follows:
Materials. Per cu. yd.
1.21 bbls. (459 lbs.) cement at $2.20 $2.657
1 cu. yd. stone at $1.58 1.580
0.5 cu. yd. sand at $0.50 0.250
2.02 lbs. burlap at $0.037 0.075
Twine and needles 0.005
------
Total materials $4.567
Labor.
Loading scow with materials $0.4114
Mixing concrete 0.8459
Depositing concrete 0.5242
-------
Total labor $1.7815
Grand total $6.348
These figures are based on some 757 cu. yds. of concrete footing. In
explanation of the items of burlap, etc., it should be said that the
cribs were carpeted with burlap to prevent waste of concrete into the
stone fill.
[Illustration: Fig. 78.--Cross Section of Marquette Breakwater Showing
Manner of Constructing Footing with Bags of Concrete.]
_Leveling Off Cribs with Concrete in Bags._--The sketch, Fig. 78, shows
the method of leveling off the cribs with concrete in bags. The concrete
was mixed by hand on shore and filled into 8-oz. burlap bags, 6 ft. long
and 80 ins. around, holding 2,000 lbs. The bags were filled while lying
in position in a skip holding one bag. A skip was lifted by gallows
frame and tackle onto a car and run out to the work where the derrick
scow handled the skip to the crib, lowered it into the water and dumped
the bag. The cost of making and placing some 375 cu. yds. of concrete in
bags is given as follows:
Materials. Total. Per cu. yd.
453 bbls. cement at $2.627 $1,190.03 $3.173
375 cu. yds. stone at $1.619 607.13 1.619
180 cu. yds. sand at $0.392 70.56 0.188
3,220 yds. burlap at $0.03304 106.39 0.283
Twine and needles 6.36 0.017
--------- ------
Total materials $1,980.47 $5.280
Labor Mixing.
108 hrs. master laborer at $0.21-7/8 $ 23.42 $0.062
1,750 hrs. labor at $0.175 306.25 0.816
Superintendence 12.55 0.033
-------- ------
Total labor mixing $ 342.22 $0.911
Labor transporting.
306 hrs. labor at $0.175 $ 53.55 $0.142
Superintendence 5.25 0.014
-------- ------
Total labor transporting. $ 58.80 $0.156
Labor Depositing.
108 hrs. engineman at $0.25 $ 27.00 $0.072
108 hrs. master laborer at $0.21-7/8 23.42 0.062
510 hrs. labor at $0.175 89.25 0.238
Superintendence 13.25 0.035
-------- ------
Total labor depositing $ 152.92 $0.407
Grand total labor $ 553.94 $1.477
Grand total materials and labor $2,534.41 $6.757
_Molding Footing Blocks._--The blocks used at the toe of the prism were
of the form and dimensions shown by Fig. 79. They were molded in a
temporary shed heated to 50° to 65° F., and provided with a 2×8-in.
dressed plank floor on 12×12-in. sills. The floor formed the bottoms of
the block molds. Four molds were used, each consisting of four sides.
Three laborers molded one block, 2.22 cu. yds. per day, wheeling,
mixing, erecting and removing forms, placing concrete and doing all
other work. The cost of making 40 blocks was recorded as follows:
Materials. Total. Per cu. yd.
126 bbls. cement at $2.75 $346.50 $3.893
88.9 cu. yds. screenings at $1.10 97.79 1.098
40.1 cu. yds. sand at $0.45 18.04 0.203
5 gals. oil at $0.65 3.25 0.036
------- ------
Total materials $465.58 $5.230
Labor.
1,000 hrs. labor at $0.125 $125.00 $1.404
Watchman 29.15 0.327
Labor cutting wood for fuel 23.80 0.267
Superintendence 42.66 0.480
------- ------
Total labor $220.61 $2.478
Total labor and materials $686.19 $7.708
[Illustration: Fig. 79.--Details of Toe Blocks for Footing, Marquette
Breakwater.]
_Molding Concrete Prism in Place._--The concrete prism was molded in
alternate sections 10 ft. long; the form for the isolated sections
consisted of eight pieces so constructed that when assembled in place
and secured with bolts and turnbuckles the form was self-contained as to
strength and required no outside support or bracing. The form once in
place, all that remained to be done was to fill it, the block with the
gallery through it being molded in one operation. The forms for the
connecting blocks consisted of two slope panels, a panel for the harbor
face and the gallery form, the blocks previously molded making the other
sides of the form. The concrete was mixed by hand on shore, conveyed to
the work in 1 cu. yd. cars and shoveled into the forms, where it was
rammed with 35-lb. rammers. The following record covers 1,231 cu. yds.
of concrete prism. In this concrete some 214 cu. yds. of rubble stone
were embedded. The costs given are as follows:
Per
Materials-- Total. cu. yd.
1,780 bbls. natural cement at $1.068 $1,901.04 $1.545
963½ cu. yds. stone at $1.619 1,559.91 1.267
53½ cu. yds. screenings at $0.392 20.97 0.017
485.6 cu. yds. sand at $0.392 190.36 0.154
Miscellaneous materials 78.15 0.063
--------- ------
Totals $3,750.43 $3.046
Labor Mixing--
254 hrs. master laborer at $0.21-7/8 $ 55.56 $0.045
4,470 hrs. labor at $0.175 782.42 0.635
Superintendence 18.20 0.015
-------- ------
Total labor mixing $ 856.18 $0.695
Labor Transporting and Placing--
35 days overseer at $2.33-1/3 $ 81.67 $0.066
1,949 hrs. labor at $0.175 342.07 0.277
Superintendence 34.98 0.028
------- ------
Total labor transporting and placing $ 458.72 $0.371
Grand total, labor $1,314.90 1.066
Total labor and materials $5,065.33 4.112
No charge is made under materials for rubble stone as the only cost for
this was cost of handling and this is included in transporting and
placing.
~BREAKWATER, BUFFALO, N. Y.~--The following methods and costs of mixing
and placing some 2,561 cu. yds. of concrete are given by Mr. Emile Low,
for 10 parapet wall sections and 17 parapet deck sections for a
breakwater at Buffalo, N. Y.
The concrete used was a 1 cement, 1 gravel, 1 sand grit and 4 unscreened
broken stone. One bag of cement was assumed to measure 0.9 cu. ft. The
voids in the sand grit and gravel were 27 per cent. and in the
unscreened stone 39 per cent. The hardened concrete weighed 152 lbs. per
cu. ft.
[Illustration: Fig. 80.--Sketch Plan of Concrete Mixing Plant for
Buffalo Breakwater.]
Figure 80 shows the arrangement of the mixing plant. The mixer was a
5-ft. cube mixer holding 125 cu. ft., mounted on a trestle and operated
by a 9×12-in. horizontal engine taking steam from a 4×10-ft. locomotive
boiler, also supplying steam to two derrick engines. The material scow
contained two pockets for sand, one for gravel and one housed over for
cement. Two inside cement men passed out the bags in lots of six to one
outside cement man who cut and emptied them into the charging bucket.
Three sand shovelers each loaded a 3.6 cu. ft. barrow and wheeled them
tandem to the bucket, and two gravel men each loaded a 2.7 cu. ft.
barrow and wheeled them tandem to the bucket. The broken stone was
loaded by eight shovelers into another bucket, also containing 21.6 cu.
ft. The two buckets were alternately hoisted and emptied into the mixer
hopper, there being a dump man on the mixer who dumped the buckets and
attended to the water supply. A charger put the mixer in operation and
when the charge was mixed the car men dumped it into a skip resting on
a small car which was then run out on the track under the mixer to the
derrick which handled the skip to the work. Derrick A handled the
materials from the scows and derrick B handled the mixed concrete. The
force on the derricks consisted of two enginemen, four tagmen and the
fireman.
The ten parapet wall sections containing 841 cu. yds. were built in 46
hours, making 17 batches of 1.07 cu. yds., or 18.2 cu. yds. placed per
hour. The 17 parapet deck sections containing 1,720 cu. yds. were built
in 88 hours, making 18.8 batches of 1.08 cu. yds., or 19.5 cu. yds.
placed per hour. For the parapet deck work the force was increased by 2
men handling materials and 1 man on the mixer. The labor cost of mixing
and placing the concrete was as follows:
Per Per
Loading Gang-- day. cu. yd.
1 assistant foreman 2.00 $0.011
3 cement handlers 5.25 0.029
3 sand shovelers 5.25 0.029
2 gravel shovelers 3.50 0.020
8 stone shovelers 14.00 0.076
1 hooker on 1.75 0.010
------ ------
Totals $31.75 $0.175
Mixer Gang--
1 dumpman $ 1.75 $0.010
1 charging man 1.75 0.010
2 car men 3.50 0.020
2 enginemen at $3.25 6.50 0.035
4 tagmen at $2 8.00 0.044
1 fireman 2.00 0.011
------ ------
Totals $23.50 $0.130
Wall Gang--
1 Signalman $ 1.75 $0.010
1 dumper 1.75 0.010
6 shovelers at $2 12.00 0.065
4 rammers 7.00 0.038
1 foreman 4.00 0.022
------ -----
Totals $26.50 $0.145
Grand totals $81.75 $0.450
[Illustration: Fig. 81.--Concrete Blocks for Pier at Port Colborne
Harbor.]
[Illustration: Fig. 82.--Forms for Molding Blocks, Port Colborne Harbor
Pier.]
[Illustration: Fig. 83.--Device for Handling Blocks, Port Colborne
Harbor Pier.]
~PIER CONSTRUCTION, PORT COLBORNE, ONT.~--In constructing the new harbor
at Port Colborne, Ont., on Lake Erie, the piers consisted of parallel
rows of timber cribs set the width of the pier apart and filled in and
between with stone blasted and dredged from the lake bottom in deepening
the harbor. The tops of the cribs terminated below water level and were
surmounted by concrete walls set on the outer edges. These walls were
filled between with stone and the top of the filling was floored part
way or entirely across, as the case might be, with a thick concrete
slab. The footings of the walls to just above the water level were made
of concrete blocks 4½×4×7 ft., constructed as shown by Fig. 81. The wall
above the footing course and the floor slab were of concrete molded in
place. The concrete work consisted of molding and setting concrete
blocks and of molding concrete wall and slab in place.
The blocks were molded on shore, shipped to the work on scows and set in
place by a derrick. Figure 82 shows the construction of the forms for
molding the blocks; the bottom tie rods passed through the partitions
forming the ends of the molds. The sides were removed in 48 hours and
used over again. Figure 83 shows the hooks used for handling the molded
blocks. Considerable trouble was had in setting these blocks level and
close jointed, owing to the difficulty of leveling up the stone filling
under water.
[Illustration: Fig. 84.--Scow Plant for Mixing and Placing Concrete,
Port Colborne Harbor Pier.]
The mass concrete was mixed and placed by the scow plant, shown by Fig.
84. The scow was loaded with sufficient sand and cement for a day's work
and towed to and moored alongside the pier. Forms were set for the wall
on top of the block footing. These forms were placed in lengths of 60 to
75 ft. of wall and resembled the block forms with partitions omitted.
The bottoms of the rear uprights were held by being wedged into the
grooves in the blocks, and the bottoms of the front uprights were held
by bolts resting on top of the blocks. The tops of the uprights were
held together across the wall by tie bolts. The forms being placed, the
mode of procedure was as follows:
The crusher fed directly into a measuring box. After some 6 ins. of
stone had run into the box the door of the crusher spout was closed. A
wheelbarrow load of sand was spread over the stone in the box and over
this were emptied and spread two or three bags of cement. Another layer
of stone and then of sand and of cement were put in and these operations
repeated until the box was full. The box was then hoisted and dumped
into the hopper of a gravity mixer of the trough type which ran along a
track on the scow and fed directly into the forms. The gang worked
consisted of 1 foreman, 1 derrickman and 18 common laborers. This gang
placed from 65 to 75 cu. yds. of concrete per day at a labor cost of 50
cts. per cu. yd.
[Illustration: Fig. 85.--Cross-Section of Concrete Pier, Superior, Wis.]
~CONCRETE BLOCK PIER, SUPERIOR ENTRY, WIS.~--The methods and cost of
constructing a concrete pier 3,023 ft. long and of the cross-section
shown by Fig. 85 at Superior entry, Wisconsin, are given in the
following paragraphs.
_Molds and Molding._--About 80 per cent. of the concrete was deposited
in molds under water, according to a plan devised by Major D. D.
Galliard, corps of engineers. In brief the concrete was built in place
in two tiers of blocks, the lower tier resting directly on piles and
being entirely under water and the upper tier being almost entirely
above water. As shown by Fig. 85, a pile trestle was built on each side
of the proposed pier and a traveler for raising and lowering the molds
spanned the space between trestles.
The molds were bottomless boxes built in four pieces, two sides and two
ends, held together by tie rods. Fig. 86 shows an end and a side of one
of the shallow water molds and Fig. 87 shows in detail the method of
fastening the end to the side. It will be seen that the 1¼-in.
turnbuckle rods pass through the ends of beams that bear against the
outside of the mold. These tie rods have eyes at each end in which rods
with wedge-shaped ends are inserted. The molds were erected on the
trestle by a locomotive crane and were then lifted by the mold traveler,
carried and lowered into place. The largest one of these molds with its
iron ballast, weighed 40 tons. To remove a mold, after the block had
hardened, the nuts on the wedge-ended rods were turned, thus pulling the
wedge end from the eye of the tie rod and releasing the sides of the
mold from the ends. The locomotive crane then raised the ends and sides,
one at a time, and assembled them ready to be lowered again for the next
block. The time required to remove one of these 40-ton molds, reassemble
and set it again rarely exceeded 60 minutes and was sometimes reduced to
45 minutes.
[Illustration: Fig. 86.--Mold for Concrete Block for Pier at Superior,
Wis.]
The concrete was deposited in alternate blocks and the molds described
were for the first blocks; for the intermediate blocks molds of two side
pieces alone were used, the blocks already in place serving in lieu of
end pieces. The two side pieces were bolted together with three tie rods
at each end; the tie rods were encased in a box of 1-in. boards 4×4 ins.
inside which served as a strut to prevent the sides from closing
together and as a means of permitting the tie rods to be removed after
the concrete had set. The mold was knocked down just as was the full
mold described above and the boxes encasing the tie rods were left in
the concrete.
[Illustration: Fig. 87.--Device for Locking End and Side of Mold for
Concrete Blocks for Pier at Superior, Wis.]
An important feature was the device for handling the molds; this, as
before stated, was a traveler, which straddled the pier site, it having
a gage of 31 ft. It carried a four-drum engine, the drums of which were
actuated, either separately or together, by a worm gear so as to operate
positively in lowering as well as in raising. The load was hung from
four hooks, depending by double blocks and 5/8-in. wire rope from four
trolleys suspended from the trusses of the traveler; this arrangement
allowed a lateral adjustment of the mold. The hoisting speed was 6 ft.
per minute and the traveling speed 100 ft. per minute. The locomotive
crane also deserves mention because it was mounted on a gantry high
enough to permit material cars to pass under it on the same trestle,
thus making it practicable to work two cranes.
[Illustration: Fig. 88.--Bucket for Depositing Concrete Under Water for
Pier at Superior, Wis.]
The concrete was received from the mixer into drop bottom buckets of the
form shown by Fig. 88. The buckets were taken to the work four at once
on cars, and there lifted by the locomotive crane and lowered into the
mold where they were dumped by tripping a latch connected by rope to the
crane. To prevent the concrete from washing, the open tops of the
buckets were covered with 3×4 ft. pieces of 12-oz. canvas in which were
quilted 110 pieces of 1/16×1×3-in sheets of lead. Two covers were used
on each bucket and were attached one to each side of the bucket top so
as to fold over the top with a lap. This arrangement was entirely
successful for its purpose.
_Concrete Mixing._--The proportions of the subaqueous concrete were
1-2½-5 by volume, or 1-2.73-5.78 by weight, cement being assumed to
weigh 100 lbs. per cu. ft.; the proportions of the superaqueous concrete
were 1-3.12-6.25 by volume, or 1-3.41-7.22 by weight. The dry sand
weighed 109.2 lbs. per cu. ft., the voids being 35.1 per cent.; the
pebbles weighed 115.5 lbs. per cu. ft., the voids being 31 per cent.
The pebbles for the concrete were delivered by contract and were
unloaded from scows by clam-shell bucket into a hopper. This hopper fed
onto an endless belt conveyor which delivered the pebbles to a rotary
screen. Inside this screen water was discharged under a pressure of 60
lbs. per sq. in. from a 4-in. pipe to wash the pebbles. From the screen
the pebbles passed through a chute into 4-cu. yd cars which were hauled
up an incline to a height of 65 ft. by means of a hoisting engine. The
cars were dumped automatically, forming a stock pile. Under the stock
pile was a double gallery or tunnel provided with eight chutes through
the roof and from these chutes the cars were loaded and hauled by a
hoisting engine up an inclined trestle to the bins above the concrete
mixer. The sand was handled from the stock pile in the same manner. The
cement was loaded in bags on a car in the warehouse, hauled to the mixer
and elevated by a sprocket chain elevator.
Chutes from the bins delivered the materials into the concrete mixer,
which was of the Chicago Improved Cube type, revolving on trunnions
about an axial line through diagonal corners of the cube. The mixer
possessed the advantage of charging and discharging without stopping. It
was driven by a 7×10-in. vertical engine with boiler. The mixer
demonstrated its ability to turn out a batch of perfectly mixed concrete
every 1-1/3 minutes. It discharged into a hopper provided with a cut-off
chute which discharged into the concrete buckets on the cars.
_Labor Force and Costs._--In the operation of the plant 55 men were
employed, 43 being engaged on actual concrete work and 12 building molds
and appliances for future work. The work was done by day labor for the
government and the cost of operation was as follows for one typical
week, when in six days of eight hours each, the output was 1,383 cu.
yds., or an average of 230 cu. yds. per day. The output on one day was
considerably below the average on account of an accident to the plant,
but this may be considered as typical.
Pebbles from Stock Pile to Mixer-- Per cu. yd.
4 laborers at $2 $0.0348
1 engineman at $3 0.0131
Coal, oil and waste at $1.03 0.0043
Sand from Stock Pile to Mixer--
5 laborers at $2 $0.0434
1 engineman at $2.50 0.0109
Coal, oil and waste at $0.82 0.0035
Cement from Warehouse to Mixer--
5 laborers at $2 $0.0434
Mixing Concrete--
1 engineman at $2.50 $0.0109
1 mechanic at $2.50 0.0108
Coal, oil and waste at $1.29 0.0056
Transporting Concrete--
4 laborers at $2 $0.0348
1 engineman at $3 0.0130
Coal, oil and waste at $0.66 0.0028
Depositing Concrete in Molds--
4 laborers at $2 $0.0348
1 engineman at $3 0.0130
1 rigger at $3 0.0130
Coal, oil and waste at $1.18 0.0051
Assembling, Transporting, Setting and Removing Molds--
4 laborers at $2 $0.0347
1 engineman at $3.25 0.0141
1 carpenter at $3 0.0130
1 mechanic at $2.50 0.0109
Coal, oil and waste at $1.39 0.0060
Care of Tracks--
1 laborer at $2 $0.0086
1 mechanic at $2.50 0.0109
Supplying Coal--
3 laborers at $2 $0.0260
Blacksmith Work--
1 laborer at $2 $0.0086
1 blacksmith at $3.25 0.0141
1 waterboy at $0.75 0.0032
-------
Total per cubic yard $0.4473
Add 75% of cost of administration 0.1388
-------
Total labor per cu. yd. $0.5861
The total cost of each cubic yard of concrete in place was estimated to
be as follows:
Per cu. yd.
Ten-elevenths cu. yd. pebbles at $1.085 $0.9864
Ten-twenty seconds cu. yd. sand at $0.00 0.0000
1 26 bbls. cement at $1.77 2.2302
Labor as above given 0.5861
Cost of plant distributed over total yardage 0.8400
-------
Total $4.6427
It will be noted that the sand cost nothing as it was dredged from the
trench in which the pier was built, and paid for as dredging. The cost
of the plant is distributed over this south pier and over the proposed
north pier work on the basis of only 20 per cent. salvage value after
the completion of both piers. It is said, however, that 80 per cent. is
too high an allowance for the probable depreciation.
~DAM, RICHMOND, INDIANA.~--The dam shown in cross-section in Fig. 89 was
built at Richmond, Ind. It was 120 ft. long and was built between the
abutments of a dismantled bridge. The concrete was made in the
proportion of 1 bbl. Portland cement to 1 cu. yd. of gravel; old iron
was used for reinforcement. The foundations were put down by means of a
cofferdam which was kept dry by pumping. On completion it was found that
there was a tendency to scour in front of the apron and accordingly
piling was driven and the intervening space rip-rapped with large
stone. Labor was paid as follows per day: Foreman, $3; carpenter, $2.50;
cement finisher, $2; laborers, $1.50. The concrete was mixed by hand and
wheeled to place in wheelbarrows. The cost of the work was as follows:
Materials-- Per cu. yd.
204 bbls. cement at $1.60 $1.485
Sand and gravel 0.800
Lumber 0.610
Tools, hardware, etc. 0.445
------
Total materials $3.34
Labor--
Clearing and excavating $0.96
Setting forms and mixing concrete 1.01
Pumping 0.27
-----
Total labor $2.24
Total materials and labor $5.58
[Illustration: Fig. 89.--Concrete Dam at Richmond, Ind.]
~DAM AT ROCK ISLAND ARSENAL, ILLINOIS.~--The dam was in the shape of an L
with one side 192 ft. and the other side 208 ft. long; it consists of a
wall 30½ ft. high, 3½ ft. wide at the top and 6½ ft. wide at the bottom
with a counterfort every 16 ft., 26 in all. Each counterfort extended
back 16 ft. and was 4 ft. thick for a height of 6 ft. and then 3 ft.
thick. There were 3,500 cu. yds. of concrete in the work, which was done
by day labor under the direction of the U. S. Engineer in charge.
The forms consisted of front and back uprights of 8×10-in. stuff 24 ft.
high, connected through the wall by ¾-in. rods which were left in the
concrete. The lagging was 2×12-in. plank dressed down 1¾ ins. placed
inside the uprights. These forms were built full height in 16-ft.
sections with a counterfort coming at the center of each section. Each
section contained 95 cu. yds. of concrete and was filled in a day's
work. The concrete was a 1-4-7 mixture wet enough to quake when rammed.
Run of crusher limestone was used of which 50 per cent. passed a 1-in.
sieve, 17 per cent. a No. 3 sieve and 9 per cent. a No. 8 sieve. The
concrete was mixed in Cockburn Barrow & Machine Co.'s screw-feed mixer
which discharged into 2-in. plank skips 2 ft. wide 5-1/3 ft. long and 14
ins. deep, holding ¼ cu. yd. These skips were taken on cars to a derrick
crane overhanging the forms and by it hoisted and dumped into the forms.
The derrick was moved along a track at the foot of the wall as the work
progressed. The concrete was spread and rammed in 6-in. layers. The men
were paid $1.50 per 8-hour's work and the work cost including footing,
as follows:
Item-- Total. Per cu. yd.
Cement $1,500.00 $0.429
Sand 400.00 0.114
Storing and hauling cement 460.00 0.131
Taking sand from barge to mixer 96.00 0.027
Crushing stone 1,450.00 0.414
Mixing concrete 4,825.00 1.378
Placing concrete 1,670.00 0.477
Lumber for forms, etc. 600.00 0.171
Erecting and taking down forms 2,450.00 0.700
---------- ------
Totals $13,451.00 $3.841
~DAM AT McCALL FERRY, PA.~--The dam was 2,700 ft. long and 48 ft. high of
the cross-section shown by Fig. 90 and with its subsidiary works
required some 350,000 cu. yds. of concrete. The plant for mixing and
placing the concrete was notable chiefly for its size and cost. Parallel
to the dam, which extended straight across the river, and just below its
toe a service bridge consisting of a series of 40-ft. concrete arch
spans was built across the river. This service bridge was 50 ft. wide
and carried four standard gage railway tracks besides a traveling crane
track of 44 ft. gage. This very heavy construction of a temporary
structure was necessitated by the frequency of floods against which only
a solid bridge could stand; it was considered cheaper in the long run to
provide a bridge which would certainly last through the work than to
chance a structure of less cost which would certainly go out with the
floods. The concrete service bridge was designed to be destroyed by
blasting when the dam had been completed. The method of construction was
to build the dam in alternate 40 ft. sections, mixing the concrete on
shore, taking it out along the service bridge in buckets on cars and
handling the buckets from cars to forms by traveling cranes.
[Illustration: Fig. 90.--Steel Forms for McCall Ferry Dam.]
The concrete mixing plant is shown by Fig. 91. Cars loaded with cement,
sand and stone were brought in over the tracks carried on the wall tops
of the bins and were unloaded respectively into bins A, B and C,
of which there were eight sets. Each set supplied material by means of
measuring cars to a 1 cu. yd. Smith mixer. Two sets of cars were used
for each mixer so that one could be loading while the other was
charging. The mixers discharged into 1 cu. yd. buckets set two on a car
and eight cars were hauled to the work in train by an 18-ton "dinky." At
the work the buckets were picked up by the traveling cranes and the
concrete dumped into the forms. Figure 90 shows the construction of the
steel forms. Six sets of forms were used. Each set consisted of five
frames spaced 10 ft. apart and braced together in the planes parallel to
the dam, and each set molded 40 ft. of dam. The lagging consisted of
wooden boxes 8½ ft. wide and 10 ft. long. For the vertical face of the
dam these boxes were attached by bolts to the vertical post, for the
curved face they were bolted to a channel bent to the curve and held by
struts from the inclined post of the steel frame.
[Illustration: Fig. 91.--Concrete Mixing Plant for McCall Ferry Dam.]
In construction the footing and the body of the dam to an elevation of 5
ft. above the beginning of the curve were built continuously across the
river; above this elevation the dam was built in alternate 40-ft.
sections. The strut back to the service bridge shown in the lower right
hand corner of Fig. 90, shows the manner of bracing the first 30-ft.
section of the inclined post to hold the lagging for the continuous
portion. The lagging was added a piece at a time as concreting
progressed. The ends of each set of frames for a 40-ft. section were for
the isolated sections closed by timber bulkheads carrying box forms to
mold grooves into which the concrete of the intermediate sections would
bond.
[Illustration: Fig. 92.--Traveler for Concreting Dam, Chaudiere Falls,
Quebec.]
The concrete used was a 1-3-5 mixture, the stone ranging in size from 2
to 5 ins. Rubble stone from one man size to ½ ton were bedded in the
concrete. The capacity of the concrete plant was 2,000 cu. yds. per day
or about 250 cu. yds. per mixer per 10-hour day.
~DAM, CHAUDIERE FALLS, QUEBEC.~--The dam was 800 ft. long and from 16 to
20 ft. high, constructed of 1-2-4 concrete with rubble stone embedded.
The rubble stones were separated at least 9 ins. horizontally and 12
ins. vertically and were kept 20 ins. from faces. At one point the
rubble amounted to 40 per cent. of the volume, but the average for the
dam was 25 to 30 per cent. The stone was broken at the work, some by
hand, but most by machine, all to pass a 2-in. ring. Hand-broken stone
ran very uniform in size and high in voids, often up to 50 per cent.
Stone broken by crusher with jaws 2 ins. apart would run 20 to 30 per
cent. over 2 ins. in size and give about 45 per cent. voids; with
crusher jaws 1½ ins. apart from 98 to 100 per cent. was under 2 ins. in
size and contained about 42 per cent. of voids. It was found that if the
crushers were kept full all the time the product was much smaller,
particularly with Gates gyratory crusher, though a little more than
rated power was required when the crusher was thus kept full. This
practice secured increased economy in both quantity and quality of
product. The concrete was made and placed by means of a movable traveler
shown by Fig. 92. Concrete materials were supplied to the charging
platform of the traveler by means of a traveling derrick moving on a
parallel track. In placing the concrete on the rock bottom it was found
necessary in order to secure good bond to scrub the rock with water and
brooms and cover it with a bed of 2 ins. of 1-2 mortar. The method of
concreting in freezing weather is described in Chapter VII.
CHAPTER XII.
METHODS AND COST OF CONSTRUCTING BRIDGE PIERS AND ABUTMENTS.
The construction of piers and abutments for bridges is best explained by
describing individual examples of such work. So far, in America, bridge
piers have been nearly always of plain concrete and of form and section
differing little from masonry piers; where reinforcement has been used
at all it has consisted of a surface network of bars introduced chiefly
to ensure monolithic action of the pier under lateral stresses. In
Europe cellular piers of reinforced concrete have been much used. Plain
concrete abutments differ little in form and volume from masonry
abutments. Reinforced concrete abutments are usually of L-section with
counterforts bracing the upright slab and bridge seat to the base slab.
Form work for reinforced abutments is somewhat complex; that for plain
abutments and piers is of simple character, the only variations from
plain stud and sheathing construction being in the forms for moldings
and coping and for cut-waters. For piers of moderate height the form is
commonly framed complete for the whole pier, but for high piers it is
built up as the work progresses by removing the bottom boards and
placing them at the top. Opposite forms are held together by wire ties
through the concrete. Movable panel forms have been successfully
employed, but they rarely cheapen the cost much. Sectional forms, which
can be shifted from pier to pier where a number of piers of identical
size are to be built, may frequently be used to advantage. An example of
such use is given in this chapter.
Derricks are the recognized appliances for hoisting and placing the
concrete in pier work; they are the only practicable appliance where the
pier is high and particularly where it stands in water and mixing barges
are employed. For abutment work and land piers of moderate height
derricks and wheelbarrow or cart inclines are both available and where
much shifting of the derricks is involved the apparently more crude
method compares favorably in cost.
The methods of placing concrete under water for pier foundations are
described in Chapter V, and the use of rubble concrete for pier
construction is illustrated by several examples in Chapter VI. The
following examples of pier and abutment construction cover both large
and small work and give a clear idea of current practice.
[Illustration: Fig. 93.--Pier and Cofferdam for a Railway Bridge.]
~COST OF CONSTRUCTING RECTANGULAR PIER FOR A RAILWAY BRIDGE.~--This pier,
Fig. 93, was built in water averaging 5 ft. deep. The cofferdam
consisted of triple-lap sheet piling, of the Wakefield pattern, the
planks being 2 ins. thick, and spiked together so as to give a cofferdam
wall 6 ins thick. The cofferdam enclosed an area 14×20 ft., giving a
clearance of 1 ft. all around the base of the concrete pier, and a
clearance of 2 ft. between the cofferdam and the outer edge of the
nearest pile. The cofferdam sheet piles were 18 ft. long, driven 11 ft.
deep into sand, and projecting 2 ft. above the surface of the water.
The concrete base resting on the foundation piles was 12×18 ft. The
concrete pier resting on this base was 7×13 ft. at the bottom, and 5×11
ft. at the top. The pier supported deck plate girders. There were 100
cu. yds. of concrete in the pier and base.
The cost of this pier, which is typical of a large class of concrete
pier work, has been obtained in such detail that we analyze it in
detail, giving the costs of cofferdam construction and excavation as
well as of mixing and placing the concrete.
Setting up and taking down derrick and platform:
4 days foreman at $5.00 $ 20.00
¾ days engineman at $3.00 2.25
¾ days blacksmith at $3.00 2.25
¾ days blacksmith helper at $2.00 1.50
22 days laborers at $2.00 44.00
-------
Total $ 70.00
Cofferdam--
7 days foreman at $5.00 $ 35.00
4 days engineman at $3.00 12.00
38 days laborers at $2.00 76.00
1 ton coal at $3.00 3.00
-------
Total labor on 7,900 ft. B. M. at $16.00 $126.00
7,900 ft. B. M. at $20.00 158.00
-------
Total for 58 cu. yds. excavation $284.00
Wet Excavation--
1.8 days foreman at $5.00 $ 9.00
1.5 days engineman at $3.00 4.50
9 days laborers at $2.00 18.00
½ ton coal at $3.00 1.50
-------
Total labor on 58 cu. yds. at 57c. $ 33.00
Foundation Piles--
960 lin. ft. at 10c $ 96.00
4 days setting up driver and driving 24 piles at $20 per
day for labor and fuel 80.00
-------
Total $176.00
Concrete--
100 cu yds. stone at $1.00 $100.00
40 cu. yds. sand at $0.50 20.00
100 bbls. cement at $2.00 200.00
5 days foreman at $5.00 25.00
50 days laborers at $2.00 100.00
5 days engineman at $3.00 15.00
2 tons coal at $3.00 6.00
-------
Total, 100 cu. yds. at $4.66 $466.00
8 days carpenters at $3.00 24.00
2,400 ft. B. M. 2-in. plank at $25.00 60.00
1,000 ft. B. M. 4×6-in. studs at $20.00 20.00
Nails, wire, etc 2.00
-------
Total forms for 100 cu. yds. at $1.06 $106.00
Summary--
Setting up derrick, etc. $ 70.00
Cofferdam (7,900 ft. B. M.) 284.00
Wet excavation (58 cu. yds.) 33.00
Foundation piles (24) 176.00
Concrete (100 cu. yds.) 466.00
Forms (3,400 ft. B. M.) 106.00
---------
Total $1,135.00
Transporting plant 20.00
20 days rental of plant at $5.00 100.00
---------
Total cost of pier $1,252.00
Regarding the item of plant rental, it should be said that the plant
consisted of a pile driver, a derrick, a hoisting engine, and sundry
timbers for platforms. There was no concrete mixer. Hence an allowance
$5 per day for use of plant is sufficient.
It will be noted that no salvage has been allowed on the lumber for
forms. As a matter of fact, all this lumber was recovered, and was used
again in similar work.
Referring to the cost of cofferdam work, we see that, in order to
excavate the 58 cu. yds. inside the cofferdam, it was necessary to spend
$284, or nearly $5 per cu. yd. before the actual excavation was begun.
The work of excavating cost only 57 cts. per cu. yd., but this does not
include the cost of erecting the derrick which was used in raising the
loaded buckets of earth, as well as in subsequently placing the
concrete. The sheet piles were not pulled, in this instance, but a
contractor who understands the art of pile pulling would certainly not
leave the piles in the ground. A hand pump served to keep the cofferdam
dry enough for excavating; but in more open material a power pump is
usually required.
The above costs are the actual costs, and do not include the
contractor's profits. His bid on the work was as follows:
Piles delivered 12 cts. per ft.
Piles driven $5 each
Cofferdam $37 per M.
Wet excavation $1.00 per cu. yd.
Concrete $8.00 per cu. yd.
In order to ascertain whether or not these prices yielded a fair profit,
it is necessary to distribute the cost of the plant transportation and
rental over the various items. We have allowed $120 for plant
transportation and rental, and $70 for setting up and taking down the
plant, or $190 in all. The working time of the plant was as follows:
Per cent. Prorated
Days. of time. plant cost.
Cofferdam 7 39 $74
Excavation 2 11 21
Foundation piles 4 22 42
Concrete 5 28 53
-- --- ----
Totals 18 100 $190
As above given, the labor on the 7,900 ft. B. M. in the cofferdam cost
$126, or $16 per M.; but this additional $74 of prorated plant costs,
adds another $9 per M., bringing the total labor and plant to $25 per
M., to which must be added the $20 per M. paid for the timber in the
cofferdam, making a grand total of $45 per M. This shows that the
contractor's bid of $37 per M. was much too low.
The labor on the excavation cost 57 cts. per cu. yd., to which must be
added the prorated plant cost of $21 distributed over the 58 cu. yds.,
or 36 cts. per cu. yd., making a total of 93 cts. per cu. yd. This shows
that the bid of $1 per cu. yd. was hardly high enough.
The labor on the 24 foundation piles cost $80, or $3.33 each. The
prorated plant cost is $42, or $1.75 per pile, which, added to $3.33,
makes a total of $5.08. This shows that the bid of $5 Per pile for
driving was too low. However there was a profit of 2 cts. per ft., or 80
cts. per pile, on the cost of piles delivered.
The concrete amounted to 100 cu. yds. Hence the prorated plant cost of
$53 is equivalent to 53 cts. per cu. yd. Hence the total cost of the
concrete was:
Per cu. yd.
Cement, sand and stone $3.20
Foreman (at $5) 0.25
Labor (at $2) 1.00
Engineman (at $3) 0.15
Coal (at $3) 0.06
Carpenters (at $3) 0.24
Forms (at $23.50, used once) 0.80
Wire, nails, etc 0.02
Prorated plant cost 0.53
-----
Total $6.25
Since the contract price for concrete was $8 per cu. yd., there was a
good profit in this item.
~BACKING FOR BRIDGE PIERS AND ABUTMENTS.~--Six piers and two abutments of
the City Island bridge were constructed in 1906 at New York city, of
masonry backed with 1-2-4 concrete below and 1-3-5 concrete above high
water. The piers and abutments were all sunk to rock or hard material by
means of timber cofferdams. Table XVI gives the labor cost of mixing and
placing the concrete backing for one abutment and three piers, after the
materials were delivered on the scows. The concrete was mixed by a
rectangular horizontal machine mixer and deposited by 2-cu. yd. bottom
dump buckets handled by derrick scows and stiff leg derricks. The high
cost of concreting on Pier 2 was due to the fact that the concrete was
improperly deposited and had to be removed and the higher cost in
Abutment 1 was probably due to the fact that the abutment was so long
and narrow that it was difficult to handle the bucket.
TABLE XVI.--COST OF CONCRETE BACKING FOR MASONRY PIERS.
[Transcriber's note: Table split to be less than 80 column width]
Abutment No. 1. Pier No. 2.
Wages Cost Cost
per No. Total per No. Total per
Hour. hrs. Cost. cu. yd. hrs. Cost. cu. yd.
Superintendent 70 24 $16.80 $0.03 47 $32.90 $0.09
Foreman 35 160 56.00 0.09 128 44.80 0.13
Laborers 15-20 2555 383.25 0.65 2038 313.60 0.92
Engineman 30 365 109.50 0.19 196 58.50 0.19
Timekeeper 40 86 34.40 0.06 46 18.40 0.06
Pier No. 3. Pier No. 4.
Wages Cost Cost
per No. Total per No. Total per
Hour. hrs. Cost. cu. yd. hrs Cost. cu. yd.
Superintendent 70 72 $50.40 $0.05 16 $11.20 $0.03
Foreman 35 324 113.40 0.12 54 18.90 0.06
Laborers 15-20 3513 526.95 0.56 940 141.00 0.44
Engineman 30 244 73.20 0.08 60 18.00 0.06
Timekeeper 40 81 32.40 0.04 10 4.00 0.01
Summary.
Wages Total Total Av.
Hrs. cost. per cu. yd.
Superintendent 70 159 $111.30 $0.05
Foreman 35 666 233.10 0.11
Laborers 15-20 9046 1364.90 0.62
Engineman 30 865 259.50 0.12
Timekeeper 40 223 89.20 0.04
~PNEUMATIC CAISSONS, WILLIAMSBURG BRIDGE.~--Mr. Francis L. Pruyn, Assoc.
M. Am. Soc. C. E., gives the following costs of concreting the pneumatic
caissons for the Brooklyn tower of the Williamsburg bridge at New York
city. The work comprised the mixing and placing of some 13,637 cu. yds.
of concrete in two caissons. Table XVII shows the itemized costs for one
caisson and Table XVIII shows them for the other caisson. The methods of
work were as follows:
After each caisson was built it was towed to its proper site, where it
was held in place by temporary pile dock built completely around it. On
these docks the concrete was placed; a 2 cu. yd. cubical mixer of the
usual pattern being used for mixing. The concrete materials, consisting
of sand, stone and cement was handled direct from barges alongside, into
the mixer. The concrete was placed by a derrick located in the center of
the caisson, which was a bad feature as the caisson was usually out of
level and considerable difficulty was experienced in swinging the
derrick. On the South caisson ¾ cu. yd. bottom dump buckets were used in
placing the concrete, on the North caisson the size of these was
increased to 1½ cu. yd. which reduced the cost of placing 15 cts. per
cu. yd. There were placed in the South caisson 3,827 cu. yds. in 32 days
of actual working time--120 cu. yds. per day of 10 hrs. The gross time
was 2 months. On the North caisson 5,693 cu. yds. were placed in 46 days
worked--124 cu. yds. per day. The gross time was 4 months.
The rates of labor were as follows per 10-hour day:
Foreman $5.00
Assistant foreman 2.50
Hoisters 2.50
Fireman 1.60
Laborer 1.50
Proportions concrete were 1: 2.5: 6.
The low price of sand in the North caisson was brought about by the
finding of good building sand in the excavation for the anchorage, which
work was done by the same contractor.
When the caissons had been sealed the iron material shafts were removed.
This left holes 5 ft.×6 ft. extending from the roof of the caisson up
to Mean H.W. which were filled with concrete. These shaft holes were 80
ft. deep on the South caisson and 100 ft. deep on the North caisson.
They were partially filled with water and the concrete had to be placed
with considerable care. Wooden chutes were used on the South caisson;
they rested on the caisson roof, were filled with concrete and then
raised allowing concrete to flow out at the bottom. The shaft holes were
too deep on the North caisson for chutes and 20 cu. ft. bottom dump
buckets were used. They had to be lowered to bottom of shaft each trip
before dumping, a slow operation, which greatly added to the cost.
Proportion for concrete 1-2.5-6.
The proportion for concrete in working chamber was the same as for all
other concrete. The specifications called for 6 in. of mortar, of 1 part
of cement to 2½ parts of sand, between the concrete and all bearing
areas; that is, under the cutting edge and directly under the roof of
the working chamber. The concrete was mixed in the cubical mixer and
dumped on the bottom door of the material lock, the top door of the lock
was then closed, the bottom door opened and the concrete fell through
the shaft to the working chamber. It was then shoveled by the sand hogs
into place. A 6-in. space was left below all bearing surfaces into which
damp mortar was tightly rammed. Concreting the South caisson took 10¼
working days of 24 hours, the gangs working night and day in twelve
2-hour shifts; 1,566 cu. yds. of concrete and mortar were placed, or at
the rate of 140 cu. yds. per 24 hours. The gross time including Sundays
was 14½ days. The sand hogs worked in shifts of 2 hours each and
received $3.50 for the two hours work. The twelve foremen received 1
dollar more: the average gang consisted of 12 sand hogs.
On the North caisson the organization was much better, owing to the
experience gained on the first caisson; and in spite of the fact that
the sand hogs, on account of the increased depth, received $4.00 for 1½
hours' work, or an increase of $22.00 per man per 24 hrs. over that on
the South caisson, the work was done for less money. There were placed
1,566 cu. yds. of concrete in 7 working days of 24 hrs., or at the rate
of 224 cu. yds. per day. The gross time was 11½ days including Sundays.
The average number of men in the sand hog gangs was 18, with one
foreman, who received $5 for 1½ hours work.
TABLE XVII.--ITEMIZED COST OF CONCRETING SOUTH CAISSON FOR BROOKLYN
TOWER OF THE WILLIAMSBURG BRIDGE: COST OF CONCRETING CAISSONS ABOVE
ROOF.
South Caisson (3,827 cu. yds.).
Materials. Quantity. Rate. Amount.
Cement 4,480 bbls. $1.57 $7,034.00
Sand 1,288 cu. yds. .60 773.00
Broken stone 3,421 cu. yds. 1.50 5,132.00
Water 36.00
------- ------ ---------
Total 3,827 cu. yds. $3.39 $12,975.00
Labor.
Mixing and placing 3,827 cu. yds. $0.90 $3,432.00
Plant charges 2,280.00
Plant labor 742.00
------- ------ ---------
Total plant 3,827 cu. yds. $0.79 $3,022.00
------- ------ ---------
Total cost 3,827 cu. yds. $5.08 $19,429.00
General expenses, 10% 3,827 cu. yds. .51 1,943.00
------- ------ ---------
Grand total 3,827 cu. yds. $5.59 $21,372.00
COST OF CONCRETING SHAFTS.
South Caisson.
Materials. Quantity. Rate. Amount.
Concrete 612½ bbls. $1.57 $962.00
Sand 193 cu. yds. .40 77.00
Stone 493 cu. yds. 1.10 542.00
------- ------ ---------
Total 541 cu. yds. $2.92 $1,581.00
Labor.
Handling, mixing and placing 541 cu. yds. $0.96 $519.00
Plant charges, etc. 541 cu. yds. 1.06 576.00
------- ------ ---------
Total 541 cu. yds. $4.94 $2,676.00
General expenses, 10% 541 cu. yds. .49 267.00
------- ------ ---------
Grand total 541 cu. yds. $5.43 $2,943.00
COST OF CONCRETE IN WORKING CHAMBERS.
South Caisson. (1,435 cu. yds.)
Materials. Quantity. Rate. Amount.
Cement for concrete 1,666 bbls. $1.57 $2,615.00
Cement for mortar 459 bbls. 1.57 720.00
Sand for both 670 cu. yds. .40 268.00
Broken stone 1,181 cu. yds. 1.10 1,299.00
------- ------ ---------
Total materials 1,435 cu. yds. $3.42 $4,902.00
Labor.
Top labor, mixing and placing 1,435 cu. yds. $1.09 $1,575.00
Pneumatic labor 1,435 cu. yds. 4.93 7,117.00
Compressor house labor 1,435 cu. yds. .19 275.00
------- ------ ---------
Total labor 1,435 cu. yds. $6.21 $8,967.00
Plant.
Coal at $2.40 per ton 1,435 cu. yds. .10 140.00
Concrete plant 1,435 cu. yds. .79 1,145.00
Pneumatic plant 1.435 cu. yds. 1.05 1,522.00
-------- ------ ---------
Total plant 1,435 cu. yds. $1.94 $2,807.00
Totals 1,435 cu. yds. $11.57 $16,676.00
General expenses, 10% 1,435 cu. yds. 1.16 1,667.00
-------- ------- ----------
Grand total 1,435 cu. yds. $12.73 $18,343.00
TABLE XVIII.--ITEMIZED COST OF CONCRETING NORTH CAISSON FOR BROOKLYN
TOWER OF THE WILLIAMSBURG BRIDGE:
COST OF CONCRETING CAISSON ABOVE ROOF (5,692 cu. yds.)
Materials. Quantity. Rate. Amount.
Cement 6,707½ bbls. $1.57 $10,531.00
Sand 2,133 cu. yds. .40 845.00
Broken stone 4,938 cu. yds. 1.10 5,432.00
Water 51.00
------- ------ ---------
Total 5,692 cu. yds. $2.96 $16,859.00
Labor.
Mixing and placing 5,692 cu. yds. $0.73 $4,159.00
Plant charges 2,952.00
Plant labor 517.00
------- ------ ---------
Total 5,692 cu. yds. $0.61 $3,469.00
Total cost 5,692 cu. yds. $4.30 $24,487.00
General expenses, 10% 5,692 cu. yds. .43 2,448.00
Grand total 5,692 cu. yds. $4.73 $26,935.00
COST OF CONCRETING SHAFTS.
Materials. Quantity. Rate. Amount.
Cement 614½ bbls. $1.57 $965.00
Sand 204 cu. yds. .40 82.00
Stone 521 cu. yds. 1.10 574.00
------- ------ ---------
Total 576 cu. yds. $2.82 $1,621.00
Labor.
Mixing and placing 576 cu. yds. 1.70 982.00
Plant charges, etc. 576 cu. yds. 1.36 795.00
------- ------ ---------
Total 576 cu. yds. $5.88 $3,398.00
General expenses, 10% 576 cu. yds. .59 339.00
------- ------ ---------
Grand total 576 cu. yds. $6.47 $3,737.00
COST OF CONCRETING WORKING CHAMBERS (1,566 cu. yds.).
Materials. Quantity. Rate. Amount.
Cement for concrete 1,559 bbls. $1.51 $2,446.00
Cement for mortar 442 bbls. 1.51 $694.00
Sand for both 630 cu. yds. .40 252.00
Broken stone 1,380 cu. yds. 1.10 1,518.00
------- ------ ---------
Total 1.566 cu. yds. $3.14 $4,910.00
Labor.
Top labor, mixing and placing 1,566 cu. yds. $0.78 $1,198.00
Pneumatic labor 1,566 cu. yds. 4.91 7,694.00
Compressor house labor 1,566 cu. yds. .11 180.00
------- ------ ---------
Total labor 1,566 cu. yds. $5.80 $9,072.00
Plant.
Coal at $2.40 per ton 1,566 cu. yds. .06 87.00
Concrete plant 1,566 cu. yds. .86 1,352.00
Pneumatic plant 1,566 cu. yds. .81 1,272.00
------- ------ ---------
Total plant 1,566 cu. yds. $1.73 $2,711.00
------- ------ ---------
Totals 1,566 cu. yds. $10.67 $16,693.00
------- ------ ---------
General expenses, 10% 1,566 cu. yds. 1.06 1,669.00
------- ------ ---------
Grand total 1,566 cu. yds. $11.73 $18,362.00
~COST OF FILLING PIER CYLINDERS.~--The following costs were obtained in
mixing and placing concrete in steel cylinder piers. The sand and gravel
were wheeled 100 ft. to the mixing board at the foot of the cylinder,
mixed and shoveled into wooden skips, hoisted 20 ft. by horsepower and
dumped into the cylinder. The foreman worked on the mixing board and the
men worked with great energy. The costs were as follows:
Item-- Per day. Per cu. yd.
6 men wheeling materials and mixing at 15
cts. per hour 9.00 $0.45
2 men dumping skips and ramming at 15 cts.
per hour 3.00 0.15
1 team and driver at 40 cts. per hour 4.00 0.20
1 foreman at 30 cts. per hour 3.00 0.15
----- ----
Totals $19.00 $0.95
~PIERS, CALF KILLER RIVER BRIDGE.~--The following methods and costs of
building two new piers and extending three old piers with concrete are
given by Mr. J. Guy Huff. The work was done by the railway company's
masonry gangs. Figure 94 shows the arrangement of the several piers and
the character of the work on each and Fig. 95 gives the detail
dimensions of the three main piers.
The sand and aggregate, consisting of blast furnace slag, were unloaded
from cars to platforms on a level with the top of rail, placed about 100
ft. south from the south end of the bridge. A cubical 1/6 cu. yd. mixer
was used. This was operated by a gasoline engine, and was located on a
platform about 50 ft. south of the south end pier. A tank near the mixer
to supply water was elevated enough to get the desired head, and was
kept filled by a pump run by another gasoline engine located down by the
river bank. The cement house was located between the mixer platform and
slag pile.
[Illustration: Fig. 94.--Diagram Arrangement of Piers, Calf Killer River
Bridge.]
[Illustration: Fig. 95.--Details of Pier for Calf Killer Elver Bridge.]
Slag and sand were delivered to the mixer by means of wheelbarrows. The
mixer was so placed that it would dump onto a platform, and the concrete
could then be shoveled into a specially designed narrow-gage car. This
car ran on one rail of the main track and an extra rail outside. A
turnout for clearing passing trains was provided at both ends of the
bridge. The track over the bridge from the mixer had a descending grade
of about 1 per cent., so that with a little start the concrete car would
roll alone down to the required points on the bridge. Only in returning
the empty cars to the mixer was it necessary to push them by hand, and
then only for a distance of never more than 400 ft.
Over the piers on the bridge in the center of the concrete car track
openings were sawed to let the concrete pass to the forms below. To get
the concrete into the forms, there were used zig-zag chutes with arms
about 10 ft. long, which sections were removed as the concrete in the
forms was increased. These chutes were a convenience by their ends
alternating from one side to the other as the arms were removed in
coming up.
The cost of the concrete work was as follows:
Unloading Material.
Rate Total days Per cu. yd.
per day. worked. Total. concrete.
Foreman $3.40 5 $17.00 $0.04
11 laborers 1.36-8/10 52 71.14 .15
-----
Total for unloading material $0.19
Building Forms, Bins, Etc.
Foreman $3.40 18 $61.20 $0.14
9 carpenters 2.25 166 373.50 .81
New lumber, 23.7 M. ft.
at $17.80 421.86 .92
Old lumber, 6 M. ft. at
$8.33 49.98 .11
-----
Total for building forms, bins, etc. $1.98
Cofferdam Excavation (45 cu. yds.)
Foreman $3.40 8 $27.20 $0.06
9 laborers 1.15 6/10 74½ 86.12 .19
-----
Total for cofferdam excavation $0.25
Cofferdam Concrete (37 cu. yds.)
Foreman $3.40 8 $27.20 $0.06
11 laborers 1.36 3/10 79 107.68 .23
Cofferdam lumber, 2.25
M. ft. at $20.00 45.00 .09
----
Total for cofferdam concrete $0.38
Concrete Mixing and Placing.
Foreman $3.40 30 $102.00 $0.22
9 laborers 1.15 6/10 282 325.99 .71
Cement, 452 bbls. at
$1.55 701.00 1.52
Slag, 437 cu. yds. at $0.20 87.40 .19
Sand, 220 cu. yds. at
$0.30 66.00 .14
-----
Total for mixing and placing $2.78
Taking Down Forms and Clearing Up.
Foreman $3.40 13 $44.20 $0.09
11 laborers 1.17 1.43 107.31 .36
-----
Total for taking down forms, etc. $200.00 $0.45
Engineering and supervision .43
-----
Grand total, 460 cu. yds. concrete $6.46
The wages given are the average wages. The men worked a 10-hour day. The
concrete was a 1-3-6 mixture. The cofferdam work was done in connection
with the construction of the fourth pier, this pier being the only one
coming in the bed of the river to be built entirely new. The work on
this was started in water about 6 ft. deep. The 37 cu. yds. of concrete
is included in the total of 460 cu. yds. in the above tabulation. By
itself the cost of the cofferdam work, not including cost of cement,
sand and slag was as follows:
Per cu. yd.
Total. Concrete.
Lumber $ 45.00 $1.21
Labor, excavating 113.32 3.06
Labor, concrete 134.88 3.64
-----
Total 37 cu. yds. concrete $7.91
[Illustration: Fig. 96.--Details of Piers for K. C., M. & O. Ry.
Bridge.]
~METHOD AND COST OF CONSTRUCTING 21 BRIDGE PIERS.~--The following account
of the methods and cost of constructing 21 concrete piers for a railway
bridge consisting of 20 50-ft. plate girder spans has been compiled from
records kept by Mr. W. W. Colpitts, Assistant Chief Engineer, Kansas
City, Mexico & Orient Ry. The shape and dimensions of the piers are
shown by Fig. 96 and Fig. 97 shows the construction of the forms. Sheet
pile cofferdams to solid rock were used for constructing the
foundations.
[Illustration: Fig. 97.--Forms for Piers for K. C., M. & O. Ry. Bridge.]
The 1-3-5 concrete was mixed in a Smith mixer having a batch capacity of
9 cu. ft. The mixer was located on the slope of the embankment
approach, with the main track at its rear and facing a temporary
material track. This temporary track turned out from the main track
about 500 ft. beyond the mixer and extended diagonally down the
embankment approach on a 3 per cent. grade and across the river bottom
alongside the pier sites. The portion of the track in the river bottom
was supported on bents of spliced ties, jetted to the rock, and wired to
the cofferdam to avoid the danger of loss in case of high water. The
sand and crushed rock were delivered by cars from the main line track,
immediately above the mixer, and the cement was stored in a shanty at
one side of the mixer. The concrete materials and machinery were, in
this manner, very conveniently located for rapid work and well above the
high water line. The concrete was transported to the pier sites in
improvised dump boxes, set on push cars. These dump boxes were hinged
longitudinally and discharged directly into the cofferdams. The grade of
the temporary track carried the push cars by gravity to the cofferdams
and they were returned by teams, for which purpose a straw and brush
road had been built paralleling the track. As the work progressed
farther into the stream, more cars were added properly to balance the
work. While the concrete in the base was still fresh, a number of steel
reinforcing bars, 8 ft. in length, were set in place along each end to
insure a good bond between the base and shaft.
In general, the work of putting in the bases was organized so that about
the same time was required in filling a cofferdam with concrete, in
excavating the sand from the next, and in driving the sheet piling for
the third. These three operations were thus carried on simultaneously
and, although interruptions in one part of the work or the other
occurred frequently, the gangs were interchangeable and no appreciable
loss was suffered, except in time, because of such delays.
In piers 19 and 20, where the rock was from 17 to 19 ft. below the
surface, some difficulty was encountered due to the presence of fissures
in the rock, from which it was necessary to remove the sand to fill with
concrete. In such cases, the larger leaks were stopped as much as
possible by driving sheet piles against the outside face of the
cofferdam and into the fissures, and the smaller leaks by manure in
canvas bags rammed into the openings.
Upon the completion of all the bases, the forms for several shafts were
set in position and the work of filling with concrete proceeded as in
the case of the bases, except that a derrick erected on a flat car and
stationed at the pier was utilized to raise the dump boxes in depositing
the concrete in the forms. As soon as the concrete in one shaft had set
sufficiently to permit of it, the forms were removed and placed on the
pier ahead. Four sets of forms were used for the shafts.
The following are the average prices paid for materials and labor:
Materials.--Lumber for forms, etc., $16.50 per M. ft., B. M.; cement,
Kansas Portland, $1.50 per bbl.; broken limestone, 45c per cu. yd.;
sand, Arkansas River, 15c per ton.
Labor.--General foreman, $110 per month; assistant foreman, $75 per
month; timekeeper, $60 per month; riveters, 35c per hour; blacksmith,
30c per hour; blacksmith assistant, 20c per hour; carpenters, 22½c and
25c per hour; enginemen, 25c per hour; firemen, 20c per hour; night
watchman, 20c per hour; laborers, 17½c and 20c per hour; team (including
driver), 40c per hour. The prices quoted for lumber, cement, limestone
and sand are prices f. o. b., Louisiana, Iola, Kan., El Dorado, Kan.,
and Wichita, Kan.
The total and unit cost of constructing the concrete piers and abutments
and of erecting the steel superstructure are given in the following
tabulation. Altogether there was about 2,300 cu. yds. of concrete in the
substructure, most of which, as stated above, was a 1-3-5 mixture.
Machinery and Supplies.
Concrete mixer, 20% of cost $ 152.10
Supplies, freight, hauling, setting up 505.04
--------
Total $ 657.14
Centrifugal sand pump, 20% of cost $ 27.00
Supplies, freight, hauling, setting up 277.50
Rent of traction engine to operate 83.25
--------
Total $ 387.75
Water pump and pipe, 20% of cost $ 29.00
Supplies, freight, hauling, setting up 177.32
--------
Total $ 206.32
Pile driver engine, 20% of cost $ 100.00
Supplies, freight, hauling, setting up 243.65
--------
Total $ 343.65
--------
Grand total $1,594.86
Cofferdams.
Materials, lumber and nails $1,285.26
Freight and train haul 306.33
Labor making piles 696.82
Labor driving piles 1,384.05
---------
Total $3,672.46
The sheet piling took 63,500 ft. B. M. of lumber; the cost per 1,000 ft.
B. M. for the sheet piling was then:
Materials, lumber and nails $ 20.08
Freight and haulage 4.82
Labor making piles 10.97
Labor driving piles 21.80
--------
Total $ 57.67
Forms, Platforms and Runways.
Lumber, hardware, etc. $ 224.59
Freight and train haul. 40.20
Labor making, removing and placing. 556.51
---------
Total $ 821.30
Concrete Materials.
Cement, freight, unloading and storing. $4,617.48
Sand, freight, unloading, etc. 1,336.05
Broken stone, freight, unloading, etc. 2,026.92
---------
Total $7,980.45
This gives us for 2,300 cu. yds. of concrete a cost of $3.47 per cu. yd.
for materials, including freight, storage, and unloading charges of all
kinds. A line on the proportion of the cost contributed by these latter
items may be got by taking the prices of the materials f. o. b. at the
places of production and assuming the proportions for a 1-3-5 concrete.
According to tables in Chapter II, a 1-3-5 broken stone concrete
requires per cubic yard 1.13 bbls. cement, 0.48 cu. yd. sand and 0.80
cu. yd. broken stone. We have then:
1.13 bbls. cement, at $1.50 $1.69
0.48 cu. yd. sand, at 20c .10
0.80 cu. yd. stone, at 45c .36
-----
Total $2.15
This leaves a charge of $1.32 per cubic yard of concrete for freight and
handling materials. The cost of mixing concrete and placing it in the
forms was $3,490.87, or $1.52 per cu. yd. We have then:
Cost of concrete materials per cu. yd. $3.47
Cost of mixing and placing concrete. 1.52
-----
Total. $4.99
The miscellaneous expenses of the work comprised:
Watchman, tools, telephone, etc. $ 722.48
Shanties, furnishings, supplies, etc. 829.04
---------
Total. $1,551.52
To this has to be added $1,134.28, the cost of excavating the
cofferdams. The total and unit costs of the different items of the
concrete substructure work can now be summarized as follows:
Item. Total. Per cu. yd.
Machinery and supplies 1,594.86 $ .69
Cofferdams 3,672.49 1.60
Forms, etc 821.30 .36
Concrete materials 7,980.45 3.47
Mixing and placing concrete 3,490.87 1.53
Excavating cofferdams 1,134.28 .49
Miscellaneous 1,551.52 .67
---------- -----
Total $20,245.74 $8.81
~COST OF PERMANENT WAY STRUCTURES KANSAS CITY OUTER BELT & ELECTRIC
RY.~--The following cost of concrete work including retaining walls,
abutments and box culverts, for the permanent way of the Kansas City
Outer Belt & Electric Ry., is given by Mr. W. W. Colpitts. These figures
are of particular interest, for the variation in prices of materials
during the two-year period while work was in progress and as giving the
average cost of the work on the whole line as well as for individual
structures. The culverts were all box culverts with wing walls and the
abutments were for girder bridges. Walls and abutments were of L section
with triangular or trapezoidal counterforts at the back between base
slab and coping. The form work was thus rather complex.
All work was reinforced concrete, and was done by contract under the
following conditions: The work of preparing foundations, including
excavation, pile driving, diversions of streams, etc., was done by the
railroad company, which also bore one-half the cost of keeping
foundations dry while forms were being built and concrete placed. The
railroad company also furnished the reinforcing bars at the site of each
opening. The concrete work was let at $9 per cu. yd., which figure
covered all the labor and materials necessary to complete the work,
other than the exceptions mentioned. The concrete proportions were
1-3-5. The cement used was Iola Portland and Atlas Portland. The sand
was obtained from the bed of the Kansas River in Kansas City. The rock
used was crushed limestone, passing a 2-in. ring and freed from dust by
screening. Corrugated reinforcing bars, having an elastic limit of from
50,000 to 60,000 lbs. per sq. in., manufactured by the Expanded Metal &
Corrugated Bar Co. of St. Louis, Mo., were used exclusively. The
concrete in the smaller structures was mixed by hand, in the larger by a
No. 1 Smith mixer. In the first structures built 2-in. form lumber was
used, with 2 by 6-in. studs placed 3 ft. on centers. This was abandoned
later for 1-in. lumber with 2 by 6-in. studs, 12 ins. on centers, and
was found to be more satisfactory in producing a better face. The
structures were built in the period from April, 1905, to May, 1907.
The cost of materials and the wages paid labor were as follows:
Cement--
Per barrel at structure, April, 1905 $1.25
Per barrel at structure, April, 1907 1.92
Average cost per barrel at mill 1.42
Freight per barrel 0.21
Hauling 1½ miles and storage 0.12
Average cost at structure 1.75
Average cost per cu. yd. concrete (1.1 bbls.) 1.93
Sand--
Per cu. yd. at structure, April, 1905 $0.625
Per cu. yd. at structure, April, 1907 0.75
Average cost per cu. yd., river bank 0.30
Freight per cu. yd 0.22
Hauling 1½ miles 0.20
Average cost at structure 0.72
Average cost per cu. yd. concrete (½ cu. yd.) 0.36
Stone--
Per cu. yd. at structure, April, 1905 $1.10
Per cu. yd. at structure, April, 1907 1.75
Average cost per cu. yd. at crusher 0.65
Hauling 4 miles 0.84
Average cost at structure 1.49
Average cost per cu. yd. concrete (0.9 cu. yd.) 1.34
Lumber--
Per M. ft. at structure, April, 1905 $15.00
Per M. ft. at structure, April, 1907 22.50
Average cost per M. at structure 19.00
Average cost per cu. yd. concrete 0.49
Labor-- Max. Min.
Common labor, cts. per hour 20 17
Carpenters, cts. per hour 40 30
With these prices and wages the average cost of concrete work for the
whole line was:
Item. Per cu. yd.
Form building and removing $1.98
Mixing and placing concrete 0.74
Placing reinforcement 0.10
Wire, nails, water, etc. 0.20
1.1 bbls. cement at $1.75 1.93
½ cu. yd. sand at $0.72 0.36
0.9 cu. yd. stone at $1.49 1.34
Lumber for forms 0.49
------
Total $7.14
The following are the costs of specific structures built at different
times:
Example I.--Indian Creek Culvert. 14×15 ft., 250 long, completed
November, 1905:
Per cu. yd.
Cement $1.37
Sand .34
Stone 1.10
Labor 2.48
Lumber .76
Miscellaneous .18
Total $6.23
Example II.--Third Street Abutments and Retaining Wall. Completed
November, 1906:
Per cu. yd.
Cement $1.78
Sand .35
Stone 1.35
Lumber .74
Labor 2.75
Miscellaneous .16
-----
Total $7.13
Example III.--Abutments, Overhead Crossing with Union Pacific and Rock
Island. Completed May, 1907:
Per cu. yd.
Cement $1.92
Sand .32
Stone 1.74
Lumber .98
Labor 2.96
Miscellaneous .16
-----
Total $8.08
~COST OF PLATE GIRDER BRIDGE ABUTMENTS.~--The following record of the
construction of 20 abutments for 10 four-track plate girder bridges over
streets in Chicago, Ill., are given by Mr. W. A. Rogers. The work was
done between May 1 and Oct. 1, 1898, in which time 8,400 cu. yds. of
concrete were placed, all the work being done by company labor. The
forms were made of 2-in. plank and 6×6-in. posts bolted together at the
top and bottom with ¾-in. rods. The lumber was used over and over again.
When the dressed plank became too poor for the face it was used for the
back. The concrete was 1 Portland cement, 3 gravel and 4 to 4½ limestone
(crusher run up to 3-in. size). A mortar face 1½ ins. thick was built up
with the rest of the concrete. The concrete was made quite wet, and each
man ramming averaged 18 cu. yds. a day rammed. The concrete was mixed by
a machine of the Ransome type, operated by a 12-HP. portable gasoline
engine. The load was very light for the engine, and 8 HP. would have
been sufficient. The engine made 235 revolutions per minute, and the
pulley wheels were proportioned so that the mixer made 12 revs, per
minute. One gallon of gasoline was used per hour, and the mixing was
carried on day and night so as not to give the concrete time to set. The
time required for each batch was 2 to 3 mins., and about ½ cu. yd. of
concrete was delivered per batch. The average output was 70 cu. yds. per
10-hr, shift, with a crew of 28 men; but as high as 96 cu. yds. were
mixed in 10 hrs. The concrete was far superior to hand mixed concrete.
The water for the concrete was measured in an upright tank and
discharged by a pipe into the mixer. The sand and stone were delivered
to the mixer in wheelbarrows, and the concrete was taken away in
wheelbarrows. No derricks were used at all. Each wheelbarrow of concrete
was raised by a rope passing over a pulley at the top of a gallows
frame, one horse and a driver serving for this raising. A small gasoline
hoisting engine would have been more satisfactory than the horse which
was worked to its full capacity. After the barrows were raised (12 ft.),
they were wheeled to the abutment forms and dumped. The empty
wheelbarrows were lowered by hand, by means of a rope passing over a
sheave and provided with a counterweight to check the descent of the
barrow. The cost of the concrete (built by company labor) was as
follows:
Per cu. yd.
Cement, gravel and stone delivered $3.28
Material in forms (used many time) .11
Carpenters building and taking down forms .34
Labor 1.18
-----
Total per cu. yd $4.91
The labor cost includes moving plant from one bridge to the next,
building runways, gasoline for engine, oil for lights at night and
unloading materials, as well as mixing, transporting and placing
concrete. Wages were $1.75 per 10-hour day for laborers and $2.50 for
carpenters.
~COST OF ABUTMENTS AND PIERS, LONESOME VALLEY VIADUCT.~--Mr. Gustave R.
Tuska gives the following on the concrete substructure of the Lonesome
Valley Viaduct, near Knoxville, Tenn. There were two U-shaped abutments
and 36 concrete piers made of a light limestone that deteriorates
rapidly when used for masonry. Derricks were not needed as would have
been the case with masonry piers, and colored labor at $1 for 11 hrs.
could be used. The piers were made 4 ft. square on top, from 5 to 16 ft.
high, and with a batter of 1 in. to the foot. The abutments average 26
ft. high, 26 ft. long on the face, with wing walls 27 ft. long; the wall
at the bridge seat is 5 ft. thick, and the wing walls are 3½ ft. wide on
top. Batters are 1 in. to the foot.
The forms were made of 2-in. tongued and grooved plank, braced by posts
of 2×10-in. plank placed 3 ft. c. to c. for the abutments, and at each
corner for the piers. At the corners one side was dapped into the other,
so as to prevent leakage of cement. The posts were braced by batter
posts from the earth. For the piers a square frame was dropped over the
forms and spiked to the posts. The abutment forms were built up as the
concreting progressed. The north abutment forms were made in sections 6
ft. high, held by ¾-in. bolts buried in the concrete. The lower sections
were removed and used again on the upper part of the work, thus saving
plank. The inside of forms was painted with a thin coat of crude black
oil. The same form was used for several piers.
The concrete was 1-2-5, the barrel being the unit of measure, making
about ¾ cu. yd. of concrete per batch. The mortar was mixed with hoes,
but shovels were used to mix in the stone. By passing the blade of a
shovel between the form and the concrete, the stone was forced back and
a smooth mortar face was secured. Rammers weighing 30 to 40 lbs. were
used for tamping. Two days after the completion of a pier the forms were
removed. The concrete was protected from the sun by twigs, and was
watered twice a day for a week. It was found by actual measurement that
1 cu. yd. Of concrete (1-2-5), the ingredients being measured in
barrels, consisted of 1¼ bbls. of Atlas cement, 10 cu. ft. of sand, and
26½ cu. ft. of stone. The total amount of concrete was 926 cu. yds. of
which two-thirds was in the two abutments. The work was done (in 1894)
by contract, for $7 per cu. yd., cement costing $2.80 per bbl., sand 30
cts. per cu. yd., and wages $1 a day. A slight profit was made at this
price. A gang of 15 men and a foreman would mix and lay about 40 cu.
yds. in 11 hrs. when not delayed by lack of materials. The cost of
making the concrete, with wages at $1 a day, was:
Cts. per cu. yd.
1 man filling sand barrels and handling water 2.7
2 men filling rock barrels 5.4
4 men mixing sand and cement 10.6
4 men mixing stone and mortar 10.6
2 men wheeling concrete 5.3
1 man spreading concrete 2.7
1 man tamping 2.7
1 foreman 5.0
----
Total labor 45.0
~COST OF HAND MIXING AND WHEELBARROW WORK FOR FOUR BRIDGE PIERS.~--The
following figures of the cost of hand-mixed concrete for bridge piers
and abutments are given by Mr. Fred R. Charles of Richmond, Ind. The
figures cover three jobs. All concrete was mixed by hand and with one
exception noted below was moved to place in wheelbarrows. The concrete
was a 1-2½-5½ mixture. In this connection it is well to note that in one
or two of the jobs where the proportion of the aggregate seems too small
for the yardage of concrete the difference is accounted for by the fact
that large stones were placed in the foundations, these stone being on
the ground and costing nothing but the labor to throw them in.
_Job I._--The first job consisted of the construction of one abutment
and six piers for a bridge over the Miami River at Fernald, O. The stone
was procured on the site and crushed by a portable crusher run by a
traction engine. The rough stone cost 10 cts. a cubic yard, and this,
with the cost of handling, fuel and hire of engine and crusher, made the
cost of crushed stone about $1 per cu. yd. Sand was obtained close to
the work, but the cement had to be teamed 10 miles. Labor was paid $1.75
per day. The cost of materials and labor per cubic yard of concrete in
place was as follows:
Item. Per cu. yd.
1.16 bbls. cement at $2.10 $1.58
Sand 0.35
Stone 0.75
Lumber 0.64
Tools, hardware, etc. 0.20
Labor (including 15 cts. per cu. yd. for pumping) 2.78
-----
Total materials and labor $6.30
_Job II._--The second job was the construction of two abutments
containing 434 cu. yds. of concrete for a viaduct at Ernst Street,
Cincinnati, O. The abutments were constructed at the street and the
excavation was clay and shale. Labor received $1.75 per day. The cost of
materials and labor per cubic yard of concrete in place was as follows:
Materials-- Per cu. yd.
376 bbls. cement at $1.70 $1.48
224 cu. yds. sand at $1.20 0.64
255 cu. yds. stone at $1.55 1.00
Lumber 0.40
Tools, hardware, etc. 0.06
Total materials $3.58
Labor--
Clearing and excavating $1.12
Mixing and placing concrete 1.13
Building forms, etc. 0.25
-----
Total labor $2.50
Total labor and materials $6.08
_Job III._--This job consisted in placing 570 cu. yds. of concrete in
the pedestals for a viaduct at Quebec Avenue, Cincinnati, O. The
pedestals were 5 ft. square on top and from 8 to 20 ft. high. The
location of the work was very inconvenient for the delivery of
materials, all materials having to be teamed or wheeled. Labor was paid
$1.75 per day. The cost of labor and materials per cubic yard of
concrete in place was as follows:
Item. Per cu. yd.
500 bbls. cement at $1.60 $1.40
239 cu. yds. sand at $1.25 0.53
560 cu. yds. stone at $1.88 1.84
Lumber 0.38
Tools, hardware, etc. 0.05
Labor 2.96
-----
Total labor and materials $7.16
_Job IV._--This job consisted in placing 2,111 cu. yds. of concrete in a
railway viaduct at Cincinnati, O. For one pier 56 ft. high the concrete
was raised to place by a derrick; for the remainder of the work it was
wheeled or teamed to place. Labor was paid $1.75 per day. The cost of
labor and materials per cubic yard of concrete in place was as follows:
Item. Per cu. yd.
1,908 bbls. cement at $1.60 $1.44
1,105 cu. yds. sand at $1.95 0.50
1,468 cu. yds. stone at $1.48 1.03
Lumber 0.54
Tools, hardware, etc. 0.25
Water 0.03
Labor 3.44
-----
Total labor and materials $7.23
CHAPTER XIII.
METHODS AND COST OF CONSTRUCTING RETAINING WALLS.
Concrete retaining walls may for construction purposes be divided into
two classes: Plain concrete walls of gravity section and reinforced
concrete walls consisting of a thin slab taking the thrust of the earth
as a cantilever anchored to a base slab or as a flat beam between
counterforts. The reinforced wall requires much less concrete for a
given height than does the plain, gravity wall, but the concrete is more
expensive owing to the reinforcement and to the more complex form of
construction, and, in some measure, to the greater cost of placing the
mixture in narrow forms and around reinforcement. It is common, too, to
require a richer concrete for the reinforced than for the plain wall.
[Illustration: Fig. 98.--Comparison of Plain and Reinforced Sections for
Retaining Walls (C. E. Graff).]
~COMPARATIVE ECONOMY OF PLAIN AND REINFORCED CONCRETE WALLS.~--Prior to
the construction of some 2,000 ft. of retaining wall ranging in height
from 2 ft. to 38 ft., at Seattle, Wash., calculation was made by the
engineers of the Great Northern Ry. to determine the comparative economy
of plain concrete and reinforced concrete sections. The sections assumed
were those shown by Fig. 98, and comparisons were made at heights of 10,
20, 30 and 40 ft., with the following results:
Height in Plain. Reinforced. Per cent.
feet. Cu. yds. per ft. Cu. yds. per ft. Saving.
10 1.63 1.29 20.4
20 4.08 2.59 36.4
30 8.40 4.73 43.3
40 14.70 8.07 45.0
The saving in concrete increased as the height of the wall increased;
for a 40-ft. wall reinforced concrete at nearly double the cost per
cubic yard in place would be as cheap as plain concrete.
[Illustration: Fig. 99.--Comparison of Plain and Reinforced Sections for
Retaining Wall (F. F. Sinks).]
Taking substantially the section of reinforced wall being used on the
Chicago track elevation work of the Chicago, Burlington & Quincy R. R.,
and comparing it with a plain wall as shown by Fig. 99, Mr. F. F. Sinks
obtained the following results:
Plain Wall, Cost per Lineal Foot--
4.8 cu. yds. concrete at $4 $19.20
115 ft. B. M. of forms at $31 3.56
------
Total 4.8 cu. yds. at $4.74 $22.76
Reinforced Wall, Cost per Lineal Foot--
3.46 cu. yds. concrete at $4.10 $14.18
115 ft. B. M. of forms at $31 3.56
109 lbs. reinforcing steel at 3¼ cts. 3.54
1.34 cu. yds. extra fill at 20 cts. 0.27
0.32 cu. yd. extra excavation at 20 cts. 0.06
-----
Total, 3.46 cu. yds. concrete at $6.25 $21.61
The saving in this case was $1.15 per lineal foot of wall with the unit
cost of reinforced concrete in place 24 per cent. greater than the unit
cost of plain concrete. It will be noted that there is some 28 per cent.
less concrete per lineal foot of wall in the reinforced section and also
that this section is so designed that the form work is about as simple
for one section as for the other. Another point to be noticed is that
there is no saving in excavation by using a reinforced section instead
of a gravity section, in fact the excavation runs slightly more for the
reinforced section.
[Illustration: Fig. 100.--Forms for Retaining Wall Work, N. Y. C. & H.
R. R. R.]
~FORM CONSTRUCTION.~--Retaining wall work often affords an opportunity for
constructing the forms in panels and this opportunity should be taken
advantage of when possible. Several of the walls described later give
examples of form work that may be studied with profit in this respect.
Figure 100 shows a panel form construction employed on the New York
Central & Hudson River R. R. The 3×8-in. studs are erected, care being
taken to get them in proper line and to true batter and also to brace
them rigidly by diagonal props. Generally the studding is erected for a
section of wall 50 ft. long at one time. The lagging, made in panels 2½
ft. wide and 10 ft. long, by nailing 2-in. plank to 2×4-in. cleats, is
attached to the studding a panel at a time and beginning at the bottom,
by means of the straps, wedges and blocks shown. Five bottom panels
making a form 2½ ft. high and 50 ft. long are placed first. When the
concrete has been brought up nearly to the top of these panels, a second
row of panels is placed on top of the first. When it is judged that the
concrete is hard enough the lowermost panels are loosened and made free
by removing the wedges, blocks and straps and the panels are drawn out
endwise from behind the studding and used over again for one of the
upper courses. The small size of the panels makes it practicable to lay
bare the concrete while it is yet soft enough to work with a float or to
finish by scrubbing as described in Chapter VIII. In cases where this
object is not sought, panels of much larger size may be used. Working
with panels 2¼×12½ ft. of 2-in. plank it was found that each panel could
be used 16 times before becoming unfit for further use, but as, owing to
the nicety of molded surface demanded, panels were discarded when
showing comparatively small blemishes, this record cannot be taken as a
true indication of the life of such forms. These panel forms are used by
the railway named for long abutments and piers as well as for retaining
walls.
A different type of sectional form construction is illustrated by Figs.
101 and 102. It has been extensively used for retaining wall work by the
Chicago, Burlington & Quincy R. R. The studding and waling are framed in
units as shown. The lagging is framed in panels for the rear of the
wall, for the face of the coping, and for the inclined toe of the wall,
and is ordinary sheathing boards for the main face of the wall. The
make-up of the several panels is shown by the drawings. The reason for
using ordinary sheathing instead of panels for the face of the wall is
stated by Mr. L. J. Hotchkiss, Assistant Bridge Engineer, to be that
"the sections become battered and warped with use, do not fit closely
together, and leave the wall rough when they are removed." The manner of
bracing the form and of anchoring it down against the up-thrust of the
wet concrete is shown by Fig. 102.
Two other examples of sectional form construction are given in the
succeeding descriptions of work for the Grand Central Station terminal
in New York City and for the Chicago Drainage Canal. In the former work
it is notable that panels 51×20 ft. were used, being handled by
locomotive crane. The panels used on the drainage canal work and in the
forms previously described are of sizes that can be taken down and
erected by hand, and the means of handling them should always be given
consideration in deciding on the sizes to be adopted for form panels not
only in wall construction but in any other class of work where sectional
forms may be used. Wet spruce or yellow pine will weigh 4½ lbs. per ft.
B. M., so that a panel 10×2½ ft. made of 2-in. plank and three 2×4-in.
battens will weigh some 225 lbs. In form work where the panels are
removed and re-erected in succession facility in handling is an
important matter. When one figures that he may handle both the concrete
and the form panels with it a cableway or a locomotive crane becomes a
tool well worth considering in heavy wall work.
[Illustration: Fig. 101.--Forms for Retaining Wall Work, C., B. & Q. R.
R.]
Three details in retaining wall form work that are often sources of
annoyance out of proportion to their magnitude are alignment, coping
construction and wall ties. Small variations from line in the face of
the wall are seldom noticeable, but a wavy coping shows at a glance.
For this reason it is often wise to build the coping after the main body
of the wall has been stripped, or if both are built together to provide
in the forms some independent means of lining up the coping molds. In
the form shown by Fig. 101 the latter is done by bracing the coping
panel so as to permit it to be set and lined up independently of the
main form. A separate form for molding the coping after the main body of
the wall is completed may be constructed as shown by Fig. 103. Bolts at
B and C permit the yokes to be collapsed and the form to be shifted
ahead as the work advances. This mold provides for beveling the top
edges of the coping and also the edge of the overhang, and the beveling
or rounding of these edges should never be omitted where a neat
appearance is desired. It is not essential, however, that this finishing
be done in the molds. By stripping the concrete while it is still
pliable the edges can be worked down by the ordinary cement sidewalk
edger.
[Illustration: Fig. 102.--Sketch Showing Method of Bracing Form Shown by
Fig. 101.]
[Illustration: Fig. 103.--Sectional Form for Constructing Coping.]
Wall ties are commonly used to hold the face and back forms to proper
spacing, but occasionally they are not permitted. In the latter case the
bracing must be arranged to hold the forms from tipping inward as well
as from being thrust outward. A good arrangement is that shown by Fig.
102. In fastening the forms with ties the choice is usually between long
bolts which are removed when the molds are taken down and wire ties
which are left embedded in the concrete. The selection to be made
depends upon the character of the work. When sectional forms are used
like the one shown by Fig. 101, for long stretches of wall of nearly
uniform cross-section bolts are generally more economical and always
more secure. If the bolts are sleeved with scrap gas pipe having the
ends corked with waste the bolts can be removed ordinarily without
difficulty. To make the pipe sleeve serve also as a spacer the end next
the face may be capped with a wooden washer which is removed and the
hole plastered when the forms are taken down. With bolt ties the forms
can be filled to a depth of 15 to 20 ft with sloppy concrete. This is
hardly safe with wire ties unless more wire and better tieing are
employed than is usual. It takes four strands of No. 10 to give the same
working stress as a ½-in. threaded rod and the tieing in of four strands
of wire so that they will be without slack and give is a task requiring
some skill. Bolts are much more easily placed and made tight. In the
matter of cost of metal left in the wall, the question is between the
cost of scrap gas pipe and of wire; the pound price of the wire is
greater but fewer pounds are used and the metal is in more convenient
shape to cut to length and to handle. This convenience in shaping the
tie to the work gives the advantage to wire ties for isolated jobs or
jobs which involve a continual change in the length and spacing of the
ties. In general the contractor will find bolts preferable where
sectional forms are used and wire ties preferable when using continuous
forms.
One objection urged against the use of wire ties is that the metal is
exposed at the face of the work when they are clipped off unless the
concrete is chipped and the cavity plastered. To obviate this objection
various forms of removable "heads" have been devised. Two such devices
are shown by Figs. 104 and 105. In both the bolt is unscrewed, leaving
the "heads" embedded. The head shown by Fig. 104 has the advantage that
it can be made by any blacksmith, while the head shown by Fig. 105 is a
special casting.
[Illustration: Fig. 104.--Tie for Wall Forms.]
[Illustration: Fig. 105.--Tie for Wall Forms.]
~MIXING AND PLACING CONCRETE.~--Where a long stretch of wall is to be
built the system of mixing and handling the concrete must be capable of
being shifted along the work. For isolated walls of short length this
problem is a simpler one. Where the mixer can be installed on the bank
above, wheeling to chutes reaching down to the work is the best
solution. As shown in Chapter IV concrete can be successfully and
economically chuted to place to a greater extent than most contractors
realize. Where the mixer has to be installed at the foot of the wall
wheelbarrow inclines, derricks, gallows frames, etc., suggest themselves
as means of handling the concrete. It is not this class of work,
however, but the long stretches of heavy section walls such as occur in
depressed or elevated railway work in cities that call for thought in
the arrangement and selection of mixing and handling plant.
In building the many miles of retaining wall in the work of doing away
with grade crossings in Chicago, Ill., trains made up of a mixer car and
several material cars have been used. The mixer is mounted on a flat car
set at the head of the train and is covered by a decking carrying two
charging hoppers set above the mixer. The material cars are arranged
behind, the sand and stone or gravel being in gondola cars. Portable
brackets hooked to the sides of the gondola cars carry runways for
wheelbarrows. Sand and stone or gravel are wheeled to the charging
hoppers, the work being continuous since one hopper is being filled
while the other is being discharged into the mixer. The mixer discharges
either into a chute, wheelbarrows or buckets. The foregoing is the
general arrangement; it is modified in special instances, as is
mentioned further on. The chief objection to the method is the
difficulty of loading the wheelbarrows standing on runways level with
the tops of the gondola sides. The lift from the bottom of the car is
excessive, and as pointed out previously, shoveling stone or gravel by
digging into it from the top is a difficult task.
The delivery of the concrete into the forms was accomplished by chute
where possible, otherwise by wheelbarrows or cranes, and in one case by
belt conveyor. In the last instance the mixer car was equipped with a
Drake continuous mixer and was set in front. Behind it came three or
four gondola cars of sand and stone, and at the rear end a box car of
cement. All material was wheeled on side runways to two charging hoppers
over the mixer. The mixer discharged onto a belt conveyor carried by a
25-ft. boom guyed to an A-frame on the car and pivoted at the car end to
swing 180° by means of a tag line. The outer end of the conveyor was
swung over the forms. A ¾-in. wire rope wrapped eight times around two
drums on the mixer car and passing through slots in the floor to anchors
placed one 500 ft. in front and one 500 ft. to the rear enabled the
train to be moved back and forth along the work. This scheme of
self-propulsion saved the hire of a locomotive. In another case the
mixer was discharged into buckets which were handled by a crane
traveling back and forth along a track laid on two flat cars.
[Illustration: Fig. 106.--Side Elevation of Traveling Mixer Plant,
Galveston Sea Wall.]
Another type of movable mixer plant used in constructing a sea-wall some
3½ miles long at Galveston, Tex., is shown by Figs. 106 and 107. Two of
these machines mixed and placed some 127,000 cu. yds. of concrete, in 1
cu. yd. batches. Two 12-HP. engines operated the derricks and one 16-HP.
engine operated the Smith mixer; all engines took steam from a 50-HP.
boiler. The rated capacity of each machine was 300 to 350 cu. yds. per
day. The method of operation is clearly indicated by the drawings.
[Illustration: Fig. 107.--End Elevation of Traveling-Mixer, Galveston
Sea Wall.]
Placing the concrete in the forms is generally required to be done in
layers; with wet mixtures this means little more than distributing the
concrete somewhat evenly along the wall and slicing and puddling it to
get rid of air and prevent segregation. Where mortar facing is required
the face form described in Chapter VIII may be used. A reasonably good
surface can be secured without mortar facing by spading the face. With
dry concrete, placing and ramming in layers, calls for such care as is
necessary in dry concrete work everywhere. Where new concrete has to be
placed on concrete placed the day before, good bond may be secured and
the chance of efflorescence be reduced by the methods described in
Chapter VIII.
~WALLS IN TRENCH.~--In canal excavation, in subway work in cities, and the
like, it is often necessary to dig trenches and build retaining walls in
them before excavating the core of earth between the walls. The
following examples of such work are taken from personal records:
_Example I._--A Smith mixer was used, the concrete being delivered where
wanted by a Lambert cableway of 400 ft. span. The broken stone and sand
were delivered near the work in hopper-bottom cars which were dumped
through a trestle onto a plank floor. Men loaded the material into
one-horse dump carts which hauled it 900 ft. to the mixer platform. This
platform was 24×24 ft. square, and 5 ft. high, with a planked approach
40 ft. long and contained 7,300 ft. B. M. The stone and sand were dumped
at the mouth of the mixer and shoveled in by 4 men. Eight men, working
in pairs, loaded the broken stone into the carts, and 2 men loaded the
sand. Each cart was loaded with about 70 shovelfuls of stone on top of
which 35 shovelfuls of sand were thrown. It took 3 to 5 minutes to load
on the stone and 1 minute to load the sand. The carts traveled very
slowly, about 150 ft. a minute--in fact, all the men on the job,
including the cart drivers, were slow. After mixing, the concrete was
dumped into iron buckets holding 14 cu. ft. water measure, making about
½ cu. yd. in a batch. The buckets were hooked on to the cableway and
conveyed where wanted in the wall. Steam for running the mixer was taken
from the same boiler that supplied the cableway engine. The average
output of this plant was 100 cu. yds. of concrete per 10-hour day,
although on many days the output was 125 cu. yds., or 250 batches. The
cost of mixing and placing was as follows, on a basis of 100 cu. yds.
per day:
Per day. Per cu. yd.
8 men loading stone into carts $12.00 $ .12
2 men loading sand into carts 3.00 .03
1 cart hauling cement 3.00 .03
8 carts hauling stone and sand 24.00 .24
4 men loading mixer 6.00 .06
1 man dumping mixer 1.50 .01
2 men handling buckets at mixer 3.00 .03
6 men dumping buckets and ramming 9.00 .09
12 men making forms at $2.50 30.00 .30
1 cable engineman 3.00 .03
1 fireman 2.00 .02
1 foreman 6.00 .06
1 waterboy 1.00 .01
1 ton coal for cableway and mixer 4.00 .04
------- -----
Total $107.50 $1.07
In addition to this cost of $1.07 per cu. yd. there was the cost of
moving the whole plant for every 350 ft. of wall. This required 2 days,
at a cost of $100, and as there were about 1,000 cu. yds. of concrete in
350 ft. of wall 16 ft. high, the cost of moving the plant was 10 cts.
per cu. yd. of concrete, bringing the total cost of mixing and placing
up to $1.17 per cu. yd. As above stated, the whole gang was slow.
The labor cost of making the forms was high, for such simple and heavy
work, costing $10 per M. of lumber placed each day. The forms were 2-in.
sheeting plank held by 4×6-in. upright studs 2½ ft. apart, which were
braced against the sides of the trench. The face of the forms was
dressed lumber and all cracks were carefully puttied and sandpapered.
The above costs relate only to the massive part of the wall and not the
cost of putting in the facing mortar, which was excessively high. The
face mortar was 2 ins. thick, and about 3½ cu. yds. of it were placed
each day with a force of 8 men! Two of these men mixed the mortar, 2 men
wheeled it in barrows to the wall, 2 men lowered it in buckets, and 2
men put it in place on the face of the wall. If we distribute this labor
cost on the face mortar over the 100 cu. yds. of concrete laid each day,
we have another 12 cts. per cu. yd.; but a better way is to regard this
work as a separate item, and estimate it as square feet of facing work.
In that case these 8 men did 500 sq. ft. of facing work per day at a
cost of nearly 2½ cts. per sq. ft. for labor.
_Example II._--The building of a wall similar to the one just described
was done by another gang as follows: The stone and sand were delivered
in flat cars provided with side boards. In a stone car 5 men were kept
busy shoveling stone into iron dump buckets having a capacity of 20 cu.
ft. water measure. Each bucket was filled about two-thirds full of
stone, then it was picked up by a derrick and swung over to the next car
which contained sand, where two men filled the remaining third of the
bucket with sand. The bucket was then lifted and swung by the derrick
over to the platform of the mixer where it was dumped and its contents
shoveled by four men into the mixer, cement being added by these men.
The mixer was dumped by two men, loading iron buckets holding about ½
cu. yd. of concrete each, which was the size of each batch. A second
derrick picked up the concrete bucket and swung it over to a platform
where it was dumped by one man; then ten men loaded the concrete into
wheelbarrows and wheeled it along a runway to the wall. One man assisted
each barrow in dumping into a hopper on the top of a sheet-iron pipe
which delivered the concrete. The two derricks were stiff-leg derricks
with 40-ft. booms, provided with bull-wheels, and operated by double
cylinder (7×10-in.) engines of 18-HP. each. About 1 ton of coal was
burned daily under the boiler supplying steam to these two hoisting
engines. The output of this plant was 200 batches or 100 cu. yds. of
concrete per 10-hr. day, when materials were promptly supplied by the
railroad; but delays in delivering cars ran the average output down to
80 cu. yds. per day.
On the basis of 100 cu. yds. daily output, the cost of mixing and
placing the concrete was as follows:
Per day. Per cu. yd.
5 men loading stone $ 7.50 $.07½
2 men loading sand 3.00 .03
4 men charging mixer 6.00 .06
2 men loading concrete into buckets 3.00 .03
1 man dumping concrete from buckets .50 .01½
10 men loading and wheeling concrete .00 .15
1 man dumping wheelbarrows 1.50 .01½
3 men spreading and ramming 4.50 .04½
2 enginemen 5.00 .05
1 fireman 2.00 .02
1 waterboy 1.00 .01
1 foreman 6.00 .06
10 men making forms 25.00 .25
1 ton coal 4.00 .04
Total 85.00 $.85
In addition there were 8 men engaged in mixing and placing the 2-in.
facing of mortar as stated above.
~CHICAGO DRAINAGE CANAL.~--The method and cost of constructing some 20,000
ft. of concrete wall by contract in building the Chicago Drainage Canal
is compiled from records kept by Mr. James W. Beardsley. The work was
done on two separate sections, Section 14 and Section 15. In both cases
a 1-1½-4 natural cement concrete was used with a 3-in. facing and a
3-in. coping of 1-3 Portland cement mortar.
_Section 14._--The average height of the wall was 10 ft., and the
thickness at base was one-half the height. The stone for the concrete
was obtained from the spoil bank of the canal, loaded into wheelbarrows
and wheeled about 100 ft. to the crusher; some was hauled in wagons. An
Austin jaw crusher was used, and it discharged the stone into bins from
which it was fed into a Sooysmith mixer. The crusher and the mixer were
mounted on a flat car. Bucket elevators were used to raise the stone,
sand and cement from their bins to the mixer; the buckets were made of
such size as to give the proper proportions of ingredients, as they all
traveled at the same speed. Only two laborers were required to look
after the elevators. The sand and cement were hauled by teams and dumped
into the receiving bins. There were 23,568 cu. yds. on Section 14 and
the cost was as follows:
Typical Wages per Cost per
General force: force. 10 hrs. cu. yd.
Superintendent 1.0 $5.00 $0.026
Blacksmith 1.1 2.75 0.016
Timekeeper 0.5 2.50 0.007
Watchman 0.6 2.00 0.007
Waterboys 3.9 1.00 0.022
Wall force:
Foreman 0.9 2.50 0.013
Laborers 8.6 1.50 0.073
Tampers 2.3 1.75 0.022
Mixer force:
Foreman 1.2 2.50 0.017
Enginemen 1.8 2.50 0.025
Laborers 6.7 1.50 0.057
Pump runner 1.0 2.00 0.010
Mixing machines 1.7 1.25 0.012
Timber force:
Foreman 0.6 2.50 0.008
Carpenters 4.7 2.50 0.057
Laborers 1.2 1.50 0.010
Helpers 5.3 2.50 0.075
Hauling force:
Laborers 2.6 1.75 0.026
Teams 6.3 3.25 0.116
Crushing force:
Foreman 0.5 2.50 0.007
Engineman 1.7 2.50 0.023
Laborers 3.5 1.50 0.032
Austin crushers 1.7 1.20 0.011
Loading stone:
Foreman 1.7 2.50 0.023
Laborers 32.9 1.50 0.280
------
Total for crushing, mixing and placing $0.975
The daily costs charged to the mixers and crushers include the cost of
coal, at $2 a ton, and the cost of oil.
The gang "loading stone" apparently did a good deal of sledging of large
stones, and they also wheeled a large part of it in barrows to the
crusher.
The plant cost $9,600, distributed as follows:
2 jaw crushers $3,000
2 mixers 3,000
Track 1,260
Lumber 500
Pipe 840
Sheds 400
Pumps 600
-----
Total $9,600
If this first cost of the plant were distributed over the 23,568 cu.
yds. of concrete it would amount to 41 cts. per cu. yd.
The cost of the concrete was as follows:
Per cu. yd.
Utica cement, at $0.65 per bbl. $0.863
Portland cement, at $2.25 per bbl. 0.305
Sand, at $1.35 per cu. yd. 0.465
Stone and labor, as above given 0.975
------
Total $2.608
First cost of plant $0.407
_Section 15._--The conditions on this section were much the same as on
Section 14, just described, except that the limestone was quarried from
the bed of the canal, and was crushed in a stationary crusher, No. 7
Gates. The stone was hauled 1,000 ft. to the crusher on cars drawn by a
cable from a hoisting engine. The output of this crusher averaged 210
cu. yds. per day of 10 hrs. The crushed stone was hauled in dump cars,
drawn by a locomotive, to the mixers. Spiral screw mixers mounted on
flat cars were used, and they delivered the concrete to belt conveyors
which delivered the concrete into the forms.
The forms on Section 15 (and on Section 14 as well) consisted of upright
posts set 8 ft. apart and 9 ins. in front of the wall, held at the toe
by iron dowels driven into holes in the rock, and held to the rear posts
by tie rods. The plank sheeting was made up in panels 2 ft. wide and 16
ft. long, and was held up temporarily by loose rings which passed around
the posts which were gripped by the friction of the rings. These panels
were brought to proper line and held in place by wooden wedges. After
the concrete had set 24 hrs. the wedges were struck, the panels removed
and scraped clean ready to be used again.
The cost of quarrying and crushing the stone, and mixing the concrete on
Section 15 was as follows:
Typical Wages per Cost per
General force-- force. 10 hrs. cu. yd.
Superintendent 1.0 $5.00 $0.024
Blacksmith 0.9 2.75 0.011
Teams 1.7 3.00 0.025
Waterboy 4.5 1.00 0.022
Wall force--
Foreman 1.1 2.50 0.010
Laborers 14.4 1.50 0.105
Tampers 0.1 1.75 0.001
Mixer force--
Foreman 2.1 2.50 0.026
Enginemen 2.1 2.50 0.022
Laborers 23.1 1.50 0.180
Mixing machines 2.1 1.25 0.022
Timber force--
Carpenters 0.8 3.00 0.013
Laborers 0.7 1.50 0.005
Helpers 10.2 2.50 0.125
Hauling force--
Foreman 0.7 2.50 0.009
Enginemen 1.4 2.50 0.019
Fireman 0.4 1.75 0.003
Brakeman 2.2 2.00 0.018
Teams 0.4 3.25 0.007
Laborers 1.5 1.50 0.010
Locomotives 1.4 2.25 0.015
Crushing force--
Foreman 1.0 2.50 0.014
Enginemen 1.0 2.50 0.014
Laborers 11.1 1.50 0.081
Firemen 1.0 1.75 0.008
Gyratory crusher 1.0 2.25 0.011
Quarry force--
Foreman 1.2 2.50 0.012
Laborers 19.0 1.50 0.140
Drillers 1.8 2.00 0.017
Drill helpers 1.8 1.50 0.013
Machine drills 1.8 1.25 0.011
------
$0.993
The first cost of the plant for this work on Section 15 was $25,420,
distributed as follows:
1 crusher, No. 7 Gates $12,000
Use of locomotive 2,200
Car and track 5,300
3 mixers 3,000
Lumber 1,200
Pipe 720
Small tools 1,000
-------
Total $25,420
This $25,420 distributed over the 44,811 cu. yds. of concrete amounts to
57 cts. per cu. yd.
It will be noted that 2 mixers were kept busy. Their average output was
100 cu. yds. each per day, which is the same as for the mixers on
Section 14.
The total cost of concrete on Section 15 was as follows:
Per cu. yd.
Labor quarrying, crushing and mixing $0.991
Explosives 0.083
Utica cement, at $0.60 per bbl. 0.930
Portland cement, at $2.25 per bbl. 0.180
Sand, at $1.35 per cu. yd. 0.476
------
Total $2,660
First cost of plant $0.567
It is not strictly correct to charge the full first cost of the plant to
the work as it possessed considerable salvage value at the end.
_Comparison._--For the purpose of comparing Sections 14 and 15 the
following summary is given of the cost per cubic yard of concrete:
Sec. 14. Sec. 15.
General force $0.078 $0.082
Wall force 0.108 0.116
Mixing force 0.121 0.250
Timbering force 0.150 0.140
Hauling force 0.142 0.081
Crushing force 0.073 0.128
Quarry force 0.303 0.275
Cement, natural 0.863 0.930
Cement, Portland 0.305 0.180
Sand 0.465 0.476
Plant (full cost) 0.407 0.567
------ -------
Total $3.015 $3.225
It should be remembered that on Section 14 there was no drilling and
blasting of the rock, but that the "quarry force" not only loaded but
hauled the stone to the crusher. The cost of mixing on Section 15 is
higher than on Section 14 because the materials were dumped on platforms
and shoveled into the mixer, instead of being discharged from bins into
the mixer as on Section 14.
[Illustration: Fig. 108.--Cross Section of Retaining Wall. New York
Central Terminal Work.]
[Illustration: Fig. 109.--Portable Concrete Mixing Tower, N. Y. Central
Terminal Work.]
~GRAND CENTRAL TERMINAL, NEW YORK, N. Y.~--In building a retaining wall of
the cross-section, shown in Fig. 108, a traveling tower moving on tracks
parallel to the wall contained the concrete mixing plant. The
construction of the tower is shown in Fig. 109. The tower had two
platforms, one at the top carrying two 10-cu. yd. bins for sand and
stone and the other directly below carrying 40 cu. ft. (4 cu. ft.
cement, 12 cu. ft. sand and 24 cu. ft. stone) Ransome mixer driven by a
30 H.P. motor and a Lidgerwood motor hoist. The elevator tower carried
two 40-cu. ft. Ransome dumping buckets traveling in guides and dumping
automatically into the bins. These buckets were operated by the
Lidgerwood motor hoist on the mixer platform. Sand and broken stone on
flat cars were brought alongside the tower. The sand was shoveled direct
from the car into the sand bucket, but the broken stone was shoveled
into wheelbarrows which were wheeled over a light bridging from car to
bucket and dumped. Wheelbarrows were used for handling the stone chiefly
because the capacity of the plant was so great that enough men could not
be worked in the limited space around the bucket to keep up the supply
by shoveling. The wheelbarrow work added materially to the cost. Cement
was carried from the cars to the sand bucket, hoisted and stored on the
mixer platform which provided storage room for 100 bags. A 1-3-6 mixture
was used; the sand and stone were chuted directly from the bins to the
charging hopper and the cement was charged by hand. The mixed concrete
was delivered to two 1 cu. yd. dump cars running on a 2-ft. gage track
laid in sections on the cross pieces connecting the uprights of the
forms. The track had no switches, so that one car had to wait for the
other. Four men were required to push each car and two more men assisted
in dumping the car and kept the track clear. The wall was built in
sections 51 ft. long, each containing 250 cu. yds. One of these sections
was filled in 8 hours with ease and by a little hustling a section was
filled in 6¾ hours, which is at the rate of 37 cu. yds. of concrete per
hour. Working 8 hours per day the cost of mixing, transporting and
placing concrete with this mixing plant, with wages for common labor of
$1.50 per day, was as follows:
Total. Per cu. yd.
2 men carrying cement $ 3.00 $0.012
6 men shoveling sand 9.00 0.036
17 men shoveling stone 25.00 0.100
11 men wheeling stone 16.00 0.064
2 men at stone and sand bins 3.00 0.012
2 men opening cement bags 3.00 0.012
1 man dumping hopper 1.50 0.006
1 man dumping mixer 1.50 0.006
1 man cleaning chute, mixer, etc. 1.50 0.006
1 motorman or engineer 3.00 0.012
------- -------
Total labor mixing $66.50 $0.266
8 men pushing 2 cars 12.00 0.048
2 men cleaning track, etc. 3.00 0.012
7 men spading concrete 10.50 0.042
------- -------
Total labor transporting, placing $ 25.50 $0.102
1 foreman 5.00 0.020
Electricity estimated 7.00 0.028
------- -------
Total general $ 12.00 $0.048
Grand total $104.00 $0.416
It will be noted that the cost of shoveling and wheeling the broken
stone amounts to 16.4 cts. per cu. yd., or nearly 40 per cent. of the
total cost of mixing and placing. The cost of spading the concrete is
also high for a sloppy mixture, but is probably accounted for by the
fact that the concrete had to be spaded so as to have 2 or 3 ins. of
clear mortar next the forms. The forms used in constructing the wall
are shown by Figs. 110 and 111. They were made in panels 51 ft. long and
a locomotive crane was used to shift the panels. This crane worked
handling forms only a small part of the time, but a form gang of 10
carpenters was kept busy all of the time moving and reassembling.
Assuming the work of the crane to amount to $5 per day and the wages of
the carpenter gang to amount to $25, we get a cost of 12 cts. per cubic
yard of concrete for shifting forms. It should be noted carefully that
the costs given for this work do not include cost of materials, interest
on plant, superintendence and other items.
[Illustration: Fig. 110.--End View of Forms for Retaining Wall, New York
Central Terminal Work.]
~WALL FOR RAILWAY YARD.~--For building a retaining wall 7 ft. high, forms
were made and placed by a carpenter and helper at $8 per M., wages being
35 cts. and 20 cts. an hour, respectively. Concrete materials were
dumped from wagons alongside the mixing board. Ramming was unusually
thorough. Foreman expense was high, due to small number in gang; 2 cu.
yds. were laid per hour by the gang.
[Illustration: Fig. 111.--Corner Detail of Retaining Wall Forms, New
York Central Terminal Work.]
Per day. Per cu. yd.
7 mixers, 15 cts. per hour $10.50 $0.53
2 rammers, 15 cts. per hour 3.00 0.15
1 foreman 30 cts. per hr., 1 waterboy 5 cts. 3.50 0.17
------- ------
Total labor $17.00 $0.85
The total cost was as follows per cubic yard:
Per cu. yd.
0.8 bbls. Portland cement, at $2 $1.60
Sand 0.30
Gravel 0.70
Labor mixing and placing 0.85
Lumber for forms, at $16 per M. 0.56
Labor on forms, at $8 per M. 0.28
------
Total, per cubic yard $4.29
The sheathing plank for the forms was 2-in. hemlock.
~CONCRETE FOOTING FOR RUBBLE MASONRY RETAINING WALL.~--In constructing a
footing for a retaining wall at Grand Rapids, Mich., a 1-2½-5 natural
cement concrete was used. It was found that 1 cu. yd. of concrete was
equivalent to 29.8 cu. ft. of material composed of 3.6 cu. ft. or 1.1
bbls. of cement, 8.4 cu. ft. or 2.7 bbls. of sand and 17.8 cu. ft. or
5.5 bbl. of broken stone. The labor cost of 15.5 cu. yds. of concrete
was as follows:
Item. Total. Per cu. yd.
Foreman, 14 hours at 40 cts. $ 5.60 $0.3613
Foreman, 20 hours at 22.5 cts. 4.50 0.2903
Laborers, 49 hours at 12.5 cts. 6.11 0.3942
Mason, 2 hours at 35 cts. 0.70 0.0451
------ --------
Total labor $16.91 $1.0909
All material was furnished by the railway company, the contractor
furnishing labor only; his contract price for this was $1 per cu. yd.
~TRACK ELEVATION, ALLEGHENY, PA.~--The wall was 6,100 ft. long and 75 per
cent. was on curves. The first wall built had a top width of 2½ ft. and
a bottom width of 0.4 the height with the back on a smooth batter. Later
the back was stepped and last the wall was proportioned as follows:
Calling the height from top of foundation to under coping, then width of
base was 0.45 (h + 3), the top measuring 2½ ft. The back was arranged
in steps 24 ins., 30 ins. and 36 ins. high, and the thickness of wall at
each step was, calling h equal to height of step from base, 0.45 (h + 3).
Several forms of expansion joints were tried. The first was tarred
paper extending through the wall every 50 ft.; the second was ½-in.
boards running through the wall every 50 ft.; the third was ½-in. board
extending 2 ft. into the wall, with a ¼-in. cove at the angles, every 25
ft. The third construction gave perfect satisfaction.
A 1-2-5 natural cement and a 1-3-6 Portland cement concrete mixed fairly
wet were used. The concrete was laid in 8-in. courses and faced with a
1-2 mortar. The forms were 2-in. white pine faced and jack planed on the
edges; upon removal of the forms board marks and other defects were
removed and a wash of neat cement was applied. One contractor used hand
mixing. The sand and gravel were measured in wheelbarrows and wheeled
onto the platform; the sand and cement were spread in thin layers, one
over the other, and thoroughly mixed dry; the gravel was then spread
over the mixture, the whole was shoveled into barrows or the pit again
shoveled into place and rammed. The other contractor used a cubical
mixer. A charging box holding 1¼ cu. yds. and graduated to show the
correct proportions of sand and gravel was filled by shoveling; cement
was placed on top and the box hoisted and dumped into the mixer. A
barrel holding the correct amount of water was emptied into the mixer
which was turned 10 or 15 times and discharged into cars. The costs of
mixing by hand and by machine were as follows:
Hand mixing. Total. Per cu. yd.
½ foreman at $3 $ 1.50 $0.025
3 men wheeling barrows at $1.50 4.50 0.075
10 men wheeling materials at $1.50 15.00 0.250
3 men mixing sand and gravel at $1.50 4.50 0.075
6 men mixing concrete at $1.50 9.00 0.150
1 man sprinkling at $1.50 1.50 0.025
------ ------
Total $36.00 $0.600
The output of the hand mixing gang was 60 cu. yds. per day.
Machine mixing. Total. Per cu. yd.
1 foreman at $3.50 $ 3.50 $0.035
1 stationary engineer at $3 3.00 0.030
½ foreman at $1.75 0.87 0.009
15 men loading charging bucket at $1.50 22.50 0.225
2 men dumping charging bucket at $1.75 3.50 0.035
2 tagmen at $2, ½ time 2.00 0.020
1 man at trap at $2, ½ time 1.00 0.010
------ ------
Total $36.37 $0.364
The output of the cubical mixer was 100 cu. yds. per day.
The costs of placing concrete in the forms above the foundation by hand
below 12 ft., and by cars and derricks any height, were as follows:
By hand (barrows) below 12 ft. Total. Per cu. yd.
4 men loading concrete at $1.50 $ 6.00 $0.100
1 foreman ½ time at $3 1.50 0.025
10 men wheeling at $1.50 15.00 0.250
1 man scraping barrows at $1.50 1.50 0.025
2 men placing concrete at $1.50 3.00 0.050
1 man placing mortar face at $1.50 1.50 0.025
2 men mixing and carrying mortar at $1.50 3.00 0.050
------ ------
Total $31.50 $0.525
By cars and derricks--
1 horse and driver at $3 $ 3.00 $0.030
2 men dumping concrete ½ time at $1.50 1.50 0.015
1 fireman ½ time at $1.75 0.88 0.009
3 tagmen at $1.50 4.50 0.045
8 men placing and ramming conc. at $1.50 12.00 0.120
2 men mixing mortar at $1.50 3.00 0.030
2 men placing mortar at $1.50 3.00 0.030
2 men carrying mortar at $1.50 3.00 0.030
1 foreman at $3 3.00 0.030
1 stationary engineer at $3 3.00 0.030
2 men attending hook at $1.50 3.00 0.030
------ ------
Total $39.88 $0.399
The costs of placing concrete in the foundations were as follows:
By hand-- Total. Per cu. yd.
1 foreman ½ time at $3 $ 1.50 $0.025
4 men shoveling concrete at $1.50 6.00 0.100
1 man placing concrete at $1.50 1.50 0.025
1 man ramming concrete at $1.50 1.50 0.025
------ ------
Total $10.50 $0.175
By machine--
1 horse and driver at $3 $ 3.00 $0.030
3 men pushing and unloading car at $1.50 4.50 0.045
5 men placing and ramming at $1.50 7.50 0.075
1 foreman at $3 3.00 0.030
2 men dumping mixer at $1.50 3.00 0.030
------ ------
Total $21.00 $0.210
~COST OF RETAINING WALL.~--The following figures of the cost of a concrete
retaining wall are given by C. C. Williams:
Cost of Material.
Unit
Kind and amount of material-- Price. Cost.
Stone, 441 tons $ .70 $308.70
Sand, 182.5 yds. .55 100.37
Cement, 536 bbls. .85 453.60
-------
Total $862.67
Lumber ¾ value $205.33
Wheelbarrows, ¾ value, 6 at $3.50 15.75
-------
Total $221.08
Excavation--
Labor, 4,002 hours at 15 cts. $600.30
Carts, 800 hours at 12½ cts. 100.00
Foreman, 460 hours at 35 cts. 171.00
Waterboy, 240 hours at 10 cts. 24.00
-------
Total $895.30
Concrete--
Labor, 2,398 hours at 15 cts. $359.70
Foreman, 224 hours at 35 cts. 77.40
-------
Total $437.10
Handling material--
Unloading cars, 380 hours at 15 cts. $ 57.00
Foreman, 40 hours at 35 cts. 14.00
-------
Total $ 71.00
Forms--
Carpenters, 997 hours at 22½ cts. $224.33
Work to support bridge--
Carpenters, 542 hours at 22½ cts. $121.95
Labor, 458 hours at 15 cts. 68.70
-------
Total $190.65
Superintendence and office--
Superintendent, 30 hours at 50 cts. $15.00
Office 20.00
--------
Total $35.00
--------
Grand total $2,937.13
Proportional costs--
Cost Per Per Cent.
Yard of of Total
Item. Cost. Concrete. Cost.
Concrete materials $ 862.67 $2.02 46.7
Laying concrete 437.10 1.03 23.4
Lumber 205.33 .48 11.3
Building forms 224.33 .53 12.3
Handling material 71.00 .17 03.8
Wheelbarrows 15.75 .04 01.0
Supt., etc. 35.00 .07 01.5
--------- ----- ------
Total $1,851.18 $4.34 100.00
Work on bridge 190.65
Excavation 895.30
---------
$2,937.13
CHAPTER XIV.
METHODS AND COST OF CONSTRUCTING CONCRETE FOUNDATIONS FOR PAVEMENTS.
Contractor's skill or want of skill in systematizing and managing labor
counts as high in street work as in any class of concrete construction.
As previously demonstrated, the cost of mixing is a very small portion
of the labor cost of concrete in place; the costs of getting the
materials to the mixer and the mixed concrete to the work are the big
items, and in street work the opportunity for increasing the cost of
these items through mismanagement is magnified by the large area of
operations involved per cubic yard of concrete placed. One cubic yard of
concrete makes 6 sq. yds. of 6-in. pavement foundations and 100 cu. yds.
of concrete make a 6-in. foundation for 300 ft. of 30-ft. street, while
4 to 5 cu. yds. will build 100 ft. of ordinary curb and gutter. Thus the
haulage per cubic yard is considerable at best, and lack of plan in
distributing stock piles and handling the concrete can easily result in
such increased haulage expenses as to change a possible profit into a
certain loss. A little thought and skill in planning street work pays a
good profit.
~MIXTURES EMPLOYED.~--A comparatively lean concrete will serve for
pavement foundations; mixtures of 1-4-8 Portland cement or 1-2-5 natural
cement are amply good and it is folly, ordinarily, to employ richer
mixtures. Until recently, natural cement has been used almost
exclusively; a 1-2-5 natural cement mixture requires about 1.15 bbls. of
cement per cubic yard of concrete. A 1-4-8 Portland cement mixture
requires about 0.7 bbl. of cement per cubic yard. In the opinion of the
authors a considerably leaner mixture of Portland concrete is
sufficiently good when it is well mixed in machine mixers--for a 6-in.,
foundation 0.5 bbl. per cu. yd. The mixtures actually employed are
proportioned about as stated and their cost, or that of any other common
mixture, may easily be computed from Tables XII and XIII, giving for
different mixtures the quantities of cement, sand and stone per cubic
yard of concrete; the product of these quantities and the local prices
of materials in the stock piles gives the cost. When the concrete is
mixed by hand the ordinary labor cost of foundations is 0.4 to 0.5 of a
10-hour day's wages per cubic yard of concrete; occasionally it may be
as low as 0.3 of a day's wages where two mixing gangs are worked side by
side under different foremen and with an exacting contractor. Data for
machine mixing are too few to permit a similar general statement for
machine work, but in one case coming under the authors' observation, the
cost figured out to a little less than 0.2 of a day's wages per cubic
yard.
~DISTRIBUTION OF STOCK PILES.~--Assuming a 30-ft. street and a 1-3-5
concrete laid 6 ins. thick, the quantities of concrete materials
required per lineal foot of street are: Cement 0.60 bbl., sand 0.27 cu.
yd., stone 0.44 cu. yd. The stock piles should be so distributed that
each supplies enough materials for a section of foundation reaching half
way to the next adjacent stock pile on each side, and they should not
contain more or less material, otherwise a surplus remains to be cleaned
up or a deficiency to be supplied by borrowing from another pile. A
little care will ensure the proper distribution and it is well paid for
in money saved by not rehandling surplus or borrowed materials. For a
given mixture and a given width and thickness of foundation, the sizes
of the stock piles are determined by their distance apart and this will
depend upon whether hand or machine mixing is employed and upon the
means adopted for hauling the raw materials and the mixed concrete. It
is worth while always in stock piles of any size, to lay a flooring of
plank particularly under the stone pile; if dumped directly on the
ground it costs half as much again to handle stone. Current practice
warrants everything from a continuous bank, to piles from 1,000 to 1,500
ft. apart, in the spacing of stock piles.
~HINTS ON HAND MIXING.~--All but a small percentage of the concrete
annually laid in street work is hand mixed. The authors are confident
that this condition will disappear as contractors learn more of the
advantages of machine mixing, but it prevails at present. The general
economics of hand mixing are discussed in Chapter II; in street work as
before stated, the big items of labor cost are the costs of handling
materials and the data in Chapter II on these processes deserve special
attention. It is particularly worth noting that it is seldom economical
to handle materials in shovels where carrying is necessary; it is a
common thing in street work to see an attempt to get the stock piles so
close to the mixing board that the material can be handled with shovels,
and this is nearly always an economic error. Street work is readily
measured; in fact, its progress can be seen at a glance, and advantage
can often be taken of this fact to profit by the rivalry of separate
gangs. The authors have known of the labor costs being reduced as much
as 25 per cent., due to pitting one gang against another where each
could see the progress made by the other.
~METHODS OF MACHINE MIXING.~--Concrete mixers have been slow to replace
handwork in laying pavement foundations. In explanation of this fact it
is asserted: (1) That frequent shifting of the mixer causes too much
lost time, and (2) that the principal item of labor cost in street work
is the conveying of materials to and from the mixer, and this item is
the same whether hand or machine mixing be employed. The records of
machine mixer work given elsewhere in this chapter go far, in the
opinion of the authors, toward disproving the accuracy of both
assertions. If the machine used and the methods of work employed are
adapted to the conditions of street work, machine mixing can be employed
to decided advantage.
A continuous and large output is demanded in a mixer for street work;
the perfection of the mixing is within limits a minor consideration.
This at once admits for consideration types of mixers whose product is
classed as unsuitable for reinforced concrete work, and also admits of
speeding up the output of the better types to a point beyond that at
which they turn out their most perfect product. Keeping these facts in
mind either of the following two systems of work may be employed: (1)
Traction plants which travel with the work and deposit concrete in
place, or so nearly in place that little shoveling is necessary; (2)
portable plants which are set up at wide intervals along the work and
which discharge the concrete into carts or dump wagons which distribute
it to the work.
The secret of economic work with plants of the class cited first is the
distribution of the stock piles so as practically to eliminate haulage
from stock pile to mixer. The mixer backs away from the work, its
discharge end being toward the work and its charging end away from it.
Then deposit the materials so as to form a continuous stock pile along
the center of the street; the mixer moving backward from the completed
foundation keeps close to the materials and if the latter are uniformly
distributed in the pile the great bulk of the charging is done by
shoveling direct into the charging bucket. The point to be watched here
is that the shovelers do not have to carry the materials; separate stock
piles within moderate hauling distance by wheelbarrows are a far more
economic arrangement than a continuous pile so irregularly distributed
that much of the material has to be carried even a few paces in shovels.
Economic work with plants of the second class depends upon efficient and
adequate means of hauling the mixed concrete to the work. The plant
should not be shifted oftener than once in 1,000 to 2,000 ft., or, say,
four city blocks. This does away with the possibility of wheelbarrow
haulage; large capacity hand or horse carts must be employed. With 6 cu.
ft. hand carts, such as the Ransome cart, a haul of 500 ft. each way
from the mixer is possible and with horse carts, such as the Briggs,
this economic distance is increased to 1,000 ft. each way from the
mixer. The mixer must be close to the stock pile and it will pay to make
use of improved charging devices. A 6-in. foundation for 2,000 ft. of
30-ft. street calls for 667 cu. yds. of concrete, and if both sides are
curbed at the same time, 100 cu. yds. more are added, or 767 cu. yds. in
all; where intersecting streets are to be paved in both directions from
the mixer plant these amounts are doubled. A very small saving per cubic
yard due to mechanical handling of the materials to the mixer amounts to
the interest on a considerable investment in such plant. A point that
should not be forgotten is that carts such as those named above spread
the concrete in dumping so that little or no shoveling is required.
~FOUNDATION FOR STONE BLOCK PAVEMENT, NEW YORK, N. Y.~--Mr. G. W. Tillson,
in "Street Pavements and Paving Materials," p. 204, gives the following
data on the cost of granite block pavement in New York City in 1899. The
day was 10 hours long:
Per Per Per
Concrete gang-- day. sq. yd. cu. yd.
1 foreman $ 3.00 $0.0125 $0.075
8 mixers on two boards, at $1.25 10.00 0.0416 0.250
4 wheeling stone and sand, at $1.25. 5.00 0.0208 0.125
1 carrying cement and supplying
water, at $1.25 1.25 0.0051 0.031
1 ramming, at $1.25 1.25 0.0051 0.031
------ ------- ------
Total, 240 sq. yds. (40 cu. yds.). $20.50 $0.0851 $0.512
The concrete was shoveled direct from the mixing boards to place.
Cost 1-2-4 concrete-- Per cu. yd.
1-1/3 bbls. natural cement, at $0.90 $1.20
0.95 cu. yd. stone, at $1.25 1.19
0.37 cu. yd. sand, at $1.00 0.37
Labor 0.51
-----
$3.27
In laying 5,167 sq. yds. of granite block pavement on one job in New
York City in 1905, the authors' records show that one laborer mixed and
laid 1.3 cu. yds. of concrete per day in a 6-in. foundation; this is a
very small output. The work was done by contract and the labor cost was
as follows:
Per Per
Item. Total. sq. yd. cu. yd.
28½ days foreman at $3.50 $ 99.75 $0.0193 $0.118
399 days laborers at $1.75 698.25 0.1351 0.826
------- ------- ------
$798.00 $0.1544 $0.944
The average day's wages was $1.86, so that the labor cost was about 0.5
of a day's wages per cubic yard of concrete.
~FOUNDATION FOR PAVEMENT, NEW ORLEANS. LA.~--Mr. Alfred E. Harley states
that in laying concrete foundations for street pavement in New Orleans,
a day's work, in running three mixing boards, covering the full width
of the street, averaged 900 sq. yds., 6 ins. thick, or 150 cu. yds.,
with a gang of 40 men. With wages assumed to be 15 cts. per hour the
labor cost was:
Cts. per cu. yd.
6 men wheeling broken stone 6
3 men wheeling sand 3
1 man wheeling cement 1
2 men opening cement 2
7 men dry mixing 7
8 men taking concrete off 8
3 men tamping 3
3 men grading concrete 3
1 man attending run planks 1
3 water boys 1
2 extra men and 1 foreman 4
--
Total labor cost 39 cts.
~FOUNDATIONS FOR STREET PAVEMENT, TORONTO, CANADA.~--The following cost of
a concrete base for pavements at Toronto has been abstracted from a
report (1892) of the City Engineer, Mr. Granville C. Cunningham. The
concrete was 1-2½-7½ Portland; 2,430 cu. yds. were laid, the thickness
being 6 ins., at the following cost per cubic yard:
0.77 bbl. cement, at $2.78 $2.14
0.76 cu. yd. stone, at $1.91 1.45
0.27 cu. yd. sand and gravel, at $0.80 0.22
Labor (15 cts. per hr) 1.03
-----
Total $4.84
Judging by the low percentage of stone in so lean a mixture as the
above, the concrete was not fully 6 ins. thick as assumed by Mr.
Cunningham. Note that the labor cost was 1½ to 2 times what it would
have been under a good contractor.
~MISCELLANEOUS EXAMPLES OF PAVEMENT FOUNDATION WORK.~--The following
records of pavement foundation work are taken from the note and time
books of one of the authors:
_Case 1._--Laying 6-in. pavement foundation; stone delivered and dumped
upon 2-in. plank laid to receive it. Sand and stone were dumped along
the street, so that the haul in wheelbarrows to mixing board Was about
40 ft. Two gangs of men worked under separate foremen, and each gang
averaged 4.5 cu. yds. concrete per hour. The labor cost was as follows
for 45 cu. yds. per gang:
Per day. Per cu. yd.
4 men filling barrows with stone and sand
ready for the mixers, wages 15 cts.
per hour $6.00 $0.13
10 men, wheeling, mixing and shoveling to
place (3 or 4 steps), wages 15 cts. per
hour 15.00 0.33
2 men ramming, wages 15 cts. per hour 3.00 0.07
1 foreman at 30 cts. per hour and 1 water
boy, 5 cts 3.50 0.08
----- -----
Total $27.50 $0.61
_Case II._--Sometimes it is desirable to know every minute detail cost,
for which purpose the following is given:
----Per cu. yd.----
Day's labor. Cost.
3 men loading stones into barrows $0.06 $0.09
1 man loading sand into barrows 0.02 0.03
2 men ramming 0.04 0.06
1 foreman and 1 water boy equivalent to 0.035 0.05
Wheeling sand and cement to mixing board 0.02 0.03
Wheeling stone to mixing board 0.026 0.04
9 men mixing mortar 0.013 0.02
Mixing stone and mortar 0.049 0.07
Placing concrete (walking 15 ft.) 0.072 0.11
------ -----
Total $0.335 $0.50
In one respect this is not a perfectly fair example (although it
represents ordinary practice), for the mortar was only turned over once
in mixing instead of three times, and the stone was turned only twice
instead of three or four times. Water was used in great abundance, and
by its puddling action probably secured a very fair mixture of cement
and sand, and in that way secured a better mixture than would be
expected from the small amount of labor expended in actual mixing.
About 9 cts. more per cu. yd. spent in mixing would have secured a
perfect concrete without trusting to the water.
_Case III._--Two gangs (34 men) working under separate foremen averaged
600 sq. yds., or 100 cu. yds. of concrete per 10-hour day for a season.
This is equivalent to 3 cu. yds. per man per day. The stone and sand
were wheeled to the mixing board in barrows, mixed and shoveled to
place. Each gang was organized as follows:
Per day. Per cu. yd.
4 men loading barrows $ 6.00 $0.12
9 men mixing and placing 13.50 0.27
2 men tamping 3.00 0.06
1 foreman 2.50 0.05
------ -----
Total $25.00 $0.50
These men worked with great rapidity. The above cost of 50 cts. per cu.
yd. is about as low as any contractor can reasonably expect to mix and
place concrete by hand in pavement work.
_Case IV._--Two gangs of men, 34 in all, working side by side on
separate mixing boards, averaged 720 sq. yds., or 120 cu. yds., per
10-hour day. Each gang was organized as follows:
Per day. Per cu. yd.
6 men loading and wheeling $ 9.00 $0.15
8 men mixing and placing 12.00 0.20
2 men tamping 3.00 0.05
1 foreman 3.00 0.05
------ -----
Total $27.00 $0.45
Instead of shoveling the concrete from the mixing board into place, the
mixers loaded it into barrows and wheeled it to place. The men worked
with great rapidity.
Mr. Irving E. Howe gives the cost of a 6-in. foundation of 1-3-5 natural
cement at Minneapolis, Minn., in 1897, as $2.80 per cu. yd., or $0.467
per sq. yd. Cement cost 76 cts. per barrel and stone and sand cost
delivered $1.15 and 30 cts. respectively. Mixers received $1.75 per
day.
Mr. Niles Meriwether gives the cost of materials and labor for an 8-in.
foundation constructed by day labor (probably colored) at Memphis,
Tenn., in 1893, as follows:
Per sq. yd.
Natural cement at $0.74 per bbl $0.195
Sand at $1.25 per cu. yd 0.075
Stone at $1.87 per cu. yd 0.355
Labor mixing and placing 0.155
-----
Total $0.780
Labor was paid $1.25 to $1.50 per 8-hour day and 1.16 bbls. of cement
were used per cubic yard of concrete. The cost of materials, as will be
noted, was high and the labor seems to have been inefficient.
~FOUNDATIONS FOR BRICK PAVEMENT, CHAMPAIGN, ILL.~--The concrete foundation
for a brick pavement constructed in 1903 was 6 ins. thick; the concrete
used was composed of 1 part natural cement, 3 parts of sand and gravel,
and 3 parts of broken stone. All the materials were mixed with shovels,
and were thrown into place from the board upon which the mixing was
done. The material was brought to the steel mixing board in wheelbarrows
from piles where it had been placed in the middle of the street, the
length of haul being usually from 30 to 60 ft. The foundation was 6 ins.
thick and it cost as follows for materials and labor:
Cost per
cu. yd.
1.2 bbls. cement, at $0.50 $0.600
0.6 cu. yd. sand and gravel, at $1 0.600
0.6 cu. yd. broken stone, at $1.40 0.840
6 men turning with shovels, at $2 0.080
4 men throwing into place, at $2 0.053
2 men handling cement, at $1.75 0.023
1 man wetting with hose, at $1.75 0.012
2 men tamping, at $1.75 0.023
1 man leveling, at $1.75 0.012
6 men wheeling stone, at $1.75 0.070
4 men wheeling gravel, at $1.75 0.047
1 foreman, at $4 0.027
------
$2.387
This is practically 40 cts. per sq. yd., or $2.40 per cu. yd. of
concrete for materials and labor. It is evident from the above
quantities that a cement barrel was assumed to hold about 4.5 cu. ft.,
hence the cement was measured loose in making the 1-3-3 concrete. The
accuracy of the quantities given is open to serious doubt. It will also
be noted that the labor cost of making and placing the concrete was only
35 cts. per cu. yd., wages being nearly $1.85 per day. This is so
remarkably low that some mistake would seem to have been made in the
measurement of the work. The authors do not hesitate to say that no gang
of men ever made any considerable amount of concrete by hand at the rate
of 5.75 cu. yds. per man per day.
[Illustration: Fig. 112.--Foote Continuous Mixer Arranged for Pavement
Foundation Work.]
~FOUNDATION CONSTRUCTION USING CONTINUOUS MIXERS.~--The following are
records of two jobs of pavement foundation work using continuous mixers
with one-horse concrete carts in one instance and wheelbarrows in the
other instance. The mixer used was the Foote mixer, as arranged for the
work being described it is shown by Fig. 112. One particular advantage
of this and similar mixers for street work is that no proportioning or
measuring of the materials is required of the men. The mixers are
provided with an automatic measuring device, by means of which any
desired proportion of cement, sand and stone is delivered to the mixing
trough. The mixer is mounted on trucks, and the hoppers that receive
the sand and stone are comparatively low down. The sand can be wheeled
in barrows up a run plank and dumped into a hopper on one side of the
mixer, and in like manner the gravel or broken stone can be delivered
into a hopper on the other side. The cement is delivered in bags or
buckets to a man who dumps it into a cement hopper directly over the
mixer. All that the operator needs to attend to is to see that the men
keep the hoppers comparatively full. The records of work on the two jobs
mentioned are as follows:
[Illustration: Fig: 113.--Briggs Cart Distributing Concrete for Pavement
Foundation.]
_Job I._--The sand was delivered from the stock pile by a team hitched
to a drag scraper, and was dumped alongside the mixer where two men
shoveled it into the hopper. On the same job the concrete was hauled
away from the mixer in Briggs' concrete carts. With a gang of 30 men and
2 to 4 horses hauling concrete in Briggs' carts, the contractor averaged
1,200 sq. yds., or 200 cu. yds., per day of 10 hours. With wages of
laborers at 15 cts. per hour, and a single horse at the same rate, the
cost of labor was 26 cts. per cu. yd., or less than 4½ cts. per sq. yd.
of concrete base 6 ins. thick. The coal was a nominal item, and did not
add 1 ct. per cu. yd. to the cost. In this case the mixer was set up on
a side street and the concrete was hauled in the carts for a distance of
a block each way from the mixer. At first four carts were used, but as
the concreting approached the mixer, less hauling was required, and
finally only two carts were used. An illustration of a Briggs cart is
given by Fig. 113; it is hauled by one horse, which the driver leads,
and is dumped by an ingenious device operated from the horse's head. The
cart dumps from the bottom and spreads the load in a layer about 8 or 9
ins. thick, so that no greater amount of shoveling is necessary than
when barrows are used. It took about 20 seconds for the cart to back up
and get its load and about 5 seconds to dump and spread the load.
_Job II._--In this job the mixer was charged with wheelbarrows and
wheelbarrows were also employed to take the mixed concrete to the work,
the mixer being moved forward at frequent intervals. The stock piles
were continuous, sand on one side of the street and stone on the other
side. A 1-3-6 Portland cement concrete was used, a very rich mixture for
a 6-in. foundation. The organization of the working gang was as follows:
Men loading and wheeling gravel 8
Men assisting in loading gravel 2
Man dumping barrows into hopper 1
Men loading and wheeling sand 3
Man dumping barrows into hopper 1
Men wheeling concrete in barrows 7
Men spreading concrete 3
Men tamping concrete 2
Man pouring cement into hopper 1
Man operating mixer 1
Man shoveling spilled concrete 1
Man opening cement bags 1
Engineer 1
--
Total men in gang 32
The average day's output of this gang was 150 cu. yds., or 900 sq. yds.
in 8 hours; but on the best day's work the output was 200 cu. yds., or
1,200 sq. yds. in 8 hours, which is a remarkable record for 32 men and a
mixer working only 8 hours.
The following is the labor cost of 8,896 sq. yds. of 4½-in. concrete
foundation for an asphalt pavement constructed in New York City in 1904:
Item. Per sq yd.
Foreman at $3.75 $0.030
Laborers at $1.50 0.242
Teams at $5 0.040
Steam engine at $3.50 0.028
------
Total $0.340
The concrete was a 1-3-6 mixture and was mixed in a Foote mixer. These
costs are compiled from data collected by the authors.
~FOUNDATION CONSTRUCTION FOR STREET RAILWAY TRACK USING CONTINUOUS
MIXERS.~--The following account of the methods and cost of constructing a
concrete foundation for street railway track at St. Louis, Mo., is
compiled from information published by Mr. Richard McCulloch. The work
was done by day labor by the United Railways Co., in 1906. Figure 114
shows the concrete construction. A 1-2½-6½ Portland cement, broken stone
concrete mixed by machine was used.
[Illustration: Fig. 114.--Concrete Foundation for Street Railway Track.]
The material for the concrete was distributed on the street beside the
tracks in advance of the machine, the sand being first deposited, then
the crushed rock piled on that, and finally the cement sacks emptied on
top of this pile. The materials were shoveled from this pile into the
concrete mixing machine without any attempt at hand mixing on the
street. Great care was taken in the delivery of materials on the street
to have exactly the proper quantity of sand, rock and cement, so that
there would be enough for the ballasting of the track to the proper
height and that none would be left over. Each car was marked with its
capacity in cubic feet, and each receiver was furnished with a table by
which he could easily estimate the number of lineal feet of track over
which the load should be distributed.
The concrete mixing machines were designed and built in the shops of the
United Railways Co. Three machines were used in this work, one for each
gang. The machine is composed of a Drake continuous worm mixer, fed by a
chain dragging in a cast-iron trough. The trough is 36 ft. long, so that
there is room for 14 men to shovel into it. Water is sprayed into the
worm after the materials are mixed dry. This water was obtained from the
fire plugs along the route. In the first machine built, the Drake mixer
was 8 ft. long. In the two newer machines the mixer was 10 ft. long.
Both the conveyor and the mixer were motor driven, current being
obtained for this purpose from the trolley wire overhead. Two types of
machines were used, one in which the conveyor trough was straight and 45
in. above the rail, and the other in which the conveyor trough was
lowered back of the mixer, being 25 in. above the rail. The latter type
had the advantage of not requiring such a lift in shoveling, but the
trough is so low that a motor truck cannot be placed underneath it. In
the high machine the mixer is moved forward by a standard motor truck
under the conveyor. In the low machine the mixer is moved by a ratchet
and gear on the truck underneath the mixer. A crew of 27 men is required
to work each machine, and under average conditions concrete for 80 lin.
ft. of single track, amounting to 22 cu. yds., can be discharged per
hour.
The costs of the concrete materials delivered per cubic yard of concrete
were: Cement, per barrel, $1.70; sand, per cu. yd., $0.675, and stone,
per cu. yd., $0.425. The cost of the concrete work per cubic yard and
per lineal foot of track was as follows:
Item. Per lin. ft. Per cu. yd.
Concrete materials $0.791 $2.92
Labor mixing and placing 0.071 0.26
------ -----
Total labor and materials $0.862 $3.18
~FOUNDATION CONSTRUCTION USING BATCH MIXERS AND WAGON HAULAGE, ST. LOUIS,
MO.~--The following record of the method and cost of laying a concrete
foundation for street pavement using machine mixing and wagon haulage is
given by Mr. D. A. Fisher. The foundation was 6 ins. thick. The gravel
was dumped from wagons into a large hopper, raised by a bucket elevator
into bins, and drawn off through gates into receiving hoppers on the
charging platform where the cement was added. The receiving hoppers
discharged into the mixers, which discharged the mixed concrete into a
loading car that dumped into wagons, which delivered it on the street
where wanted. The longest haul in wagons was 30 mins., but careful tests
showed that the concrete had hardened well. The wagons were patent dump
wagons of the drop-bottom type. Mr. Fisher says:
"You may consider the following figures a fair average of the plant
referred to, working to its capacity. To these amounts, however, must be
added the interest on the investment, the cost of wrecking the plant and
the depreciation of the same, superintendence, and the pay roll that
must be maintained in wet weather. I am assuming the street as already
brought to grade and rolled.
"With labor at $1.75 per day of 10 hours, teams at $4, engineer and
foremen at $3, and engine at $5 per day, concrete mixed and put in place
by the above method costs:
Per cu. yd.
To mix $0.12 to $0.15
To deliver to street 0.10 to 0.14
To spread and tamp in place 0.08 to 0.11
--------------
Total $0.30 to $0.40
"The mixers are No. 2½ Smith, sold by the Contractors' Supply Co.,
Chicago, Ill., and a ½ yd. cube, sold by Municipal Engineering &
Contracting Co., Chicago.
"The above figures are on the basis of a batch every 2 minutes, which is
easily maintained by using the loading car, as by this means there will
be no delay in the operation of the plant owing to the irregularity of
the arrival of the teams.
"My experience leads me to believe that a better efficiency can be
obtained by using mixers of 1 cu. yd. capacity, and that the batch
mixer is the only type of machine where any certainty of the proportion
of the mixture is realized."
[Illustration: Fig. 115.--Chicago Improved Cube Traction Mixer for
Pavement Foundation.]
~FOUNDATION CONSTRUCTION USING A TRACTION MIXER.~--In laying a 6-in.
foundation for an asphalt pavement in Buffalo, N. Y., an average of 100
sq. yds., or 16.6 cu. yds., of concrete in place was made per hour using
the traction mixer shown by Fig. 115. This mixer was made by the
Municipal Engineering & Contracting Co., of Chicago, Ill., and consisted
of one of that company's improved cube mixers operated by a gasoline
engine and equipped with the regulation mechanical charging device and
also with a swinging conveyor to deliver the mixed concrete to the work.
The feature of the apparatus in its application to paving work is the
conveyor. This was 25 ft. long and pivoted at the mixer end so as to
swing through an arc of 170°. The mixer discharged into a skip or bucket
traveling on the conveyor frame and discharging over the end spreading
its load anywhere within a radius of 25 ft. In operation the mixer
traveled along the center of the street, backing away from the finished
foundation and toward the stock pile, which was continuous and was
deposited along the center of the street. The bulk of the sand and stone
was thus shoveled direct into the charging bucket and the remainder was
wheeled to the bucket in barrows. As the charging bucket is only 14 ins.
high the barrows could be dumped directly into it from the ground. The
gang worked was 17 including a foreman and one boy, and with this gang
100 sq. yds. of 6-in. foundation was laid per hour. Assuming an average
wage of 20 cts. an hour the cost of mixing and placing the foundation
concrete was 3.4 cts. per sq. yd. or 20.4 cts. per cu. yd. for labor
alone.
~FOUNDATION CONSTRUCTION USING CONTINUOUS MIXER.~--The foundation was 6
ins. thick for an asphalt pavement and was laid in Chicago, Ill. The
concrete used was exceptionally rich for pavement foundation work, it
being a 1-3-6 Lehigh Portland cement, broken stone mixture. The mixing
was done by machine, a mixer made by the Buffalo Concrete Mixer Co.,
Buffalo, N. Y., being used. This mixer was equipped with an elevating
charging hopper and was operated as a continuous mixer. The mixer was
mounted on wheels and was pulled along the center of the street ahead of
the work with its discharge end toward the work. Moves of about 25 to 30
ft. were made, the mixer being pulled ahead for this distance each time
that the concrete came up to its discharge end. The stock piles were
continuous, sand on one side and stone on the other side of the street.
Cement was stored in a pile at each end of the block. All materials were
wheeled from stock piles to mixer in wheelbarrows. The men wheeling sand
and stone loaded their own barrows, wheeled them to the mixer and
discharged them directly into the elevating hopper. No runways were
used, the barrows being wheeled directly on the ground. The cement was
brought in barrows, two or three bags being a load, and dumped alongside
a cement box which was located close to and at one side of the elevating
hopper. A man untied the bags and emptied them into the cement box and
another man scooped the cement out of the box in bucketfuls and emptied
it over the sand and stone in the elevating hopper. The mixer discharged
onto a sheet iron shoveling board, and the concrete was carried in
shovels from shoveling board to place, the length of carry being a
maximum of 25 to 30 ft. Two men were required to pull down the cone of
concrete at the discharge end of the mixer and to keep the stone from
separating and rolling down the sides. The gang was organized as
follows:
No. Men.
Loading and wheeling stone 10
Loading and wheeling sand 3 to 4
Loading and wheeling cement 2
Untieing and emptying cement bags 1
Charging cement to hopper 1
Operating mixer and hopper 1
Pulling down and tending discharge 2
Carrying concrete in shovels 8
Spreading concrete 2
Tamping concrete 2
Sweeping concrete 1
General laborers 3
Foreman 1
Watchman 1
Timekeeper 1
--
Total gang 40
This gang averaged 1,000 sq. yds. of 6-in. foundation per 10-hour day; a
maximum of 1,400 sq. yds. was laid in a day. We have thus an average of
167 cu. yds. and a maximum of 234 cu. yds. of concrete foundation mixed
and placed per 10-hour day. At an average wage of $2 per day the average
labor cost of mixing and placing concrete was 48 cts. per cu. yd. or 8
cts. per sq. yd. of 6-in. foundation. It was stated that the gang was
larger by three men than was ordinarily used owing to certain extra work
being done at the time that the above figures were collected. Taking out
three extra men and the timekeeper and watchman we get 34 men actually
working in mixing and placing concrete. This reduced gang gives us a
labor cost for mixing and placing of about 41 cts. per cu. yd. or 6.8
cts. per sq. yd. of 6-in. foundation.
~FOUNDATION CONSTRUCTION USING A BATCH MIXER.~--The following figures are
an average of several jobs using a Ransome ½-cu. yd. mixer for
constructing 6-in. foundations. The mixer was moved 1,000 ft. at a time
and the work conducted 500 ft. in each direction from each station. The
concrete materials were delivered from stock pile to mixer in
wheelbarrows and the mixed concrete was hauled to the work in
two-wheeled Ransome carts. Run planks were laid for the carts and one
man readily pushed a cart holding 6 cu. ft. The men had to work fast on
the long haul but had an easy time when the haul was short. The
organization of the gang was as follows, wages being $1.50 per day:
10 men loading and wheeling stone $15.00
4 men loading and wheeling sand 6.00
2 men handling cement 3.00
1 fireman 2.00
1 man dumping mixer 1.50
5 men wheeling carts 7.50
3 men spreading and ramming 4.50
1 foreman 3.50
------
Total wages per day $43.00
This gang averaged 1,080 sq. yds. of 6-in. foundation or 180 cu. yds. of
concrete in place per day which gives a labor cost of 24 cts per cu. yd.
or 4 cts. per sq. yd. for mixing and placing.
CHAPTER XV.
METHODS AND COST OF CONSTRUCTING SIDEWALKS, PAVEMENTS AND CURB AND
GUTTER.
Next to pavement foundations the most extensive use of concrete in
street work is for cement walks and concrete curb and gutter. Usually
the mixing and placing of the concrete is hand work, practically the
only exceptions being where pavement base, curbing and sidewalks are
built all at once, using machine mixers. The same objections that have
been raised to machine mixers in laying pavement foundation are raised
against them for curb and walk construction, and owing to the much
smaller yardage per lineal foot of street in walk and curb work these
objections carry more force than they do in case of paving work. Another
argument against the use of mixers is that both walk and curb and gutter
work involve the use of forms and the application of mortar finish, the
placing of which are really the limiting factors in the rate of progress
permissible, and this rate is too slow to consume an output necessary to
make a mixer plant economical as compared with hand mixing where so much
transportation is involved. Concrete sidewalk and curb work are
essentially hand mixing work; they, therefore, involve a careful study
of the economies of hand mixing and wheelbarrow haulage which are fully
discussed in Chapter II.
CEMENT SIDEWALKS.
Sidewalk construction consists in molding on a suitably prepared
sub-base a concrete slab from 3½ to 7½ ins. thick, depending on
practice, and finishing its top surface with a ½ to 1½-in. wearing
surface of cement mortar.
~GENERAL METHOD OF CONSTRUCTION.~--The excavation and preparation of the
sub-grade call for little notice beyond the warning that they should
never be neglected. The authors have seen many thousands of feet of
cement walk laid in the middle West in which the sub-base was placed
directly on the natural sod, often covered with grass and weeds a foot
high. Such practice is wholly vicious. The sod should always be removed
and the surface soil excavated to a depth depending upon the climate and
nature of the ground and the foundation bed well tamped. From 4 to 6
ins. depth of excavation will serve where the soil is reasonably hard
and there are no heavy frosts; with opposite conditions a 12-in.
excavation is none too deep. The thickness of the broken stone, gravel,
cinder or sand sub-base should likewise be varied with the character of
the soil, the conditions of natural drainage and the prevalence of
frost. In well drained sandy soils 6 to 8 ins. of sub-base are
sufficient, but in clayey soils with poor natural drainage the sub-base
should be from 10 to 12 ins. thick at least; the local conditions will
determine the thickness of sub-base necessary and in places it may be
desirable to provide by artificial drainage against the accumulation of
water under the concrete. Tile drains are better and cheaper than
excessively deep foundations. The thorough tamping of the sub-base is
essential to avoid settling and subsequent cracking of the concrete
slab. This is a part of sidewalk work which is often neglected.
Portland cement concrete, sand and broken stone or gravel mixtures in
the proportions of 1-3-5 and 1-3-6 are used for base slabs. For walks up
to 7 ft. wide the slab is made 3½ ins. thick for residence streets and
4½ to 5 ins. thick for business streets; for wider walks the thickness
is increased to 7 ins. for 8-ft. width and 7½ ins. for 9 to 10-ft.
width. Roughly the thickness of the walk in inches (base and top
together) is made about equal to its width in feet. The concrete is
deposited in a single layer and tamped thoroughly, either in separate
blocks behind suitable forms or in a continuous slab which is while
fresh cut through to make separate blocks. For walks up to 8 ft. wide
the slab is divided by transverse joints spaced about the width of the
walk apart, but for the wider walks the safety of this division depends
upon the thickness of the base; an 8-ft. walk with a 5-in. base can
safely be laid with joints 8 ft. apart, but if the slab is only 4 ins.
thick it had better be laid in 4×4-ft. squares. The mode of procedure in
base construction is as follows:
The sub-base being laid, side forms held by stakes are placed as shown
by Fig. 116, with the top edges of the boards exactly to the grade of
the top surface of the finished walk. The concrete is then deposited
between these side forms and tamped until it is brought up to the level
marked by the templet A. If the plan is to deposit the base in
sections transverse plates of 3/8 to ¼ in. steel are set across the walk
between the side boards at proper intervals and the concrete tamped
behind them; sometimes the concreting is done in alternate blocks. When
the steel plate is withdrawn an open joint is left for expansion and
contraction. Where the plan is to lay the base in one piece which is
afterwards cut into blocks, the cutting is done with a spade or cleaver.
[Illustration: Fig. 116.--Sketch Showing Method of Constructing Cement
Walks.]
[Illustration: Fig. 117.--"Jointer" for Cement Sidewalk Work.]
Portland cement mortar mixed 1 to 1½ to 1 to 2 is used for the wearing
surface, and is laid from ½ in. to 1½ ins. thick, depending upon the
width of the walk and the thickness of the base. As a rule the mortar is
mixed rather stiff; it is placed with trowels in one coat usually, but
sometimes in two coats, and less often by tamping. The mortar coat is
brought up flush with the top edges of the side forms by means of the
templet B, and the top finished by floating and troweling. The
wearing coat is next divided into sections corresponding with the
sections into which the base is divided, by cutting through it with a
trowel guided by a straight edge and then rounding the edges of the cut
with a special tool called a jointer and shown by Fig. 117. An edger,
Fig. 118, is then run around the outside edges of the block to round
them. The laying of the mortar surface must always follow closely the
laying of the base so that the two will set together.
[Illustration: Fig. 118.--"Edger" for Cement Sidewalk Work.]
~BONDING OF WEARING SURFACE AND BASE.~--Trouble in securing a perfect bond
between the wearing surface and the base usually comes from one or more
of the following causes: (1) Applying the surface after the base
concrete has set. While several means are available for bonding fresh to
old concrete as described in Chapter XXIV, the better practice is not to
resort to them except in case of necessity but to follow so close with
the surfacing that the base will not have had time to take initial set.
(2) Poor mixing and tamping of this base concrete. (3) Use of clayey
gravel or an accumulation of dirt on the surface. In tamping clayey
gravel the water flushes the clay to the surface and prevents the best
bond. (4) Poor troweling, that is failure to press and work the mortar
coat into the base concrete. Some contractors advocate tamping the
mortar coat to obviate this danger. Conversely, to make the surface coat
adhere firmly to the base it must be placed before the base concrete has
set; the base concrete must be thoroughly cleaned or kept clean from
surface dirt; the surface coat must be tamped or troweled forcibly into
the base concrete so as to press out all air and the film of water which
collects on top of the concrete base.
~PROTECTION OF WORK FROM SUN AND FROST.~--Sun and frost cause scaling and
hair cracks. For work in freezing weather the water, sand and gravel
should be heated or salt used to retard freezing until the walk can be
finished; it may then be protected from further action of the frost by
covering it first with paper and then with a mattress of sawdust,
shavings or sand and covering the whole with a tarpaulin. Methods of
heating concrete materials and rules for compounding salt solutions are
given in Chapter VII. The danger from sun arises from the too rapid
drying out of the surface coating; the task then is to hold the moisture
in the work until the mixture has completely hardened. Portable frames
composed of tarpaulin stretched over 2×4-in. strips may be laid over the
finished walk to protect it from the direct rays of the sun; these
frames can be readily removed to permit sprinkling. Practice varies in
the matter of sprinkling, but it is the safe practice in hot weather to
sprinkle frequently for several days. Moisture is absolutely necessary
to the perfect hardening of cement work and a surplus is always better
than a scarcity. In California the common practise is to cover the
cement walk, as soon as it has hardened, with earth which is left on for
several days.
~CAUSE AND PREVENTION OF CRACKS.~--Cracks in cement walks are of two
kinds, fractures caused by any one of several construction faults and
which reach through the surface coating or through both surface and
base, and hair cracks which are simply skin fractures. Large cracks are
the result of constructive faults and one of the most common of these is
poor foundation construction; other causes are poor mixing and tamping
of the base, too large blocks for thickness of the work, failure to cut
joints through work. Hair cracks are the result of flushing the neat
cement to the surface by excessive troweling or the use of too wet a
mixture. The prevention of cracks obviously lies in seeing that the
construction faults cited do not exist. If expansion joints are not
provided, a long stretch of cement walk will expand on a hot day and
bulge up at some point of weakness breaking the walk.
~COST OF CEMENT WALKS.~--The cost of cement walks is commonly estimated in
cents per square foot, including the necessary excavation and the cinder
or gravel foundation. The excavation usually costs about 13 cts. per
cu. yd., and if the earth is loaded into wagons the loading costs
another 10 cts. per cu. yd., wages being 15 cts. per hr. The cost of
carting depends upon the length of haul, and may be estimated from data
given in Chapter III. If the total cost of excavation is 27 cts. per cu.
yd., and if the excavation is 12 ins. deep, we have a cost of 1 ct. per
sq. ft. for excavation alone. Usually the excavation is not so deep, and
often the earth from the excavation can be sold for filling lots.
In estimating the quantity of cement required for walks, it is well to
remember that 100 sq. ft. of walk 1 in. thick require practically 0.3
cu. yd. concrete. If the concrete base is 3 ins. thick, we have 0.3 × 3,
or 0.9 cu. yd. per 100 sq. ft. of walk. And by using the tables in
Chapter II we can estimate the quantity of cement required for any given
mixture. In cement walk work the cement is commonly measured loose, so
that a barrel can be assumed to hold 4.5 cu. ft. of cement. If the
barrel is assumed to hold 4.5 cu. ft., it will take less than 1 bbl. of
cement to make 1 cu. yd. of 1-3-6 concrete; hence it will not require
more than 0.9 bbl. cement, 0.9 cu. yd. stone, and 0.45 cu. yd. sand per
100 sq. ft. of 3-in. concrete base. The 1-in. wearing coat made of 1-1½
mortar requires about 3 bbls. of cement per cu. yd., if the barrel is
assumed to hold 4.5 cu. ft., and since it takes 0.3 cu. yd. per 100 sq.
ft., 1 in. thick, we have 0.3 × 3, or 0.9 bbl. cement per 100 sq. ft.
for the top coat. This makes a total of 1.8 bbls. per 100 sq. ft., or 1
bbl. makes 55 sq. ft. of 4-in. walk.
As the average of a number of small jobs, the authors' records show the
following costs per sq. ft. of 4-in. walk such as just described:
Cts. per sq. ft.
Excavating 8 ins. deep 0.65
Gravel for 4-in. foundation, at $1.00 per cu. yd. 1.20
0.018 bbl. cement, at $2.00 3.60
0.009 cu. yd. broken stone, at $1.50 1.35
0.006 cu. yd. sand, at $1.00 0.60
Labor making walk 1.60
----
Total cents 9.00
This is 9 cts. per sq. ft. of finished walk. The gangs that built the
walk were usually two masons at $2.50 each per 10-hr. day with two
laborers at $1.50 each. Such a gang averaged 500 sq. ft. of walk per
day.
~Cost at Toronto, Ont.~--Mr. C. H. Rust, City Engineer, Toronto, Ont.,
gives the following costs of constructing concrete sidewalks by day
labor. The sidewalks have a 4-in. foundation of coarse gravel or soft
coal cinders, thoroughly consolidated by tamping or rolling, upon which
is placed a 3½-in. layer of concrete composed of 1 part Portland cement,
2 parts clean, sharp, coarse sand, and 5 parts of approved furnace slag,
broken stone or screened gravel. The wearing surface is 1 in. thick, or
1 part Portland cement, 1 part clean, sharp, coarse sand, and 3 parts
screened pea gravel, crushed granite, quartzite or hard limestone. Costs
are given of a 6-ft. and a 4-ft. walk as follows:
COST OF 6 FT. SIDEWALK.
Per 100
Item. sq. ft.
Labor $ 5.59
Cement, 1.66 bbls., at $1.54 2.49
Gravel, 2.7 cu. yds., at $0.80 2.21
Sand, 0.46 cu. yd., at $0.80 0.37
Water 0.05
----
Total $10.71
COST OF 4 FT. SIDEWALK.
Per 100
Item. sq. ft.
Labor $ 6.73
Cement, 2.04 bbls., at $1.54 3.15
Gravel, 2.06 cu. yds., at $0.80 1.65
Sand, 0.49 cu. yd., at $0.80 0.39
Water 0.07
----
Total $11.99
The rates of wages and the number of men employed were as follows: 1
foreman, at $3.50 per day; 1 finisher, at 30 cts. per hour; 1 helper, at
22 cts. per hour; 15 laborers, at 20 cts. per hour.
~Cost at Quincy, Mass.~--The following costs are given by Mr. C. M.
Saville for constructing 695 sq. yds. of granolithic walk around the top
of the Forbes Hill Reservoir embankment at Quincy, Mass. This walk was
laid on a broken stone foundation 12 ins. thick; the concrete base was 4
ins. thick at the sides and 5 ins. thick at the center; the granolithic
finish was 1 in. thick. The walk was 6 ft. wide and was laid in 6-ft.
sections, a steel plate being used to keep adjacent sections entirely
separate. The average gang was 6 men and a team on the base and 2 masons
and 1 tender on the finish. The average length of walk finished per day
was 60 ft. The cost was as follows:
Stone Foundation: Per cu. yd. Per sq. ft.
Broken stone for 12-in. foundation $ 0.40 $0.015
Labor placing at 15 cts. per hour 1.50 0.056
----- ------
Totals $ 1.90 $0.071
Concrete Base 4½ ins. Thick:
1.22 bbls. cement per cu. yd. at $1.53 $ 1.87 $0.026
0.50 cu. yd. sand per cu. yd. at $1.02 0.51 0.007
0.84 cu. yd. stone per cu. yd. at $1.57 1.32 0.019
Labor (6 laborers, 1 team) 3.48 0.050
---- -----
Total for 90 cu. yds. $ 7.18 $0.102
Granolithic Finish 1 in. Thick:
4 bbls. cement per cu. yd. at $1.53 $ 6.12 $0.019
0.8 cu. yd. sand at $1 0.80 0.002
Lampblack 0.29 0.001
Labor (2 masons, 1 helper) 6.36 0.016
---- -----
Totals $13.57 $0.038
The two masons received $2.25 per day each and their helper $1.50 per
day, and they averaged 360 sq. ft. per day, which made the cost 1-2/3
cts. per sq. ft. for labor laying granolithic finish. The cost of
placing the foundation stone is very high and the cost of concrete base
also runs unusually high, the reasons for these high costs are not
evident.
~Cost at San Francisco.~--Mr. George P. Wetmore, of the contracting firm
of Cushing & Wetmore, San Francisco, gives the following figures
relating to sidewalk work in that city. The foundations of cement walks
in the residence district of San Francisco are 2½ ins. thick, made of
1-2-6 concrete, the stone not exceeding 1 in. in size. The wearing coat
is ½ in. thick, made of 1 part cement to 1 part screened beach gravel.
The cement is measured loose, 4.7 cu. ft. per barrel. The foundation is
usually laid in sections 10 ft. long; the width of sidewalks is usually
15 ft. The top coat is placed immediately, leveled with a straight edge
and gone over with trowels till fairly smooth. After the initial set and
first troweling, it is left until quite stiff, when it is troweled again
and polished--a process called "hard finishing." The hard finish makes
the surface less slippery. The surface is then covered with sand, and
watered each day for 8 or 10 days. The contract price is 9 to 10 cts.
per sq. ft. for a 3-in. walk; 12 to 14 cts. for a 4-in. walk having a
wearing coat ¾ to 1-in. thick. A gang of 3 or 4 men averages 150 to 175
sq. ft. per man per day of 9 hrs. Prices and wages are as follows:
Cement, per bbl. $2.50
Crushed rock, per cu. yd. 1.75
Gravel and sand for foundation, per cu. yd. 1.40
Gravel for top finish, per cu. yd. 1.75
Finisher wages, best, per hr. 0.40
Finisher helper, best, per hr. 0.25
Laborer, best, per hr. 0.20
~Cost in Iowa.~--Mr. L. L. Bingham sent out letters to a large number of
sidewalk contractors in Iowa asking for data of cost. The following was
the average cost per square foot as given in the replies:
Cts. per sq. ft.
Cement, at $2 per bbl. 3.6
Sand and gravel 1.5
Labor, at $2.30 per day (average) 2.2
Incidentals, estimated 0.7
---
Total per sq. ft 8.0
This applies to a walk 4 ins. thick, and includes grading in some cases,
while in other cases it does not. Mr. Bingham writes that in this
respect the replies were unsatisfactory. He also says that the average
wages paid were $2.30 per man per day. It will be noted that a barrel of
cement makes 55½ sq. ft. of walk, or it takes 1.8 bbls. per 100 sq. ft.
The average contract price for a 4-in. walk was 11½ cts. per sq. ft.
CONCRETE PAVEMENT.
Concrete pavement is constructed in all essential respects like cement
sidewalk. The sub-soil is crowned and rolled hard, then drains are
placed under the curbs; if necessary to secure good drainage a sub-base
of gravel, cinders or broken stone 4 to 8 ins. thick is laid and
compacted by rolling. The foundation being thus prepared a base of
concrete 4 to 5 ins. thick is laid and on this a wearing surface 2 to 3
ins. thick. As showing specific practice we give the construction in two
cities which have used concrete pavement extensively.
~Windsor, Ontario.~--The street is first excavated to the proper grade and
crown and rolled with a 15-ton roller. Tile drains are then placed
directly under the curb line and a 6×16-in. curb is constructed, vising
1-2-4 concrete faced with 1-2 mortar. Including the 3-in. tile drain
this curb costs the city by contract 38 cts. per lin. ft. The pavement
is then constructed between finished curbs, as shown by Fig. 119.
[Illustration: Fig. 119.--Concrete Pavement. Windsor, Canada.]
The fine profile of the sub-grade is obtained by stretching strings from
curb to curb, measuring down the required depth and trimming off the
excess material. The concrete base is then laid 4 ins. thick. A 1-3-7
Portland cement concrete is used, the broken stone ranging from ¼ in. to
3 ins. in size, and it is well tamped. This concrete is mixed by hand
and as each batch is placed the wearing surface is put on and finished.
The two layers are placed within 10 minutes of each other, the purpose
being to secure a monolithic or one-piece slab. The top layer consists
of 2 ins. of 1-2-4 Portland cement and screened gravel, ¼ in. to 1 in.,
concrete. This layer is put on rather wet, floated with a wooden float
and troweled with a steel trowel while still wet. Some 20,500 sq. yds.
of this construction have been used and cost the city by contract:
Per sq. yd.
Bottom 4-in. layer 1-3-7 concrete $0.57
Top 2-in. layer 1-2-4 concrete 0.32
Excavation 0.10
-----
Total $0.99
This construction was varied on other streets for the purpose of
experiment. In one case a 4-in. base of 1-3-7 stone concrete was covered
with 2 ins. of 1-2-2 gravel concrete. In other cases the construction
was: 4-in. base of 1-3-7 stone concrete; 1½-in. middle layer of 1-2-4
gravel concrete, and ½-in. top layer of 1-2 sand mortar. All these
constructions have been satisfactory; the pavement is not slippery. The
cost to the city by contract for the three-layer construction has in two
cases been as follows:
Church St., 8,000 sq. yds.: Per sq. yd.
4-in. base 1-3-7 concrete $0.57
1½-in. 1-2-4 and ½-in 1-2 mixture 0.32
Excavation 0.10
-----
Total $0.99
Albert and Wyandotte Sts., 400 sq. yds.: Per sq. yd.
4-in. base 1-3-7 concrete $0.66
1½-in. 1-2-4 and ½-in. 1-2 mixture 0.39
Excavation 0.10
-----
Total $1.15
The cost of materials and rates of wages were about as follows:
Portland cement f. o. b. cars Windsor, per bbl. $2.05
River sand, per cu. yd. 1.15
River gravel, screened, per cu. yd. 1.25
Crushed limestone, ¼ to 3 ins., per ton 1.15
Labor, per day 1.75 to 2.00
At these prevailing prices the contractor got a fair profit at the
contract price of $1.15; at 99 cts., any profit is questionable,
according to City Engineer George S. Hanes, who gives us the above
records. Expansion joints are located from 20 to 80 ft. apart and are
filled with tar.
~Richmond, Ind.~--The first concrete pavement was built in 1896 and since
then it has been used extensively, especially for wide alleys and narrow
streets where traffic is heavy and concentrated in small space. The
method of construction has varied from time to time but the construction
shown by Fig. 120 is fairly representative. Usually a 1-3-5 concrete is
used for the base, 5 ins. thick, and a 1-2 mortar for the top coat, 1½
ins. thick. In 1904 this pavement cost the city by contract 16 cts. per
sq. ft. or $1.54 per sq. yd, with wages and prices as follows: Stone on
the work, $1.25 per cu. yd.; gravel and sand, $0.75 per cu. yd.; cement,
$2.25 per barrel; common laborers, 16½ cts. per hour, and cement
finishers, 40 cts. per hour.
[Illustration: Fig. 120.--Concrete Pavement, Richmond, Ind.]
~CONCRETE CURB AND GUTTER.~
Current practice varies materially in constructing concrete curb and
gutter. The more common practice is to lay the curb and water table in
one piece, or as a monolith, but this is by no means universal practice.
In much work the curb wall and the water table slab are constructed
separately, the construction joint being sometimes horizontal where the
curb wall sits on the slab and sometimes vertical where the water table
butts against the wall. Again it is the common practice to construct
curb and gutter in sections, laid either alternately or in succession,
separated by sand joints to provide for expansion and contraction, but
this is not universal practice, much of such work being constructed as a
continuous wall with no provision for temperature movements except the
natural breaks at driveways. All of these types of construction appear
to have given reasonable satisfaction, but exact data for a final
comparison are not available, so that we are forced to reason on general
principles. Such a course of reasoning indicates that the best results
should be expected where the curb and water table are built in one
piece and in sections of reasonable length separated by expansion
joints.
[Illustration: Fig. 121.--Box Form for Concrete Curb.]
[Illustration: Fig. 122.--Continuous Form for Concrete Curb.]
~FORM CONSTRUCTION.~--The form construction for curb and gutter work is
determined by the general plan of construction followed,--whether
monolithic or two-piece construction. In monolithic construction two
types of forms are employed, sectional or box forms and continuous
forms. A good example of box form is shown by Fig. 121. This form was
designed for a curb 14 ins. high at the back, 6 ins. high in front and
24 ins. from face of curb to outer edge of gutter, constructed in
sections 7 ft. long. The form, it will be observed, is a complete box,
in which alternate sections of curb are molded and after having set are
filled between using the same form but dispensing with the end boards
which are replaced by the completed sections of curb. A fairly
representative example of continuous form is shown by Fig. 122; in this
construction a continuous line of plank is set to form the back of the
curb and another line to form the face of the gutter slab, both lines
being held in place by stakes. When the gutter slab concrete has been
placed and surfaced the form for the front of the curb is set as shown
and the upper portion of the curb wall concreted behind it. The method
in detail of constructing curb and gutter, with this type of form, at
Ottawa, Ont., is described in a succeeding section. Here the joints
were formed by inserting a partition of 3/8-in. boiler plate every 12
ft., which was withdrawn just previous to finishing up the surface; the
sections between partitions were concreted continuously. Another method
is to make the partitions of plank, concrete every other section, then
remove the partition plank and concrete the remaining spaces against the
previously finished work. A different method of supporting the plank
forming the face of the curb wall, is to clamp it to the back form (Fig.
123), spacers being inserted to keep the two their proper distances
apart. The forms shown by Figs. 121 to 123 are for monolithic curb and
gutter. In two-piece construction where the curb wall is constructed on
the finished gutter slab practically the same method of construction is
employed as is illustrated by Fig. 122 except that no attempt is made to
concrete the curb wall before the slab concrete has begun to set. The
more common and the preferable method of two-piece construction is
illustrated by Fig. 124; the curb proper is built first using the simple
box form shown at the right hand, then the water table is built using
the completed curb as the form for the back and a board held by stakes
as a form for the front. This board is set with its top edge exactly to
the grade of the finished water table so as to serve as a guide for one
end of the template, the other end of which rides on the top of the
finished curb wall. Forms for curves at street intersections are best
constructed by driving stakes to the exact arc of the curve and bending
a 3/8-in. steel plate around them or bending and nailing 7/8×1¼-in.
strips. Soaking the wood strips thoroughly will make them bend easily.
The cost of form work in constructing curb and gutter is chiefly labor
cost in erecting and taking down the forms.
[Illustration: Fig. 123.--Continuous Form for Concrete Curb.]
[Illustration: Fig. 124.--Form for Two-Piece Curb Construction.]
~CONCRETE MIXTURES AND CONCRETING.~--The curb body is usually made of a
1-3-5 or 6 concrete and the curb finish of a 1-2 mortar. Portland cement
is employed almost exclusively. The concrete mixture commonly used is of
such consistency that thorough ramming is necessary to flush the cement
to the surface. The cubical contents of combined curb and gutter of the
forms illustrated will run from 3 to 5 cu. yds. per 100 ft., and about
one-eighth of this will be facing mortar 1 in. thick; thus a curb
running 5 cu. yds. per 100 ft. will contain per 100 ft. about 0.83 cu.
yd. of mortar and 4.17 cu. yds. of concrete. The usual method of
concreting is to erect the forms for the back of the curb wall and the
front of the gutter slab and concrete to the height of the water table
clear across; then shape the exposed top of the water table to section
and place the mortar finish, and then erect the face form for the gutter
wall, bring the concrete backing and vertical face finish up together
and, finally, finish the top. The finish coat is placed by troweling on
the horizontal surfaces; on the vertical face of the curb wall it may be
placed in any one of several ways. Frequently the mortar coat is simply
plastered against the face board and filled behind with concrete.
Another method is to lay a 1-in. board against the inside of the form,
concrete behind it, then withdraw the board, fill the space with mortar
and tamp concrete and mortar to a thorough bond. The special face forms
shown in Chapter VIII may be used in place of the board. The securing of
a good bond between the backing concrete and the mortar facing is
governed by the same conditions that govern sidewalk work.
~COST OF CURB AND GUTTER.~--The cost of concrete curb and gutter is
commonly estimated in cents per lineal foot. The cost of excavating,
loading and carting will run about the same per cubic yard as for
sidewalks. Excavating the trench and preparing the sub-grade usually
runs from ½ ct. to 2 cts. per foot of curb, but sometimes it amounts to
3 cts. Placing the sub-base will cost for placing and tamping 1 ct. per
ft., to which is to be added the cost of materials; a 6-in. sub-base 30
ins. wide contains 4.7 cu. yds., tamped measure, of materials per 100
ft. The amount of materials per foot depends upon the cross-section of
the curb; it equals in cubic yards the area of cross-section in square
feet divided by 27, and of this volume about one-eighth will be 1-2
mortar and seven-eighths 1-3-6 concrete. The tables in Chapter II give
the amounts of materials per cubic yard of these mixtures; the product
of these quantities and the cost of the materials on the ground gives
the cost. The labor cost of mixing and placing, including the form work,
will run from 10 to 14 cts. per foot. In round figures curb and gutter
of the section shown in the accompanying illustrations may be estimated
to cost in the neighborhood of 40 cts. per lineal foot. The following
sections give records of cost of individual jobs of curb and gutter
construction.
~Cost at Ottawa, Canada.~--The method and cost of constructing 1,326 ft.
of concrete curb and gutter at Ottawa, Ont., are given in some detail by
Mr. G. H. Richardson, Assistant City Engineer, in the annual report of
the City Engineer for 1905. We have remodeled the description and
rearranged the figures of cost in the following paragraphs.
The concrete curb was built before doing any work on the roadway, and
the first task was the excavation of a trench 2½ ft. wide and averaging
1 ft. 8 ins. in depth through light red sand. On the bottom of this
trench there was placed a foundation of stone spalls 8 ins. thick; in
width this foundation reached from 3 ins. back of the curb to 6 ins.
beyond the front of the water table. The curb was made 5 ins. thick and
ran from 10 ins. to 5½ ins. in height, and the water table was 14 ins.
wide and 4 ins. thick, with a fall of 1¼ ins. from front to back. The
concrete used was a mixture of 1 Portland cement, 3 sand, 3 5/8-in.
screened limestone, and 4 2-in. stone. It was deposited in forms and
tamped to bring the water to the face and then smoothed with a light
troweling of stiff mortar.
The forms were constructed by first setting pickets and nailing to them
a back board 2 ins. thick and 12 ins. wide and a front board 2 ins.
thick and 6 ins. wide. The concrete for the water table was deposited in
this form in sections and brought to surface by straight edge riding on
wooden strips nailed across the form and properly set to slope, etc.
After the water table had been troweled down and brushed a 1×10-in.
board was set to mold the front face of the curb. This board was
sustained by small "knee frames" made of three pieces of 1×2-in. stuff,
one conforming to the slope of the water table and long enough to extend
beyond the front of the 2×6-in. front board, a second standing plumb and
bearing against the 1×10-in. face board, and the third forming a small
corner brace between the two former to hold them in their proper
relative positions. The 1×10-in. face board, etc., was separated from
the 2×12-in. back board by a 5-in. block at each end, and then braced by
the knee frames every 3 or 4 ft. In this way it was possible to bring
this 1×10-in. board into perfect line by moving the knee braces in or
out, and when correct nailing them to the 2×6-in. front board. The
1×10-in. face board being in position and braced and lined, the curb
material was thoroughly tamped in, and when ready was troweled and
brushed on the top, a small round being worked onto the top front corner
with the trowel.
Expansion joints were provided for by building into the curb every 12
ft., a piece of 3/8-in. boiler plate, which was afterward withdrawn and
the joint filled with sand and faced over. As soon as the concrete had
set sufficiently the face board was taken down and face of curb finished
and brushed, the fillet between curb and water table being finished to
2½ ins. radius. Circular curb and gutter of same construction was built
at each corner, ½-in. basswood being used for forms, instead of 2×1-in.
lumber.
In addition to the actual construction of curb and gutter the cost given
below includes the cleaning up of the street, spreading or removal of
all surplus material from excavation, and the extension of all sidewalks
out to the curbs at the corners. It was also necessary to maintain a
watchman on this work, which duty, under ordinary circumstances, would
be done by the general watchman. The total length built was 1,326 ft.,
of which 1,209 ft. is straight and 117 ft. curved to a 12-ft. radius.
The rates of wages paid were $2 for horse and cart, $1.65 for watchman,
and an average of $1.90 per day for labor, including foreman; all for
nine hours' work per day. The working force consisted of foreman,
finisher, handy man. four concrete men, and three laborers.
The labor cost of the work was as follows:
Per ft. P. C. of
Item. Total. cts. total.
Excavation and setting boards $ 88.90 6.7 30
Laying stone foundation 43.30 3.3 14
Concreting 61.30 4.6 20
Finishing 45.15 3.4 15
Carting 9.85 0.76 3
Watchman 25.00 1.89 8
Clearing up 13.60 1.04 4
Extras (sidewalk extensions) 17.23 1.31 6
------- ----- --
Total $304.33 23.00 100
The cost of materials for curb and foundation were as follows:
Per lin. ft.
Total. cts.
171.112 tons spalls $102.93 7.76
42 tons 2-in. stone 41.16 3.09
30.8 tons 5/8-in. stone 42.57 3.21
33,000 lbs. cement 161.70 12.19
24 cu. yds. sand 19.20 1.45
------- -----
Total $367.56 27.70
The cost of supplies and tools was as follows:
1,000 ft. B. M. 2×12 boards charged off $ 9.25
500 ft. B. M. 2×6 boards charged off 4.12
1,000 ft. B. M. 1×10 boards charged off 14.25
½-in. basswood 4.30
½ keg 3-in. nails 1.42
½ keg 4-in. nails 1.43
Pickets 3.25
Tools charged off 3.15
------
Total $41.17
This total, when divided by 1,326 lin. ft. of curb, gives the cost per
lineal foot as about 3 cts. We can now summarize as follows:
Per lin. P. C. of
Item. Total. ft. total.
Labor $304.33 23 43
Material 367.56 28 51
Supplies 41.17 3 6
------- ---- ---
Total $713.06 $0.54 100
As indicated above, on more extensive work the costs of carting,
watchman, cleaning up, and extras would be avoided. They cost on this
work 5 cts. and the work could therefore be done for 49 cts. if no such
charges were included. On such work also the charge for supplies would
be lower per foot and on any future work the labor cost could be
materially lowered, this curb having been somewhat of an experiment as
to method of construction. It is thought that with no charges for
carting, cleaning, watchman, and extras, and with the experience
obtained, this curb could be built for about 46 cts. The proportions
adopted and the method of construction followed, produce a very strong,
dense, homogeneous curb and gutter.
[Illustration: Fig. 125.--Concrete Curb and Gutter at Champaign, Ill.]
~Cost at Champaign, Ill.~--The following costs were recorded by Mr.
Charles Apple, and relate to work done at Champaign, Ill., in 1903. The
work was done by contract, at 45 cts. per lin. ft. of the curb and
gutter shown in Fig. 125.
The concrete curb and gutter was built in a trench as shown in the cut.
The earth was removed from this trench with pick and shovel at a rate of
1 cu. yd. per man per hour. The concrete work was built in alternate
sections, 7 ft. in length. A continuous line of planks was set on edge
to form the front and back of the concrete curb and gutter; and wood
partitions staked into place, were used. The cost of the work was as
follows:
No. of Total Cost per
Item. men. wages. 100 ft.
Opening trench, 18×30-in. 2 $3.50 $2.43
Placing and tamping cinders 2 3.50 1.00
Setting forms:
Boss setter 1 3.00 ...
Assistant setter 1 2.00 ...
Laborer 1 1.75 ...
-- ----- -----
3 $6.75 $1.69
Mixing and placing concrete:
Clamp man 1 $1.75 ...
Wheelers 3 5.25 ...
Mixing concrete 4 7.00 ...
Mixing finishing coat 2 3.50 ...
Tampers 1 1.75 ...
Finishing:
Foreman and boss finisher 1 4.00 ...
Assistant finisher 1 3.00 ...
Water boy 1 .50 ...
-- ------ -----
Total making concrete 14 $26.75 $7.64
Total for labor per 100 ft $12.76
Materials for 100 lin. ft.: Quantity. Price.
Portland cement 8-1/3 bbls. $1.85 $15.42
Cinders 7.5 yds. .50 3.75
Gravel 2.5 yds. 1.00 2.50
Broken stone 2.5 yds. 1.40 3.50
Sand 1.0 1.00 1.00
Total for material per 100 ft $26.17
Total for material and labor per 100 ft. $38.93
This is the total cost, exclusive of lumber, tools, interest, profits,
etc., and it is practically 40 cts. per lin. ft.
In 100 lin. ft. of curb and gutter there were 4.6 cu. yds. of concrete
and mortar facing, 4 cu. yds. of which were concrete; hence the 9 men in
the concrete gang laid 14 cu. yds. of concrete per day, whereas the 4
men mixing and placing the mortar finishing laid only 2½ cu. yds. of
mortar per day, assuming that the mortar finishing averaged just 1 in.
thick. Since these 4 men (2 mixers and 2 finishers) received $10.50 a
day, it cost more than $4 per cu. yd. to mix and place the 1-2 mortar,
as compared with $1.41 per cu. yd. for mixing and placing the concrete.
The concrete was built in alternate sections 7 ft. long. The 3 men
placing forms averaged 400 lin. ft. a day, so that the cost of placing
the forms was $1 per cu. yd. of concrete. The 2 men placing and tamping
cinders averaged 16 cu. yds. of cinders per day, or 8 cu. yds. per man.
This curb and gutter was built by contract at 45 cts. per lin. ft.
For several jobs, in which a curb and gutter essentially the same as
shown in Fig. 125 was built, our records show a general correspondence
with the above given data of Mr. Apple. Our work was done with smaller
gangs, 1 mason and 2 laborers being the ordinary gang. Such a gang would
lay 80 to 100 lin. ft. of curb and gutter per 10-hr. day, at the
following cost:
1 mason at $2.50 $2.50
2 laborers at $1.50 3.00
-----
Total $5.50
This made a cost of 5½ to 7 cts. per lin. ft. for labor, and it did not
include the cost of digging a trench to receive the curb and gutter.
CHAPTER XVI.
METHODS AND COST OF LINING TUNNELS AND SUBWAYS.
[Illustration: Fig. 126.--Section Showing Lining for Capitol Hill
Tunnel. Washington, D. C.]
Tunnel lining work is of two distinct classes: Lining work, done during
original construction and relining of tunnels in service. The methods of
work to be adopted and the cost of work will be different in the two
cases. In relining work the costs are increased by the necessity of
providing for the movement of trains and by the delays due to these
movements and also by the labor of removing the old lining and, often,
of enlarging the excavation. Comparatively few published figures are
available on the cost of concrete tunnel lining, and such as exist are
commonly incomplete. The common practice is to record the cost as so
much per lineal foot of tunnel. This should be done, but the record
should also show the cost per cubic yard of concrete in the lining. The
notions of engineers vary as to the proper thickness of lining to use
and this dimension also varies with the character of the ground. One
tunnel lining may easily contain twice as many cubic yards of concrete
per lineal foot of lining as another tunnel contains.
The two problems in form construction for tunnel work are: First, to
construct the form work so that it does not interfere with train
movements, and, second, to construct it so that it can be taken down,
transported and re-erected and thus used over and over. The examples of
practice given in the succeeding sections are the best instructions that
can be laid before the reader in regard to possible ways of solving
these problems and, also, the problem of handling the concrete and other
materials to the work.
[Illustration: Fig. 127.--Traveling Derrick for Constructing Side and
Center Walls, Capitol Hill Tunnel.]
[Illustration: Fig. 128.--Steel Forms for Side Walls for Capitol Hill
Tunnel.]
~METHOD OF LINING CAPITOL HILL TUNNEL, PENNSYLVANIA R. R., WASHINGTON, D.
C.~--The tunnel through Capitol Hill for the Pennsylvania R. R. approach
to its new Union Station at Washington, D. C, is a two-track, double
tube tunnel 4,000 ft. long through earth. Figure 126 shows the lining
construction; it consists of stone masonry center wall, mass concrete
inverts and side walls and a brick roof arch backed with concrete. For
building the center and side walls the traveling derrick shown by Fig.
127 was employed. This traveler moved ahead with the work on a 14-ft.
gage track and it handled the stone and concrete buckets from the
material cars to the workmen on the walls. In connection with the
derrick in the concrete side wall construction use was made of steel
plate forms for the inside faces of the walls. These forms were made of
4×10 ft. sections of steel plate, constructed as shown by Fig. 128, and
connected together by bolting through the flanges. The steel forms were
erected by hand in advance of the derrick, 20 ft. of form on each side
at a time. The concrete buckets were brought into the tunnel on cars
hauled by electric motors from the mixing plant at the portal, and the
buckets were lifted by the derricks and emptied into the forms. The side
walls were concreted to the springing line and then the five-ring brick
roof arches were constructed on traveling centers and in 20-ft.
sections. The remainder of the concrete was then placed over the arches
by means of the special back-filling machine, shown by Fig. 129. This
machine also handled the earth used to fill behind the masonry. It
consisted of a platform mounted on wheels and of the same general
construction as the derrick platform. On the forward end of this
platform a stationary hoist was mounted and behind this a belt conveyor
platform.
[Illustration: Fig. 129.--Device for Placing Concrete Back Filling for
Roof Arch, Capitol Hill Tunnel.]
The latter structure was pivoted near the forward end so that it could
swing right and left on a circular track under its rear end. It carried
a 30-cu. ft. hopper on its forward end, from under which a belt conveyor
ascended an incline toward the rear and was carried back into the space
behind the roof arch on a cantilever arm. In operating the back-filling
machine the material bucket was lifted from the car below, carried back
on the trolley beam until over the hopper and then dumped by hand into
the hopper. From the hopper the material dropped onto the conveyor belt
and was carried back over the arch and dumped in place ready for
tamping. The trolley beam of the hoist was so arranged that the hoisting
movement was vertical until the bucket hit the trolley and was then up
and backward until the stop at the end of the trolley beam was reached.
This point was directly over the hopper. Hoisting was done by a Lambert
engine, driven by a 15 H.P. electric motor. The conveyor belt was 20
ins. wide and was operated at a speed of 180 ft. per minute by a 7½ H.P.
electric motor. The machine required two men to operate and was
considered to save the labor of twelve shovelers.
~METHOD OF CONSTRUCTING SIDE WALLS IN RELINING THE MULLAN TUNNEL.~--The
Mullan Tunnel, 3,850 ft. long, on the Northern Pacific Ry., about 20
miles west of Helena, Mont., had its original timber lining replaced in
1894 with a lining consisting of concrete side walls and a brick roof
arch. The construction of the old and new linings is shown by Fig. 130.
The method of constructing the side walls was as follows:
The original timbering consisted of sets of 12×12-in. posts carrying
five segment arches of 12×12-in. timbers joined by ½-in. dowels. For a
portion of the lining the posts carried plates on which the arches set;
elsewhere the arches rested directly on the post tops. The arches and
posts carried 4-in. lagging filled behind with cordwood. The timber
lining was removed to make place for the new work in the manner shown by
Fig. 130. When there were no plates a 7-ft. section AB was first
prepared by removing one post and supporting the undermined arch ribs by
struts SS. The timbering in this section was cut out and excavation
made for the wall footing. Two temporary posts FF were then set up,
fastened by hook bolts L and lagged behind to make the wall form.
Several of these 7-ft. sections were cut out at once, each two being
separated by a 5-ft. section of timbering. The mortar car shown in Fig.
130 was then run alongside the sections in order and enough 1-3 mortar
was run by chute into each to make an 8-in. layer. As the car moved
ahead to succeeding sections enough broken stone was shoveled into the
last preceding section to take up the mortar. The walls were thus built
in 8-in. layers and became hard enough to support the arches in from 10
to 14 days. The arches were then allowed to take footing on the wall,
and the posts of the remaining 5-ft. sections were removed and the
concrete wall built up as for the 7-ft. sections. Where the posts
carried wall plates the struts SS were not needed, the wall plate
supporting the undermined post as a beam. English Portland cement was
used and the concrete mixture was about 4 parts mortar to 5 parts broken
stone--a very rich mixture. The average progress was about 30 ft., or 45
cu. yds. of side wall per working day; the average cost of the walls,
including everything, was $8 per cu. yd. of concrete. The brick arch
cost $17 per cu. yd. Mr. H. C. Relf is authority for these figures.
[Illustration: Fig. 130.--Sketches Showing Method of Lining Mullan
Tunnel.]
~METHOD AND COST OF LINING A SHORT TUNNEL, PEEKSKILL, N. Y.~--The
following methods and costs of lining a double track railway tunnel 275
ft. long near Peekskill, N.Y., are given by Mr. Geo. W. Lee. In
presenting these data it is important to note that while some of the
methods described are applicable to so short a tunnel they could not be
used on a long tunnel. Figure 131 is a cross-section of the tunnel
showing the lining. The tunnel was through rock, which stood up without
timbering, and the rock section was excavated from 6 ins. to 3 ft.
outside the lining. A 1-2-4 concrete using crusher run stone below 1 in.
in size was used for the lining and portal head wall coping and a 1-3-6
concrete for the portal head walls proper. The cost of the portal head
walls is included in the costs given further on.
[Illustration: Fig. 131.--Cross-Section of Peekskill Tunnel, Showing
Lining.]
The side wall foundation trenches were first excavated from 1 to 3 ft.
deep and footing concreted and leveled up, the back of the footing being
carried up against the rock and the front lined to forms giving a 12-in.
offset to the side wall. The footings contained 200 cu. yds. of
concrete. Platforms 25 ft. square and level with the springing lines
were then erected at each end of the tunnel. A derrick was placed at
each platform to handle skips between it and the material tracks which
ran underneath and through the tunnel with a turnout at each end for
switching back empty cars. A 60 H.P. portable boiler supplied steam for
the derrick engines and a pump. The wall forms were built and erected in
panels 12 ft. long; these panels had 4×6-in. plates and sills, 4×4-in.
studs 3 ft. on centers and 2-in. dressed and matched spruce sheeting.
Four panels were set up, two on each side, midway of the tunnel and
braced to the tunnel track. Wheelbarrow runways carried on bents were
built from the platforms to the forms, one from one platform to one
side, another from the other platform to the opposite side. Temporary
bulkheads were erected to close the ends of the forms and they were
filled. Meanwhile carpenters were setting other panels at each end of
the two first erected on each side. After 24 hours the panels first set
were taken down and moved ahead and the processes described continued
until the full length of side wall was completed. The side walls were
not concreted back to the rock; back forms of 1-in. hemlock were used
and the space remaining was filled with spalls. The side walls contained
692 cu. yds. of concrete.
Arch forms were erected for 96 ft. at the center of the tunnel, using
12-ft. lagging, so that sections of this length could be taken down and
moved ahead, nine at each end. The lagging was first laid to a height of
3 ft. above the springing line on each side and the concrete dumped
directly in place from runways laid on the lower chords of the arch
ribs, which were placed 4 ft. apart. When the concrete reached a height
too great for direct discharge into the forms it was dumped on the
runway and passed over with shovels. On the upper portion of the ring
the concrete was first shoveled to a platform erected on the center
posts of the ribs about 2 ft. below the crown and then passed in on the
lagging which was laid in 4-ft. instead of 12-ft. lengths at this stage
of the work. As soon as each section of arch ring was completed it was
waterproofed with six layers of tar paper laid in hot tar and then
packed behind with spalls. The arch centers were struck in a
comparatively short time; in one instance they were struck 90 hours
after the last concrete was placed and no settlement was apparent. The
arch forms stuck so fast to the concrete, however, that they had to be
jacked down by chiseling out the lagging so as to get a bearing on the
arch concrete and by nailing thrust blocks to the rib posts. The section
was then hauled ahead by passing the main fall of the derrick through a
snatch block on the first rib. When hauled clear of the lining all but
the first 3-ft. of lagging on each side was removed; they were then
jacked into position. The arch ring contained 932 cu. yds. of concrete.
Including the portal head walls 1,948 cu. yds. of concrete were laid at
the following costs for labor and materials:
Item. Total. Per cu. yd.
Cement at $1.63 per bbl. $ 5,755.50 $2.951
Sand at $0.75 per cu. yd. 662.94 0.339
Stone at $0.80 per cu. yd. 1,303.20 0.668
Lumber--
Mixing platforms and runways 336.89 0.174
Ribs, including hand sawing 234.10 0.120
Backing boards 134.44 0.069
Lagging 341.04 0.176
Sheathing 268.49 0.137
Plates, sills, studs, braces 182.75 0.093
Coal 118.73 0.061
Oil 16.12 0.008
Hardware, nails, spikes, etc. 224.39 0.118
Tools 181.10 0.093
Freight on stone, cement, etc. 3,089.86 1.584
Labor of all kinds 8,036.31 4.121
---------- -------
Total $20,885.86 $10.712
~METHOD OF LINING CASCADE TUNNEL, GREAT NORTHERN RY.~--The Cascade Tunnel,
13,813 ft. long, built in 1897-1900, was lined throughout with concrete
from 24 ins. to 3½ ft. thick, mixed and placed in the following manner:
It was necessary to place the lining without interfering with the
transportation of materials and excavated material to and from the work
ahead. The arrangement adopted to secure this end is shown by Fig. 132.
A platform 500 ft. long was constructed at the elevation of the wall
plates; the rear end of this platform was reached by an incline, up
which the cars loaded with concrete were hauled by an air hoist and
cable and delivered to any point on this platform. While each 500 ft. of
tunnel was being concreted, the next 500 ft. of platform in advance was
being built, with its approach incline, so that there was no delay in
the work.
Complete concrete plants were installed at each portal, advantage being
taken of the side hills of the approach into the mountain to handle as
much material as possible by gravity. Each plant was equipped with a No.
6 Gates crusher, 40-in.×8-ft. rock screens, and 16-in.×16-ft. screw
concrete mixers. Large storage bins for the cement, sand and stone were
built adjacent to the mixer plant. A 1-3-5 concrete was used. The stone
was crushed from the best rock obtained in the tunnel excavation. This
rock was loaded into the regular muck cars, taken to the portal by
electric motors, and then dumped into other cars below the level of the
muck cars. These cars were hauled by hoisting engine and cable to the
crusher floor and then dumped and sorted to avoid danger from pieces of
unexploded dynamite. It was then run through the crushers, washers and
screens to the stone bin and thence to the mixers. The mixed concrete
was discharged into cars on the level of the muck car tracks and these
cars were taken by motor into the tunnel to the incline, up which they
were hauled by cable and dumped on the platform. From the platform the
concrete was shoveled into the wall forms or onto the centers as
desired.
[Illustration: Fig. 132.--Traveling Platform Used in Lining Cascade
Tunnel.]
The walls were concreted in alternate 12-ft. sections, the weight on the
timber arch thus being gradually transferred from the plumb posts to the
walls. The roof arch was also built in 12-ft. sections, the centers
being in sections of corresponding length which were moved forward on
dollies and jacked up as the work advanced. Ten sections of centering
were used at each end. An average of 7 bbls. of cement were used per
lineal foot of lining. The average monthly progress of lining was about
600 ft. at each end. The concrete lining cost $44 per lin. ft. of
tunnel, done by company forces.
~METHOD OF RELINING HODGES PASS TUNNEL, OREGON SHORT LINE RY.~--The
centers and side wall forms and the methods of work adopted in relining
the Hodges Pass tunnel on the Oregon Short Line Ry. are explained in the
accompanying illustrations. This tunnel is 1,425.8 ft. long and when
constructed in 1882 was lined with timber. The new lining consists of
concrete side walls carrying a brick roof arch. Both the old and the new
linings are shown in the drawings. The tunnel is through a variety of
rock and clay strata, and through the soft strata an invert was
required. Altogether about one-third of the length of the tunnel was
provided with an invert. It will be noted also that the new lining
occupies materially more space than the old; this made necessary
considerable excavation in enlarging the section.
[Illustration: Fig. 133.--Method of Placing Invert Concrete, Hodges'
Pass Tunnel.]
The work of relining consisted of three operations, viz., the invert
construction, the construction of the side walls and the arch
construction.
[Illustration: Fig. 134.--Method of Constructing Concrete Side Walls,
Hodges' Pass Tunnel.]
The form of the invert is shown in Fig. 136. It, of course, had to be
constructed without entailing a break in the track, and the method
adopted was as follows: The ties and ballast were removed from a section
of track about 12 ft. long and in their place was substituted the timber
frame shown in Fig. 133. Under the middle portion of this frame a trench
reaching clear across the tunnel and having a width of 6 to 7 ft. in the
direction of the track was excavated to sub-grade of the invert. The
concrete was filled into this trench, formed to shape on top, and
allowed to harden. The bridging frame was then taken out and the ties
and ballast were replaced. Another section of track was then bridged,
trenched and concreted and so on until the length of invert required was
constructed.
[Illustration: Fig. 135.--Side Wall Forms for Plans A and B, Fig. 134.]
The side wall construction was a more complex operation. It comprised
first the removal of the old lining, the enlarging excavation and the
form erection and concreting. Two methods of performing this task were
employed. Both are illustrated in Fig. 134. By the first method,
designated as Plan A, the concreting was done continuously in sections
of considerable length. The forms used are shown in detail by Fig. 135.
By the second method, the concreting was done in alternate short panels.
This method is designated Plan B on the drawings, Fig. 134. The forms
used are shown in detail by Fig. 135. The only difference in the form
construction for the two plans is in the connection of the posts at the
top.
[Illustration: Fig. 136.--General Plan of Centers for Roof Arch, Hodges'
Pass Tunnel.]
The construction of the centering for the roof arch is shown by Figs.
136 and 137, Fig. 137 giving detail dimensions of the ribs and lagging.
The center, as shown by Fig. 136, consisted of four ribs spaced 3 ft. on
centers. Each rib consists of two side posts and an arch piece. The side
posts on each side are connected at the bottoms by a sill and at the top
by a cap. Jacks between the sill and a mud sill laid on the concrete
invert or in the ditch held the center in place during arch
construction. Lowering these jacks dropped the center onto trucks
traveling on the mud sills. Thus the center was moved along as the work
progressed. As will be noted from Figs. 134 and 135, the side wall forms
carried the work only to the bottoms of the old caps. The arch center
completed the concrete wall work and the roof arch. Only about one-third
of the new lining had the brick arch, as shown by the drawings; in the
remaining two-thirds the concrete was carried up much further on each
side; in fact, the brickwork constituted only the top third of the arch.
[Illustration: Fig. 137.--Details of Centers for Roof Arch, Hodges' Pass
Tunnel.]
In describing the forms and centers we have left much of the explanation
to the drawings. These show all dimensions and details, and indicate in
a measure the mode of procedure. The work done consisted of excavation
enlarging the section, of removing the old timber lining and of the form
work, concreting and bricklaying for the new lining. All of it above
convenient reach from the ground was done from a movable staging formed
by a deck fixed on a flat car so as to be adjustable in height. The
concrete was mixed by hand on this car platform and shoveled directly
into the forms, the platform being raised as the work increased in
height. The concrete used was a 1-3-5 mixture of 2½-in. broken stone.
The organization of the working force is not easily stated since the
work was done as the traffic permitted and varied with the conditions.
Generally from 12 to 16 men were all that could be employed to
advantage. Complete records of cost were kept, but they were destroyed
by fire, so that the only figures available on this point are the
totals. These are as follows:
Item. Totals. Per lin. ft.
Labor $21,129 $14.81
Materials 13,939 9.77
------- -------
Total $35,068 $24.58
These amounts average the cost of the invert, which was required for
about one-third of the length, over the whole tunnel.
~RELINING A SHORT TUNNEL.~--The following figures show the cost of
relining with concrete a timber lined railway tunnel. The concrete side
walls were 14 ft. high and had an average thickness of 2½ ft. Therefore
each side wall averaged nearly 1.3 cu. yds. per lin. ft., and the two
walls averaged 2.59 cu. yds. per lin. ft. of tunnel. The concrete was
mixed 1-3-5, being, we believe, unnecessarily rich in cement. The
average amount of concrete placed in the walls per day was 50 cu. yds.
Cost of Side Walls.
Materials-- Per cu. yd.
1.33 bbl. cement at $2.00 $2.66
0.5 cu. yd. sand at 0.18 0.09
0.75 cu. yd. stone at 0.55 0.41
-------
Total $3.16
Labor on concrete--
0.01 day foreman at $5.00 $0.05
0.03 day foreman at $3.00 0.09
0.03 day engineman at $3.00 0.09
0.35 day laborer at $1.75 0.61
------- -------
0.42 Total $0.84
Labor, removing timber, building forms, excavating, etc.--
0.02 day foreman at $5.00 $0.10
0.05 day foreman at $3.00 0.15
0.40 day laborer at $1.75 0.70
------- -------
0.47 Total $0.95
Miscellaneous--
0.02 day engineer and superintendent at $5.00 $0.10
Falsework and forms, timber and iron 0.07
Tools, light, etc. 0.10
Interest and depreciation of $1,800 plant at 20% per annum 0.09
Train service, 0.03 day work train at $25 0.75
Summary concrete side walls-- Per cu. yd.
Materials $3.16
Labor on concrete 0.84
Labor removing timber, etc. 0.95
Train service 0.75
Miscellaneous 0.34
-------
Total $6.04
In the two side walls there were 2.59 cu. yds. of concrete per lin. ft.
of tunnel, hence the cost of the side walls was $6.04 × $2.59 = $15.64
per lin. ft. of tunnel. The concrete arch varied in thickness,
averaging from 14 to 20 ins. at the springing line to 8 to 14 ins. at
the crown. The arch averaged 1.2 cu. yds. per lin. ft. of tunnel. About
20 cu. yds. of arch were placed per day. The arch concrete was mixed
1-3-5 and the cost was as follows:
Cost of Concrete Arch.
Materials-- Per cu. yd.
1.36 bbls. cement, $2.00 $2.72
0.05 cu. yd. sand, 0.18 0.09
0.75 cu. yd. stone, 0.55 0.41
-------
Total $3.22
1.8 cu. yds. dry rock backing at 0.55 $0.99
Labor on concrete--
0.02 day foreman at $5.00 $0.10
0.12 day foreman at 3.00 0.36
0.88 day laborer at 1.75 1.54
------- ------- ------
1.02 Total $1.96 $2.00
Labor placing 1.08 cu. yds. rock backing--
0.01 day foreman at $5.00 $0.05
0.51 day foreman at 3.00 0.15
0.55 day laborer at 1.75 0.96
------- ------- -------
0.61 Total $1.90 $1.16
Labor removing timbers, forms, excavations, etc.--
0.02 day foreman at $5.00 $0.10
0.04 day foreman at 3.00 0.12
0.06 day carpenter at 2.50 0.15
0.40 day laborer at 1.75 0.70
------- ------- -------
0.52 Total $2.06 $1.07
Train service--
0.06 day at $25 $1.50
Miscellaneous--
Engineering and superintendence. .07
Falsework, timber and iron .13
Tools, light, etc .12
Interest and depreciation, $1,800 plant, 20% per annum 0.09
Summary concrete arch--
Concrete materials $3.22
Dry rock backing (1.8 c. y.) 0.99
Labor and concrete 2.00
Labor placing 1.8 cu. yds. rock backing 1.16
Labor removing timber, etc 1.07
Train service hauling materials 1.50
Engineering and superintendence 0.07
Falsework, timber and iron 0.13
Tools, light, etc. 0.12
Interest and depreciation plant 0.09
------
Grand total $10.35
It will be noted that the "train service" is an item that really should
be considered as a part of the cost of the materials, for the cost of
the sand and stone is the cost f. o. b. cars at the sand pit and at the
quarry, to which should be added the cost of hauling them to the
tunnel--to-wit, the "train service."
Summing up, we have the following as the cost per lineal foot for lining
this single-track tunnel with concrete: Per lin. ft.
2.59 cu. yds. side walls at $6.04 $15.64
1.20 cu. yds. arch at 10.33 12.40
------- ------ -------
3.79 cu. yds. Total $9.38 $28.04
It should be remembered that the higher cost of the arch concrete is due
in large measure to the fact that 1.8 cu. yds. of dry rock packing above
the arch are included in the cost of the concrete. Strictly speaking,
this dry rock packing should not be charged against the arch concrete,
and, segregating it, we have the following:
Per lin. ft.
2.59 cu. yds. concrete side walls at $6.04 $15.64
1.20 cu. yds. concrete arch at 8.18 9.82
2.16 cu. yds. dry rock at 0.55 1.19
Labor placing 2.16 cu. yds. at 0.64 1.39
------
Total $28.04
This is a much more rational analysis of the cost and a still further
reduction in the cost of the arch concrete might be made by prorating
the train service item ($1.50 per cu. yd. concrete). At least half of
this train service should be charged to the dry rock backing, for there
are 1.25 cu. yds. of sand and broken stone to 1.80 cu. yds. of dry rock
backing.
The amount of this dry rock backing, or packing, varies greatly in
different parts of a tunnel. In the first half of this tunnel it
averaged 1.8 cu. yds. per lin. ft., while in the second half it averaged
nearly 2.4 cu. yds. per lin. ft.
~METHOD OF MIXING AND PLACING CONCRETE FOR A TUNNEL LINING.~--The tunnel
known as the Burton tunnel is located on the Jasper-French Lick
extension of the Southern Ry., and about 4 miles from French Lick, Ind.
It is a single track tunnel 2,200 ft. long with 300 ft. at one end on a
4°-30' curve and 1,900 ft. on tangent. The material penetrated was slate
and loose rock, requiring solid timbering throughout. This timbering is
shown by Fig. 138, which also shows the concrete lining; the timbering
was embedded in the concrete lining.
[Illustration: Fig. 138.--Sections Showing Concrete Lining for Burton
Tunnel.]
The original timber lining was composed as follows: Posts 10×12 ins. and
spaced 3 ft. apart were set on 3×12-in. sills and carried 10×12-in.
wall plates which supported 10×12-in. segmental arch ribs spaced 3 ft.
apart. The lagging behind the posts was 3×6-in. stuff and the lagging
over the arch ribs was 4×6-in. stuff. The section of the concrete lining
is shown by Fig. 138, it required 4,132 cu. yds. of concrete and 161.43
lbs. of reinforcement per lin. ft. The concrete was a 1-2½-5 crushed
stone--between 2 in. and ¼ in. size--mixture; it required 1.16 bbls. of
cement, 0.52 cu. yds. sand and 0.92 cu. yds. of stone per cubic yard of
concrete. The amount of reinforcement per cubic yard of concrete was
39.1 lbs.
[Illustration: Fig. 139.--View of Mixer Plant Showing Car Tracks, Burton
Tunnel.]
[Illustration: Fig. 140.--View of Mixer Plant Showing Method of
Unloading Materials, Burton Tunnel.]
All the concrete was mixed and handled from one end of the tunnel. The
mixing plant was located in the approach cut at one end. A standard gage
main track ran through the cut. About 20 ft. in the clear to one side of
this track a trestle 500 ft. long was built, carrying an 18-ft. gage
derrick track and a narrow gage 3-cu. yd. dump car track. A stiff leg
derrick operating a 1 cu. yd. orange peel or a 1½ cu. yd. clam-shell
Hayward bucket was mounted on a carriage traveling on the 18-ft. gage
track. The side of the trestle nearest the railway track was sheeted
vertically and the space between this sheeting and the track was floored
over at track level for stock piles. Near the end of the trestle toward
the tunnel and on the same side of the track was the mixer plant. This
consisted of two 85 cu. yd. bins, one for sand and one for stone,
carried by a tower so that their bottoms were 25 ft. above track level.
Below the bins was a charging platform pierced by a measuring hopper.
Below the measuring hopper was a 1½ cu. yd. cubical mixer and below the
mixer was a 3-ft. gage track for 1½ cu. yd. Koppel side dump cars. To
the rear of the tower at ground level there was a 20-cu. yd. sand bin
and a 20-cu. yd. stone bin set side by side with a continuous bucket
elevator leading from each to the corresponding bin on the tower. The
cement house was located directly across the railway track from the
tower. At the side of the cement house nearest the track there was an
inclined bag elevator leading up to a bridge spanning the railway track
at the level of the charging floor of the mixer plant. On this bridge
ran a car for carrying bags of cement. The plant as described is shown
by Figs. 139 and 140.
In operation the derrick unloaded the stone and sand cars by means of
the Hayward buckets either into the bins at the feet of the bucket
elevators or onto stock piles on the flooring beside the trestle. When
put into stock piles the materials had to be reloaded by derrick into
the 3 cu. yd. cars on the trestle narrow gage track and carried by these
cars to the elevator boots. The sand and stone were chuted from the
tower bins directly into the charging hopper below. Here the cement
bags, brought across the bridge on the car into which they were loaded
directly by the bag elevator, were opened and the cement added to the
sand and stone. The charge was then dropped into the mixer and from the
mixer the batch dropped into the Koppel concrete cars.
In the tunnel a traveling platform was constructed on two standard gage
flat cars so coupled that a platform 100 ft. long and slightly narrower
than the clear space between side wall forms was obtained. Connecting
the end of the platform toward the mixing plant was a rampe or inclined
platform mounted on wheels. The Koppel car tracks from the mixer were
carried up the incline and the full length of the level platform. The
cars were hauled to the foot of the incline by a light locomotive. A
cable was then hooked to them; this cable was run through a block on the
level platform, its free end coming back to the locomotive, which thus
pulled the cars up the incline by moving back toward the mixer. On the
level platform the cars were pushed by hand and dumped on the floor,
whence the concrete was shoveled into the forms.
The platform construction deserves mention in the particular that it
provided for adjusting the platform vertically. At each corner of the
car a vertical post some 7 or 8 ft. high was set up. The side stringers
of the platform carried two vertical posts at each end; these two posts
were spaced just far enough apart to slide over the corner post, one on
each side of it. A block at the top of the corner posts with the hoist
line connected to the bottoms of the platform posts and the lead line
going to a winch head, thus made it possible to lift the platform any
distance within the height of the vertical post guide and hold it there
by blocking under the posts. The arrangement is shown roughly by the
sketch, Fig. 141. There was block and tackle for each corner post and a
winch at each end of the car. The vertical movement of the platform was
between 6 and 7 ft.
The floor was cemented first, then the side walls and finally the roof
arch. Floor construction was begun at the portal farthest from the
mixing plant. Koppel car tracks were laid through the tunnel and the
concrete was dumped from them directly on the ground. The cars were
hauled by a light locomotive. As the concreting advanced the dump car
track was raised and suspended from timbers across tunnel so that the
concrete could be placed under it. As fast as the floor hardened the
permanent standard gage track was laid and a temporary third rail placed
to give also a dump car track.
[Illustration: Fig. 141.--Sketch Showing Telescopic Support for
Concreting Platform, Burton Tunnel.]
When the floor had been finished the side walls were constructed, using
the traveling platform and beginning at the far portal. The wall forms
consisted of 4×6-in. studs, spaced 3 ft. apart and carrying 2×12-in.
lagging. A 6×6-in. waling outside the studs at about mid-height held the
studs to the timbering by lag bolts reaching through the wall to the
10×12-in. posts. A strip of plank nailed across wall between stud and
post held the form at the top. Wall forms were erected for 100 ft. of
wall at a time. These forms required about 45 ft. B. M. lumber per
lineal foot of form on one side or 90 ft. B. M. for both sides. Two sets
of side wall forms or 200 ft. of wall forming were built, and used over
and over again. The concrete was shoveled into the wall forms from the
traveling platform, the lagging being placed a board at a time as the
work progressed upward and the platform being elevated as required, its
final position being at about springing line level. When 100 ft. of side
walls had been completed the traveling platform was moved ahead for
another 100-ft. section.
[Illustration: Fig. 142.--Sketch Showing Device for Removing Centering
Ribs, Burton Tunnel.]
The centers consisted of 6×12-in. ribs, made up of 3×12-in. plank. The
feet of the ribs rested on folding wedges on 6×12-in. wall plates,
supported by 6×6-in. posts setting close against the finished wall.
The ends of the ribs were held from closing in by 6×6-in. walings, one
on each side, lag-bolted through the lining to the timbering. The
centering required about 315 ft. B. M. of lumber per lineal foot of
center. The method of removing the centers was novel. A flat car had
erected on it a narrow working platform high enough to reach well up
into the arch. Along this platform at the center was erected a sort of
"horse," which could be elevated and lowered by jacks. The sketch, Fig.
142, shows the arrangement. At each end and at the middle of the
platform two guide posts a a were erected and braced upright. Between
these guide posts set plunger posts which were raised and lowered by
screw jacks. The three plunger posts carried a longitudinal timber c.
The car was run under the ribs of centering to be removed and the timber
c raised by working the jacks until it came to close bearing under the
ribs d. The railings and the wedges at the foot of the ribs were then
removed, leaving the ribs hanging on the timber c. This timber was
then jacked down to clear the lining and the ribs rotated horizontally
on the point of suspension as a pivot until their ends swung in over the
platform. The car was then moved ahead to where the centers were to be
used again; the ribs were rotated back to their normal position across
tunnel; the timber c was jacked up, and the wedges and railings placed
at the first of the ribs.
The concreting on the roof arch was begun at the portal. Two shifts were
worked and 42 ft. of arch were concreted each shift.
~METHOD AND COST OF LINING GUNNISON TUNNEL.~--The costs are for concrete
in place in the side walls and the arch of the tunnel, for a length of
440 lin. ft. The quantity of concrete considered in estimating the cost
per cubic yard was 616 cu. yds. The material was mixed and placed in ½
cu. yd. batches, the proportion of the mixtures being 1-2.2-4.4. The
final cost includes the labor of excavating and screening gravel and
sand, the hauling of the same from the bins at the pit to the storage
bins at the main shaft, the care of the chutes in the shaft and the
mixing of the concrete in the tunnel at the bottom of the shaft, the
transportation of the concrete from the mixer to the traveler, the
deposition of the concrete, the setting up and taking down of forms and
the cost of the cement. It does not include the construction of the
gravel pit chutes that hold the screens, the building of the road from
the gravel pit to the storage bins at the shaft, the concrete mixer and
its installation, the traveler and its installation, the cost of
material and labor in the construction of the concrete forms, the
requisite power to run the machinery and other expenses of a similar
nature.
The gravel used for the concrete was obtained from a pit situated on top
of a hill not far from the main shaft leading down to the tunnel. This
gravel bed contains very closely the proper proportions of sand and
gravel for the concrete aggregates. The gravel was excavated and loaded
by hand into side dump cars of 35 cu. ft. capacity. These cars were run
to the edge of the hill where the gravel was dumped upon a screen from
which it ran by gravity, passing thence into storage bins. From the
storage bins the sand and gravel were drawn off into dump wagons having
a capacity of 2 cu. yds. and hauled a distance of one-half mile to a
second set of storage bins located at the top of the shaft leading into
the tunnel. The road from the storage bins at the gravel pit to the
storage bins at the head of the shaft was down grade. A two-horse team
could readily haul 2 cu. yds. of gravel over this road. The storage bins
at the top of the shaft leading into the tunnel communicated with the
measuring boxes at the bottom of the shaft by means of chutes. The
measuring boxes discharged directly into tram cars. The average length
of haul from the mixer to the place of deposition of concrete was about
4,500 ft.
The concrete was placed in the side walls by means of a traveler, which
was so operated in the tunnel as to allow the passage of the concrete
trains beneath it. The traveler was 64 ft. long and was provided with a
slow motion electric hoist, by which the cars containing the concrete
were elevated to the top of the traveler and thence transferred to any
desired position. The concrete was dumped from these cars into boxes
where any remixing or tempering that was required was done, after which
the concrete was shoveled directly into the forms. The entire operation
of handling the materials of the concrete, it will be seen, utilized
gravity to the greatest possible degree.
In order to get a good average cost per cubic yard for handling gravel
and sand, this analysis has been based on five months' operation, from
November, 1906, to March, 1907. In these five months there were 4,123
cu. yds. of sand and gravel handled. The concrete considered was placed
during the month of March. Below is given the distribution of the cost
of the concrete as to the specified divisions of the work and as to the
class of work involved in each division. Measurements taken at the mixer
show that each cubic yard of concrete contained 0.74 cu. yds. of gravel,
0.445 cu yds. of sand and 5.6 sacks of Portland cement. The total of the
aggregates is, therefore, 1.185 cu. yds. per cubic yard of concrete. The
cement costs $0.62 per sack on the work, making a cost of $3.472 per
cubic yard of concrete.
Excavating and screening 4,123 cu. yds. gravel--
Total Per cu. yd.
cost. gravel.
Foreman, 66-7/8 days at $3.04 $ 203.30 $0.049
Labor, 397½ days at $2.56 1,017.60 0.247
Labor, 116¼ days at $2.08 241.80 0.059
-------- ------
Total $1,462.70 $0.355
Hauling 4,123 cu. yds. gravel and sand--
2-horse team and driver, 210 days at
$3.60 $756.00 $0.183
2-horse team and driver, 4½ days at $4 18.00 0.005
------- ------
Total $774.00 $0.188
As there were 1.185 cu. yds. of gravel per cubic yard of concrete the
cost of gravel per cubic yard of concrete was for--
Excavating and screening (1.185 × $0.355) $0.421
Hauling (1.185 × $0.188) 0.223
------
Total $0.644
Adding to this the cost of cement $0.62 × 5.6 = $3.472, we have $0.644 +
$3.472 = $4.116, as the cost of concrete materials per cubic yard of
concrete. The cost of labor, mixing and placing was as follows for 616
cu. yds.:
Total Per cu. yd.
Mixing 616 cu. yds. concrete-- cost. concrete.
Superintendent, 2 days at $5.83-1/3 $ 11.67 $0.020
Foreman, 1 day at $4.50 4.50 0.007
Labor, 45 days at $3.04 130.72 0.215
Labor, 93 days at $2.56 238.08 0.381
Hoist engineer, 34 days at $3.52 119.68 0.196
------- ------
Total $504.65 $0.819
Transporting 616 cu. yds. concrete--
Superintendent, 1 day at $5.83-1/3 $ 5.83 $0.009
Foreman, 1 day at $4.50 4.50 0.007
Motorman, 34 days at $3.04 103.36 0.175
Brakeman, 34 days at $2.56 87.04 0.135
------- ------
Total $200.73 $0.326
Depositing 616 cu. yds. concrete--
Superintendent, 4 days at $5.83-1/3 $ 23.33 $0.038
Foreman, 4 days at $4.50 18.00 0.029
Foreman, 68 days at $3.04 200.72 0.326
Labor, 238½ days at $2.56 610.56 0.991
------- ------
Total $852.61 $1.384
Setting and moving forms--
Superintendent, 2 days at $5.83-1/3 $ 11.67 $0.018
Foreman, 2 days at $4.50 9.00 0.014
Carpenter foreman, 10 days at $5 50.00 0.080
Carpenter, 13 days at $3.20 41.60 0.067
Labor, 49 days at $3.04 148.96 0.241
Labor, 19 days at $2.56 48.64 0.078
------- ------
Total $309.87 $0.498
Summarizing we have the following cost:
Materials--
Cement, 5.6 bags at $0.62 $3.472
Gravel (excavating and screening) 0.421
Hauling gravel and sand 0.223
------
Total, materials $4.116
Labor--
Mixing concrete $0.819
Transporting concrete 0.326
Depositing concrete 1.394
Setting and moving forms 0.498
------
Total, labor $3.037
Grand total $7.153
~COST OF CONCRETE WORK IN LINING NEW YORK RAPID TRANSIT SUBWAY.~--The
costs given here refer alone to the concrete work in constructing the
jack arch and steel beam lining of the original standard subway. Figure
143 shows the character of this construction. Arch panel forms were set
up between the wall beams and hung from the floor beams and filled
behind and above with 1-2-4 trap rock concrete. The form panels were
used over and over and the concrete was machine mixed. Common labor was
paid $1.50 per 8-hour day; foremen, $3; carpenters, $3; enginemen,
$3.50; and masons, $4. The costs cover three sections and are in each
case the averages for the whole section. They are, we believe, the only
itemized costs that have been published for concrete work on this road.
[Illustration: Fig. 143.--Cross-Section of New York Rapid Transit
Subway.]
_Two-Track Subway._--In this section of two-track subway there were
8,827 cu. yds. of foundation concrete and 6,664 cu. yds. of concrete in
wall and roof arches. The two classes of work cost as follows:
Foundations-- Total. Per cu. yd.
Labor mixing $ 4,669 $0.53
Labor placing 5,142 0.58
Materials and plant 211 0.02
Cement, sand, stone, etc. 30,719 3.48
-------- -------
Total $40,741 $4.61
Roof and side walls--
Labor mixing $ 5,444 $0.82
Labor placing 5,623 0.84
Labor setting forms 14,746 2.21
Labor plastering arches 431 0.06
Materials and plant 1,176 0.18
Cement, sand, stone, etc. 23,888 3.58
-------- ------
Total $51,308 $7.69
Averaging the work we have 15,491 cu. yds. of concrete placed at a cost
of $5.94 per cu. yd.
_Four-Track Subway._--On two sections of four-track subway the labor
cost of mixing and placing concrete similarly divided was as follows:
Section A. Section B.
Foundations-- Per cu. yd. Per cu. yd.
Labor mixing $0.97 $0.94
Labor placing 0.96 0.95
Power 0.14 0.16
-------- --------
Total $2.07 $2.05
Roof and side walls--
Labor mixing $0.79 $0.91
Labor placing 0.85 0.94
Labor setting forms 2.01 1.20
Labor plastering arches 0.16 0.23
Power 0.28 0.15
------- -------
Total $4.09 $3.43
[Illustration: Fig. 144.--Traveling Form for Side Walls, New York Subway
Tunnels.]
~TRAVELING FORMS FOR LINING NEW YORK RAPID TRANSIT RY. TUNNELS.~--In
constructing the tunnels under Park Ave. and under the north end of
Central Park for the New York Rapid Transit Ry., traveling centers and
side wall forms were used for the concrete lining. The mixing plants
were installed in the shafts and consisted generally of gravity mixers
charged at the surface and discharging into skip cars running on the
tunnel floor.
[Illustration: Fig. 145.--Traveling Form for Roof Arch. New York Subway
Tunnels.]
The forms used in the Park Ave. tunnel are shown by Figs. 144 and 145;
those used in the Central Park tunnel differed only in details. The
method of work was slightly different in the two tunnels, but was
substantially as follows: Three platforms mounted on wheels were used in
each set and two sets were employed. Ahead came a traveler carrying the
side wall forms, next came a shorter traveler carrying a derrick, and
last came the traveler carrying the roof centers. The arrangement
as operated in the Central Park tunnel is shown by Fig. 146. In the Park
Ave. tunnel the "bridges" were dispensed with, the skips being hoisted
through the open end bays of the derrick car and set directly on the
cars on the center traveler.
[Illustration: Fig. 146.--Sketch Plan of Traveling Forms, New York
Subway Tunnels.]
The traveler carrying the side wall forms was set in position and
blocked, the grade and line being given by the track rails, which had
been set exactly for that purpose. The side wall forms differed slightly
in the two tunnels; those for the Park Ave. tunnel shown by Fig. 144
formed the vertical portion of the wall only so that when the arch
forms, Fig. 145, followed a space A B was left which had to be molded
by separate sector-like forms. The side wall forms for the Central Park
work were constructed as shown by Fig. 147, being curved at the top to
merge into the arch centers. In the Park Ave. work the wall studs were
adjusted in or out by means of wedges and slotted bolt holes. In the
Central Park work the studs A Fig. 145 were hung by ¾-in. bolts from
the pieces B spiked to line onto the cross-braces. The bottom was then
lined up by means of wedges at D. The side wall studs being lined up,
the bottom lagging boards were placed and filled behind by shoveling the
concrete into them direct from skip cars on the adjacent tracks on the
tunnel floor. In this way the side walls were built up to the tops of
the forms.
[Illustration: Fig. 147.--Sketch Showing Detail of Side Wall Forms. New
York Subway Tunnels.]
As soon as the side wall concrete had set the forms were struck and the
traveler was moved ahead and set for another section of wall. The
derrick and roof arch travelers were then moved into position between
the finished walls, and the arch traveler was jacked up and aligned.
Skip cars coming from the mixer were run under the derrick traveler,
where the skips were lifted by the derrick and set on the platform cars
to be run alongside the work. The arch lagging was placed a piece at a
time and filled behind by shoveling direct from the skips. As the crown
was approached the lagging was placed in short lengths and filled in
over the ends, the concrete being shoveled in two lifts; in Fig. 145 the
line C D indicates the position of the shoveling board. The centers
were struck by lowering the jack supported traveler down onto the track
rails.
~COST OF MIXING AND PLACING SUBWAY LINING, LONG ISLAND R. R., BROOKLYN,
N. Y.~--The subway carrying the two tracks of the Long Island R. R. under
Atlantic Ave., in Brooklyn, New York city, has a lining consisting of an
invert arch 12 ins. thick at the center, side walls 4½ ft. thick at
the base and 3 ft. thick at the top, and a roof of jack arches between
steel I-beams 5 ft. apart. The dimensions inside the concrete are 16×20
ft. A 1-8 mixture of cement, sand, gravel and stone was used in the
floor and walls and a 1-6 mixture of the same materials in the jack
arches. A bag of cement was called 1 cu. ft., so that a barrel was 4 cu.
ft. A Hains gravity mixer and a batch mixer were used and careful
records were kept of all quantities.
_General Data._--During 1903, about 13,880 cu. yds. of the 1-8 concrete
were placed, 90 per cent. of which was mixed in the gravity mixer and 10
per cent. in the batch mixer. Of the 1-6 concrete 5,320 cu. yds. were
placed, 85 per cent, of which was mixed in the gravity mixer and 15 per
cent, in the batch mixer.
_Gravity Mixer Work._--During 1903, there were 16,940 cu. yds. of
concrete mixed in gravity mixers, requiring 2,860 days' labor mixing and
4,000 days' labor placing. Wages were $1.50 a day and the cost was 26
cts. per cu. yd. for mixing and 33 cts. for placing, making a total of
59 cts. per cu. yd. During the month of August when 2,800 cu. yds. were
mixed the cost was as low as 24 cts. for mixing, plus 22 cts. for
placing, or a total of 46 cts. per cu. yd. for mixing and placing. The
mixer averaged about 113 cu. yds. per day with a gang of 19 men mixing
and 26 men placing. The average size of batch was 0.46 cu. yd. In 1904,
20,000 cu. yds. were mixed in 190 days, worked with a gang of 19 men
mixing; the gang placing consisted of 25 men. The cost was as follows:
Item. Total. Per cu. yd.
2,950 days labor mixing $ 4,870 24 cts.
4,760 days labor placing 7,300 36 cts.
--------- --------
Total $12,170 60 cts.
During the best month of 1904, the labor cost was 16 cts. for mixing and
29 cts. for placing, or a total of 45 cts. per cu. yd.
_Batch Mixer Work._--During 1903 the batch mixer mixed 2,390 cu. yds. in
970 labor days mixing and 740 labor days placing at a cost of 59 cts.
per cu. yd. for mixing and 55 cts. per cu. yd. for placing, or a total
of $1.04 per cu. yd. During the month of June the cost was as low as 40
cts. for mixing and 30 cts. for placing, or 70 cts. per cu. yd. for
mixing and placing. The wages paid were $1.50 per day and the average
gangs were 11 men mixing and 14 men placing; the average batch mixed was
0.57 cu. yd. and the average output was 35 cu. yds. per day. During
1904, the mixer worked 153 days and averaged 46 cu. yds. per day; the
average size of batch was 0.44 cu. yd. The average gangs were 13 men
mixing and 11 men placing. The labor cost of 7,000 cu. yds. was as
follows:
Item. Total. Per cu. yd.
1,910 days labor mixing $3,175 45 cts.
1,740 days labor placing 2,660 38 cts.
------- --------
Total $5,835 83 cts.
_Haulage._--The costs given comprise in mixing, the cost of delivering
the materials to the mixer, and, in placing, the cost of hauling the
concrete away. A Robins belt conveyor was used to deliver materials to
the gravity mixer and this accounts, in a large measure, for the lower
cost of mixing by gravity. The mixed concrete was hauled from both
mixers in dump cars pushed by men.
_Form Work._--The labor cost of forms for 19,300 cu. yds. of concrete
placed in 1903 was $16,800, or 87 cts. per cu. yd. of concrete. The
total labor days consumed on form work was 6,340 at $2.70 per day. The
total cost of concrete in place for mixing, placing and form work was
$1.46 per cu. yd., not including lumber in forms, fuel, interest and
depreciation.
CHAPTER XVII.
METHODS AND COST OF CONSTRUCTING ARCH AND GIRDER BRIDGES.
The construction problems in arch and girder bridges of moderate spans
are simple, and with the exception of center construction and
arrangement of plant for making and placing concrete, are best explained
by citing specific examples of bridge work. This is the arrangement
followed in this chapter.
~CENTERS.~--The construction of centers is no less important a task for
concrete arches than for stone arches. This means that success in the
construction of concrete arches depends quite as much upon the
sufficiency of the center construction as it does upon any other portion
of the work. The center must, in a word, remain as nearly as possible
invariable in level and form from the time it is made ready for the
concrete until the time it is removed from underneath the arch, and,
when the time for removal comes, the construction must be such that that
operation can be performed with ease and without shock or jar to the
masonry. The problem of center construction is thus the two-fold one of
building a structure which is immovable until movement is desired and
then moves at will. Incidentally these requisites must be obtained with
the least combined expenditure for materials, framing, erection and
removal, and with the greatest salvage of useful material when the work
is over. The factors to be taken count of are it, will be seen, numerous
and may exist in innumerable combinations.
[Illustration: Fig. 148.--Center for 50 ft. Arch Span (Supported).]
[Illustration: Fig. 149.--Center for 50-ft. Arch Span (Cocket).]
Centers may be classified into two types: (1). Centers whose supports
must be arranged so as to leave a clear opening under the center for
passing craft or other purposes, and (2) centers whose supports can be
arranged in any way that judgment and economy dictate. Centers of the
first class are commonly called cocket centers. As examples of a cocket
and of a supported center and also as examples of well thought out
center design we give the two centers shown by Figs. 148 and 149, both
designed for a 50-ft. span segmental arch by the same engineer. The
development of the center shown by Fig. 148 into the cocket center shown
by Fig. 149 is plainly traceable from the drawings. In respect to the
center shown by Fig. 149 which was the construction actually adopted we
are informed that 16,464 ft. B. M. were required for a center 36 ft.
long, that the framing cost about $12 per M. ft. B. M., with carpenters'
wages at $4 per day, and that the cost of bolts and nuts was about $1.50
per M. ft. B. M. With lumber at $20 per M. ft. B. M., this center framed
and erected would cost about $35 per M. ft. B. M. As an example of
framed centers for larger spans we show by Fig. 158 the centers for the
Connecticut Avenue Bridge at Washington, D. C., with costs and
quantities; other references to costs are contained in the index.
A center of very economical construction is shown by Fig. 159, and is
described in detail in the accompanying text. The distinctive feature of
this center is the use of lagging laid lengthwise of the arch and bent
to curve. Another example of this form of construction may be found in a
3-span arch bridge built at Mechanicsville, N. Y., in 1903. The viaduct
was 17 ft. wide over all, and consisted of two 100-ft. spans and one
50-ft. span. Pile bents were driven to bed rock, the piles being spaced
6 ft. apart and the bents 10 ft. apart. Each bent was capped with
10×12-in. timber. On these caps were laid four lines of 10×12-in.
stringers, and 8×10-in. posts 3 ft. apart were erected on these
stringers, and each set of four posts across the arch was capped with
8×10-in timbers the ends of which projected 3 ft. beyond the faces of
the arch. The tops of these cross caps were beveled to receive the
lagging which was put on parallel with the center line of the viaduct,
sprung down and nailed to the caps. This lagging consisted of rough
1-in. boards for a lower course, on top of which was laid 1-in. boards
dressed on the upper sides. Hardwood wedges were used under the posts
for removing the centers. In the centers, forms and braces for the three
arches there were used 140,000 ft. B. M. of lumber. The structure
contained 2,500 cu. yds. of concrete.
Another type of center that merits consideration in many places is one
developed by Mr. Daniel B. Luten and used by him in the construction of
many arches of the Luten type of reinforced concrete arch. The
particular feature of this type of arch is that in shallow streams for
bridges of ordinary span the ends of the arch ring are tied together
across stream by a slab of concrete reinforced to take tension. This
slab is intended to serve the double purpose of a tie to keep the arch
from spreading and thus reduce the weight of abutments and of a pavement
preventing scour and its tendency to undermine the abutments.
Incidentally this concrete slab, which is built first, serves as a
footing for the supports carrying the arch center.
As an illustration of the center we choose a specific structure. In
building a 95-ft. span, 11-ft. 1-in. rise arch bridge at Yorktown, Ind.,
in 1905, the centers were designed so as to avoid the use of sand boxes
or wedges. Ribs of 2×12-in. pieces cut to the arc of the arch soffit
were supported on uprights standing on the concrete stream bed pavement.
The uprights were so proportioned by Gordon's formula for columns that
without bracing they would be too light to support the load of concrete
and earth filling that was to come upon them, but when braced at two
points dividing the uprights approximately into thirds they would
support their loading rigidly and without buckling. The design in detail
was as follows: The uprights near the middle of the span were about 15
ft. long and were spaced 7 ft. apart across the stream and 3 ft. apart
across the bridge. Each upright then was to support a loading of
concrete of 7 ft.×3 ft.×26 ins. and an earth fill 1 ft.×7 ft.×3 ft., or
a total load of about 9,000 lbs. Applying Gordon's formula for struts
with free ends,
f S
P = -------------------
l²
I + --------
125h²
where P is the total load = 9,000 lbs., f is fibre stress for
oak--1,600 lbs., l is length of strut in inches and h is least
diameter of strut in inches, it was found that for a length of 15 ft. a
7×7-in. upright would be required to satisfy the formula, but for a
length of 5 ft., which would result from bracing each strut at two
points, a 4×4-in. timber satisfied the formula. Therefore, 4×4-in.
timbers braced at two points were used for the longest uprights. About
30 days after the completion of the arch the bracing was removed from
the uprights, beginning at the ends of the span and working towards the
middle. As the bracing was being removed the uprights gradually yielded,
buckling from 4 to 6 ins. from the vertical and allowing the arch to
settle about ¼ in. at the crown. This type of center has been
successfully employed in a large number of bridges.
Figure 150 shows a center for a 125-ft. span parabolic arch with the
amount and character of the stresses indicated and with a diagram of the
actual deflections as measured during the work.
[Illustration: Fig. 150.--Center for 125-ft. Span Parabolic Arch with
Diagram of Deflections.]
In calculating centers of moderate span there is seldom need of more
than the simple formulas and tables given in Chapter IX. When the spans
become larger, and particularly when they become very large--over 200
ft.--the problem of calculating centers becomes complex. None but an
engineer familiar with statics and the strengths of materials and
knowing the efficiency of structural details should be considered for
such a task. Such computations are not within the intended scope of this
book, and the design of large centers will be passed with the
presentation of a single example, the center for the Walnut Lane Bridge
at Philadelphia, Pa.
The main arch span of the Walnut Lane Bridge consists of twin arches
spaced some 16 ft. apart at the crowns and connected across by the
floor. Each of the twin arch rings has a span of 232 ft. and a rise of
70¼ ft., is 9½ ft. thick and 21½ ft. wide at the skewback and 5½ ft.
thick and 18 ft. wide at the crown. The plan was to build a center
complete for one arch ring and then to shift it along and re-use it for
building the other arch ring. The centering used is shown in diagram by
Fig. 151. It consists of five parts: (1) Six concrete piers running the
full width of the bridge upon which the structure was moved; (2) a steel
framework up to E G, called the "primary bent"; (3) a separate timber
portion below the heavy lines E I and W' I'; (4) the "main staging"
included in the trapezoid E I W' I', and (5) the "upper trestle"
extending from I I' to the intrados.
[Illustration: Fig. 151.--Center for 232-ft. Span Arch at Philadelphia,
Pa.]
The primary bent consists of four I-beam post bents having channel
chords, the whole braced together rigidly by angles. Each bent is
carried on 1½ ft.×6 in. steel rollers running on a track of 19×½ in.
plate on top of the concrete piers. Between the primary bents and the
main staging, and also between the main staging and the upper trestles
are lifting devices. The mode of operation planned is as follows: When
the center has been erected as shown and the arch ring concreted the
separate stagings under K I and K' I' are taken down. Next the
portions under the lines I E and I' W' will be taken down and
erected under the second arch. Finally the remainder of the center will
be shifted sidewise on the rollers to position under the second arch.
~MIXING AND TRANSPORTING CONCRETE.~--The nature of the plant for mixing
and handling the concrete in bridge work will vary not only with varying
local conditions but with the size and length of the bridge. For single
span structures of moderate size the concrete can be handled directly by
derricks or on runways by carts and wheelbarrows. For bridges of several
spans the accepted methods of transport are cableways, cars and cars and
derricks. Typical examples of each type of plant are given in the
following paragraphs, and also in the succeeding descriptions of the
Connecticut Avenue Bridge at Washington, D. C., and of a five-span arch
bridge.
~Cableway Plants.~--The bridge was 710 ft. long between abutments and 62
ft. wide; it had a center span of 110 ft., flanked on each side by a
100-ft., a 90-ft. and an 80-ft. span. The mixing plant was located at
one end of the bridge and consisted of a Drake continuous mixer,
discharging one-half at the mixer and one-half by belt conveyor to a
point 50 ft. away, so as to supply the buckets of two parallel
cableways. The mixer output per 10-hour day was 400 cu. yds. and the
mixing plant was operated at a cost of $27 per day, making the cost of
mixing alone 6¾ cts. per cu. yd. The sand and gravel were excavated from
a pit 4½ miles away and delivered by electric cars to the bridge site at
a cost of 50 cts. per cu. yd. Two 930-ft. span Lambert cableways set
parallel with the bridge, one 25 ft. each side of the center axis, were
used to deliver the concrete from mixer to forms. The cableway towers
were 70 ft. high and the cables had a deflection of 35 ft.; they were
designed for a load of 7 tons, but the average load carried was only 3
or 4 tons. These cableways handled practically all the materials used in
the construction of the bridge. They delivered from mixer to the work
400 cu. yds. of concrete 450 ft. in 10 hours at a cost of 2 cts. per cu.
yd. for operation.
[Illustration: Fig. 151a.--Cableway for Concreting Bridge Piers.]
Another example of cableway arrangement for concreting bridge piers is
shown by Fig. 151a. The river was about 800 ft. wide, about 3 ft. deep
and had banks about 20 ft. high. The piers were about 21 ft. high. The
towers for the cableway consisted of a 55-ft. derrick without boom,
placed near the bank on the center line of the piers and well guyed and
a two-leg bent placed in the middle of the river and held in place by
four cable guys anchored to the river bottom. A ¾-in. steel hoisting
cable was stretched from a deadman on shore, about 150 ft. back of the
derrick, and followed along the center line of the piers, past the
derrick just clearing it, to the bent in the middle of the river. At the
top of this bent was a 16-in. cable block. Through this block the cable
passed down and was made fast to a weight, consisting of a skip loaded
with concrete until the cable had the required tension, and a pitch of
18 to 20 ft. from center of river to anchor on shore. In order to secure
the required pitch from the shore to the river bent the boom fall of the
derrick was hooked onto the cable at the foot of the mast, and then, by
going ahead on the single drum hoisting engine, was raised to the mast
head. This gave the cable a pitch of 18 to 20 ft. from mast head to top
of bent in river. The carriage vised on the cableway consisted of two
16-in. cable sheaves with iron straps, forming a triangle, with a chain
hanging from the bottom point, to which was attached the 5 cu. ft.
capacity concrete bucket. The concrete was mixed on a platform at the
foot of the mast. When ready for operation the chain on the carrier was
hooked to the bucket of concrete, the engine started, and both bucket
and cable raised, the former running by gravity to the pier. The speed
of descent was governed by the height to which the cable was raised on
the derrick, and as the bucket neared the dumping point the engine was
slacked off and the cable leveled. The bucket was dumped by a man on a
staging erected on the pier form. For the return of the bucket the
engine was slacked off and the weight on the river bent would pull the
cable tight so that the pitch would be toward the shore and the bucket
could run down the grade to the mixing platform, the speed being
governed as before by leveling the cable. When the piers were completed
to the middle of the river the engine and derrick were taken over to
opposite side of the river, the bent being left in the middle, and the
work continued. By using the extreme grade of the cable it was found
that the bucket would run from the platform to the bent (400 ft.) in
less than 35 seconds.
[Illustration: Fig. 152.--Sketch Showing Car and Trestle Plant for
Concreting an Arch Bridge.]
~Car Plant for 4-Span Arch Bridge.~--The bridge had four 110-ft. skew
spans, and a total length of 554 ft. The mixing plant was located
alongside one abutment on a side hill so that sand and stone could be
stored on the slope above. The mixer was set on a platform high enough
to clear cars below. Above it and to the rear a charging platform
reached back to the stone and sand piles. Side dump cars running on a
track on the charging platform took sand and stone to the mixer and
cement was got from a cement house at charging platform level. The
concrete for the abutment adjacent to the mixer was handled in buckets
by a guy derrick. A trestle, Fig. 152, was then built out from the mixer
to the first pier; this trestle was so located as to clear the future
bridge about 20 ft. and was carried out from shore parallel to the
bridge until nearly opposite the pier site, where it was swung toward
and across the pier. The concrete was received from the mixer in bottom
dump push cars; these cars were run out over the pier site and dumped.
When the first pier had been concreted to springing line level, the main
trestle was extended to opposite the second pier and the branch track
was removed from over the first pier and placed over the second pier.
This operation was repeated for the third pier. The last extension of
the main track was to the far shore abutment, where the bodies of the
cars were hoisted by derrick and dumped into the abutment forms. The
derrick was the same one used for the first abutment having been moved
and set up during the construction of the intermediate piers. To
construct the arches a second trestle was built composed partly of new
work and partly of the staging for the arch centers. This trestle rose
on an incline from the mixer to the first pier across which it was
carried at approximately crown level of the arch. The concrete for the
portion of the pier above springing line and for the lower portions of
the haunches was dumped direct from the cars. For the upper parts of the
arch the concrete was brought to the pier track in two-wheel carts on
push cars and thence these carts were taken along the arch toward shore
on runways. When the first arch had been concreted the second trestle
was extended to pier two and the operation repeated to concrete the
second arch.
~Hoist and Car Plant for 21-Span Arch Viaduct.~--The double track concrete
viaduct replaced a single track steel viaduct, being built around and
embedding the original steel structure which was maintained in service.
The concrete viaduct consisted of 21 spans of 26 ft., 7 spans of 16 ft.,
and 2 spans of 22 ft. With piers it required about 15,000 cu. yds. of
concrete. Two Ransome concrete hoists, one on each side of the original
steel structure near one end, were supplied with concrete by a No. 4
Ransome mixer. The mixer discharged direct into the bucket of one hoist
and by means of a shuttle car and chute into the bucket of the other
hoist.
The shuttle car ran from the mixer up an incline laid with two tracks,
one narrow gage and one wide gage, having the same center line. The car
was open at the front end and its two rear wheels rode on the broad gage
rails and its two forward wheels rode on the narrow gage rails. At the
top of the incline the narrow gage rails pitched sharply below the grade
of the broad gage rails so that the rear end of the car was tilted up
enough to pour the concrete into a chute which led to the bucket of the
hoist. The sand and gravel bins were elevated above the mixer and
received their materials from cars which dumped directly from the steel
viaduct.
The hoist buckets discharged into two hoppers mounted on platforms on
the old viaduct. These platforms straddled two narrow gage tracks, one
on each side of the old viaduct parallel to and clearing the main track.
These side tracks were carried on the cantilever ends of long timbers
laid across the old viaduct between ties. At street crossings the
overhanging ends of the long timbers were strutted diagonally down to
the outside shelf of the bottom chords of the plate girder spans. Six
cars were used and the concrete was dumped by them directly into the
forms; the fall from the track above being in some cases 40 ft. The
hoists and shuttle car were operated by an 8½×12-in. Lambert derrick
engine, the boiler of which also supplied steam to the mixer engine. The
concrete cars were operated by cable haulage by two Lambert 7×10-in.
engines.
The labor force employed in mixing and placing concrete, including form
work, was 45 men, and this force placed on an average 200 cu. yds. of
concrete per day. Assuming wages we get the following costs of different
parts of the work for labor above:
Item. Per day. Per cu. yd.
1 timekeeper at $2.50 $ 2.50 $0.0125
1 general foreman at $5 5.00 0.0250
3 enginemen at $5 15.00 0.0750
1 carpenter foreman at $4 4.00 0.0200
12 carpenters at $3.50 42.00 0.2100
1 foreman at $4 4.00 0.0200
8 men mixing and transporting at $1.75 14.00 0.0700
13 men placing concrete at $1.75 22.75 0.1137
1 foreman finishing at $4 4.00 0.0200
4 laborers finishing at $1.75 7.00 0.0350
------ -------
45 men at $2.70 $120.25 $0.6012
It is probable that the carpenter work includes merely shifting and
erecting forms and not the first cost of framing centers. No materials,
of course, are included. It should be kept in mind that while the output
and labor force are exact the wages are assumed.
~Traveling Derrick Plant for 4-Span Arch Bridge.~--The bridge consisted of
four 70-ft. arch spans and was built close alongside an old bridge which
it was ultimately to replace. The approach from the west was across a
wide flat; at the east the ground rose more abruptly from the stream.
Conditions prevented the use of a long spur track and also made it
necessary to install all plant at and to handle all material from the
west bank. A diagram sketch of the arrangement adopted is shown by Fig.
153.
[Illustration: Fig. 153.--Sketch Showing Traveling Derrick Plant for
Concreting an Arch Bridge.]
The track from the west approached the existing bridge on an embankment
25 ft. high. A spur track 175 ft. long from clear post to end was built
on trestle as shown. The cement house and mixer platform were placed at
the foot of the embankment at opposite ends of the spur track. Between
the two the slope of the embankment was sheeted with 1-in. boards and a
timber bulkhead 4 ft. high was built along the toe of the sheeting.
Stone, sand and coal were stored behind the bulkhead on the sheeting. A
runway close to the bulkhead connected the cement house with the mixer
platform, all materials to the mixer being wheeled in barrows on this
runway. A ¾-cu. yd. Smith mixer was set on a platform 5 ft. above ground
with its discharge end toward the stream. Beginning under this platform
a service track was carried across the flat and stream to the extreme
end of the east abutment. This track consisted of three rails, two rails
4 ft. apart next to the work and a third rail 25 ft. from the first. The
4-ft. gage provided for cars carrying concrete buckets from the mixer
and the 25-ft. gage provided for a traveling derrick; 18-lb. rails were
used and they proved to be too light, 40-lb. rails are suggested. The
derrick consisted of a triangular platform carrying a stiff leg derrick
with a 25-ft. mast and mounted on five wheels. The wheels were double
flange 16 ins. diameter and cost $30 each, being the most expensive part
of the derrick. The derrick was made on the ground and took four
carpenters between 3 and 4 days to build. Derrick and 350 ft. of service
track, including pole trestle across the stream, cost between $600 and
$800. The derrick was moved by means of a cable wrapped around one spool
of the Flory double-drum hoisting engine and leading forward and back to
deadmen set at opposite ends of the service track. Cars carrying
concrete buckets were run out on the 4-ft. gage track and the buckets
were hoisted by the derrick and dumped into a ½-cu. yd. car running on a
movable transverse track across the bridge. This transverse track was
necessary to handle the concrete to the far side of the work, the
derrick being set too low and the boom being too short to reach. The
derrick was used to handle material excavated from the pier foundations
and also to tear down the centers and spandrel forms. Some rather
general figures on the cost of this bridge are given by Mr. H. C.
Harrison, the contractor. They are:
Materials: Total.
6,000 bbls. cement at $2.05 $12,300
2,500 cu. yds. sand at $0.80 2,000
5,000 cu. yds. stone at $0.85 4,250
260 M. ft. B. M. lumber at $17 4,420
-------
Total $22,970
Labor:
Cofferdams, excavation and pumping $ 3,000
Forms, falseworks and centers 2,000
Mixing and placing concrete 4,000
Placing reinforcement 400
Removing falseworks, forms, etc. 1,200
One coat pitch and paper 150
Building plant, etc. 2,250
-------
Total $13,000
Mr. Harrison states that including plant cost, delays, floods and
incidentals the cost per cubic yard of concrete was $8 and that
excluding these items the cost was $6 per cu. yd.
~COST OF CONSTRUCTING CONCRETE HIGHWAY BRIDGE, GREENE COUNTY, IOWA.~--The
following is the itemized cost of constructing a reinforced concrete
slab highway bridge, one of several built by the Highway Commissioners
of Greene County, Iowa, in 1906. The figures are given by Messrs. Henry
Haag and D. E. Donovan, the last being the foreman of the concrete gang
doing the work. All bridges consist of 10 to 12-in. slabs reinforced
with old steel rails and of abutments and wing walls reinforced with old
rods, bars or angles selected from junk. This junk metal cost 0.6 cts.
per pound and the rails cut to length cost 1.15 cts. per pound f. o. b.
cars. The work was done by a special gang, the men receiving $1.50 per
day and board. As a rule the footings were made 2 ft. wide and as high
as need be to get above the water and dirt. Before the footing concrete
set steel rods, bars or angles were placed; they were long enough to
reach the height of the wall and 3 to 6 ins. into the slab. The forms
for the abutment and wing walls and for the floor slab were then erected
complete before any more concrete was placed. No carpenter was employed,
every man on the job having been taught to take his certain place in the
work, then, the forms being erected, every man had his particular place
in the work of mixing and placing the concrete. The foreman saw that the
reinforcement was properly placed and watched over the accuracy of the
work generally. The concrete was allowed to set on the centers for from
30 to 40 days; the other form work was taken down after three days and
travel over the bridge permitted after three or four days. The concrete
was mixed wet. The bridge whose cost is given was 22 ft. wide and 16 ft.
span with 2-ft. wing walls.
The foundations are 4 ft. deep and 2½ ft. wide. The walls on top of the
foundations are 7 ft. high, 18 ins. wide at the base, and battered up to
14 ins. at the top for wings and 12 ins. at top for walls. The floor is
22 ft. by 18 ft. and 1 ft. thick. The wheel guard is 12 ins. thick by 14
ins. wide and 32 ft. long. The itemized cost of this bridge, containing
73 cu. yds. of concrete, is as follows:
Materials. Total. Per cu. yd.
70 cu. yds. gravel at 70 cts $ 49.00 $0.6726
10 cu. yds. broken stone at 70 cts 7.00 0.0959
75 bbls. cement at $2.20 165.00 2.2603
7,000 lbs. steel rails at 1.15 cts 80.50 1.1027
1,000 lbs. junk rails at 0.6 cts 6.00 0.0819
200 ft. B. M. lumber wasted at $29 5.80 0.0794
15 lbs. nails at 3 cts 0.45 0.0061
Labor and Supplies:
2 days excavation at $14 28.00 0.3835
¾ day foundation at $14 10.00 0.1369
1½ days building forms at $14 21.00 0.2876
2 days filling forms at $14 28.00 0.3835
Hauling lumber and tools 8.00 0.1096
Hauling cement and tools 18.00 0.2465
Taking off forms 2.30 0.0315
1,000 lbs. coal at $4 per ton 2.00 0.0274
------ -------
Total cost $431.05 $5.9054
In round figures the cost per cubic yard of concrete in the finished
bridge was $5.90. Summarizing we have the following cost per cubic yard
of concrete in place:
Item. Per cu. yd.
Cement $2.26
Steel 1.22
Lumber 0.22
Gravel and stone 0.76
Labor 1.41
Coal 0.03
-----
Total $5.90
The average cost of concrete in place for all the work done in Greene
County by day labor was $6.25 per cu. yd. In the job itemized above the
bank caved in, causing an extra expense for removing the earth. The
gravel used in this bridge was very good clean river gravel.
~METHOD AND COST OF CONSTRUCTING TWO HIGHWAY GIRDER BRIDGES.~--The
following account of the methods and costs of constructing two slab and
beam highway bridge decks on old masonry abutments is taken from
records kept by Mr. Daniel J. Hauer. The first bridge was a single span
15 ft. long that replaced wooden stringers and floor that had become
unsafe; the second was two short spans of a steel bridge that was too
light for the traffic of the road, and it was torn down and moved
elsewhere, by the county authorities. The work was done by contract, and
in each case consisted of building the reinforced floor and girders on
the old masonry walls that were in good condition. While the work was
going on traffic was turned off the bridges, fords being used instead.
Figure 154 shows a sketch of the cross-section of the floor and girders.
In Example I the girders had a depth below the floor of 12 ins. and were
of the same width. In Example II the girders were 14 ins. wide and had a
depth below the floor of 18 ins. The floors on both bridges were 6 ins.
thick. Kahn bars were used for reinforcement.
[Illustration: Fig. 154.--Cross-Section of Concrete Girder Bridge.]
_Example I._--This bridge was but little more than 5 ft. above the
stream, which was shallow and not over 7 ft. wide, unless swollen by
floods. The bottom for several hundred feet on either side of the bridge
was covered with coarse sand and gravel, that had pebbles in it from the
size of a goose egg down. This was taken from the stream by men with
picks and shovels and hauled to the site of the work with wheelbarrows,
and then screened so as to separate the gravel from the sand. As it was
found that the sand was so coarse that it would take more cement than
the specifications called for in a 1-2½-5 mixture, some much finer sand
was bought and mixed with it. For the privilege of taking the sand from
the stream $1 was paid the property owner. This was done to get a
receipt and release from him, rather than as an attempt to pay royalty
on the gravel and sand. This dollar is included in the cost of the labor
in getting these materials.
The cost of materials per cubic yard for the bridge was as given below,
the mixture being as stated above. The cement cost $1.40 per barrel,
delivered at the bridge.
Per Cu. Yd.
Steel $2.50
Gravel and sand .75
Sand (bought) .30
Cement 1.57
-----
Per cubic yard $5.12
It is of interest to note the cost of the gravel and sand, as this
includes the cost of digging it, wheeling it in a wheelbarrow an average
distance of 100 ft., and then screening it and putting it in two stock
piles. The proportion of bought sand used with the creek sand was
one-half.
The old wooden floor and stringers had to be torn down. This was done at
a cost of $1.30 per M. ft. B. M., and furnished 60 per cent. of the
lumber needed for forms. The floor boards were 3-in. yellow pine planks,
and the stringers 6×12-in. timbers, rather heavy, but money was saved by
using them. The 6×12-in. timbers were used for props for the centering.
Additional lumber was bought, delivered at the site of the bridge, for
$20.84 per M. ft. B. M.
In framing and erecting the forms the carpenter had laborers helping
him, he doing only carpenter's work, the laborers carrying and lifting
all pieces wherever possible. The carpenter's work was about 40 per
cent. of the total labor cost, which was as follows per cubic yard of
concrete:
Tearing down old bridge $0.08
Lumber .85
Nails .15
Labor, carpenter .77
Labor, laborers .96
-----
$2.81
The forms were torn down by laborers, with the assistance of a man and
his helper, who were given the boards for this labor and to haul them
away. This reduced this item somewhat, as it only amounted to 20 cts.
per cu. yd.
The cost of the forms per thousand feet board measure was:
New lumber $20.82
Nails 1.44
Labor, carpenter 7.60
Labor, laborers 9.50
Tearing down 2.00
------
$41.36
All the men, including the carpenter, worked 10 hours per day, and were
paid at the following rates:
Carpenter $2.50
Sub-foreman 2.00
Laborers 1.50
A regular foreman was not employed, but an intelligent and handy workman
was given 50 cts. additional to lead the men and look after them when
the contractor was not present.
A gang of six men did the work of mixing and placing, and as the stock
piles were close by the mixing board no extra men were needed to handle
materials. Water was secured from the stream in buckets for mixing. The
mixture was made very wet. The cost per cubic yard for the entire
structure was as follows:
Preparing for mixing $0.04
Cleaning out forms .06
Handling steel .03
Mixing and placing 1.15
Ramming .23
-----
$1.51
The cost of the contractor's expense of bidding, car fare, etc., is
listed under general expense, and gives a total cost per cubic yard of:
Materials $ 5.12
Erecting forms 2.81
Tearing down forms .20
Labor 1.51
General expense 2.00
------
$11.64
_Example II._--For this bridge both the stone and sand had to be bought.
The bridge floor was nearly 14 ft. above the bottom of the stream, which
was shallow. The wages paid were as follows for a 10-hour day:
Foreman $3.00
Laborers 1.50
Carpenters were paid $3 for an 8-hour day and time and a half for all
overtime, which they frequently made.
For the girders a 1-2-4 mixture was used. The cement, delivered at the
bridge, cost $1.21 per barrel, there being 8 cts. a barrel storage and 8
cts. a barrel for hauling included in this. The sand was paid for at an
agreed price per cartload delivered, which averaged $1.34 per cu. yd.
The stone was crushed so as to pass a 1½-in. ring in all directions. It
was delivered at the bridge for $2.75 per cu. yd. This makes the cost
per cubic yard for materials as follows:
Steel $1.41
Cement 2.18
Sand .67
Stone 2.75
-----
$7.01
For the floor a 1-3-5 mixture was used, making a cost for material of:
Steel $1.02
Cement 1.69
Sand .67
Stone 2.75
-----
$6.13
Two-inch rough pine boards were used to make the troughs for the
girders, while 1-in. rough boards were used for the floors. These were
all supported by 3×4-in. pine scantlings. This lumber cost delivered
$17.50 per M. ft. B. M. Carpenters did all the framing, and erected it
with the help of laborers. All the carrying of the lumber was done by
laborers. This reduced the cost of the work, as the laborers' wages
amounted to one-third of the whole cost. As soon as the forms were all
in place, which was before the mixing of concrete commenced, the
carpenters were discharged. The cost per cubic yard for forms was:
Lumber $2.82
Nails .05
Labor, carpenters 1.24
Laborers .62
-----
$4.73
The tearing down of the forms was done entirely by laborers at a cost of
61 cts. per cu. yd.
On concrete work it is also advisable to keep the cost of forms per
thousand feet board measure, so as to have such data for estimating on
new work. The cost per M. ft. on this job was:
Lumber $17.50
Nails .30
Labor, carpenters 7.65
Laborers 3.85
Tearing down 3.80
------
$33.10
The concrete was mixed by hand, water being carried in buckets from the
creek. Ten to twelve men were worked in the gang under a foreman, and
the concrete was wheeled from the mixing board to the forms in
wheelbarrows. The mixture was made wet enough to run. The cost per cubic
yard for the girders in detail was as follows:
Foreman $0.41
Preparing for mixing 0.14
Cleaning out forms 0.07
Handling materials 0.30
Handling and placing steel 0.40
Mixing and placing 0.87
Ramming 0.45
-----
$2.64
The cost of labor for the floor was:
Foreman $0.28
Preparing for mixing 0.08
Cleaning out forms 0.05
Handling materials 0.14
Handling and placing steel 0.08
Mixing and placing 0.87
Ramming 0.36
-----
$1.86
This gives a total cost per cubic yard for the concrete in the girders
in the completed bridge as follows:
Materials $ 7.01
Erecting forms 4.73
Tearing down forms 0.61
Labor 2.57
General expense 1.60
------
$16.52
The cost per cubic yard for the floor was:
Materials $ 6.13
Erecting forms 4.73
Tearing down forms 0.61
Labor 1.86
General expense 1.60
------
$14.93
Included with this is an item for general expense, being expenses of the
contractor in bidding on the work, car fare, and other items of expense
in looking after the contract.
It will be noticed that a record is here given of three different
mixtures and that the labor cost of mixing and placing increases with
the richness of the mixture. This is because it takes a greater number
of batches to the cubic yard. Record has also been given of cost of
preparing the mixing board and other work necessary to start and clean
up each day; also when stock piles could not be arranged close to the
mixing board, of the cost of handling the materials. These items, it
will be noticed, are large enough to be considered in estimating on new
work. The cost of sweeping and cleaning out the forms has also been
listed, as this work is extremely important.
The cost of the reinforcing steel is given in with the materials, but
the labor of handling it and placing it in the forms is listed under
labor. This naturally varies with the amount of steel needed, and with
the Kahn bar it will vary from 10 cts. to 75 cts. per cubic yard, as the
prongs of the bar must be bent into proper position and at times
straightened, when bent in shipment. This cost seems large, but it is
done with the ordinary labor, while with round rods a large amount of
blacksmith work has to be done and a smith and his helper frequently
must place them. The patent bars are all lettered and numbered as
structural steel is, and can be placed under the direction of the
foreman.
One striking lesson can be learned from the forming. It will be noticed
that the cost for common labor for handling and helping to erect the
forms was much larger in Example I than in Example II, although the
bridge was higher in the latter instance. This was caused by the heavy
timber that was used, and equaled an extra cost nearly 50 per cent. of
the price of new lumber. It certainly speaks volumes against the use of
unnecessarily heavy timber for concrete forms.
In bridge work the height of the floor above the stream to some extent
governs the cost of the forms. This is made so by the extra lumber
needed as props or falsework to support the forming, and also by the
fact that men at some height above the ground do not work as quickly or
as readily as they do nearer the ground. For high and long spans a
derrick is sometimes needed for the work of placing the centering.
On these jobs the concrete was made so wet that with the proper tamping
and cutting of the concrete in the forms the surfaces were so smooth
that no plastering was needed.
~MOLDING SLABS FOR GIRDER BRIDGES.~--The bridges carry railway tracks
across intersecting streets; the slabs rest on two abutments and three
rows of columns so that there are two 24¼-ft. spans over the street
roadway and one 10¾-ft. span over each sidewalk. The larger slabs were
24 ft. 3 ins. long, 33 ins. thick and 7 ft. wide; each contained 16¾
cu. yds. of concrete and weighed 36¾ tons. The smaller slabs were 10 ft.
9 ins. long, 17 ins. thick and 7 ft. wide; each contained 3.65 cu. yds.
of concrete and weighed 7.8 tons. The weights were found by actual
weighing. They make the weight of the reinforced slab between 160 and
162 lbs. per cu. ft. The concrete was generally 1 part cement and 4
parts pit gravel. The reinforcement consisted of corrugated bars. The
method of molding was as follows:
[Illustration: Fig. 155.--Arrangement of Tracks and Forms for Molding
Slabs for Girder Bridge.]
[Illustration: Fig. 156.--Form for Molding Slabs for Girder Bridge.]
A cinder fill yard was leveled off and tamped, then the forms were set
up on both sides of two lines of railway track arranged as shown by Fig.
155. The exact construction of the forms for one of the larger slabs is
shown by Fig. 156. The side and end pieces were so arranged as to be
easily taken down and erected for repeated use. About 100 floors were
used and they had to be leveled up each time used as the lifting of the
hardened slab disarranged them. The side and end pieces were removed in
about a week or ten days, but the slabs stood on the floor 90 days,
being wetted each day for two weeks after molding.
The plant for mixing and handling the concrete was mounted on cars. A
flat car had a rotary drum mixer mounted on a platform at its forward
end. Beneath the mixer was a hopper provided with a deflector which
directed the concrete to right or left as desired. Under the hopper were
the ends of two inclined chutes extending out sidewise beyond the
car--one to the right and one to the left--and over the slab molds on
each side. Above the mixer was another platform containing a charging
hopper, and from the rear of this platform an incline ran down to the
rear end of the car and then down to the track rails. A car loaded with
cement and gravel in the proper proportions was hauled up the incline by
cable operated by the mixer engine, until it came over the topmost
hopper into which it was dumped. This hopper directed the charge into
the mixer below; the mixer discharged its batch into the hopper beneath
from which it flowed right or left as desired into one of the chutes and
thence into the mold. The chutes reached nearly the full length of the
molds and discharged as desired over the ends into the far end of the
mold or through a trap over the end of the mold nearest the car.
To the rear of the mixer car came a cement car provided with a platform
overhanging its forward end. Two hoppers were set in this platform each
holding a charge for one batch. Coupled behind the cement cars came
three or four gravel cars. These were gondola cars and plank runways
were laid along their top outer edges making a continuous runway for
wheelbarrows on each side from rear of train to front of cement car. The
sand and gravel were wheeled to the two measuring hoppers and the cement
was handed up from the car below and added, the charge was then
discharged into the dump car below and the car was hauled up the incline
to the mixer as already described. Two measuring hoppers were used so
that one was being filled while the other was emptied, thus making the
work continuous.
The molding gang consisted of 33 laborers, two foremen and one
engineman. This gang averaged 7 of the large slabs per 10-hour day and
at times made as many as 9 slabs. When molding small slabs an average
of 12 were made per day. This record includes all delays, moving train,
switching gravel cars on and off, building runways, etc. The
distribution of the men was about as follows:
Handling Materials: No. Men.
Shoveling gravel into wheelbarrows 9
Wheeling gravel to measuring hoppers 9
Emptying cement into measuring hoppers 2
Handling cement to men emptying 1
In charge of loading dump car 1
On top of cement car 1
Sub-foreman in charge 1
Mixing and Placing:
Engineer 1
In charge of mixer 1
Hoeing and spreading in mold 2
Spading in mold 2
Finishing sides of block 2
General laborers 3
Foreman in charge 1
--
Total men 36
This gang mixed and placed concrete for 7 blocks or 117¼ cu. yds. of
concrete per day. Assuming an average wage of $2 per day the cost of
labor mixing and placing was 61.4 cts. per cu. yd. or $10.28 per slab.
It is stated that the slabs cost $11.80 per cu. yd. on storage pile.
This includes labor and materials (concrete and steel); molds; loading
into cars with locomotive crane, hauling cars to storage yard and
unloading with crane into storage piles, and inspection, incidentals,
etc. To load the slabs into cars from storage piles, transport them to
the work and place them in position is stated to have cost $2 per cu.
yd. The slabs were placed by means of a locomotive crane being swung
from the flat cars directly into place.
[Illustration: Fig. 157.--Sections Showing Construction of Connecticut
Ave. Bridge.]
~METHOD AND COST OF CONSTRUCTING CONNECTICUT AVE. BRIDGE, WASHINGTON, D.
C.~--The Connecticut Ave. Bridge at Washington, D. C., consists of nine
150-ft. spans and two 82-ft. spans, one at each end, all full centered
arches of mass concrete trimmed with tool-dressed concrete blocks.
Figure 157 is a part sectional plan and elevation of the bridge,
showing both the main and spandrel arch construction. This bridge is one
of the largest concrete arch bridges in the world, being 1,341 ft. long
and 52 ft. wide, and containing 80,000 cu. yds. of concrete. Its total
cost was $850,000 or $638.85 per lin. ft., or $10.63 per cu. yd. of
masonry. It was built by contract, with Mr. W. J. Douglas as engineer in
charge of construction. The account of the methods and cost of
construction given here has been prepared from information obtained from
Mr. Douglas and by personal visits to the work during construction.
_General Arrangement of the Plant._--The quarry from which the crushed
stone for concrete was obtained was located in the side of the gorge at
a point about 400 ft. from the bridge. Incidentally, it may be added,
the fact that the contractor had an option on this quarry gave him an
advantage of some $30,000 over the other bidders. The stone from the
quarry was hoisted about 50 ft. by derricks and deposited in cars which
traveled on an incline to a Gates gyratory crusher, into which they
dumped automatically. The stone from the crusher dropped into a 600-cu.
yd. bin under the bottom of which was a tunnel large enough for a dump
car and provided with top gates by which the stone above could be
dropped into the cars. The cars were hauled by cable to the mixer
storage bin and there discharged. Sand was brought in by wagons and
dumped onto a platform about 50 ft. higher than the bottom of the main
stone bin. A tunnel exactly similar to that under the stone bin was
carried under the sand storage platform. The sand car was hauled from
this tunnel by cable to the mixer storage bin using the same cable as
was used for the stone cars, the cable being shifted by hand as was
desired. Cement was delivered to the mixer platform from the crest of
the bluff by means of a bag chute.
The mixer used was one of the Hains gravity type. It had four drops and
was provided with four mixing hoppers at the top. The concrete was made
quite wet. The proportions of sand and water were varied to suit the
stone according to its wetness and the percentage of dust carried by it.
The head mixer regulated the proportions and his work was checked by the
government inspector. From the bottom hopper the mixed concrete dropped
into a skip mounted on a car.
[Illustration: Fig. 158.--Center for Connecticut Ave. Bridge
(Elevation).]
To distribute the skip cars along the work a trestle was built close
alongside the bridge and at about springing line level. This trestle had
a down grade of about 2 per cent. from the mixer. Derricks mounted along
the centering and on the block molding platform lifted the skips from
the cars and deposited them where the concrete was wanted. The skip
cars were large enough for three skips but only two were carried so
that the derricks could save time by depositing an empty skip in the
vacant space and take a loaded skip away with one full swing of the
boom. Altogether nine derricks were used in the bridge, four having
70-ft. booms and five having 90-ft. booms. These derricks were jacked up
as the work progressed.
[Illustration: Fig. 158.--Center for Connecticut Ave. Bridge
(Details).]
_Forms and Centers._--The forms for wall and pier work consisted of
1-in. lagging held in place by studs about 2 ft. on centers and they in
turn supported by wales which were connected through the walls by bolts,
the outer portions of which were removed when the forms were taken down.
The centers for the five 150-ft. arches were all erected at one time;
those for the 82-ft. arches were erected separately. The seven centers
required 1,500,000 ft. B. M. of lumber or 1,404 ft. B. M. per lineal
foot of bridge between abutments, or 1,640 ft. B. M. per lineal foot of
arch span. The centers for the main arch spans are shown in detail by
Fig. 158; this drawing shows the sizes of all members and the maximum
stresses to which they were subjected from the loading indicated, that
is the arch ring concrete. The centers as a rule rested on pile
foundations. Four piles to each post were used for the intermediate
posts and two piles for the posts in the two rows next the piers.
Concrete foundations, however, were put in Rock Creek and on the line of
Woodley Lane Bridge where it was impracticable to drive piles. As
considerable difficulty was experienced in driving the piles, the ground
consisting mostly of rotten rock, it is thought that it would have cost
less if the contractor had used concrete footings throughout.
Some of the costs of form work and centering are given. The cost of
lumber delivered at the bridge site was about as follows:
M. ft. B. M.
Rough Virginia pine $25
Dressed Virginia pine lagging 23
Rough Georgia, sizes up to 12×12 ins. 33
Rough Georgia, sizes over 12×12 ins. 35
Rough oak lumber 35
The following wages were paid: Foreman carpenter, $3.50; carpenters, $2
to $3; laborers, $1.70, with a few at $1.50. An 8-hour day was worked.
The cost, of formwork is given in summary as follows:
Lagging per M. ft. (used twice):
Lumber at $23 $11.50
Erection 15.00
------
Total cost erected $26.50
Studding and rough boards used in place of lagging per M. ft. (used twice):
Lumber at $25 $12.50
Erection 10.00
------
Total cost erected $22.50
Wales per M. ft. (used six times):
Lumber at $36 $ 6.00
Erection 10.00
------
Total cost erected $16.00
The total cost of the main arch span centers to the District of Columbia
was $54,000 or $59 per lineal foot of arch span, or $37.33 per M. ft. B.
M. The cost of center erection and demolition was as follows:
Erection below springing line per M. ft. $15
Erection above springing line per M. ft. 25
Demolition 5
The salvage on the centers amounted to $11 per M. ft. B. M.
The spandrel arch centers were each used twice and cost per M. ft. B. M.
for
Lumber at $25 per M. ft. $12.50
Erecting at $25 per M. ft. 25.00
Moving at $5 per M. ft. 5.00
Total per M ft. 42.50
_Molding Concrete Blocks._--The bridge is trimmed throughout with molded
concrete blocks, comprising belt courses, quoin stones, chain stones,
ring stones, brackets and dentils. The blocks were made of a 1-2-4½
concrete faced with a 1-3 mixture of Dragon Portland cement and
bluestone screenings from 3/8-in. size to dust. They were cast in wooden
molds with collapsible sides held together by iron rods. Each mold was
provided with six bottoms so that the molded block could be left
standing on the bottom to harden while the side pieces were being used
for molding another block. The molding was done on a perfectly level and
tight floor on mud sills, the perfect level of the molding platform
having been found to be an important factor in securing a uniform
casting. The blocks were molded with the principal showing face down and
the secondary showing faces vertical. The facing mortar was placed
first and then the concrete backing. Care was taken to tamp the concrete
so as to force the concrete stone into but not through the facing. Mr.
Douglas remarks that the back of the block should always be at the top
in molding since the laitance or slime always flushes to the surface
making a weak skin which will develop hair cracks. In this work the
backs of the blocks were mortised by embedding wooden cubes in the wet
concrete and removing them when the concrete had set. These mortises
bonded the blocks with the mass concrete backing. The blocks were left
to harden for at least 30 days and preferably for 60 days and were then
bush hammered on the showing faces, some of the work being done by hand
and some with pneumatic tools.
Some precautions necessary in the molding and handling of large concrete
blocks were discovered in this work and merit mention. In designing
blocks for molding it is necessary to avoid thin flanges or the flanges
will crack and break off; blocks molded with a 2¼ in. flange projecting
1¾ ins. gave such trouble from cracking on this work that a flange 5
ins. thick was substituted. Provide for the method of handling the block
so that dog or lewis holes will not come in the showing faces. Dog holes
can be made with a pick when the concrete is three or four weeks old.
When it is not practicable to use dogs, two-pin lewises can be used. The
lewis holes should be cast in the block and should be of larger size
than for granite; they should not be located too near the mortar faces.
In turning blocks it is necessary to provide some sort of cushion for
them to turn on or broken arrises will result. When the work will
permit, it is desirable to round the arrises to about a 3/8-in. radius.
The following general figures of the cost of block work are available.
Foreman cutters were paid $5 per day; foreman concrete workers $3 per
day; stonecutters $4 per day; concrete laborers $1.70 per day, and
common laborers $1.50 to $1.70 per day. Plain and ornamental blocks cost
about the same, the large size of the ornamental blocks bringing down
the cost. The following is given as the average cost of block work per
cubic yard:
Cement $ 1.95
Sand 0.35
Stone 1.14
Forms, lumber and making 0.80
Mixing and placing concrete 1.50
Dressing 4.73
Handling and setting 2.00
Superintendence, plant, incidentals at 25 per cent. 3.12
Condemnation at 5 per cent. 0.78
------
Total cost blocks in place $16.37
It will be seen that the largest single item in the above summary of
costs is the item of dressing. This was done, as stated above, partly by
hand and partly by pneumatic tools. Hand tooling cost about twice as
much as machine tooling, but its appearance was generally better. The
average cost of tooling the several forms of blocks is shown by Table
XIX. For 42,190 sq. ft. the average cost was 26 cts. per sq. ft. or
$2.34 per sq. yd., or $4.73 per cu. yd. of block work. This tooling was
done by stone cutters, and was unusually high in cost.
_Mass Concrete Work._--All parts of the bridge except the molded block
trim were built of concrete deposited in place. Briefly, the molded
blocks were set first and then backed up with the mass concrete
deposited in forms and on centers. The only features of this work that
call for particular description are those in connection with the main
arch ring and the spandrel arch construction.
The main arch rings were concreted in transverse sections; Fig. 158
shows the size and order of construction of these sections. Back forms
were necessary up to an angle of 45° from the spring line after which
the concrete was made somewhat drier and back forms were not used. After
Sections 1, 2, 3 and 4 had been concreted they were allowed to set and
then the struts and back forms were taken out and the intervening
sections were concreted. The large Sections 6 and 7 were concreted in
five sections each, in order to permit the taking out of the timber
struts supporting the sections above. The concrete in all sections was
placed in horizontal layers as a rule and it is the judgment of the
engineers in charge of this work that this is the preferable method.
TABLE XIX.--SHOWING COST OF TOOLING CONCRETE ORNAMENTAL BLOCKS FOR
CONNECTICUT AVENUE BRIDGE.
===============================================================================
| | Per Superficial Foot of
| Per Cubic Foot. | Showing Face.
+------+-----+------+-----+------+------+------+------
DESCRIPTION. | | Num-| | | | | |Number
| | ber | | |Super-| |Cost |super.
1: 2: 4½ Concrete Backing| Total|cubic|Total |Cost |ficial|Total |per |ft. to
1: 3 (Mortar Face). |Number|feet |cubic |per | feet |super-|super-| one
|Stones|in | feet |cubic| in |ficial|ficial| cubic
| Cut. |each.| cut. |foot.| each.| feet.|foot. | foot.
-------------------------+------+-----+------+-----+------+------+------+------
Brackets under Lamps and | | | | | | | |
Rail Posts (Cap and Base)| 344| 16.0| 5,500|$0.27| 10.5 | 3,630|$0.41 | 0.66
Moulding under coping | 770| 5.9| 4,560| 0.30| 3.8 | 2,930| 0.47 | 0.64
Dentils between Moulding | 520| 5.5| 2,860| 0.20| 8.0 | 4,160| 0.14 | 1.45
Coping | 494| 61.2|30,220| 0.12| 35.4 |17,490| 0.21 | 0.58
Pedestal (3 courses) | 162| 27.2| 4,400| 0.15| 14.1 | 2,290| 0.29 | 0.52
Rail Posts (Top and Base)| 296| 7.1| 2,100| 0.50| 17.3 | 5,100| 0.21 | 2.43
Lamp Posts and Parapets | | | | | | | |
over Piers (Top and Base)| 248| 22.9| 5,690| 0.17| 26.5 | 6,580| 0.15 | 1.16
-------------------------+------+-----+------+-----+------+------+------+------
Average of above--Totals | 2,834| 19.5|55,330|$0.17| 14.8 |43,190|$0.26 | 0.77
-------------------------+------+-----+------+-----+------+------+------+------
TABLE XX.--SHOWING COST OF MASS CONCRETE WORK PER CUBIC YARD.
[Transcriber's note: Table split]
===========================================================================
| | | Cost Delivered | |
| | | on Mixer. | |
Description. | | +--------+------+-------+ |
| | Average | | | | |
| | Yardage | | | | |
| Propor-| for Days| | | | Total |
| tions.| Run. | Cement.| Sand.| Stone.| Materials.|
-------------------+--------+---------+--------+------+-------+-----------+
Class A, in Piers | 1:2:4½ | 150 | 1.65 | 0.39 | 1.08 | 3.12 |
Class A, in Arches | 1:2:4½ | 200 | 1.65 | 0.39 | 1.08 | 3.11 |
Class B, in Piers | | | | | | |
--Solid Work | 1:3:6 | 160 | 1.40 | 0.42 | 1.23 | 3.05 |
Class B, in Piers | | | | | | |
--Hollow Work | 1:3:6 | 110 | 1.40 | 0.42 | 1.23 | 3.05 |
Class B, in | | | | | | |
Spandrel Walls | 1:3:6 | 110 | 1.40 | 0.42 | 1.23 | 3.05 |
Class B, in | | | | | | |
Spandrel Arches | 1:3:6 | 200 | 1.40 | 0.42 | 1.23 | 3.05 |
Class B, | | | | | | |
in Abutments | 1:3:6 | 150 | 1.40 | 0.42 | 1.23 | 3.05 |
Class C, Filling | | | | | | |
over Bridge | 1:3:10 | 145 | 0.90 | 0.31 | 1.30 | 2.51 |
-------------------+--------+---------+--------+------+-------+-----------+
===============================================
| Cost of |
| Mixing and Placing. |
Description. +--------+--------+--------+
| | | Total |
| | | Mixing |
| | | and |
| Mixing.| Placing| Placing|
-------------------+--------+--------+--------+
Class A, in Piers | 0.09 | 0.21 | 0.30 |
| | | |
Class A, in Arches | 0.05 | 0.28 | 0.33 |
Class B, in Piers | | | |
--Solid Work | 0.09 | 0.18 | 0.27 |
Class B, in Piers | | | |
--Hollow Work | 0.11 | 0.36 | 0.47 |
Class B, in | | | |
Spandrel Walls | 0.11 | 0.40 | 0.51 |
Class B, in | | | |
Spandrel Arches | 0.07 | 0.26 | 0.33 |
Class B, | | | |
in Abutments | 0.11 | 0.24 | 0.35 |
Class C, Filling | | | |
over Bridge | 0.11 | 0.28 | 0.39 |
-------------------+--------+--------+--------+
=========================================================================
| Cost of Form Work. | |
Description. +----------+-------+--------+-----------+-------------+
| | Taking| | Total | Total Cost |
| Erecting.| Down | Lumber.| Form Work | per Yard.[G]|
-------------------+----------+-------+--------+-----------+-------------+
Class A, in Piers | 0.17 | 0.05 | 0.16 | 0.38 | $3.80 |
| | | | | |
Class A, in Arches | 0.08 | 0.03 | 0.10 | 0.21 | 3.66 |
Class B, in Piers | | | | | |
--Solid Work | 0.17 | 0.05 | 0.16 | 0.38 | 3.70 |
Class B, in Piers | | | | | |
--Hollow Work | 0.77 | 0.25 | 0.64 | 1.66 | 5.18 |
Class B, in | | | | | |
Spandrel Walls | 0.85 | 0.28 | 0.73 | 1.86 | 5.42 |
Class B, in | | | | | |
Spandrel Arches | 0.94 | 0.30 | 0.86 | 2.10 | 5.48 |
Class B, | | | | | |
in Abutments | 0.10 | 0.03 | 0.12 | 0.25 | 3.65 |
Class C, Filling | | | | | |
over Bridge | 0.00 | 0.00 | 0.00 | .... | 2.90 |
-------------------+----------+-------+--------+-----------+-------------+
[Footnote G: Add 25% to the cost here tabulated for superintendence,
plant and incidentals.]
Considerable difficulty was experienced in building the large arches
with a concrete block facing on account of the fact that the edges of
the blocks are liable to chip off when any concentrated pressure is
brought on them. In order to permit the ring of blocks to deform as the
centering settled under its load, sheet lead was placed in the joints
between blocks at the points corresponding with the construction joints
between sections of the mass concrete backing. The deflection of the
centers at the crown was a maximum of 3¼ ins. and a minimum of 2½ ins.
TABLE XXI--Detail Cost of Engineering and Inspection for Different
Classes of Work.
Engineering. Inspection.
Kind of Work. Total. Unit. Total. Unit.
Class A, concrete, 23,500 cu. yds $3,055.00 $0.13 $1,762.50 $0.075
Class B, concrete, 36,580 cu. yds 3,658.00 0.10 1,646.10 0.045
Class C, concrete, 2,150 cu. yds 107.50 0.05 53.75 0.025
Class D, concrete, 6,250 cu. yds 1,875.00 0.30 4,687.50 0.75
1,000 M. ft. B. M. centering 1,000.00 1.00 440.00 0.44
Cement, 73,000 barrels 365.00 0.005 730.00 0.01
Earth filling, 50,000 cu. yds 1,000.00 0.02 500.00 0.01
The centering of the main arches was not struck until the spandrel
arches and all the work above the main arches to the bottom of the
coping had been completed. The first and third spandrel arch on each
side of the piers was made with an expansion joint in the crown. To
permit further of the adjustment of the portion of the masonry above the
backs of the main arches, the crown of the middle arch of each set of
spandrel arches was left unconcreted until the center of the main arches
had been struck. It may be noted here that the expansion joints in the
first and third arches were carried up through the dentils and coping,
and observations show that these joints are about 1/8 in. larger in
winter than in summer.
The cost of the mass concrete work is shown in Table XX. These figures
are based on the wages already quoted and the following: Foreman
riggers, $4.50; riggers, $1.50 to $1.75 and $2; skilled laborers, $2;
engineers, $3.50. The detail cost of engineering and inspection is shown
in Table XXI.
~ARCH BRIDGES, ELKHART, IND.~--At the new Elkhart, Ind., yards of the Lake
Shore & Michigan Southern Ry. the tracks are carried over a city street
by concrete arches 40, 60 and 160 ft. long. These arches all have a span
of 30 ft., a height of 13 ft. and a ring thickness at crown of 28 ins.
The reinforcement consists of arch and transverse bars; the arch bars
are spaced 6 ins. on centers 2½ ins. from both extrados and intrados,
and the transverse bars are spaced 24 ins. on centers inside both lines
of arch bars. The proportions of the concrete were generally 1 cement, 3
gravel and 6 stone. The gravel was a material dug from the foundations
and was about 50 per cent. sand and 50 per cent. gravel, ranging up to
the size of pigeons' eggs. The concrete was machine mixed and was mixed
very wet.
The work was done by the railway company's forces, and Mr. Samuel
Rockwell, Assistant Chief Engineer, gives the following figures of cost:
Total. Per cu. yd.
Temporary buildings, trestles, etc. $ 752.33 $0.15
Machinery, pipe fittings, etc. 416.34 0.08
Sheet piling and boxing 1,006.12 0.21
Excavation and pumping 1,619.74 0.33
Arch centers and boxing 3,528.92 0.73
--------- -----
Total $7,323.45 $1.50
Concrete masonry:
Cement 8,860.55 1.84
Stone 1,788.50 0.36
Sand 240.00 0.05
Drain tile 103.03 0.02
Labor 8,091.41 1.68
---------- -----
Total concrete $19,083.49 $3.95
Steel reinforcing rods $ 3,028.39 $0.63
Engineering, watching, etc. 508.40 0.11
---------- -----
Grand total (4,833 cu. yds. concrete) $29,943.73 $6.19
~ARCH BRIDGE, PLAINWELL, MICH.~--The following figures of cost of a
reinforced concrete arch bridge are given by Mr. P. A. Courtright. The
bridge crosses the Kalamazoo River at Plainwell, Mich., and is 446 ft.
long over all with seven arches of 54 ft. span and 8 ft. rise. The arch
rings were reinforced with 4-in., 6-lb. channels bent to a radius of 70
ft. and spaced 1.9 ft. c. to c. The contract price of the bridge was
$19,900.
The concrete was made of Portland cement and a natural mixture of sand
and gravel in the proportions of 1-8 for the foundations, 1-6 for arches
and spandrel walls and 1-4 for the parapet wall. The proportions were
determined by measure; the wagon boxes being built to hold a cubic yard
of sand and gravel. A sack of cement was taken as 1 cu. ft. For
foundations the pit mixture was used without screening; stones over 4
ins. in diameter being thrown out at the pit or on the mixing board. For
the arches and spandrel walls the gravel was passed over a 2-in. mesh
screen on the wagon box. The aggregate for the parapet walls was
screened to 1 in. largest diameter. The concrete was mixed in a McKelvey
continuous mixer which turned the material eight times. The mode of
procedure was as follows: The gravel was loaded upon wagons in the pit
and hauled to a platform at the intake of the mixer. Half of the cement
required in the concrete was then spread over the top of the load in the
wagon box and the whole was dumped through the bottom of the wagon box
onto the platform and spread with shovels. The remainder of the cement
was spread over the mixture and the whole was shoveled by one man to a
second man who shoveled it into the mixer. Water was added after the
mixture had passed about one-third of the way through the mixer. The
mixer delivered the concrete directly into wheelbarrows, by which it was
delivered to the work. The concrete was spread in layers from 2 to 4
ins. in thickness and thoroughly rammed with iron tampers; two men were
employed tamping for each man shoveling. The arches were concreted in
three longitudinal sections, each section constituting a day's work. The
work was done in 1903 and the concrete cost for mixing and placing:
Labor: Per day. Per cu. yd.
13 men at $1.80 $23.40 $0.78
Engine and mixer 5.00 0.17
1 team 3.00 0.10
1 foreman 3.00 0.10
------ -----
Totals for labor $34.40 $1.15
Materials:
0.65 bbl. cement at $2 $1.30
0.9 cu. yd. gravel at $0.50 0.45
-----
Total for materials $1.75
Grand total $2.90
~METHODS AND COST OF CONSTRUCTING A FIVE-SPAN ARCH BRIDGE.~--This bridge
consisted of five elliptical arch spans of 40, 45, 60, 87 and 44 ft.,
carried on concrete piers. The arch rings were 12 ins. thick at the
crowns and 18 ins. thick 5 ft. from the centers of piers and carried
4-in. spandrel walls; there were 1,000 cu. yds. of concrete in the
arches and 600 cu. yds. in the piers. Each arch ring was reinforced by a
grillage of longitudinal and transverse rods.
[Illustration: Fig. 159.--End View of Center for Short Elliptical Arch
Spans.]
_Forms and Centers._--Figure 159 is an end view of the center arch. It
consists of a series of bents, 6 ft. c. to c., the posts of each bent
being 5 ft. c. to c. These posts are made of 2×6-in. Washington fir.
Upon the heads of the posts rest 2×6-in. stringers, extending from bent
to bent. Resting on these stringers are wooden blocks, or wedges, which
support a series of cross-stringers, also of 2×6-in. stuff, spaced 2 ft.
c. to c. On top of these cross-stringers rest the sheeting planks,
which are 1×6-in. stuff, dressed on the upper side, and bent to the
curve of the arch. This sheeting plank was not tongue and grooved, and a
man standing under it, after it is nailed in place, could see daylight
through the cracks. It looked as if it would leak like a sieve, and let
much of the wet concrete mortar flow through the cracks, but, as a
matter of fact, scarcely any escapes. Figure 160 shows a front view of a
bent, and indicates the manner of sway bracing it with 1×4-in. stuff.
Figure 161 shows the outer forms for the parapet wall, or concrete hand
railing, and it will be noted that the cross-stringers are allowed to
project about 3 ft. so as to furnish a place to fasten the braces which
hold the upright studs. The inner forms for the parapet wall are shown
in dotted lines. They are not put in place until all the concrete arch
is built. Then they are erected and held to the outer forms by wire, and
are sway braced to wooden cleats nailed to the top surface of the
concrete arch.
[Illustration: Fig. 160.--Front View of Center for Short Elliptical Arch
Spans.]
[Illustration: Fig. 161.--Form for Parapet Wall for Arch Bridge.]
For the five spans the total amount of lumber in the centers was in
round figures 28 M. ft., distributed about as follows:
Item. Ft. B. M.
1×6-in. sheeting 5,600
2×6-in. longitudinal stringers 2,600
2×6-in. cross stringers 2,600
2×6-in. posts 4,000
3×8-in. sills 1,500
1×4-in. braces 3,000
Outer forms for spandrel walls 4,000
Inner forms for spandrel walls 4,000
------
Total 27,300
The aggregate span length of the arches was 276 ft., so that a little
less than 100 ft. B. M. of lumber was used for centering per lineal foot
of span. The superintendent at $5 per day and five carpenters at $3.50
per day erected the five centers in 18 days at a cost of $400, or a
trifle more than $14 per M. ft. B. M.; the cost of taking down the
centers was $2 per M. ft. B. M., and the lumber for the centers cost $24
per M. ft. B. M. making a grand total of $40 per M. ft. B. M. for
materials and labor. As there were 1,000 cu. yds. of concrete in the
arches and spandrels, the cost of centers and forms was $1.12 per cu.
yd. This form lumber was, however, after taking down, used again in
erecting a reinforced concrete building. Assuming that the lumber was
used only twice, the cost of centers and forms for these five arches was
less than 80 cts. per cu. yd. of concrete.
_Shaping and Placing Reinforcement._--The 60 and 87-ft. spans were
reinforced with 32 1½-in. round longitudinal rods held in place by
½-in. square transverse rods wired at the intersections; the
reinforcement of the smaller spans was exactly the same except that
1-in. diameter rods were used. To bend the longitudinal rods to curve,
planks were laid on the ground roughly to the curve of the arch; the
exact curve was marked on these planks and large spikes were driven part
way into the planks along this mark. The end of a rod was then fastened
by spiking it against the first projecting spike head and three men
taking hold of the opposite end and walking it around until the rod
rested against all the spikes on the curve. It took three men two 8-hour
days to bend 46,000 lbs. of rods. Their wages were $2.50 each per day,
making the cost of bending 0.03 ct. per pound, or 60 cts. per ton. It
took a man 5 mins. to wire a cross rod to a longitudinal rod. With wages
at $2.50 per day the cost of shaping and placing the reinforcement per
ton was as follows:
Item. Per ton.
Bending rods $0.60
Shearing rods to lengths 0.40
Carrying rods onto bridge 0.40
Placing and wiring rods 2.35
-----
Total $3.75
Including superintendence the labor cost was practically $4 per ton, or
0.2 cts. per lb. Altogether 66,000 lbs. of steel was used for
reinforcing 1,000 cu. yds. of concrete, or 66 lbs. per cu. yd. The cost
of steel delivered was 2 cts. per lb., and the cost of shaping and
placing it 0.2 ct. per lb., a total of 2.2 cts. per lb. or 2.2 × 66 =
$1.45 per cu. yd. of concrete.
_Mixing and Placing Concrete._--A Ransome mixer holding a half-yard
batch was used. The mixer was driven by an electric motor. The concrete
for the piers was a mixture of 1 part Portland cement to 7 parts gravel;
for the arches, the concrete was mixed 1 to 5. The gravel was piled near
the mixer, a snatch team being used to assist the wagons in delivering
the gravel into a pile as high as possible. Run planks supported on
"horses" were laid horizontally from the mixer to the gravel, so that
big wheelbarrow loads could be handled. The barrows were loaded with
long-handled shovels, and the men worked with great vigor, as is shown
by the fact that four men, shoveling and wheeling, delivered enough
gravel to the mixer in 8 hrs. to make 100 cu. yds. of concrete. We have,
therefore, estimated on a basis of six men instead of four. The mixer
crew was organized as follows:
Per day.
6 men shoveling and wheeling $12
2 men handling cement 4
1 man handling water 2
1 man dumping concrete 2
2 men handling dump cars 4
2 men handling hoisting rope 4
4 men spreading and ramming concrete 8
1 engineman 4
1 foreman 5
Fuel, estimated 3
---
Total $48
The output of this crew was 100 cu. yds. per day. The concrete was
hauled from the mixer in two small dump cars, each having a capacity of
10 cu. ft. The average load in each car was ¼ cu. yd. Ordinary mine cars
were used, of the kind which can be dumped forward, or on either side.
The cars were hauled over tracks having a gage of 18 ins. The rails
weighed 16 lbs. per yard, and were held by spikes ¼×2½ ins. Larger
spikes would have split the cross-ties, which were 3×4 ins. Only one
spike was driven to hold each rail to each tie, the spikes being on
alternate sides of the rail in successive ties. No fish plates or splice
bars were used to join the rails, which considerably simplifies the
track laying.
[Illustration: Fig. 162.--Trestle for Service Track.]
Two lines of track were laid over the bridge. The tracks were supported
by light bents, the cross-tie forming the cap of each bent, as shown in
Fig. 162. The bents were spaced 3 ft. apart. There were two posts to
each bent, toe-nailed at the top of the tie, and at the bottom to the
arch sheeting plank. Two men framed these crude bents and laid the two
rails at the rate of 150 lin. ft. of track per day, at a cost of 4 cts.
per lin. ft. of track. As stated, there were two tracks, one on each
side of the bridge, but they converged as they neared the concrete
mixer, so that a car coming from either track could run under the
discharge chute of the mixer; Fig. 163 shows the arrangement of the
tracks at the mixer. The part of each rail from A to B (6 ft. long)
was free to move by bending at A, the rail being spiked rigidly to the
tie at A, leaving its end at B free to move. To move the end B, so
as to switch the cars, a home-made switch was improvised, as shown in
Figs. 163 and 164.
[Illustration: Fig. 163.--Arrangement of Service Tracks at Mixer.]
[Illustration: Fig. 164.--Improvised Switch for Service Cars, General
Plan.]
It will be remembered that this bridge was a series of five arches.
There was a steep grade from the two ends of the bridge to the crown of
the center arch. Hence the two railway tracks ascended on a steep grade
from the mixer for about 175 ft., then they descended rapidly to the
other end of the bridge. Hence to haul the concrete cars up the grade by
using a wire cable, it was necessary to anchor a snatch block at the
center of the bridge. This was done by erecting a short post, the top
of which was about a foot above the top of the rails. The post stood
near the track, and was guyed by means of wires, and braced by short
inclined struts. To the top of the post was lashed the snatch block
through which passed the wire rope. Fig. 165 shows this post, P. About
10 ft. from the post P, on the side toward the mixer, another post,
Q, was erected, and a snatch block fastened to it. When the hoisting
engine, which was set near the concrete mixer, began hauling the car
along the track, a laborer would follow the car. Just before the car
reached the post Q, he would unhook the hoisting rope from the front
end of the car, then push the car past the post Q, and hook the
hoisting rope to the rear of the car. The car would then proceed to
descend in the direction T, being always under the control of the wire
rope, except during the brief period when the car was passing the post
Q. Each of the two cars was provided with its own hoisting rope, and
one engineer, operating a double drum hoist, handled the cars. The hoist
was belted to an 8 HP. gasoline engine, no electric motor being
available for the purpose.
[Illustration: Fig. 165.--General Plan of Rope Haulage System.]
[Illustration: Fig. 166. Fig. 167. Details of Haulage Rope Guides.]
Where hauling is done in this manner with wire ropes, it is necessary to
support the ropes by rollers wherever they would rub against
obstructions. A cheap roller can be made by taking a piece of 2-in. gas
pipe about a foot long, and driving a wooden plug in each end of the gas
pipe. Then bore a hole through the center of the wooden plugs and drive
a 1-in. round rod through the holes, as shown in Fig. 166. The ends of
this rod are shoved into holes bored into plank posts, which thus
support the roller. Where the rope must be carried around a more or less
sharp corner, it is necessary to provide two rollers, one horizontal and
the other vertical, as shown in Fig. 167.
When conveying concrete to a point on the bridge about 300 ft. from the
mixer, a dump car would make the round trip in 3 mins., about ¼ min. of
its time being occupied in loading and another ¼ min. in dumping. One
man always walked along with each car, and another man helped pull the
wire rope back.
Including the cost of laying the track and installing the plant, the
cost of mixing and placing the 1,600 cu. yds. of concrete was only 55
cts. per cu. yd., in spite of the high wages paid. However, the men were
working for a contractor under a very good superintendent.
Summing up the cost of the concrete in the arches of this bridge, we
have:
Per cu. yd.
1.35 bbl. cement at $3 $4.05
1 cu. yd. gravel at $1 1.00
66 lbs. of steel in place at 2.2 cts. 1.45
Centers in place (lumber used once) 1.12
Labor, mix and place concrete 0.55
-----
Total $8.17
The cost of the nails, wire, excavation and plant rental is not
available, but could not be sufficient to add more than 10 cts. per cu.
yd. under the conditions that existed in this case.
~CONCRETE RIBBED ARCH BRIDGE AT GRAND RAPIDS, MICH.~--The bridge consisted
of seven parabolic arch ribs of 75 ft. clear span and 14 ft. rise. The
five ribs under the 21-ft roadway were each 24 ins. thick, 50 ins. deep
at skewbacks and 25 ins. deep at crown; the two ribs under the sidewalks
were 12 ins. thick and of the same depth as the main ribs. Each rib
carried columns which supported the deck slab. Columns and ribs were
braced together across-bridge by struts and webs. All structural parts
of the bridge were of concrete reinforced by corrugated bars. The
abutments were hollow boxes with reinforced concrete shells tied in by
buttresses and filled with earth. There were in the bridge including
abutments 884 cu. yds. of concrete and 62,000 lbs. of reinforcing metal,
or about 70 lbs. of reinforcing metal per cu. yd. of concrete. Of the
884 cu. yds. of concrete 594 cu. yds. were contained in the abutments
and wing walls and 290 cu. yds. in the remainder of the structure. (Fig.
168.)
[Illustration: Fig. 168.--Details of Ribbed Arch Bridge.]
_Centers._--The center for the arch consisted of 4-pile bents spaced
about 12 ft. apart in the line of the bridge. The piles were 12×12
in.×24 ft. yellow pine and they were braced together in both directions
by 2×10-in. planks. Each bent carried a 3×12-in. plank cap. Maple
folding wedges were set in these caps over each pile and on them rested
12×12-in. transverse timbers, one directly over each bent. These
12×12-in. transverse timbers carried the back pieces cut to the curve of
the arch. The back pieces were 2×12-in. plank, two under each sidewalk
rib and four under each main rib of the arch. The back pieces under each
rib were X-braced together. The lagging was made continuous under the
ribs but only occasional strips were carried across the spaces between
ribs. This reduced the amount of lagging required but made working on
the centers more difficult and resulted in loss of tools from dropping
through the openings. Work on the centers and forms was tiresome owing
both to the difficulty of moving around on the lagging and to the
cramped positions in which the men labored. Carpenters were hard to keep
for these reasons.
_Concrete._--A 1-7 bank gravel concrete was used for the abutments and a
1-5 bank gravel concrete for the other parts of the bridge. The concrete
was mixed in a cubical mixer operated by electric motor and located at
one end of the bridge. The mixed concrete was taken to the forms in
wheelbarrows. The mixture was of mushy consistency. No mortar facing was
used, but the exposed surfaces were given a grout wash. In freezing
weather the gravel and water were heated to a temperature of about 100°
F.; when work was stopped at night it was covered with tarred felt, and
was usually found steaming the next morning.
_Cost of Work._--The cost data given here are based on figures furnished
to us by Geo. J. Davis, Jr., who designed the bridge and kept the cost
records. Mr. Davis states that the unit costs are high, because of the
adverse conditions under which the work was performed. The work was done
by day labor by the city, the men were all new to this class of work,
the weather was cold and there was high water to interfere, and work was
begun before plans for the bridge had been completed, so that the
superintendent could not intelligently plan the work ahead. Cost keeping
was begun only after the work was well under way. Many of the items of
cost are incomplete in detail.
The following were the wages paid and the prices of the materials used:
Materials and Supplies:
No. 1 hemlock matched per M. ft. $20
No. 1 hemlock plank per M. ft. 17
No. 2 Norway pine flooring per M. ft. 19
No. 2 yellow pine flooring per M. ft. 20
12×12-in.×16-ft. yellow pine per M. ft. 29
12×12-in.×24-ft. yellow pine, piling per M. ft. 27
Maple wedges per pair 50 cts.
½-in. corrugated bars per lb. 2.615 cts.
¾-in. corrugated bars per lb. 2.515 cts.
7/8-in. corrugated bars per lb. 2.515 cts.
Coal per ton $4
Electric power per kilowatt 6 cts.
Medusa cement per bbl. $1.75
Aetna cement per bbl. 1.05
Bank gravel per cu. yd. 0.85
Sand per cu. yd. 0.66
Carpenters per day $3 to 3.50
Common labor per day 1.75
The summarized cost of the whole work, with such detailed costs as the
figures given permit of computation, was as follows:
General Service: Total. Per cu. yd.
Engineering $451 $0.512
Miscellaneous 75 0.084
Pumping: Total 110 days.
Coal at $4 per ton $210
Machinery, tools and cartage 283
Labor 497
----
Total $990
This gives a cost of $9 per day for pumping.
Excavation: Total cost. P. C. Total.
Timber cartage, etc. $ 375 17.6
Tools 69 3.3
Labor at $1.75 1,687 79.1
------ -----
Total $2,131 100.0
Filling 5,711 cu. yds.: Total. Per cu. yd.
Earth $1,142 $0.20
Labor including riprapping 396 0.07
------ -----
Total $1,538 $0.27
Removing Old Wing Walls: Total.
Labor and dynamite $ 346
Tools and sharpening 64
-----
Total $ 410
Hand Rail, 150 ft.: Total. Per lin. ft.
Material $ 278 $1.85
Labor 29 0.19
----- -----
Total $ 307 $2.04
Wood Block Pavement, 296 sq. yds.: Total. Per sq. yd.
Wood block, etc. $ 695 $2.35
Labor 57 0.19
----- -----
Total $ 752 $2.54
Steel, 62,000 lbs.: Total. Per lb.
Corrugated bars, freight, etc. $1,498 2.41 cts.
Plain steel, wire, etc. 75 0.12 cts.
Blacksmithing, tools and placing 438 0.71 cts.
------ ----
Total $2,011 3.24 cts.
Concrete.
Centering: Total. Per cu. yd.
Lumber and piles $ 332 $1.14
Labor 272 0.95
----- -----
Total $ 604 $2.09
Total. Per cu. yd.
Forms $ 3,312 $ 3.75
Concrete 5,532 6.25
------- ------
Grand total $18,113 $20.50
In more detail the cost of the various items of concrete work was as
follows for the whole structure, including abutments, wing walls and
arch containing 884 cu. yds.:
Form Construction: Total. Per cu. yd.
Lumber and cartage $1,547 $1.75
Nails and bolts 129 0.15
Tools 110 0.12
Labor, erecting and removing 1,526 1.72
------ -----
Total $3,312 $3.74
Concrete Construction.
Materials:
Aetna cement at $1.05 $1,218 $1.37
Medusa cement at $1.75 499 0.56
Sand at 66 cts. per cu. yd. 37 0.04
Gravel at 85 cts. per cu. yd. 915 1.04
------ -----
Total materials $2,669 $3.01
Mixing:
Machinery and supplies $ 549 $0.62
Power at 6 cts. per kw. 52 0.06
Tools 22 0.02
Labor 737 0.83
----- -----
Total mixing $1,360 $1.53
Placing concrete $ 609 $0.69
Tamping concrete $ 481 $0.54
Heating Concrete:
Apparatus and cartage $ 47 $0.05
Fuel 96 0.11
Labor 270 0.31
----- -----
Total heating $ 413 $0.47
Grand total $8,844 $9.98
Considering the abutment and wing wall work, comprising 594 cu. yds.,
separately, the cost was as follows:
Forms: Per cu. yd.
Materials $1.20
Labor 1.09
-----
Total $2.29
Concrete:
Materials $2.92
Labor 2.38
-----
Total $5.30
Heating water and gravel $0.70
Grand total $8.29
Considering the arch span, comprising 290 cu. yds., separately, the cost
was as follows:
Forms: Per cu. yd.
Materials $3.70
Labor 3.03
-----
Total $6.73
Concrete:
Materials $3.22
Labor 3.57
Total $6.79
Grand total $13.52
CHAPTER XVIII.
METHODS AND COST OF CULVERT CONSTRUCTION.
Culvert work is generally located on the line of a railway or a highway,
so that the facilities for getting plant and materials onto the work are
the best, and as culverts are in most cases through embankment, under
trestle or in trench below the ground level the advantage of gravity is
had in handling materials to mixer and to forms. Ordinarily individual
culverts are not long enough for any material economy to be obtained by
using sectional forms unless these forms are capable of being used on
other jobs which may occasionally be the case where standard culvert
sections have been adopted by a railway or by a state highway
commission. Various styles of sectional forms for curvelinear sections
are given in Chapter XXI, and centers suitable for large arch culverts
are discussed in Chapter XVII. Figure 169 shows an economic form for box
sections; it can be made in panels or with continuous lagging as the
prospects of reuse in other work may determine. For curvelinear sections
of small size some of the patented metal forms have been successfully
used.
~BOX CULVERT CONSTRUCTION, C., B. & Q. R. R.~--Mr. L. J. Hotchkiss gives
the following data. Box sections of the type shown by Fig. 169 are used
mostly; they range in size from single 4×4-ft. to double 20×20-ft. and
triple 16×20-ft. boxes. These boxes are more simple in design and
construction than arches, and for locations requiring piles they are
less expensive. The form work is plain and the space occupied is small
as compared with arches, so that excavation, sheeting and pumping are
less and the culvert can be put through an embankment or under a trestle
with less disturbance of the original structure. Finally, less expensive
foundations are required.
For small jobs where it does not pay to install a power mixer a hand
power mixer mounted on a frame carried by two large wheels has been
found at least as efficient as hand mixing; more convenient and easier
on the men. The machine is turned by a crank driving a sprocket chain;
it is charged at the stock piles and then hauled to the forms to be
discharged. Local conditions determine the capacity of power mixer to be
used. Difficulties in supplying material or in taking away the concrete
may readily reduce the output of a large machine to that of one much
smaller, and the small machine is cheaper in first cost and in
installation and operation. Where the yardage is sufficient to justify
the installation of equipment for handling the materials and output of a
large mixer it is found preferable to a small one, as the increase in
plant charges is not proportionately so great as the increase in the
amount of concrete handled. Again it may occur on a small job that the
concrete must be taken a long distance from the mixer, that a large
batch can be moved as quickly and as easily as a small one and the time
consumed in doing it is sufficient for the charging and turning of a
large mixer before the concrete car or bucket returns to it. Here a
large mixer, while it may stand idle part of the time, is still
economic.
[Illustration: Fig. 169.--Box Culvert and Form, C., B. & Q. R. R.]
The plant lay-outs vary with the local conditions, as the following will
show. In one case of a culvert located under a high, short trestle the
following arrangement of plant was employed: A platform located on each
side of the approach embankment about 8 ft. below the ties was built of
old bridge timbers. A track was laid on each platform and ran out over a
mixer located on the end slope of the embankment. Two mixers, one for
each platform, were used. From each mixer a track led out over the
culvert form and a track along the top of this form ran the full length
of the culvert. Gravel and sand were dumped from cars onto the side
platforms and thence shoveled into small bottom dump cars, which were
pushed out over the mixer and dumped directly into it. Cars on the short
tracks from mixers to culvert form took the mixed concrete and dumped it
into the distributing cars traveling along the form. The cars were all
hand pushed.
An entirely different lay-out was required in case of a long box culvert
located in a flat valley some 600 ft. from the track. A platform was
built at the foot of the embankment with its outer edge elevated high
enough to clear two tracks carrying 5 cu. yd. dump cars. The sand and
gravel was dumped from cars onto the side of the embankment, running
down onto the platform so that scraper teams moved it to holes in the
platform where it fell into the dump cars. These cars were hauled by
cable from the mixer engine and dumped at the foot of an inclined
platform leading to a hopper elevated sufficiently to let a 1½ cu. yd.
dump car pass under it. A team operating a drag scraper by cable moved
the material up the inclined platform into the hopper, whence it fell
directly into the car to which cement was added at the same time. The
charging car was then pulled by the mixer engine up another incline, at
the top of which it dumped into the mixer. The concrete car was hauled
up another incline to a track carried on the forms and reaching the full
length of the culvert work.
The placing of the reinforcement is given close supervision. When a wet
concrete is used it is found necessary to securely fasten the bars in
place to prevent them being swept out of place by the rush of the
concrete. A method of supporting the invert bars is shown by Fig. 169;
2×2-in. stakes are large enough and they need never be spaced closer
than 6 ft. The longitudinal bars are held on the stakes by wire nails
bent over and the transverse bars are wired to them at intersections by
stove pipe wire. The vertical wall bars are placed by thrusting the
ends into the soft footing concrete and nailing them to a horizontal
timber at the top; the horizontal wall bars are wired at intersections
to the verticals. In the roof slab the stakes are replaced by metal
chairs, or by small notched blocks of concrete.
The form construction is shown by Fig. 169. It is not generally made in
panels, since, as the work runs, the locations of boxes of the same size
are usually so far apart that transportation charges are greater than
the saving due to use a second time. No general rule is followed in
removing forms, but they can usually be taken down when the concrete is
a week old.
The boxes are built in sections separated by vertical joints, one
section being a day's work. The vertical joints are plain butt joints;
tongue and groove joints give trouble by the tenons cracking off in the
planes of the joints. A wet mixture is used and smooth faces obtained by
spading.
~ARCH CULVERT COSTS, N. C. & ST. L. RY.~--The cost of arch culvert
construction for the Nashville, Chattanooga & St. Louis Ry. is recorded
in a number of cases as follows:
~18-ft. Arch Culvert.~--Mr. H. M. Jones is authority for the following
data: An 18-ft. full-centered arch culvert was built by contract, near
Paris, Tenn. The culvert was built under a trestle 65 ft. high, before
filling in the trestle. The railway company built a pile foundation to
support a concrete foundation 2 ft. thick, and a concrete paving 20 ins.
thick. The contractors then built the culvert which has a barrel 140 ft.
long. No expansion joints were provided, which was a mistake for cracks
have developed about 50 ft. apart. The contractors were given a large
quantity of quarry spalls which they crushed in part by hand, much of it
being too large for the concrete. The stone was shipped in drop-bottom
cars and dumped into bins built on the ground under the trestle. The
sand was shipped in ordinary coal cars, and dumped or shoveled into
bins. The mixing boards were placed on the surface of the ground, and
wheelbarrow runways were built up as the work progressed. The cost of
the 1,900 cu. yds. of concrete in the culverts was as follows per cu.
yd.:
1.01 bbls. Portland cement $2.26
0.56 cu. yds. of sand, at 60 cts. .32
Loading and breaking stone .25
Lumber, centers, cement house and hardware .64
Hauling materials .04
Mixing and placing concrete 1.17
Carpenter work .19
Foreman (100 days at $2.50) .13
Superintendent (100 days at $5.50) .29
------
Total per cu. yd. $5.29
It will be seen that only 19 cu. yds. of concrete were placed per day
with a gang that appears to have numbered about 21 laborers, who were
negroes receiving about $1.10 per day. This was the first work of its
kind that the contractors had done. It will be noticed that the cost of
42 cts. per cu. yd. for superintendence and foremanship was
unnecessarily high.
~Six Arch Culverts 5 ft. to 16 ft. Span.~--All these arches were built
under existing trestles, and in all cases, except No. 2, bins were built
on the ground under the trestle and the materials were dumped from cars
into the bins, loaded and delivered from the bins in wheelbarrows to the
mixing boards, and from the mixing boards carried in wheelbarrows to
place. Negro laborers were used in all cases, except No. 5, and were
paid 90 cts. a day and their board, which cost an additional 20 cts.;
they worked under white foremen who received $2.50 to $3 a day and
board. In culvert No. 5, white laborers, at $1.25 without board, were
used. There were two carpenters at $2 a day and one foreman at $2.50 on
this gang, making the average wage $1.47 each for all engaged. The men
were all green hands, in consequence of which the labor on the forms in
particular was excessively high. The high rate of daily wages on
culverts Nos. 1 and 3 was due to the use of some carpenters along with
the laborers in mixing concrete. The high cost of mixing concrete on
culvert No. 2 was due to the rehandling of the materials which were not
dumped into bins but onto the concrete floor of the culvert and then
wheeled out and stacked to one side. The cost of excavating and
back-filling at the site of each culvert is not included in the table,
but it ranged from 70 cts. to $2 per cu. yd. of concrete.
Cost of Six Concrete Culverts on the N., C. & St. L. Ry. & St. L. Ry.
No. of culvert 1 2 3 4 5 6
Span of culvert 5 ft. 7.66 ft. 10 ft. 12 ft. 12 ft. 16 ft.
Cu. yds. of concrete. 210 199 354 292 406 986
Ratio of cement to
stone 1:5.5 1:6.5 1:5.8 1:5.8 1:6.1 1:6.5
Increase of concrete
over stone 16.0% 9.9% 6.3% 12.3% 8.3% 5.3%
Bbls. cement per cu.
yd. 1.02 0.90 1.06 1.01 1.00 1.09
Cu. yds. sand per cu.
yd. 0.43 0.49 0.44 0.46 0.46 0.47
Cu. yds. stone per
cu. yd. 0.86 0.90 0.95 0.89 0.94 0.94
Total days labor
(inc. foremen and
supt.) 702 607 784 726 768 1,994
Av. wages per day
(inc. foremen and
supt.) $1.61 $1.33 $1.59 $1.19 $1.47 $1.46
Cost per cu. yd.--
Cement 2.18 1.94 2.27 1.82 2.11 2.01
Sand 0.17 0.20 0.18 0.18 0.19 0.14
Stone 0.52 0.52 0.47 0.54 0.47 0.58
Lumber 0.88 0.43 0.48 0.43 0.31 0.57
Unload, materials 0.23 0.17 0.18 0.18 0.16
Building forms 1.07 0.33 0.62 0.47 0.72 0.41
Mixing & placing 1.59 1.74 1.69 1.35 1.23 1.26
------ ------ ------ ------ ----- -----
Total per cu. yd. $6.64 $5.33 $5.89 $4.97 $5.19 $4.97
~14-ft. 9-in. Arch Culvert.~--Mr. W. H. Whorley gives the following
methods and cost of constructing a 12-ft. full centered arch culvert 204
ft. long. The culvert was built in three sections, separated by vertical
transverse joints to provide for expansion; the end sections were each
61 ft. long and the center section was 70 ft. long. Fig. 170 is a
cross-section at the center; for the end sections the height is 14 ft. 9
ins., the crown thickness is 1 ft. 9 ins., and the side walls at their
bases are 5 ft. thick. The concrete was a 1-3-6 mixture, using slag
aggregate for part of the work and stone aggregate for a part. The
culvert was built underneath a trestle which was afterwards filled in.
_Mixing and Handling Concrete._--The height of the track above the
valley permitted the mixing plant to be so laid out that all material
was moved by gravity from the cars in which it was shipped until finally
placed in the culvert. Sand and aggregate were received in drop bottom
cars and were unloaded into bins in the trestle. These bins had hopper
bottoms with chutes leading to a wheeling platform, which was placed
between two trestle bents and extended over a mixer placed outside the
trestle. The cement house was erected alongside the trestle at the
wheeling platform level and a chute from an unloading platform at track
level to the opposite end of the house enabled the bags to be handled
directly from the car to the chute and thence run by gravity to the
cement house. Sand and aggregate were chuted from the bins into
wheelbarrows, wheeled about 23 ft., and dumped into a hopper over the
mixer. Water was pumped by a gasoline engine from a well just below the
trestle to a tank on the trestle, whence it was fed to the mixer by a
flexible connection, a valve so regulating the flow that the necessary
amount was delivered in the time required to mix a batch.
[Illustration: Fig. 170.--Section of Arch Culvert, N., C. & St. L. R.
R.]
The mixer was a No. 5 Chicago Improved Cube Mixer, operated by a
gasoline engine; a larger size would have been preferable since a batch
required only two-thirds of a bag of cement which had to be measured
which required the services of an additional man. The mixer was in
operation 194 hours and mixed 7,702 batches (1,217 cu. yds.), or a batch
every 87 seconds, or 6.3 cu. yds. per hour. During the last ten days it
mixed a batch every 78 seconds while running. The best short record made
was 291 batches in five hours, or one batch every 63 seconds, this being
at the rate of 58 batches equal to 9.2 cu. yds. of concrete in place per
hour, or nearly 1/6 cu. yd. per batch. It took about ½ minute to mix the
concrete and about the same length of time to charge and discharge the
mixer.
To convey the concrete from the mixer to the culvert walls a 1 cu. yd.
drop bottom car was used. This car ran on 30-in. gage tracks carried on
a trestle straddling the culvert walls and having its floor high enough
to clear the arch. A track ran lengthwise of the trestle over each
culvert wall, and a cross track intersecting both with turntables ran to
the mixer. Three men handled the car, a round trip to the extreme end of
the trestle being made in about 3 minutes. In the meantime the mixer was
discharging into a small hopper which unloaded into the car on its
return. One only of the three sections, of the culvert was built at a
time, both walls being brought up together. After a point had been
reached about 2 ft. above the springing on both walls, one track was
removed and the other was shifted to the center of the trestle.
_Forms._--There was used in the forms 15,000 ft. B. M. of 2-in. dressed
lagging for face work, 21,000 ft. B. M. rough lumber for back work, and
old car sills for studding. No charge was made for studding except the
cost of loading, the cost of the remaining lumber was $16 per M. for
dressed and $12.50 per M. for rough. A credit of one-third the cost was
allowed for the old material recovered. The total cost of the labor of
erecting the material in forms, bins and platforms was $666. The work
was done by a bridge crew of white men, the average rate of wages per
man, including the bridge foreman's time, being $2.20 per day. In
addition a mason at $3.50 per day and a carpenter at $2.25 per day
worked with the bridge crew in erecting forms.
_Cost._--The cost of the 1,217 cu. yds. of concrete in the culvert was
as follows:
Item. Per cu. yd.
1.08 bbls. cement at $1.72 $1.85
0.47 cu. yd. sand at 30 cts. 0.14
0.25 cu. yd. broken stone at 51 cts. 0.13
0.8 cu. yd. slag at 26 cts. 0.21
Lumber in forms, etc. 0.30
Miscellaneous materials 0.05
Labor, unloading materials 0.11
Labor, mixing and placing concrete 0.42
Labor, building forms 0.55
Labor, not classified 0.18
Labor, excavating 40 cts. per cu. yd. 0.28
Labor, back filling and tearing down forms 0.10
-----
Total $4.32
~CULVERTS FOR NEW CONSTRUCTION, WABASH RY.~--The following data relate to
culvert work carried out in constructing the Pittsburg extension of the
Wabash Ry. in 1903. All the work was done by contract.
_Plant I_: This plant was located on a hillside with the crushing bins
above the loading floor or platform which extended over the top of the
mixer, so that the crushed stone could be drawn directly from the chutes
of the bins and wheeled to the mixer. The sand was hauled up an incline
in one-horse carts and dumped on this floor, and was also wheeled in
barrows to the mixer. The proportions used were 4 bags of cement, 4
barrows of sand and stone dust and 7 barrows of crushed stone. A 7/8-cu.
yd. mixer was used and it averaged 40 cu. yds. per 10-hour day at the
following cost for labor:
Item. Per day. Per cu. yd.
1 foreman $ 3.00 $0.08
3 men charging with barrows 4.50 0.11
1 man attending engine and mixer 2.50 0.06
2 men loading concrete barrows 3.00 0.08
4 men wheeling concrete barrows (100 ft.) 6.00 0.15
4 men ramming concrete 6.00 0.15
4 men wheeling and bedding rubble stones 6.00 0.15
------ -----
Totals $31.00 $0.78
Assuming 1/3 ton of coal per day at $3 per ton, we have 2 cts. more per
cubic yard for fuel.
_Plant II._--At this plant a Smith mixer was used with a loading floor 4
ft. above the ground, this low platform being made possible by having a
hole or sump in which the skip receiving the concrete was set. A derrick
handled the skips between the sump and the work. The batch was made up
of 2 bags of cement, 2 barrows of sand and 4 barrows of stone. The
output was 50 cu. yds. per day of 10 hours at the following cost:
Item. Per day. Per cu. yd.
1 man feeding mixer $1.50 $0.03
1 mixer runner 2.50 0.05
1 derrick engineman 2.50 0.05
2 tagmen swinging and dumping 3.00 0.06
6 men wheeling materials 9.00 0.18
2 men tamping concrete 3.00 0.06
1 foreman 3.00 0.06
------ -----
Totals $24.50 $0.49
The cost of fuel would add about 3 cts. per cubic yard to this amount.
~SMALL ARCH CULVERT COSTS, PENNSYLVANIA R. R.~--Mr. Alex. R. Holliday
gives the following figures of cost of small concrete culvert work
carried out under his direction. The culvert section used is shown in
Fig. 171. This section gives a slightly larger waterway than a 36-in.
cast iron pipe. Eight culverts, having an aggregate length of 306 ft.
were built, using a mixture of Portland cement and limestone and
screenings. Each culvert had a small spandrel wall at each end.
The work was done by a gang of six men, receiving the following wages:
Foreman, cents per hour 27.5
Assistant " " " 17.5
Laborers " " " 15.0
Teams " " " 35.0
The materials were hauled about 1 mile from railway to site of work.
Cement, including freight and haulage, cost $1.97 per barrel. Limestone
and screenings cost 50 cts. per cu. yd. f. o. b. at quarry. No freight
charges are included in cost of any of the materials except cement. The
cost of the 306 ft. of culvert was as follows:
Item. Total. Per lin. ft. Per cu. yd.
Labor $443.14 $1.45 $3.35
Stone and screenings 78.50 0.25 0.60
Cement 307.53 1.01 2.34
Forms 12.00 0.04 0.09
------- ----- -----
Total $841.17 $2.75 $6.38
[Illustration: Fig. 171.--Small Culverts, Pennsylvania R. R.]
~26-FT SPAN ARCH CULVERT.~--The culvert was 62 ft. long and 26-ft. span
and was built of 1-8 and 1-10 concrete mixed by hand. The wages paid
were: General foreman, 40 cts. per hour; foreman, 25 cts. per hour;
carpenters, 22½ to 25 cts. per hour, and laborers, 15 cts. per hour. The
cost of the concrete in place, exclusive of excavation but including
wing walls and parapet, was as follows:
Per cu. yd.
0.96 bbl. cement, at $1.60 $1.535
1.03 tons coarse gravel, at $0.19 0.195
0.40 tons fine gravel, at $0.21 0.085
0.32 tons sand, at $0.36 0.115
Tools, etc. 0.078
Lumber for forms and centers 0.430
Carpenter work on forms (23 cts. hr.) 0.280
Carpenter work platforms and buildings 0.050
Preparing site and cleaning up 0.210
Changing trestle 0.085
Handling materials 0.037
Mixing and laying, av. 15½ cts. per hr. 1.440
------
Total per cu. yd $4.540
There were 1,493 cu. yds. of concrete in the work. The excavation cost
$463 and the total cost was $7,243.
~COST OF RAILWAY CULVERT.~--The culvert was for a single track railway and
contained 113 cu. yds. of concrete and required 36 cu. yds. of
excavation. The figures are given by C. C. Williams as follows:
Cost of Material.
Kind and Amount of Material. Unit Price. Cost.
Stone, 113.2 tons $.70 $ 79.24
Sand, 46.8 yds. .55 25.74
Cement, 137 bbls. .85 116.45
-------
Total $221.43
Lumber 52.50
Rail and bolts 36.60
-------
Total $ 89.10
Excavation.
Labor, 189 hours at .15 $ 28.35
Foreman, 60 hours at .30 18.00
-------
Total $ 46.35
Concrete.
Labor, 683 hours at .15 $102.45
Foreman, 130 hours at .30 39.00
-------
Total $141.45
Forms.
Carpenters, 313 hours at .225 $ 70.42
Labor, 30 hours at .15 4.50
-------
Total $ 74.92
Handling Materials.
Moving material, 245 hours at .15 $ 36.75
Unloading material, 95 hours at .15 14.25
Foreman, 20 hours at .30 6.00
-------
Total $ 57.00
Superintendence and Office.
Superintendent, 6 hours at .50 $ 3.00
Office 10.00
-------
Total $ 13.00
-------
Grand total $643.25
Proportional Costs.
Per cent.
Cost of Total
Per Yard Cost of
Item. Cost. Concrete. Concrete.
------
Concrete material $221.43 $1.96 7.1
Laying concrete 141.45 1.25 23.6
Lumber 52.50 .46 08.7
Rail and bolts 36.60 .32 06.1
Building forms 74.92 .67 13.3
Handling material 56.90 .50 09.0
Superintendent and office 13.00 .12 02.2
----- ------
Total $5.28 100.00
Excavation 46.35 1.28
-------
Total $643.15
Contractor's Receipts.
113 yds. concrete at $5.95 $672.35
36 yds. excavation at .30 10.80
-------
Total $683.15
Total cost 643.15
-------
Profit, 5.9% of contract price $ 40.00
~12-FT. CULVERT, KALAMAZOO, MICH.~--A portion 1,080 ft. long of a new
channel built in 1902-3 for a small stream flowing through the city of
Kalamazoo, Mich., was constructed as an arch culvert of the form shown
by Fig. 172. The concrete section is reinforced on the lines indicated
by a double layer of woven steel wire fabric. The concrete was
approximately a 1 cement, 6 sand and gravel mixture.
[Illustration: Fig. 172.--Cross-Section of Culvert at Kalamazoo, Mich.]
The centers were built in sections 12½ ft. long of the form and
construction shown by Fig. 173, and a sufficient number was provided to
lay twelve sections of invert and six sections of arch. The arch centers
were arranged to be uncoupled at the crown; this with the hinges at the
quarter points permitted the two halves to be separated and each half to
be folded so that it could be carried from the rear of the work through
the forms still in place and erected again for new work. When in place
the center ribs rested on the side forms which set on the invert
concrete and are braced apart by the hinged cross-strut. This
cross-strut was the key that bound the whole structure together; the
method of removing this key is indicated by Fig. 174. From his
experience with these centers the engineer of the work, Mr. Geo. S.
Pierson, remarks:
"In work of this kind it is very important to have the centering
absolutely rigid so it will not spring when concrete is being tamped
against it and thus weaken the cohesion of the concrete. It is also
important to have the arrangement such that all the centering can be
removed without straining or jarring the fresh concrete. The centers
were generally removed in about three or four days after the concrete
arch was in place."
[Illustration: Fig. 173.--Center for Culvert at Kalamazoo, Mich.]
The invert concrete was brought to form by means of templates, Fig. 173,
and straight edges. The side forms were then placed and braced apart by
the struts and concreting continued to the skewback plane indicated in
Fig. 173. The arch form was then placed; it rested at the edges on the
side forms and was further supported by center posts bearing on boards
laid on the bottom of the invert. A template, Fig. 175, was used to get
the proper thickness and form of arch ring. Outside forms were used to
confine the concrete at the haunches but nearer the crown they were not
required.
[Illustration: Fig. 174.--Hinged Cross Strut for Center for Culvert at
Kalamazoo, Mich.]
Much of the work was done when the thermometer, during working hours,
ranged from 12° to 25° above zero. When the temperature was below
freezing, hot water was used in mixing the concrete and on a few of the
coldest days salt was dissolved in the water. In addition each section
of the work was covered with oiled canvas as soon as completed, and the
conduit was kept closed so far as was practicable to retain the heat.
Concreting was never stopped on account of cold weather.
[Illustration: Fig. 175.--Templet for Arch Ring for Culvert at
Kalamazoo, Mich.]
Account was kept of the cost of all work, and the figures obtained are
given in the following tables:
Labor Force, Materials Used and Progress of Work.
Average progress per day in feet 18.0
Greatest number of feet laid in one day 28
Average number of laborers per day mixing and wheeling 10.04
Average number of laborers per day placing concrete 5
Average number of laborers per day setting up forms 4.57
Cubic yards of concrete mixed and wheeled per day per man 1.96
Cubic yards of concrete placed per day per man 3.54
Cubic yards of concrete per lin. ft. 0.95
Barrels of cement per lin. ft. 1.18
Barrels of cement per cu. yd. 1.24
Proportion of cement to sand and gravel 1-6
Itemized Cost per Lineal Foot.
Sand and gravel $0.42
Cement 2.44
Mixing and wheeling concrete 0.98
Labor placing concrete 0.47
Forms and templates 0.30
Metal fabric 0.39
Setting up forms 0.43
Finishing 0.09
Tools, general and superintendence 0.43
-----
Total per lineal foot $5.95
The cost per cubic yard was thus $6.26. Wages were $1.75 per day.
~METHOD AND COST OF MOLDING CULVERT PIPE, CHICAGO & ILLINOIS WESTERN R.
R.~--During 1906, the Chicago & Illinois Western R. R., Mr. O. P.
Chamberlain, Chief Engineer, built a number of culverts of concrete pipe
with an interior diameter of 4 ft., and 6-in. shells. Fig. 176 shows the
forms in which the pipe was molded. Both forms are of ordinary wooden
tank construction. The inner form has one wedge-shaped loose stave which
is withdrawn after the concrete has set for about 20 hours, thus
collapsing the inner form and allowing it to be removed. The outer form
is built in two pieces with 2×5/8-in. semi-circular iron hoops on the
outside, the hoops having loops at the ends. The staves are fastened to
the hoops by wood screws 1¾ ins. long driven from the outside of the
hoop. When the two sides of the outer form are in position, the loops on
one side come into position just above the loops on the other side, and
four ¾-in. steel pins are inserted in the loops to hold the two sides
together while the form is being filled with concrete and while the
concrete is setting. After the inner form has been removed, the two pins
in the same vertical line are removed and the form opened horizontally
on the hinges formed by the loops and pins on the opposite side. The
inner and outer forms are then ready to be set up for building another
pipe.
[Illustration: Fig. 176.--Form for Molding Culvert Pipe.]
The concrete used in manufacturing these pipes was composed of American
Portland cement, limestone screenings and crushed limestone that has
passed through a ¾-in. diameter screen after everything that would pass
through a ½-in. diameter screen had been removed. The concrete was mixed
in the proportions of one part cement to three and one-half parts each
of screenings and crushed stone. All work except the building of the
forms was performed by common laborers. In his experimental work Mr.
Chamberlain used two laborers, one of whom set the forms, and filled
them and the other of whom mixed the concrete. The pipes were left in
the forms till the morning of the day after molding. The two laborers
removed the forms filled the day before, the first thing in the morning,
and proceeded to refill them. The average time the concrete was allowed
to set before the forms were removed was 16 hours. Mr. Chamberlain
believes that with three men and six forms the whole six forms could be
removed and refilled daily. Based on the use of only two forms with two
laborers removing and refilling them each day, and on the assumption
that a single set of forms costing $40 can be used only 50 times before
being replaced, Mr. Chamberlain estimates the cost of molding 4-ft.
pipes as follows:
2 per cent, of $40 for forms $0.80
1.1 cu. yds. stone and screenings at $1.85 2.04
0.8 bbls. cement at $2.10 1.68
10 hours' labor at 28 cts. 2.80
-----
Total per pipe $7.32
This gives a cost of $1.83 per lineal foot of pipe or practically $7 per
cu. yd. of concrete. The pipe actually molded cost $2.50 per lin ft., or
$9.62 per cu. yd. of concrete, owing to the small scale on which the
work was carried on--the laborers were not kept steadily at work.
The pipes were built under a derrick and loaded by means of the derrick
upon flat cars for transportation. At the culvert site they were
unloaded and put in by an ordinary section gang with no appliances other
than skids to remove the pipes from the cars. As each four-foot section
of this pipe weighs about two tons, it was not deemed expedient to build
sections of a greater length than 4 ft., to be unloaded and placed by
hand. On a trunk line, however, where a derrick car is available for
unloading and placing the pipes, there is no reason why they should not
be built in 6 or 8-ft. sections.
CHAPTER XIX.
METHODS AND COST OF REINFORCED CONCRETE BUILDING CONSTRUCTION.
If we set aside concrete block construction, virtually all concrete used
in building construction is reinforced; plain monolithic or mass
concrete now, as in the past, is one of the secondary building
materials. It is reinforced concrete building construction that is
discussed in this chapter. In no class of concrete work is the
contractor's responsibility for the successful outcome of the work
greater than in reinforced concrete building construction. No degree of
excellence in design can make up for incompetent, careless or dishonest
work in construction. This is true not merely in the general way that it
is true of all engineering construction--it is true in a special way
peculiar to the material. Except for the reinforcing steel, the
contractor for concrete building work has no guarantee of the quality of
any element of his work except his own faithful care in performing every
task that combines to produce that element. The quality of his concrete
depends upon the care with which he has chosen his cement, sand and
stone, and on the perfection with which he has incorporated them into a
homogeneous mixture. The quality of his beam or column, then, depends
upon the care with which the concrete is placed in position with the
reinforcement and with which the supporting forms are maintained until
the member is amply strong to do without support. There is no certainty
of any detail except the certainty that is had by performing every part
of the work as experience has taught that it should be performed if
perfect results are to be attained. We have dwelt thus emphatically on
the responsibility in concrete building work of the contractor for the
reason that in the past it has been upon the contractor that the burden
of failure has been generally shifted.
The construction work of buildings is divided into (1) construction,
erection and removal of forms; (2) fabrication and placing of
reinforcement; (3) mixing, transporting and placing concrete.
CONSTRUCTION, ERECTION AND REMOVAL OF FORMS.
The stereotyped text-book statement that forms must be true to
dimensions and shape and rigid enough in construction to maintain this
condition under all loads that they have to sustain mentions only one of
the factors that the constructing engineer or the contractor has to keep
in mind in designing such forms. His design must be made true and rigid
at the least possible cost for first construction of lumber and
carpenter work; it must be made with the plan in mind of using either
the same forms as a whole or the same form material several times in one
structure; it must be made with a view to convenience in taking down,
carrying and re-erecting the forms the second or third time; and it must
be made with the object in sight of securing the greatest salvage value
either in forms fit for use again or in form lumber that can be sold or
worked up for other purposes.
The general conditions governing the computation and design of economic
form work are discussed in Chapter IX.
~COLUMN FORMS.~--Concrete columns are usually square or rectangular in
section, with, commonly, chamfered or beveled corners. The popularity of
these sections is due very largely to the simplicity of the forms
required. When hooped reinforcement is used, the column section is
always circular or polygonal. Hollow sections, T-section and channel
sections are rarely employed and then only for wall columns.
Column forms should be made in units which can readily be assembled,
taken apart and re-assembled. The number, arrangement and size of the
units are determined by the shape and size of the column and the means
adopted for handling the forms. For square or rectangular columns there
will be usually four units of lagging, one for each side, plus the
number of clamps or yokes used to bind the sides together. Yokes or
clamps will seldom be spaced over 3 ft. apart unless very heavy lagging
is used; 2 ft. spacing for yokes is common. For circular columns two
units of lagging are necessary and this is the number commonly used; the
yokes or hoops are spaced about as for rectangular columns. Metal forms
can be used to good advantage for cylindrical columns. Forms for
polygonal columns are difficult to construct in convenient units. Forms
built complete a full story high and concreted from the top are
essential where wet and sloppy concretes are used. In Europe, where
comparatively dry concretes are employed and where the reinforcement is
commonly placed a piece at a time as concreting progresses, three sides
of a rectangular form are erected full height and the fourth side is
built up as the concrete and metal are placed. This construction is now
less common, even abroad, than it was, since wetter mixtures are coming
to be approved by European engineers to a greater extent now than
formerly. It is a time consuming method and with wet mixtures it has
nothing to recommend it. For lagging 1¼ and 2-in. plank are commonly
used; with yokes spaced 2 ft. apart the lighter plank is amply strong
and reduces the weight of the units to be handled as well as the amount
of form lumber required.
[Illustration: Fig. 177.--Form for Rectangular Column for Factory
Building, Cincinnati, O.]
Column forms should always be constructed with an opening at the bottom
by means of which the reinforcement can be adjusted and sawdust,
shavings and other material cleaned out.
~Rectangular Columns.~--The form shown in section by Fig. 177 was used in
constructing a factory building at Cincinnati, O. Two 2×4-in. studs at
each corner carry the horizontal side lagging boards and are clamped
together by yokes composed of four hardwood corner saddles connected
around the form by a hooked rod with center turnbuckle on each side. No
nails are used in assemblying the parts; the same studding and yokes
serve for several sizes of column, the lagging alone being changed. The
lumber required for studding is 5½ ft. B. M. per foot of column length.
The lumber required for lagging, using 1 in. boards, would be 2-2/3 ft.
B. M. for a 12-in. column, and 2/3 ft. B. M. would be added for every
2-in. increase in size of the column. About 3½ ft. B. M. is required for
each set of four corner saddles. With the studs rabbeted at the mill,
the carpenter work is reduced to the simple task of sawing the boards
and struts to length. The form is taken down by simply unscrewing the
turnbuckles; it can be erected by common labor in charge of one
carpenter to attend to the plumbing and truing-up. The form can be used
over and over and for columns of different sizes without change except
in the length of the lagging boards.
The form shown by Fig. 178 was used in constructing a nine-story
warehouse at St. Paul, Minn.; it is a design which has become almost
standard with a number of large building contractors. In this
construction lagging boards the full length of the column are used and
are held without nails by yokes. The yokes consist of two heads of wood
held together by threaded rods with nuts; between the rods and the
lagging are struts or blocks serving both as spacers and to hold the
lagging to plane and surface. The yoke proper is adjustable to the
extent of the threaded portions of the tie rods. It is to be noticed
that the lagging boards are not connected by battens or cleats,
therefore, two or three widths of stock serve for all ordinary changes
in size of columns and carpenter work is limited to sawing them to
length. Furthermore as the boards are full column length, their salvage
value when removed from the forms is high. Common laborers under a
carpenter foreman can assemble and erect the form. For a 12-in. column
and using 3×4-in. yokes spaced 2 ft. apart and 1¼-in. lagging, this form
requires about 12 ft. B. M. of lumber per foot length of column. The
column form shown by Fig. 226 for the six-story building described in a
succeeding section differs from the one described only in the details
of the yoke construction. In place of the struts between the wooden
heads of the yoke a cleat is nailed across the projecting ends which has
to be pried loose every time the yoke is removed and nailed into place
again every time the yoke is put onto another form; these repeated
nailings soon destroy the yoke heads. This form as constructed requires
about 8¾ ft. B. M. of lumber per foot length of 12-in. column, which is
3¼ ft. B. M. less than is required for the form shown by Fig. 177. The
saving comes entirely in the yoke construction.
[Illustration: Fig. 178--Form for Rectangular Column for Warehouse at
St. Paul, Minn.]
The form shown by Fig. 238 is of the same general type as are the two
just described, the chief difference in detail being in the yoke
construction and in the forming of the lagging boards into a panel or
unit for each side by means of battens. This panel construction makes a
lagging unit which is more convenient to handle, but less convenient to
adapt to changes in size of column. The salvage value of the lumber is
also reduced by the nailing. Assuming 1¼-in. lagging and a yoke spacing
of 2 ft., to permit direct comparison, this form requires 10½ ft. B. M.
of lumber per foot length of 12-in. column as compared with 12 ft. B. M.
for the form shown by Fig. 177 and 8¾ ft B. M. for the form shown by
Fig. 178. As actually constructed with 2-in. lagging the form shown by
Fig. 238 requires about 14 ft. B. M. of lumber per foot length of 12-in.
column.
The French constructor, Hennebique, uses the column form construction
shown by Fig. 179. Three sides of the forms are built full length of
vertical plank and the fourth is built up of horizontal lagging nailed
on a board at a time as concreting progresses. In place of rectangular
yokes, steel clamps of special form are used to hold the lagging in
place. To tear down this form requires drawing the nails in the
horizontal lagging and the knocking loose of the clamps. The vertical
lagging is of necessity connected by battens into panels to make it
possible to hold it in place by the form of clamp used. Assuming 2-in.
vertical lagging with 7/8×3-in. battens every 3 ft., and 7/8-in.
horizontal lagging this form requires about 12 ft. B. M. of lumber for
every foot length of 12-in. column. This form seems to offer no
particular merits to American eyes: there is practically no saving in
lumber over forms with rectangular yokes and the clamp shown, while
adjustable, is not nearly so rigid and secure a bond for the lagging as
is a good yoke.
[Illustration: Fig. 179.--Form Used by Mr. Hennebique for Rectangular
Columns.]
[Illustration: Fig. 180.--Form for Rectangular Column for a Factory
Building, New York City.]
The form shown by Fig. 180 is an extreme example of nailed construction
throughout, no yokes or clamps being used. It was used in constructing a
factory building in New York City. Horizontal lagging nailed to
vertical studs was used for all four sides; three sides were built up
full height and the fourth side was placed a board at a time as
concreting progressed. This form required 7-1/3 ft. B. M. of lumber per
foot length of 12-in. column, which is probably about as low in lumber
as column form construction can be got. The labor of tearing down and
re-erecting the form would be high as also would the waste of lumber.
Nailed forms of this type are rarely used.
[Illustration: Fig. 181.--Form for T-Section Wall Column.]
[Illustration: Fig. 182.--Form for Corner Wall Column.]
The form shown by Fig. 181 was used for molding T-section wall columns
for a power station. It is noteworthy for its section; because of the
provision for molding grooves in the two sides to which the curtain
walls join, and because of the manner in which three of the eight sides
were built up as the concreting progressed. The sides a b c, d e and
f g h were erected in full column units and the sides c d, e f and
h a were erected in sections 2 ft. high as concreting progressed. The
yokes were spaced 2 ft. apart. Using 1¼-in. stuff for yokes and lagging
this form as built required about 16 ft. B. M. per foot length of
column. Except for the beveling of the mold for the curtain wall
recesses, the framing is all plain saw and hammer work.
[Illustration: Fig. 183.--Core Form for Hollow Column.]
A corner wall column form is shown by Fig. 182 and as this was an
example of hollow column work the section of the concrete within the
form is shown. Forms of this shape and of T-section are properly classed
as special form work so that the examples given here are helpful merely
as indicating general methods that may be followed. This particular form
required 15¾ ft-B. M. of 7/8-in. lagging per foot of column length, and,
neglecting the special top frame, about 16 ft. B. M. of "staging" per
foot to support the lagging. The core forms for molding the hollow
spaces in the columns of this particular building are shown in Fig. 183.
The cross pieces or keys carried on the 5/8-in. bolts as pivots are
revolved a quarter turn to slip clear of the slots and permit the sides
to close together and free the core for withdrawal. In many cases the
contractor will find it preferable to use thin sheet metal core molds or
light wooden cores and leave them in place. In one case known to the
authors where hollow wall columns were used as hot air ducts for a
heating system the duct was laid up of one row of bricks, encircled by
the column form and the annular space concreted around the brick duct as
a core. The rare use of irregular columns makes form and core
construction for them a special problem requiring special detailed
estimates in each case. The channel section wall column form shown by
Fig. 230 is a case in point; here the form became practically a portable
mold for duplicating columns as many times as was desired.
[Illustration: Fig. 184.--Form for Large Rectangular Columns.]
As an example of form work for very large columns or pillars that shown
by Fig. 184 is particularly good; it was used for constructing eight
3-ft. square pillars for a water tank tower. The lagging consists of
four panels made by nailing horizontal boards to vertical studs. The
panels are clamped together by rectangular yokes spaced 3 ft. apart.
There are nearly 27½ ft. B. M. of lumber per foot length of 3-ft. column
in this form.
[Illustration: Fig. 185.--Adjustable Form for Rectangular Columns.]
The form shown by Fig. 185 was used by Mr. R. W. Maxton in constructing
a large factory building at St. Louis, Mo., and is notable for the means
adopted for centering the forms and for reducing their lateral
dimensions to fit them for molding the decreasingly smaller columns of
the upper floors. To center the forms the short angles A A are molded
into the concrete so as to project slightly above the tops of the floor
slab. Also the pieces of wood C are molded into the floor slab. The
form is set over the angles and lined up truly by nailing the blocks B
to the blocks C. It will be noticed also that the column mold bears
only at the four corners the lagging being cut away somewhat on each
side so as to afford an opening for cleaning. The lagging for the sides
of the column mold is battened together to form four units or panels
which are held together by iron clamps of the form shown. Lag screws
are used everywhere in place of nails. The notable feature, however, is
the piecing out of the lagging panels with 1-in. strips, one or more of
which can be ripped off on each side to reduce the size of the forms as
the columns grow smaller toward the top of the building.
~Polygonal Columns.~--Forms for polygonal columns require more lumber and
more carpenter work and are less susceptible of ready arrangement into
units than forms for rectangular columns. There is no approach to a
uniform practice in their construction and the few forms shown here are
merely specific examples.
[Illustration: Fig. 186.--Form for Octagonal Column for a Factory
Building.]
The form shown by Fig. 186 was used for interior columns of octagonal
section with hooped reinforcement for a factory building. This form for
a 12-ft. octagonal column 24 ins. across between sides requires
approximately 325 ft. B. M. of lumber. The form shown by Fig. 187 was
used by the same engineer in another building; it is, as will be noted,
in four units coming apart in joints at diagonally opposite corners.
This form for an octagonal column 18 in. across between sides required
about 13 ft. B. M. of lumber per foot of column length, with yokes
spaced 3½ ft. apart.
The form shown by Fig. 188 was used in a large warehouse at Chicago,
Ill. It will be noted from the dotted lines that one yoke clamps the
sides a a, the next the sides b b and so on. This does away with
triangular blocking to hold the corner boards that is used in the form
shown by Fig. 187. Six pairs of yokes were used for each column so that
the yoke spacing was about 2 ft. With 2×6-in. yokes and 1½-in lagging a
form for a column 18 ins. between sides would require some 17 ft. B. M.
per foot of column length.
[Illustration: Fig. 187.--Form for Octagonal Column for Factory
Building.]
[Illustration: Fig. 188.--Form for Octagonal Column for a Warehouse,
Chicago, Ill.]
~Circular Columns.~--Circular columns have been most frequently molded in
steel forms, and these are by all odds the best for general work. Made
in two parts of sheet steel and in sections that are set end to end one
on another a form is obtained which is easy to erect, remove and
transport. Wood forms for circular columns are rather clumsy affairs and
are expensive to construct. Such a form, Fig. 190, is described in the
succeeding section; another is shown by Fig. 189. This form was used
successfully for filling and encasing steel columns for a fireproof
building in Chicago, Ill., and is a favorite circular form construction
in Europe. It is apparent that the hooping needs to be very heavy and
that the form is one that will be hard to handle and rather expensive to
make.
In several instances, where hooped reinforcement has been used, the
hooping has been wrapped with, or made of, expanded metal or other
mesh-+work, and the concrete deposited inside the cylinder thus formed,
without other form work. A six-story factory building in Brooklyn, N.
Y., was built with circular interior columns from 28 ins. to 12 ins. in
diameter, reinforced by a cylinder of No. 10 3-in. mesh expanded metal,
stiffened lengthwise by four round rods 1 in. in diameter for larger
columns to ½ in. in diameter for smaller columns. This reinforcement was
set in place and wrapped with No. 24 ½-in. mesh metal lath, and the
cylinder was filled with concrete and plastered outside. A moderately
dry concrete is essential for such construction.
[Illustration: Fig. 189.--Form for Circular Column.]
The method of molding shells with the hooping embedded described for the
Bush terminal factory work in another section is another way of avoiding
form work of the usual type.
Light steel forms as well as the special construction noted must be
supplemented by staging to hold them in line and to carry the ends of
the girder forms that are ordinarily carried by the column forms. Four
uprights arranged around the column so as to come under the connecting
girders are commonly used; they are set close enough to the column to
hold the form plumb by means of blocks or wedges.
~Ornamental Columns.~--Forms for ornamental columns call for special
design and construction. For many purposes, such as porch and portico
work, the best plan is to mold the columns separately and erect them as
stone columns of like character are erected. Metal forms of various
patterns are made by firms manufacturing concrete block molds and can be
purchased from stock or made to order. Where the column is to be molded
in place form construction becomes a matter of pattern making, the
complexity and cost of which depends entirely upon the architectural
form and ornament to be reproduced. The molding of ornament and
architectural forms in concrete is discussed in Chapter XXIII, and the
two examples of ornamental column form work given here from recent work
indicate the task before the builder.
[Illustration: Fig. 190.--Form for Molding Fluted Cylindrical Column.]
The form shown by Fig. 190 was used for molding in place fluted columns
used in a court house constructed at Mineola, N. Y. The lagging in the
form of staves forms a 24-sided polygon and is held in position by hoops
and yokes. The molds for the flutes were formed by inserting screws from
the outside so as to penetrate the staves and molding half-round ribs of
plaster of Paris over them by means of the simple device shown. To
dismantle the form the screws were removed and the lagging taken down
leaving the plaster of Paris in place as a protection to the thin edges
until the final finishing of the building.
The methods illustrated by Fig. 191 were employed in molding columns in
place for a church at Oak Park, Ill. The bottom portions of these
columns were plain square sections molded in place in square molds. The
top portions were heavily paneled. The four corner segments were cast in
glue molds backed by wood with wires embedded as shown. After becoming
hard they were set on end on the plain column and tied and braced as
shown. The side openings were then closed by wooden forms and the
interior space was filled with concrete. The surface facing for these
columns was bird's-eye gravel and cement, with very little sand, mixed
very dry and placed and tamped with the coarse concrete backing.
[Illustration: Fig. 191.--Form for Ornamental Column for Church at Oak
Park, Ill.]
~SLAB AND GIRDER FORMS.~--Slab and girder construction for roofs and
floors is of three kinds: (1) Concrete slab and steel beam construction
in place; (2) concrete slab and girder construction in place (3)
separately molded slab and beam construction. The third method of
construction is distinct from the others in respect to form work as well
as other details and is considered separately in Chapter XX.
~Slab and I-Beam Floors.~--Centers for floor slabs between steel I-beams
are made by suspending joists from the beam flanges and covering them
with lagging. Frequently the joists and lagging are framed together into
panels of convenient size for carrying and erecting. The construction is
a simple one in either case where slabs without haunches or plain arches
form the filling between beams. Figure 192 shows an arch slab center;
plain hook bolts, with a nut on the lower end, passing through holes in
the joists are more commonly employed. For 1-in. lagging the joist
spacing is 2 ft., for 1½-in lagging, 4 ft., and for 2-in. lagging, 5 ft.
[Illustration: Fig. 192.--Form for Arch Slab Between I-Beams.]
[Illustration: Fig. 193.--Form for Flat Slab Floor Between I-Beams.]
A more complex centering is required where the slab has to be haunched
around the I-beams. The center shown by Fig. 193 was designed by Mr. W.
A. Etherton for the floor construction of the U. S. Postoffice Building
erected at Huntington, W. Va., in 1905. The center consists essentially
of the pieces A (2×4 ins. for spans not exceeding 6 ft.) and the
2×3-in. triggers B, which rest on the lower flanges of the floor beams
and thus support the forms. The trigger is secured at one end to the
piece A by a 1×3-in. cleat C and at the other end by 1×3-in. cleats
D on either side of A, which serve also as supports for the batter
boards E. The six-penny nail F is but partly driven and it is to be
drawn before removing the forms. When the supports of the beams are not
fireproofed the cleats D extend to the bottom of the trigger B, but
otherwise one cleat extends lower to secure the cross-strip G. To
remove the forms, draw the partly driven nail F; knock off the strip
G or loosen it enough to draw the nails in B>; pull the triggers on
one beam, and the forms will drop. If the soffit board H is used it is
necessary first to remove the strip G. For larger beams use the
spacing blocks H as shown; for smaller beams omit the trigger B and
extend A to rest on the flange of the beam, then to remove the form
A must be cut preferably near the beam.
No complete records of the cost of these forms were obtained, but the
following partial information is furnished by Mr. Etherton: Considering
a panel 6 ft. span by 19 ft. long on 15-in. I-beams, the lumber
consisting of 1-in. boards supported by 2×4-in. cross-pieces on 2×3-in.
triggers spread 3 ft. on centers, soffit of beams not fireproofed, it
required one carpenter five hours at 30 cts. per hour to complete the
panel. Figuring from this alone I should say that 10 cts. per sq. yd. is
a fair estimate for carpenter work. In working over the forms for
another floor the 1-in. boards require more time to handle and I should
say that the saving in cost of work over the first floor would be not
over 2 cts. per sq. yd. Two laborers moved their scaffolding and took
down the forms from three completed panels of 13 sq. yds. each in one
hour. Smaller panels require a longer time per yard. Counting for the
proper piling of lumber I should allow one hour for one man to take down
the forms for a 13-sq. yd. panel when conditions are the best. We
contracted with two laborers to remove the forms from the third floor
and roof and pile them in good shape on the ground just outside of the
building for an amount averaging about 4½ cts. per sq. yd., and the men
made but small wages on the contract. The lumber was used on three
floors and the roof, and the best of the 1-in. boards and all of the
2×4-in. and 2×3-in. stuff were used on a second job. For a safe estimate
based on the data secured I should figure the cost of labor and
materials for a three or four-story building about as follows:
Per sq. yd.
Lumber at $20 per thousand 28 cts.
Carpenter work at 30 cts. per hour 10 cts.
Labor tearing down at 15 cts. per hour 4 cts.
-------
Total per square yard 42 cts.
Figure 194 shows an arrangement of centering between steel beams which
is novel in that it provides for molding a slab with girders. The form
was used in building the roof of a locomotive roundhouse. This
roundhouse was of the usual circular form and had a radial width of 80
ft. Each radial roof girder, which was an 18-in. I-beam was carried by
an outside wall pier and three I-beam columns encased in concrete. The
space between main roof girders was spanned by reinforced concrete
girders and roof slab. The center illustrated was employed for molding
the concrete girders and slab, and carries out the idea of making a
stiff and light center for considerable spans of slab without support by
staging. The truss construction of the frames supporting the girder box
will be noted.
[Illustration: Fig. 194.--Form for Slab and Girder Floor Between
I-Beams]
~Concrete Slab and Girder Floors.~--The construction of forms for this
type of floor should be such that the slab centers and the sides of the
girder molds can be removed without disturbing the bottoms of the girder
molds. This permits the beams to be supported as long as desirable and
at the same time releases the greater part of the form work for use
again. It is of advantage also to lay bare the concrete as soon as
possible to the hardening action of the free air. The slabs may be
similarly supported by uprights wedged up against plank caps; no very
great amount of lumber is required for this staging and it gives a
large assurance of safety. It is well also to give the girder molds a
camber or to crown them to allow for settling of the falsework.
The form shown by Fig. 195 was used in constructing girders from 14 to
23 ft. long in a factory building at Cincinnati, O. The sides are
separate from the bottom, being supported at the ends by cleats on the
column form and at intermediate points by struts under the yokes. The
floor lagging is carried by 2×4-in. stringers supported by the yokes.
Uprights set under the bottom plank keep the girder supported after the
sides and slab centers are removed. It will be noted that the form is
given a camber of 1-in. The structural details are evident from the
drawing. The form shows a method of molding a bracket for wind bracing;
a simple modification fits it for molding girders without brackets. A
rough computation gives 10 ft. B. M. of lumber per lineal foot of girder
form as shown.
[Illustration: Fig. 195.--Girder and Slab Form for Factory Building,
Cincinnati, O.]
[Illustration: Fig. 196.--Girder and Beam Forms for Factory Building,
Beverly, Mass.]
The form construction shown in Fig. 196 was employed in building the
slab and girder floors for the United Shoe Machinery Co.'s factory at
Beverly, Mass. In these buildings the main girders cross the building at
20-ft. intervals and midway between the main girders is a bridging beam
also reaching across the building. Floor beams span the 10-ft. spaces
between bridging beams and main girders at intervals of 3 and 4 ft.
Referring first to the main girder form, tall horses are set up at 3-ft.
intervals and connected by stringers laid on the caps. These stringers
carry a cross piece, with a cleat at each end, over each horse. The
bottom boards of the mold rest on these cross pieces and the side pieces
are set up between verticals wedged tight between the cleats. The beam
molds are a modification of the girder molds. The slab centers consist
of panels just large enough to span the openings between beams and
girders and composed of 1-in. boards fastened together by four 1×5-in.
cleats. Except in attaching the quarter round and triangular moldings
for fillets no nailing is necessary in erecting and taking down the
forms.
[Illustration: Fig. 197.--Girder and Slab Form for Concrete Building
Work.]
The form construction shown by Fig. 197 is one used by a large firm of
reinformed concrete builders. The slab centers can be struck and the
sides of the girder mold removed without disturbing the support for the
bottom of the beam. This form runs quite low in lumber, requiring for a
9×12-in. beam box including posts some 9 ft. B. M. per lineal foot of
box. The joists and lagging as shown require about 2 ft. B. M. per
square foot of floor slab. The practice is to give these girder boxes a
camber of ½-in. in 10 ft.
The construction shown by Fig. 198 is designed to provide adjustability,
to enable quick erection and removal and to do away with all nailing.
The construction is as follows: Wooden posts carry at their tops steel
T-beam cross-arms knee braced to the posts by steel straps. The
cross-arms carry the two jaws of a clamp, each consisting of a vertical
plate, and two diagonal braces, slotted so as to slide on the T-beam. A
cut nail or other piece of metal driven into the slots fastens the jaws
on the T-beam. The cross-arms carry the bottom boards of the girder
molds and the vertical plates of the jaws support the side pieces. A
blocking piece slipped between the braces carries the end of the joist
for the floor slab centers. This form is the invention of Mr. W. H.
Dillon and was used in constructing the nine-story, 260×150-ft.
wholesale hardware store Of Farwell, Osman & Kirk Co., St. Paul, Minn.
[Illustration: Fig. 198.--Girder and Slab Form for Warehouse at St.
Paul, Minn.]
[Illustration: Fig. 199.--Girder and Slab Form for Factory Building, New
York, N. Y.]
The form shown by Fig. 199 was used in constructing a factory building
in Long Island City, N. Y., and it is given here chiefly for the purpose
of exhibiting the unnecessary complexity of form work. Comparing this
form with that of nearly any of the preceding designs will bring out
the point. The design, however, was one of the earlier ones to recognize
the advantage of stripping the slab centers and the sides of the girder
boxes without disturbing the bottom plank of the boxes or the staging.
The drawing shows the independent support of the bottom board and side
pieces of the girder mold on the transverse caps of the staging posts.
These posts are 6×8 ins. in section and are spaced from 6 to 8 ft.
apart. Briefly described the bottom board is a single plank from 1 to 3
ins. thick, to which the side pieces are lag-screwed at the bottom. The
side pieces are panels composed of 4×7/8-in. vertical boards nailed to
top and bottom 2×4-in. horizontal timbers. A third horizontal timber
near the top serves as a seat for the ends of the joists carrying the
slab lagging and is braced from the bottom horizontal by vertical
stiffeners. The edge boards of the slab lagging are nailed to the top
edges of the side pieces of the girder mold and the tops of these side
pieces are connected across the trough by strips of board; all the slab
lagging boards except those at the edges of the girder molds are laid
loose. In the building referred to, after the floor concrete had set
about seven days the joists carrying the slab lagging were turned a
quarter over thus dropping the slab form about 2 ins. A few days later
the joists and lagging were taken down and the side pieces of the girder
mold were unscrewed and removed. The bottom board and staging posts were
left in position about three weeks longer and then dropped about 1 in.
by removing fillers from the staging post caps. In another week the
bottom boards and staging posts were taken down. This construction of
form and method of removing it permitted the concrete to be stripped so
that the air could get at it as fast as it was safe to take the support
from any part and at the same time kept the supports in such position
that they form a safety platform in case of collapse. A more important
advantage is that the form timber can be removed as fast as any part of
it is free and used again. Thus the lagging boards and joists and the
side pieces for the girder molds were free for use again about every two
weeks and yet the main supports of the girders were undisturbed until
they were fully a month old.
Other examples of girder and slab forms are shown in the succeeding
sections describing the construction of a six-story building and of a
garage constructed at Philadelphia, Pa.
[Illustration: Fig. 200.--Collapsible Core Forms for Girder and Slab
Floors.]
Another type of slab and girder form construction that deserves brief
mention because of its variation from usual practice and also because of
its extensive use by one prominent builder is shown by Fig. 200. Cores,
or inverted boxes, with four vertical sides and rounded corners, are set
side by side, with ends on stringers carried by the column forms, at
intervals wide enough to enable the beam to be molded between. A plank
resting on cleats on the sides of the cores forms the bottom of the beam
mold. The main girders are molded in similar spaces between the ends of
the cores in one panel and of those in the next panel. To permit the
core to be loosened readily it is hinged; when in place spacers inside
the core keep the sides from closing. These are knocked out, the core
sides close together and the core is removed for use in another place.
Cores similar to these were used in molding the ribbed floor for the
Bush terminal factory building described in a succeeding section. These
cores are capable of repeated use so that while they are somewhat
expensive to frame they give a very low cost of form work when the beam
and girder spacing is arranged largely in duplicate from floor to floor.
It will ordinarily be cheaper to have these cores made to pattern by
regular woodworking shops, and shipped to the building ready to erect.
~WALL FORMS.~--Wall work in modern commercial and manufacturing buildings,
when we come to eliminate windows and wall columns and girders, is
confined very largely to isolated curtain wall panels between windows
and framework. In such buildings, therefore, wall forms consist merely
of wooden panels, one for each face of the wall, constructed to fit the
spaces to be walled up. Where these spaces are duplicated from bay to
bay or story to story the same form panels will serve repeatedly. For
residences and other buildings having greater proportionate area of
blank wall the builder has a choice between continuous forms carried by
staging and movable panel forms.
[Illustration: Fig. 201.--Continuous Form for Wall Construction.]
For one and two-story buildings, with the usual variation in
architectural detail, panel work and window work, the continuous form
has many advantages, and the superior economy of movable panels in
retaining and other plain wall work is by no means always true here. One
good type of continuous wall form construction is shown by Fig. 201. The
gallows frames are spaced about 6 ft. apart along the wall and connected
by horizontal stringers nailed to the uprights or by diagonal bracing.
Each frame may be made up of 6×6-in. posts connected by 2×4-in.
cross-struts and diagonals with bolted connections so that the frame can
be taken down and put together easily and so that the bracing can be
removed as the wall is built upward. The other details of the form work
are shown by the drawing. This construction leaves a clear space for
placing the concrete and the cross pieces give support to runways; it
has been successfully used in a large amount of low building work.
[Illustration: Fig. 202.--Sectional Form for Wall Construction.]
Movable panel forms are of great variety in detail but are generally of
either one or the other types shown by Figs. 202 to 204.
The form shown by Fig. 202 was used in constructing a church at Oak
Park, Ill. For the back of the wall it consists of continuous lagging
held by 2×4 studs. For the face 1×6-in. lagging 12 ft. long was nailed
to 2×4-in. studs to form panels. It will be noted that the ends of the
studs are scarfed so as to interlock in succeeding panels. This
construction also shows a method of supporting the reinforcing bars
inside the form.
The form shown by Fig. 203 was used in constructing a large factory
building, and consisted of two side pieces or panels 3 ft. high and 16
ft. long, the distance between wall columns. For the first course these
were seated on the carefully leveled and rammed ground and securely
braced by inclined or horizontal struts inside and outside of the
building. After the concrete had set for three days the molds were
loosened and lifted until the lower edges were 2 ins. below the top of
the concrete and there they were held by horizontal bolts through their
lower edges and across the top of the concrete by ties nailed across
their tops every 3 ft. and by bracing to the falseworks supporting the
column and floor forms. The cross bolts passed through pasteboard
sleeves which were left permanently embedded in the wall. By starting
the molds level and finishing each course level with their tops no
difficulty was had in keeping the forms plumb and to level as they were
moved upward. This type of form has to be exteriorly braced to staging
or adjacent column forms, etc.
[Illustration: Fig. 203.--Sectional Form for Wall Construction.]
The type of movable panel form shown by Fig. 204 depends for all support
on the wall alone. The sketch shows the form filled ready to be shifted
upward; this operation consists in removing the bottom bolts and
loosening the top bolts enough to permit the studs to be slid upward the
full length of the slots. The lagging boards left free are then removed
and placed on top and the bolts are tightened, completing the form for
another section of wall.
[Illustration: Fig. 204.--Movable Panel Form for Wall Construction.]
[Illustration: Fig. 205.--Sullivan's Plank Holders for Wall Forms.]
A type of wall form construction intended to do away with studding and
bracing is illustrated by Figs. 205 and 206. In both cases metal plank
holders are used in place of studs, and practically the only difference
between the two is in the shape and material of the holders. The mode of
procedure is to work in horizontal courses one plank high around the
wall, removing the bottom plank and placing it on top as each new course
is begun after the first few courses have been laid. Using the
arrangement shown by Fig. 205 in constructing a building 100×54 ft. in
plan and 36 ft. high with 12-in. walls, a height of two 12×2-in planks
was all the form work that was ever necessary at any one time, so that
the amount of form lumber required for the building was 2,464 ft. B. M.
plus 205 ft. B. M. of 2×4-in. flooring strip, or altogether 2,669 ft. B.
M., or 0.24 ft. B. M. per square foot of exterior wall surface, or 6½
ft. B. M. per cubic yard of concrete. This same form lumber with 16
additional plank was then used to construct a building 100×100 ft.×16
ft. high, so that some 3,000 ft. of form lumber sufficed for 17,548 sq.
ft. (exterior surface) of wall or for 617 cu. yds. of concrete in 12-in.
wall, which gives 0.17 ft. B. M. per square foot or 4.8 ft. B. M. per
cubic yard of concrete.
[Illustration: Fig. 206.--Farrell's Plank Holders for Wall Forms.]
~ERECTING FORMS.~--The organization of the erecting gang will depend very
largely on the manner in which the forms have been constructed. If they
have been constructed in sections which go together with wedges and
clamps common laborers with a foreman carpenter in charge to direct and
to line and level the work will do the erecting, but if they have to be
largely built in place carpenters are necessary for all the work except
carrying and handing. There should be at least one foreman for every 15
to 20 men and a head foreman in charge of all form work. The mode of
procedure will differ for every job, but the following general
directions apply to all work in greater or less measure.
Clamps, bolts and wedges and not nails should be used wherever possible
in assembling parts of forms in erection; these devices are not only
quickly and easily applied in erection but they are just as quickly and
easily loosened in taking down forms and they can be loosened without
jarring the concrete member.
Lining girder forms and lining and plumbing column and wall forms is
high-class carpenter work and should be directed by competent
carpenters. A column or girder which is out of line or plumb not only
looks bad but may be required to be removed and corrected by the
engineer. The expense for one such correction will be many times that
which would have been involved by proper care in the first place.
Supports or staging for the forms should be used freely and well braced
in both directions. Uprights should be set on wedges and bear against a
cap piece and on a sill piece to distribute the load.
Erect, line and plumb the column forms first; then erect, line and level
the girder forms and set the girder staging, and finally erect and level
the slab centers and their supports.
Leave the foot of each column form open on one side at the bottom so
that the column reinforcement can be adjusted and connected up and so
that a clear view can be had through the form to detect any object that
may have fallen into the form and become wedged; this same opening makes
it possible to clean the form.
Give the forms a final inspection before concreting to check line and
level, to close open joints and to tighten up clamps and wedges. Finally
clean each form and wet it down thoroughly before placing the
concrete--do this just before placing the concrete.
~REMOVING FORMS.~--Good judgment and extreme care are essential in
removing centers. It goes without saying that forms should never be
removed until the concrete has set and hardened to such strength that it
will sustain its own dead weight and such live load as may come upon it
during construction. The determination of this condition is the matter
that calls for knowledge and judgment. Some cements set and harden more
rapidly than others, and concrete hardens more and more slowly as the
temperature falls. These and other circumstances must all be taken into
account in deciding upon the safe time for removal. Many large
contractors mold a cube of concrete for each day's work and leave it
standing on the finished floor exposed to the same conditions as the
concrete in the forms; examination of this sample block gives a line on
the condition of the concrete in the work and on the probable safety of
removing the forms at any time. In all cases it should be the
superintendent's duty to determine when to remove forms, and he should
satisfy himself by personal inspection that the concrete is in condition
to stand without support. It is also wise at least as a matter of
precaution for the contractor to secure the engineer's or the
architect's approval before removing any formwork.
Care in removing forms is essential for the reason that green concrete
is particularly susceptible to injury from shock or sudden strain. It is
well, therefore, to have a separate gang always doing the work. These
men will in a few days become trained under an experienced foreman so
that they will not only do the work with greater safety but also more
rapidly. This gang should, furthermore, be required to follow a regular
system in its work; a system which may not be departed from without
direct orders from the superintendent. An example of such a system is
outlined below.
The time of beginning this work of removal shall be given by the
superintendent. In warm, dry weather, with other conditions favorable,
removal may be begun after seven days. Then the following schedule may
be followed: At the end of seven days remove the sides of the column
forms. This gives an opportunity to determine the soundness of the
column casting and also serves the further desirable purpose of baring
the concrete to the curing and hardening action of the air. At the end
of 14 days loosen the wedges of the posts supporting the slab centers
and drop these centers a couple of inches: leave the centers in this
position for another day, meanwhile examining the tops of the slabs to
note their condition. Then remove the sides of the beam molds and the
slab centers, replacing the latter with temporary uprights supporting a
plank bearing against the underside of the slab. This precaution is
often neglected and with very little reason considering the importance
of the safeguard thus secured. Ordinarily the shores need not be left in
place more than a week, so that the amount of lumber thus tied up is
small. At the end of three weeks remove the uprights under the beam and
girder molds and strip the bottom plank. In this schedule it is assumed
that the floor is free from any great load and that no unusual loading
is put upon it; if a load of any consequence is to come on the floor the
shores and uprights should be left in place longer. No schedule of
removal can be blindly followed, and that given above is certain only
when the conditions are right and as stated.
FABRICATION AND PLACING OF REINFORCEMENT.
The amount of reinforcing steel used varies from 50 lbs. to 275 lbs. per
cu. yd. of concrete; the highest figure will be had only in very heavy
work and where very heavily reinforced raft foundations are employed,
and the lowest only in one-story buildings consisting of walls and roof.
A fair average is perhaps 150 lbs. per cu. yd. The cost of fabricating
and placing reinforcement will run from 1/3 ct. to 1½ cts. per pound,
but the last figure is exceedingly high; ¾ ct. per pound for fabricating
and placing is a reasonable labor charge.
Contractors frequently have their choice whether the steel shall be
fabricated into frames and placed as units or whether it shall be placed
in separate bars. For girders and columns the difference in cost of the
two methods is not so very great for steel in place when the fabrication
is done in the field. The unit frames cost considerably more than
separate bars to fabricate, but the cost of handling and placing them in
the forms is materially less; on an average the differences balance each
other. Where the frames are made up in regular mills unit frames
generally cost less to fabricate and place than do separate bars. The
use of unit frames in wall and floor slab reinforcement is generally
more expensive than the use of separate bars. The chief gain that comes
from the use of unit frames is the gain due to the certainty that the
reinforcing bars, stirrups, etc., are all there and are properly spaced
and placed.
~FABRICATION.~--Fabrication includes all the work necessary to prepare the
reinforcement ready to place in the forms. It amounts to very little
where separate bar types of reinforcement are used. Plain bending and
shearing operations comprise the whole task. Where the beam or column
reinforcement has to be made up into complete frames which can be
handled and placed as units this task is more complex and considerable
apparatus is essential to rapid and economical work. For this reason it
is wise usually to contract with some metal working shop to assemble and
connect up the various units and to furnish them ready for installation.
In many cases these unit frame types of reinforcement are patented and
the proprietors contract to fabricate and furnish them complete
according to the plans of the engineer or architect. Even where the
frame construction is not so controlled it will be economy generally to
have the fabrication done at regular shops where the necessary tools and
skilled workmen are had. In any case the bars should be ordered cut to
length at the mill so far as possible.
[Illustration: Fig. 207.--Rack for Storing Reinforcing Bars.]
Assuming the fabrication to be done in the field, the mode of procedure
will be as follows: Order the bars or rods to be shipped in bundles of
corresponding sizes and lengths of pieces with each bundle tagged with
its proper shop number or mark. The bundles should weigh about 200 lbs.;
this is a load easily handled by two men and so long as possible all
handling should be done in the original package, for when once broken it
is very hard to get men to carry a full load. As received, the bars of
each size and length should be stored by themselves. For ordinary bars
not having long prongs a rack of the general form shown by Fig. 207
serves the purpose excellently. When a great deal of metal must be kept
stored for some time it is wise to roof over the racks, not only to
protect the metal from rain and snow, but to enable the men to work dry
shod in stormy weather. Usually it will pay to have one man whose sole
duty it is to receive and check all metal and to attend to its
systematic arrangement on the racks; this same man will also direct the
removal of the metal to the shop where it is bent and otherwise worked
up, and can, if he is competent, earn his pay many times over in time
saved all along the line in handling and working up the reinforcement.
The authors have seen enough time wasted in hauling over and rehandling
metal in piles to get at what was wanted to pay for shed, racks and the
wages of a storekeeper several times during a moderate sized job. In
large work provide the storekeeper with a schedule showing the order in
which the metal is wanted for the work so that he can arrange it in that
order and can check up his receipts from the mills and report missing
items in time for the deficit to be made up before some part of the work
has to be stopped because of material missing. System in receiving and
storing the metal is absolutely essential to rapid and accurate work at
the bending and erecting tables.
The work done on the metal consists chiefly of bending. The metal can
usually be bent cold, but for sizes 1½-in. and upward some makes of bars
require heating; this can be done by laying the bars side by side on the
ground and arranging sticks and shavings on top of them in a strip 18
ins. to 2 ft. wide across the portion where the bend is to be. Only
moderate heating is usually required. Ordinary bending is a simple
process and can be done with very simple apparatus. Figures 208, 209 and
210 show frequently used devices, any of which can be made by an
ordinary carpenter. For heavy bars, 1½ and 2 ins., the device shown by
Fig. 210, with its heavy, swinging beam, is particularly efficient. An
example of more elaborate methods is had in the following description of
the processes employed in fabricating girder frames and hooped column
reinforcement for a large factory building. The building was 500×75 ft.,
with six stories and a basement, built for the Bush Terminal Co.,
Brooklyn, N. Y., in 1905. Three longitudinal rows of round columns and
two rows of rectangular wall columns carry heavy longitudinal girders
supporting floor slabs with corrugated undersides as shown by Fig. 211,
which also shows the floor slab reinforcement. About 12,000 cu. yds. of
concrete and 1,000 tons of reinforcing steel were required; hence 167
lbs. of steel were required for each cubic yard of concrete. The floors,
however, were designed to carry a load of 800 lbs. per sq. ft. The
particular feature of interest in this building was the fabrication of
all the column and girder reinforcement into unit frames and cylinders
in temporary workshops on the site.
[Illustration: Fig. 208.--Table for Bending Reinforcing Bars.]
[Illustration: Fig. 209.--Table for Bending Reinforcing Bars.]
[Illustration: Fig. 210.--Table for Bending Reinforcing Bars.]
[Illustration: Fig. 211.--Column and Floor Slab Construction for Factory
Building.]
The circular interior columns, varying from 30 ins. to 12 ins., in
diameter were molded in permanent shells of cinder concrete. The shells
were made in sections about 30 ins. long, with walls 1½ ins. thick,
which were set one on another with mortar joints to form the column
mold. In fabricating the shells the first step was to wind a helix of
steel wire on a collapsible mandrel about 4 ft. long; the mandrel was
set with the axis horizontal and was revolved by hand, the wire being
fed on also by hand and under a slight tension. After the wire helix was
completed it was wrapped with a sheet of expanded metal, the
longitudinal edges of which lapped a few inches and were tied by wire
ties. The expanded metal covering was also wire tied to the helix. Each
of these cylinders of expanded metal and wire was 30 ins. long and
formed the inner mold for making the shell. The outer mold consisted of
a sheet metal cylinder in two parts assembled and supported by wooden
yokes and framework. The two molds were assembled on a plank platform,
one inside the other, and about a common center. The annular space was
then filled with a 1-5 cinder concrete mixed moderately dry so that
while it would exude slightly through the expanded metal mesh it would
not waste to any extent. After from 18 to 24 hours the outer mold was
removed for reuse and the shell was left standing on the molding
platform until safe to handle. The larger shells, 30×30×1½ ins., weighed
about 150 lbs. each.
[Illustration: Fig. 212.--Device for Bending Reinforcing Rods.]
Some 2,000,000 lbs. of plain round steel rods from ¼ in. to 1½ ins. in
diameter were required for reinforcing the concrete. For the main
girders these rods were cut, bent and assembled into frames or trusses
which were placed as units. The main rods were ordered cut to length,
but the stirrup rods were ordered in lengths of 20 ft. and cut to
lengths as required. The rods were brought to the work in carload lots
and were stored according to lengths and sizes in racks under sheds.
Another shed was provided for the steelworkers, who cut and bent the
rods and assembled the girder frames ready for the workmen on the
building. There were about 50 different patterns of frames required.
They were made entirely by hand. For bending large size rods, heavy
compound levers were used; the lighter rods were bent by the device
shown in Fig. 212. The assembling of the trusses was accomplished as
shown by Fig. 213, using the steel framework of the erection shed as a
staging. Across the horizontals of the framework were placed two false
temporary top chord bars marked to the stirrup spacing of the truss
being assembled. On these bars, at the spaces marked, were suspended
stirrups with their lower ends hooked. The lower chord bars were then
suspended in the stirrup hooks and the whole assemblage of bars and
stirrups was then clamped rigid by the lever bars and intermediate
clamps. The loop ends of the stirrups were then bent by special wrenches
to the position shown at _2_, then closed by hammering to the position
shown at _3_, and finally they were wire tied. The process was a simple
one, and by adopting a regular routine the men became so expert that two
of them could complete many trusses in a working day. The contract price
for shaping the steel and assembling it into frames was 1 ct. per lb.;
the cost of the work to the contractor has been stated by Mr. E. P.
Goodrich, Engineer, Bush Terminal Co., to have been about ¾ ct. per lb.
The cost of placing the steel in the building was ¼ ct. per lb.
[Illustration: Fig. 213.--Sketches Showing Methods of Fabricating Girder
Reinforcing Frames.]
~PLACING.~--With unit frame reinforcement the number, size and location of
the bars have been made certain in the shops where the frames are
fabricated so that the erector has nothing to do but to line and level
up the frames in the forms, place such temporary braces as are needed to
hold them true, and make the end connections with abutting frames. Such
frames are usually provided with "chairs" to hold the bottom bars up
from the form so that little bracing or none is required. With separate
bar reinforcement the erector may either place the reinforcement
complete in the form by wire-tying the bars to each other, to temporary
braces or templates and to the forms, or he may insert the various
pieces of reinforcement in the concrete as the pouring advances,
depending on the surrounding concrete to retain them where inserted.
Generally a combination of both methods is employed.
The processes in detail of placing reinforcement are particularized in
several places in other sections; they will differ for nearly every job.
Here, therefore, general rules only will be given.
(1) See that the correct number and size of reinforcing bars, splices
and stirrups are used and that they are spaced and placed strictly
according to the working plans.
(2) Bars must be properly braced, supported and otherwise held in
position so that the pouring of the concrete will not displace them.
(3) Splices are the critical parts of column reinforcement. See that the
bars butt squarely at the ends and are held by pipe sleeves or wired
splice bars; see that the longitudinal rods are straight and vertical;
see that the horizontal ties or hooping are tight and accurately spaced.
When the reinforcement is built up inside the form one side is left open
for the work; ordinarily the column reinforcement will be fabricated
into unit frames, then an opening in the form at the bottom to permit
splicing will suffice.
(4) Take extreme care that beam and girder reinforcement is placed so
that the bottom bars lie well above the bottom board of the mold; use
metal or concrete block chairs for this purpose.
(5) See that the end connections and bearings of beam and girder frames
are connected up and have the bearings called for by the plans.
(6) See that line and level of all bars and of the reinforcement as a
whole are accurate; make particularly certain that expanded metal or
other mesh-work reinforcement lies smooth and straight.
(7) Give all reinforcement a final inspection just previous to pouring
the concrete; this is particularly essential where the reinforcement is
placed some time in advance of the concreting.
MIXING, TRANSPORTING AND PLACING CONCRETE.
A reinforced concrete building requires from 0.2 to 0.5 cu. yd. of
concrete per 100 ft. of cubical volume of the building, assuming walls,
floors and roof to be all of concrete. The amount of concrete to be
mixed, transported and placed is, therefore, large enough, even for a
building of moderate dimensions, to warrant close study of and careful
planning for this portion of the work. A few general principles can be
set down, but as a rule there is one best way for each building and that
way must be determined by individual conditions.
~MIXING.~--Concrete for building work has to be of superior quality so
that no chances may be taken either in the process of mixing or with the
type of mixer employed. Machine mixing and batch mixers should always be
employed. Machine mixing gives generally a more homogeneous and uniform
concrete than does hand mixing and is cheaper. Batch mixers are
generally superior and more reliable than continuous mixers where a
uniformly well mixed concrete is required. The capacity of the mixing
plant is determined by the amount of concrete to be placed and the time
available for placing it. Its division and arrangement is determined by
the area of the work and the type and arrangement of the plant for
transporting the materials and the mixed concrete. The following general
principles may be laid down: Make the most use possible of gravity; it
is frequently economy to carry all materials to the top of bins from
which point they can move by gravity down through the mixer to the hoist
buckets, and where natural elevations or basement floors below street
level permit gravity handling they should be taken advantage of. The
mixing should be done as near the place of concreting as practicable; in
building work this is the point on the ground which is directly under
the forms being filled. It is, of course, impracticable to secure so
direct a route as this from mixer to forms, but it can be more or less
closely approached; using two mixers, for example, one at the front and
one at the rear of a building cuts down the haul from hoist to forms
one-half. Other ways will suggest themselves upon a little thought. In
the matter of the mixing itself, it must never be forgotten that a batch
of concrete without cement which goes into a girder or column will
result in the failure of that member and possibly the failure of the
building. In massive concrete work a batch without cement will not
endanger the stability of the structure, but in column and floor work in
buildings it is certain disaster. Formanship at the mixer is, therefore,
highly important and a cement man who realizes the responsibility of his
task is equally important.
~TRANSPORTING.~--Transporting the mixed concrete is divided into three
operations--delivering concrete from mixer to hoist, hoisting, and
delivering hoisted concrete to the forms. The delivery from mixer to
hoist may be by direct discharge into hoist bucket, by carts or
wheelbarrows, or by cars carrying concrete or concrete buckets. Hoisting
may be done by platform hoists or elevators, by bucket hoists, or by
derricks. Handling from hoist to form may be direct in buckets, by carts
or wheelbarrows, or by cars. These several methods can be worked in
various combinations, and the following examples of plants show such
combinations as are most typical of current practice.
In any system of transportation it is getting the concrete to the hoist
and from hoist to form that eats up the money. Hoisting makes but a
small part of the total transportation cost, and, moreover, the
difference in cost of operation for different hoists is very small. Mr.
E. P. Goodrich states that on three buildings the actual costs for the
hoists installed and removed after the completion of the work were as
follows:
Platform hoist $330
Bucket hoist 465
Derrick 225
In figuring on the form of hoist to be adopted, the capability of the
hoist for general service has to be kept in mind. Platform hoists and
derricks can be used for hoisting form lumber and reinforcing steel as
well as for hoisting concrete, while bucket hoists cannot be so used
except where they may be fitted with special carriages for lumber or
steel. On the other hand, the bucket hoist is usually the quickest
method of hoisting concrete, and it can readily be extended upward as
the work progresses. The last is true also of platform hoists. The use
of derricks necessitates frequent shifting for high work or else the
building of expensive staging to raise the derrick into a position to
command the final height of the building. The probable costs of moving
and extending must be allowed for in choosing the hoist to be used.
Direct discharge of the mixer into the hoisting bucket is, of course,
the ideal manner of transporting the concrete from mixer to hoist, and
this can generally be obtained by planning, particularly where bucket
hoists or derricks are employed. For platform hoists direct discharge is
impossible; it can be somewhat closely approached, however, where
conditions permit car tracks to be laid on the floors being built, so
that a car holding a batch of concrete can be run onto the platform,
hoisted and then run to shoveling boards near the forms that are being
filled. The successful use of such an arrangement of car tracks is
described in Chapter XX, but it was for handling concrete blocks. A
direct discharge from hoisting bucket to forms is frequently possible
where derricks are used for hoisting, but with bucket and platform
hoists, wheeling or carting is necessary.
Where wheeling or carting has to be done either at the bottom or at the
top of the hoist, or at both points, a great factor in the economy of
work is the arranging of the operations in cycles. For example, in
wheeling concrete to forms from a hopper fed by a bucket hoist, arrange
the runways so that each man makes a circuit, passing by the form at one
end and by the hopper at the other end, and goes and comes by a
different route. The speed gained by avoiding confusion and delay saves
many times the additional cost of runways which is small. In fact it is
economy to employ a few extra men to arrange runways and keep them
clean, because of the additional speed thus gained. Good organization
effects more economy than special methods of hoisting as far as the
labor of handling the concrete is concerned.
[Illustration: Fig 214.--Bucket Hoist for Building Work
(Wallace-Lindesmith).]
~Bucket Hoists.~--A bucket hoist construction which has been extensively
used in building work on the Pacific coast is shown by the drawings of
Figs. 214 to 216. Two T-bar guides made in sections connected by
fishplates furnish a track for an automatic dumping bucket hoisted and
lowered by steel cable from engine on the ground to head sheaves as
shown. The sectional construction of the T-bar guides permits the hoist
to be any height desired, it being lengthened and shortened by adding
and taking out sections. The bucket is dumped automatically at any point
desired by means of a tripping device attached to a chute which receives
the contents of the bucket and delivers them to carts, wheelbarrows, or
other receptacle. The hoist is set outside of the building with the
mixer arranged, if possible, to discharge directly into the bucket. By
setting the guide frame in a pit or on blocking any height of edge of
bucket can be secured. The buckets are ordinarily 13½ or 20 cu. ft.
capacity. It is recommended, when greater hoisting capacity is
necessary, to use two hoists set side by side and operated by one cable
in the same manner as double wheelbarrow cages; as the weight of one
bucket counterbalances the weight of the other, the power required for
hoisting is reduced. To adapt this hoist to handling form lumber the
bucket is replaced by the lumber carriage shown by Fig. 216; this
carriage discharges over the head of the mixer and the spring buffer
shown by Fig. 214 is to take the shock of the rising carriage. This
buffer is omitted when concrete only is to be hoisted. In one case this
device has hoisted 520 batches of 12 cu. ft. each to the fourth floor in
8 hours, or nearly 19 cu. yds. per hour. In another case 65 trips per
hour were averaged to the fifth floor with a 12-cu. ft. load each trip;
this is nearly 30 cu. yds. per hour. With the lumber carriage 8 men have
unloaded 14,000 ft. B. M. of 2×10-in. stuff from car to the second floor
and distributed it in 43 minutes. A ½-cu. yd. combination outfit for
concrete and lumber, with 40 ft. of guide track, weighs 1,750 lbs.,
without the lumber carriage the outfit weighs 1,600 lbs. This hoist is
made by the Wallace-Lindesmith Co., Los Angeles, Cal.
[Illustration: Fig, 215.--Wallace-Lindesmith Hoist Bucket in Discharging
Position.]
[Illustration: Fig. 216.--Lumber Carriage for Wallace-Lindesmith Hoist.]
[Illustration: Fig. 217.--Mixer Plant with Gravity Feed from Material
Bins to Hoisting Bucket.]
A popular construction for automatic bucket hoists is that shown by
Figs. 217 and 218 by Mr. E. L. Ransome. The bucket is held upright by
guides at its front and rear edges; to dump it a section of the front
guide is removed at the desired dumping point which allows the bucket to
overturn as shown. A friction crab hoist operated from the mixer engine
runs the bucket. The mixer is located as shown. Figure 218 shows the
foot of the hoist set in a pit with the mixer at surface level, but the
hoist can be set on the surface and the mixer mounted on a platform. In
the latter case a charging bucket, traveling from stock pile up an
inclined track to the mixer platform, is generally used. A hoist like
that illustrated, equipped with a ½-cu. yd. Ransome mixer, will cost
about $1,500 and will deliver 15 cu. yds. of concrete per hour. Mr. F.
W. Daggett gives the following figures of the cost of operation:
Mixing Gang:
Total 1 hr.
1 mixer foreman, also engineer, 25c. $.25
1 man charging mixer, 20c. .20
1 man running hoist, 20c. .20
2 men wheeling sand, 17½c. .35
4 men wheeling and shoveling stone, 17½c. .70
1 man helping up runway, 17½c. .17½
2 men carrying cement, 17½c. .35
Gang Placing Cement:
1 foreman, 25c. .25
9 men wheeling concrete, 17½c. 1.57½
3 men tamping concrete, 17½c. .52½
1 man filling carts, 17½c. .17½
------
Total labor cost per hour $4.75
Fuel, etc. .50
------
5.25
This gives a cost of 35 cts. per cu. yd. for mixing and placing
concrete.
In this particular case the mixer was charged by wheelbarrows.
Frequently the stone and sand bins can be arranged to chute the
materials directly into the charging hopper as shown by Fig. 217. In
place of barrows two-wheeled carts of the type shown by Fig. 12 can be
used. Mention has already been made of operating the charging bucket on
an incline from stock pile to mixer. Such arrangements are described in
Chapter IV.
[Illustration: Fig. 218--Bucket Hoist for Building Work (Ransome).]
In constructing a 9-story store at St. Paul, Minn., the concrete was
hoisted by continuous bucket elevators. A lay-out of the construction
plant is shown by Fig. 219. In the alley near the center of the north
side of the building the surface grade was about 6 ft. above the third
story level. A hopper was constructed at grade and provided with two
chutes running to the basement. These chutes discharged on opposite
sides of a vertical partition separating the sand and stone bins, and by
closing either chute at its top by a suitably arranged deflector plate
either sand or stone could be dumped into the same hopper and chuted to
its proper bin. Cement was brought to the work in cars over the tracks
shown and was wheeled from the cars over runways leading to the charging
platforms near each mixer. Other runways connecting with these platforms
provided for wheeling the sand and stone to the mixers. The runways were
placed at the proper height to permit the barrows to be emptied directly
into the charging hoppers. Two Smith mixers were used, located as shown,
and each discharged through a chute into one of the bucket elevator
boots. There were two elevators which were "raised" two stories at a
move as the work progressed. Each elevator discharged into a hopper
holding 1½ batches, and from these hoppers the concrete was fed into
wheelbarrows and wheeled to the forms. The bucket elevators were carried
no higher than the eighth floor. When this floor had been completed the
hoppers were moved down to the fifth floor and the wheelbarrows were
taken to platform elevators and carried to the remaining floors and
roof. Special 4-cu. ft. wheelbarrows were used for handling the
concrete. A maximum of 155 cu. yds. of concrete was mixed, transported
and placed in a 10-hour day with a gang of 28 men.
~Platform Hoists.~--The common builders' hoist or elevator, operating
single or double platforms or cages, needs no special description. The
wheelbarrow, cart or car containing the concrete is run onto the
platform, hoisted and then run to the forms. The chief advantage of this
device in concrete work is that it will handle all classes of material
without any change of carriage or arrangement, it can thus be used for
handling form lumber and reinforcing steel as well as for handling
concrete.
[Illustration: Fig. 219.--Plan of Concrete Mixing and Handling Plant for
9-Story Building.]
~Derricks.~--The use of derricks for hoisting in concrete building work is
limited by the necessity of supporting them independently of the
structure being built; the formwork or the completed concrete work
cannot be utilized to carry derricks during construction. For low
structures the derrick can be set on the ground, but for high buildings
a supporting tower or staging is necessary. The arrangement of such
falsework can be illustrated best by specific examples.
In constructing a 7-story factory at Cincinnati, O., concrete was mixed
on the ground and hoisted by a derrick with an 80-ft. boom mounted on a
tower 55 ft. high. The derrick was located to one side of the building.
For the lower floors the boom swing covered so large an area that the
bucket was dumped at various places, but for the upper floors it was
found more economical to dump buckets into a hopper from which
wheelbarrows were filled. By this plan less time was consumed in placing
the bucket and no tag rope man was required, as the engineman could
swing the boom to a certain point on the wall which would bring the
bucket directly over the hopper. A Smith mixer discharged directly into
derrick buckets, which rested on a track long enough to hold two
buckets. The buckets were filled and emptied alternately by shuttling
the truck and attaching first one and then the other to the derrick.
In constructing an 11-story and basement office building in New York
City a four-legged tower starting from the bottom of the excavation was
erected at about the center of the lot. It was built of timber and
extended upward as the progress of the work demanded until it overtopped
the roof 11 stories above the street. The tower was square in plan and
was divided into stories corresponding approximately to the several
stories of the building. A floor was constructed in the tower at each
story to be used in storing materials. For hoisting a 75-ft. boom was
swung from each leg of the tower, each boom being operated by a separate
engine and having a nominal capacity of 5 tons. The four booms covered
the whole building area and were kept about two stories above the work
by being shifted upward as the work progressed. This arrangement of
derricks was used to handle the steel, lumber and concrete, the building
being built up around the tower, which was so located that its only
interference with the building structure was in the shape of square
holes left in the floor slabs to accommodate the tower legs.
In constructing an 8-story warehouse covering some three acres of ground
in Chicago, Ill., the derrick plant shown by Figs. 220 to 222 was
installed. Some 7,500 tons of reinforcing steel, 125,000 cu. yds. of
concrete and 4,000,000 ft. of form lumber had to be handled.
Incidentally it is worth noting that there were about 120 lbs. of
reinforcing steel and 32 ft. B. M. of form lumber used per cubic yard of
concrete.
The controlling conditions governing the arrangement and character of
the construction plant were as follows: The building, to be built
entirely of reinforced concrete, was 135 ft. high. Its west front
abutted on the river and its south front on the street; at the north
end there was some ground available for plant and along the east front
there was a strip about 20 ft. wide between the building wall and the
main line tracks of a railway. At best, therefore, the area outside of
the building and available for plant and storage was limited, while
inside the building area the contractor was confronted by the insistence
of the architect that an unbroken monolithic construction be obtained as
nearly as possible, by reducing the floor openings for construction work
to a minimum. The sketch plan, Fig. 220, shows the plant designed to
meet the conditions.
To get the large amount of construction material onto the work a side
track was built along the 20-ft. area on the east side of the building
and another was turned into the area at the north end of the building.
These side tracks handled all construction materials coming onto the
work. Over the first there were built two sets of storage bins for sand
and gravel and all concrete materials brought in in carload lots are
unloaded at these two points, as will be described further on. Lumber
for forms and steel for reinforcement shipped in similar manner were
taken by the second siding to the lumber yard and steel mill at the
north end of the building.
[Illustration: Fig. 220.--Plan of Concrete Mixing and Handling Plant for
Large Warehouse Building.]
The raw materials after being worked up in the mixer plants and the saw
and steel mills were distributed over the work by an industrial railway.
The track system of this railway is shown by the dotted lines; it was
located on the basement floor, with rampes leading to the No. 1 mixer
plant and to the saw and steel mill tracks. The two main lines of track
passed close to or under the elevator and stairway shaft openings in the
several floors. This permitted the derrick buckets, lowered and hoisted
through the shafts, to be loaded directly from the car tracks. All mixed
concrete, forms and reinforcing frames were distributed by this railway
to the several shafts and thence hoisted and placed by the derrick
plant.
[Illustration: Fig. 221.--Derrick for Handling Concrete for Large
Warehouse Building.]
The derrick plant consisted of four derricks arranged as shown by the
circles in Fig. 220. The view, Fig. 221 shows the first derrick
installed and illustrates the general construction quite clearly.
Briefly the derrick consisted of a vertical steel-work tower 10 ft.
square and 85 ft. high, within which operated a steel mast 135 ft. high
and carrying an 80-ft. boom connected just above the tower. The mast was
pivoted at the bottom and had rollers turning against a horizontal ring
inside the tower at the top. It was operated by a bull wheel above the
top of the tower, the turning ropes running down inside the mast to the
foot block and thence horizontally to the operating motor. The topping
and hoisting lines also followed this route. The top of the tower was
guyed by four ropes to anchorages in the basement floor. The boom
commanded a circle 170 ft. in diameter and could lift 150 ft. above the
base of the mast. The derrick was operated by a 25-HP. double drum
electric hoist with a derrick swinging spool; this hoist was set on the
basement floor. It will be noted that the guys are below the bull wheel
so that the boom has a clear swing through a complete circle.
As stated above, four of these derricks were employed. Together they did
not cover the entire building area, but by the use of a derrick bucket
so designed that it could be used as a storage bin for feeding
wheelbarrows, it was found possible to keep the number of derricks down
to four.
This derrick plant possessed several advantages of importance. In the
first place the derricks would handle all classes of material--concrete,
forms, steel frames--equally well and could be transferred from one
class of work to the other with practically no delay. In the second
place, for a large area of the building, they handled the material from
the basement direct to the place it was to occupy in the work, and did
it in one operation. Finally they permitted the handling and erection
of the forms and reinforcement in large units. Thus a column form would
be assembled complete at the mill, moved as a unit by car to the proper
shaft and then hoisted and set in place as a unit by the derrick. Girder
forms, floor slab forms, girder and column reinforcing, etc., could be
similarly assembled and handled. The derricks occupied only the area of
four floor panels, the remainder of the area of each floor was left
unobstructed for the work to be done. No materials or supplies needed be
stored on the floors until they were in perfect condition to accommodate
them, and not then, even, so far as the prosecution of form erection and
concreting were concerned.
The sand and gravel for concrete were brought in by bottom or side dump
gondola cars from pits located about 30 miles out on the Chicago,
Milwaukee & St. Paul Ry. The cars were switched onto the main side track
and unloaded under the bins which straddle this track. A receiving
hopper, with its top at rail level and long enough to permit two cars to
be unloaded at once, received the sand or gravel and distributed it
through twelve gate openings onto an 18-in. horizontal belt conveyor 65
ft. long. This conveyor discharged into a second conveyor, 133 ft. long,
which ran up a 22° incline, extending away from the bins and discharged
onto a third conveyor 117 ft. long, which doubled back on a 22° incline
reaching to and over the top of the bins. This third conveyor had two
fixed trippers and an end discharge to distribute its cargo. All three
conveyors were operated by a 35-HP. motor located at the junction of the
two inclined conveyors, both of which were driven from the same shaft. A
chain belt from the idler shaft of the first incline conveyor to the
driving shaft of the horizontal conveyor operated that unit of the
plant. This belt was operated as a cross belt by reversing alternate
links. No manual labor was required to handle the sand and gravel from
the cars to the storage bins.
The mixer arrangement at the two bins differed. At the No. 1 bins the
mixer was located as shown in Fig. 220, close to the bin. Chutes led
directly from the sand and gravel bins to the charging hopper and the
bags of cement were stacked alongside this hopper. The mixer discharged
either directly into the bucket of the first derrick or into cars for
transportation on the railways. At the No. 2 bins a belt conveyor took
the concrete materials down into the basement to a mixer located close
enough to one of the distribution tracks to permit it to discharge
directly into the cars.
[Illustration: Fig. 222.--Special Concrete Bucket for Large Warehouse
Building.]
The derrick buckets by which the concrete was hoisted and handled to the
work were of special construction. A bucket was desired which would
serve several distinct purposes. It must first be able to hold a full
mixer batch of material, since, with the derrick arrangement, economy in
hoisting necessitated hoisting in large units and also because storage
capacity was required of the bucket for wheelbarrow work. The four
derricks did not command the entire area of a floor; there were corners
and other irregular areas outside of the circles covered by the several
booms over which the concrete must be distributed by barrows or carts.
A bucket large enough to supply the barrows, while a second bucket was
being lowered, charged from the mixer and hoisted, was required. In the
second place, a bucket was required whose contents could be discharged
all at once or in smaller portion at will. Finally a bucket was desired
which could be made to distribute its load along a narrow girder form or
in a thin sheet for a floor slab.
To meet these requirements the bucket shown in Fig. 222 was designed. It
held 42 cu. ft., or about 1.55 cu. yds. of concrete. It had a hopper
bottom terminating in a short rectangular discharge spout closed by a
lever operated under cut gate, which could be opened as much or as
little as desired. To the underside of the bucket there was attached a
four-leg frame in which the bucket stood when not suspended. Ordinarily,
that is within the circles commanded by the derricks, the buckets were
discharged suspended and directly into the forms, the character of the
discharge gate permitting a thin sheet to be spread for floor slabs or a
narrow girder or wall form to be filled without spilling or shock. For
wheelbarrow work outside the reach of the derricks the mode of procedure
was as follows: A timber platform about 3 ft. high and having room for
standing two buckets was set just on the edge of the circle commanded by
the derrick boom. Two buckets were used. A full bucket was hoisted and
set on the platform, with its spout overhanging. This bucket served as a
storage bin for feeding the wheelbarrows while the second bucket was
being lowered, charged and hoisted to take its place on the platform,
and serve in turn as a storage hopper.
~PLACING AND RAMMING.~--A wet concrete is usually used in building work
except on occasions, for exterior wall work and except for pitch roof
work, where a wet mixture would run down the slope. Placing and tamping
are therefore, essentially pouring and puddling operations. The pouring
should be done directly from the barrows, carts, or buckets if possible;
dumping onto shoveling boards and shoveling makes an extra operation and
increases the cost by the wages of the shoveling gang. Where shoveling
boards are necessary, take care that they are placed close to the forms
being filled, as it is wasteful of time to carry concrete in shovels,
even for a half dozen paces. Before pouring any concrete, the inside of
the forms should be wet down thoroughly with a hose or sprinkler, if a
hose stream is not available. The final inspection of forms and
reinforcement just before concreting will have made certain that they
are ready for the concrete, so far as line and level of forms and
presence and proper arrangement of the reinforcement are concerned, but
the concrete foreman must watch that no displacement occurs in pouring
and puddling, and must make certain particularly that the forms are
clean.
In pouring columns it is essential that the operation be continuous to
the bottom of the beam or girder. It is also advisable to pour columns
several hours ahead of the girders. Puddling should be thorough, as its
purpose is to work the concrete closely around the reinforcement and
into the angles of the mold and to work out air bubbles. A tool
resembling a broad chisel is one of the best devices for puddling or
slicing. In slab and girder construction, the pouring should be
continuous from bottom of girder to top of slab. Work should never be
stopped-off at horizontal planes. As in columns, careful puddling is
essential in pouring beams. In slab work, the concrete is best compacted
by tamping or rolling. A broad faced rammer should be used for tamping
wet concrete, or a wooden roller covered with sheet steel, weighing
about 250 lbs., and having a 30-in. face.
Theoretically, concreting should be a continuous operation, but
practically it cannot be made so. Bonding fresh concrete to concrete
that has hardened, though it has been done with great perfection by
certain methods as described in Chapter XXIV, must still be held as
uncertain. Ordinarily, at least, a plane of weakness exists where the
junction is made and in stopping off work it should be done where these
planes of weakness will cause the least harm. Experts are by no means
agreed on the best location of these planes, but the following is
recognized good practice. Work once started, pouring a column, should
not be stopped until the column is completed to the bottom of the
girder. For beams and girders; stop concrete at center of girder with a
vertical face at right angles to the girder, or directly over the center
of the columns; in beams connecting with girders, stop concrete at
center of span, or directly over center of connecting girder; stop
always with a vertical face and never with a sloping face, and never
with a girder partly filled. For slabs; stop concrete at center of span,
or directly over middle of supporting girder or beam; stop always with
vertical joints. If for any cause work must be stopped at other points,
than those stated, the fresh concrete and the hardened concrete must be
bonded by one of the methods described in Chapter XXIV.
~CONSTRUCTING WALL COLUMNS FOR A BRICK BUILDING.~--The columns, 12 in
number, were constructed to strengthen the brick walls of a power
station and were built as shown by Figs. 223 and 224, one at a time. The
staging, 50 ft. high and 4×6 ft. in plan, was erected against the wall
which had been shored, a portion of the wall was cut out and forms
erected and the concrete column substituted for the section of wall
which was removed. The staging was then moved into position for another
column.
[Illustration: Fig. 223.--Section of Rectangular Wall Column.]
Two men, with sledge and drill, cut out the brick work amounting to
about 12 cu. yds. for each column in 15 hours, at a cost of about 70
cts. per cu. yd., including removal to the street. The cost of moving
and re-erecting the scaffolding was $2.94 per each move. The character
of the reinforcement is shown by Fig. 223; it was erected as the
concreting progressed, the main bars being in sections 15 ft. long,
spliced with and distanced by side bars and cross bolts at the splices.
[Illustration: Fig. 224.--Staging and Forms Used in Building Column
Shown by Fig. 223.]
The concrete was hand mixed in 6-cu. ft. batches at the foot of the
column, by three men with a fourth turning over and filling the buckets.
The buckets, 12 ins. in diameter and 16 ins. high, were hoisted by a
pulley line arranged as shown and pulled by a mule driven by a man, at
$1 per day for the mule and $1.50 for the man, the cost of hoisting
being 25 to 40 cts. per cu. yd., depending on the rapidity of the man
inside the form. This man tamped the concrete which was emptied from the
buckets by a man on the scaffolding. Each batch raised the level in the
form 15 ins., and between batches a set of ties for the column rods was
placed by the man during the tamping. It took from 1½ to 2 days to
concrete a column of 12 cu. yds. The concrete was a 1-3.8-5.7 limestone
screenings mixture, mixed wet enough to be easily pushed into the forms
and worked around the reinforcement. The form construction is shown by
Fig. 224. The form for one column required 650 ft. B. M. of lumber, and
on an average, each form was used twice. As a matter of fact, the side
strips and outside braces were used three times, while much of the
7/8-in. sheathing was destroyed by being used once. The lumber for
shoring cost $23 per M. ft. B. M., and the light lumber for forms cost
$18 per M. ft. B. M. All lumber was yellow pine. All labor was negro, at
15 cts. per hour; foremen who worked. 22½ cts. per hour. The cost of the
several parts of the work compiled from records furnished by Mr. Keith
O. Guthrie, engineer in charge, was as follows:
Cost per Cost per
Concrete. column cu. yd.
Lumber for forms $ 4.81 $0.40
Setting up and removing forms 11.32 0.95
Cement, 10.17 bbls. at $2.40 24.40 2.03
Sand, 5.87 yds. at $0.90 5.28 0.44
Stone, 8.75 yds. at $1.35 10.94 0.91
Mixing and wheeling 15.73 1.31
Hoisting by mule with driver 4.80 0.40
Handling bucket on scaffold 2.93 0.25
Tamping inside column 2.93 0.25
Painting with grout 3.89 0.32
Clearing away rubbish 1.97 0.16
Rigging, etc. 2.64 0.21
Tools 0.59 0.05
Moving scaffold 2.94 0.25
Moving mix board and rigging hoist 1.62 0.14
------ -----
Total cost of concrete $96.79 $8.07
Cost per Cost cts. per
Reinforcement. column. lb. of bars.
Iron bars, 1,034 lbs. $20.68 $2.00
Drilling iron bars 1.44 0.14
Setting iron bars in place 1.23 0.12
Bolts for splicing and spacing 3.98 0.40
Wire cross ties at 2½, cts. lb. 1.39 0.14
Labor forming 130 cross ties 1.13 0.11
------ -----
Total cost of iron and steel $29.85 $2.91
Summary of Cost.
Per column. Per cu. yd.
Concrete in place $96.79 $8.07
Steel in place 29.85 2.49
Cutting out and removing brick 8.36 0.70
Shoring floors and roof, labor 5.87 0.49
Ditto for lumber used 3 times 3.44 0.29
------- ------
Total $144.31 $12.04
[Illustration: Fig. 225.--Girder Plan for 6-Story Building.]
~FLOOR AND COLUMN CONSTRUCTION FOR SIX-STORY BUILDING.~--The building was
91×112 ft.; 56 columns spaced 16 ft. apart carried the girder system
shown by Fig. 225, which in turn supported a 3½-in. floor slab. The
walls and partitions were not concrete. The following records were kept
by the authors:
_Forms._--The column forms were built as shown by Fig. 226. The boards
were 1½-in. stuff, surfaced on four sides; the yokes were spaced 2 ft.
apart. The 1×6-in. pieces were nailed to the 2×4's with 8-d. nails with
heads left projecting for easy pulling. The girder forms, Fig. 227,
rested on the column forms and on intermediate posts half-way between
columns. These intermediate posts were 3×4's with 4×4×12-in. head blocks
nailed to their tops and wedges under their bottoms. The girder molds
were 1½-in. stuff, and to the side pieces were nailed 1×4-in. cleats;
the bottom and side pieces were connected by 3/8×4-in. lag screws spaced
28 ins. apart. The floor slab stringers were carried on the 1×4-in.
cleats; they were spaced 28 ins. apart and were not nailed; neither were
the 1×6-in. lagging boards nailed to the stringers. The point to be
noted is the design and construction of the forms so that they could be
put together and taken apart easily. The lumber required for forms for
one floor 91×112 ft., or, say, 10,200 sq. ft., was as follows:
Lumber for columns, ft. B. M. 9,000
Lumber for 10×10-in. beams, ft. B. M. 7,600
Lumber for 5×10-in. beams, ft. B. M. 2,700
Intermediate 3×4-in. posts, ft. B. M. 1,000
Lagging, 1×6-in. boards, ft. B. M. 9,000
Stringers, 3×4 ins., ft. B. M. 4,500
------
Total ft. B. M. 33,800
[Illustration: Fig. 226.--Column Form for 6-Story Building.]
In round numbers, we can say that 34,000 ft. B. M. of lumber were used
for 10,000 sq. ft. of floor area, or 3.4 ft. B. M. per 1 sq. ft. Enough
forms were provided to erect two complete floors; the forms for the
lower floor being removed and erected again for the second floor above,
thus using all the lumber three times. With carpenters at $3.50 for 8
hours, the forms were framed ready for erection for $4 per M. ft. B. M.
The lumber framed ready to erect cost them:
Lumber, cost per M. ft. B. M. $26.00
Labor, framing per M. ft. B. M. 4.00
------
Total per M. ft. B. M. $30.00
[Illustration: Fig. 227.--Girder and Slab Forms for 6-Story Building.]
Since the lumber was used three times, $30 ÷ 3 = $10 is the charge
against each 1,000 ft. B. M. needed to encase the concrete on a floor.
There were nearly 34,000 ft. B. M. per floor, hence the cost of lumber
ready for erection was $340 per floor. There were as shown below, 200
cu. yds. of concrete per floor, so that the cost was $340 ÷ 200 = $1.70
per cu. yd. of concrete for forms ready for erection. It took a gang of
5 men 7 days to tear down and carry up the forms for one floor; hence 5
× $2 × 7 = $70 per floor, or practically $2 per M. ft. B. M., or $0.35
per cu. yd. of concrete for taking down and carrying forms two stories.
It took a gang of 10 carpenters 7 days to erect these forms, which at
$3.50 per day was $245 per floor, or $7 per M. ft. B. M., or $1.20 per
cu. yd. of concrete.
_Concrete._--The amount of concrete per floor was as follows:
Floor slab 3½ ins. thick, 10,200 sq. ft. 110 cu. yds.
Beams, 10×10 ins. 40 cu. yds.
Beams, 5×10 ins. 20 cu. yds.
Columns, 15×15 ins. (average) 30 cu. yds.
-----
Total concrete per floor 200 cu. yds.
A concrete mixer, a hoist and a gang of 14 men mixed and placed the
concrete for a floor in 7 days. At $2 per day for labor this gives 14 ×
7 × $2 = $196, or say $1 per cu. yd. for mixing and placing the
concrete.
_Reinforcement._--In each of the 10×10-in. beams there were 4, 1-in.
round rods, 2 straight and 2 bent, and stirrups of 1/8×1-in. straps
spaced 5 ins. apart at columns and 15 ins. at the center. In each
5×10-in. beam there was half as much steel as in a 10×10-in. beam. The
floor slab reinforcement consisted of ¼-in. rods spaced 5 ins. apart and
2 cross-rods in 7-ft. panel. The column reinforcement consisted of 4
rods averaging 1 in. in diameter. In round numbers the amount of steel
required for each floor was, therefore, as follows:
Lbs. steel rods in 10×10-in. beams 16,200
Lbs. steel rods in 5×10-in. beams 4,000
Lbs. stirrups in beams 3,000
Lbs. steel rods in floor slabs 3,800
Lbs. steel rods in columns 1,400
------
Total pounds steel per floor 28,400
This is equivalent to 142 lbs. of steel per cubic yard of concrete, or
about 1 per cent of the total volume of reinforced concrete was steel.
The steel in the beams was about 3 per cent. It required a gang of 5
laborers 7 days at $2.25 per day, to bend and place the steel for each
floor or $86 for labor on 28,400 lbs. of steel. This is equivalent to
0.3 ct. per lb., or 45 cts. per cu. yd. of concrete.
_Summary of Costs._--Summarizing the figures given we have the following
cost per cubic yard of concrete in floors and columns:
Per cu. yd.
142 lbs. steel at 2½ cts. $ 3.55
1 bbl. cement 2.50
1 cu. yd. gravel 1.10
½ cu. yd. sand 0.55
170 ft. B. M. lumber ready to erect at $10 (1/3 of $30) 1.70
170 ft. B. M. torn down at $2 0.35
170 ft. B. M. erected by carpenters at $7 1.20
Mixing and placing concrete 1.00
Shaping and placing steel 0.45
Superintendence 0.25
------
Total $12.65
~WALL AND ROOF CONSTRUCTION FOR ONE-STORY CAR BARN.~--The barn was 50 ft.
wide and 190 ft. long, divided into three rooms by two transverse
partitions and covered with a 4-in. roof having a pitch of ½ in. per
foot. The main walls were 12 ins. thick and the partition walls 10 ins.
thick. The main room 110 ft. long had four car tracks its whole length
with pits under each and a 6-in. reinforced concrete floor slab between.
The floor girders, one under each rail, were 12 ins. square, each
reinforced by three 1¾-in. rods, and were carried on 12×12-in. pillars.
The total yardage of concrete was 874 cu. yds. divided as follows:
Walls and foundations, cu. yds. 614
Pillars and girders in track pits, cu. yds. 44
Reinforced floors, cu. yds. 55
Roof 160
---
Total, cu. yds. 873
A 1-2½-5 concrete was used for floors, roofs and girders and a 1-3-6
concrete for foundations and walls. There were 26½ tons of reinforcing
steel, or 61 lbs. per cu. yd., or 0.45 per cent. of the volume of the
concrete was steel. The wages paid were: Foreman, $2.50; blacksmith, $2;
engineer, $1.75; laborers, $1.50; two-horse team and driver, $3.67;
one-horse team and driver, $2.92; carpenter, $2.25; carpenters worked 9
hours; all others 10 hours.
_Forms._--Carpenters framed and erected forms and common laborers under
foreman carpenter took them down. Lagging was all 2-in. stuff and
uprights 3×4-in. stuff. Props for roof forms were 18-ft. round timber
procured on the job. They were 6 ins. in diameter at the top and cost 50
cts. each, 91 being used. These props are not included in the lumber
listed below, but their cost is included in the costs given. No record
was kept of the number of times the lumber was used, but as 54,643 ft.
B. M. were bought and about twice this much would be needed to enclose
the concrete if used only once, we will assume that all lumber was used
twice. Including the props there were about 60,000 ft. B. M., or 70 ft.
B. M. per cu. yd. of concrete. The cost of the lumber was $1,520.86, and
the cost of labor on the forms was $1,660.60, so that the cost of forms
was:
Item. Per cu. yd. Per M. ft. Per sq. ft.
Lumber $1.74 $13.50 $0.038
Labor 1.90 14.07 0.041
----- ------ ------
Total $3.64 $27.57 $0.079
If the lumber had been used only once the cost per cubic yard would have
been $5.38, and per M. ft. B. M., $41.07.
_Concrete._--A railway track was run the full length of the building
upon what was eventually the fourth track of the car barn and a Ransome
mixer was set up as close to the track as possible allowing a platform
to be built between it and the track. Cars were brought up to this
platform and the materials handled by wheelbarrows direct from cars to
mixer. Both platform and mixer were moved twice as the work progressed.
The concrete was taken by wheelbarrows on runways to the side walls. For
the roof it was hoisted by a horse by means of a mast having an arm with
a three-quarters swing; the barrows were hoisted direct using a hook for
the wheel and two rings for the handles.
The cost of the concrete for materials was:
1.1 bbl. cement at $1.21, per cu. yd. $1.33
¾ ton sand at 75 cts., per cu. yd. 0.55
Aggregate, per cu. yd. 0.88
61 lbs. steel at 1.9 cts., per cu. yd. 1.15
Lumber, 70 ft. B. M. at $27, per cu. yd. 1.74
-----
Total per cu. yd. $5.65
The cost of labor per cubic yard was:
Forms, per cu. yd. $1.900
Mixing, per cu. yd. 0.210
Placing, per cu. yd. 0.310
Finishing, per cu. yd. 0.143
Handling cement, per cu. yd. 0.017
Handling sand, per cu. yd. 0.104
Handling steel, per cu. yd. 0.270
Handling aggregate, per cu. yd. 0.222
Coal, at $4.25 per ton, per cu. yd. 0.010
Foreman, per cu. yd. 0.133
Teams and laying pipe line, per cu. yd. 0.087
------
Total, per cu. yd. $3.406
Summarizing, we have the following cost per cubic yard:
Concrete materials, per cu. yd. $2.76
Labor mixing and placing concrete 1.01
Forms, materials and labor 3.64
Reinforcement, materials and labor 1.42
Fuel, foreman and pipe line labor 0.23
-----
Total, per cu. yd. $9.06
The cost for handling steel, making stirrups, welding, etc., was $8.90
per ton, or 0.45 ct. per lb.
_CONSTRUCTING WALL COLUMNS FOR A ONE-STORY MACHINE SHOP._--The building
was 53×600 ft.; each side wall consisted of 40 columns of channel
section carried on footings of channel section somewhat heavier than
that of the column. The columns were spaced 15 ft. on centers and each
was 7½ ft. wide so that there were 7½ ft. spaces between columns, which
were filled with 3-in. curtain walls extending 7½ ft. above the floor.
Figures 228 and 229 show the column and footing construction. Each
column contained 125 cu. ft., or 4.63 cu. yds. of 1-3-5 1-in. crushed
slag concrete above the footing and the costs given here relate only to
the columns above footings. In the 80 columns there were 370 cu. yds. of
concrete.
_Forms._--A column form is shown by Fig. 230; it contains approximately
1,000 ft. B. M. of lumber. Ten of these forms were used, so that 10,000
ft. B. M. of form lumber were required for 370 cu. yds. of concrete, or
27 ft. B. M. per cu. yd. of concrete. Each column had a superficial area
excluding ends of about 420 sq. ft., so that 420 × 80 = 33,600 sq. ft.
was the superficial area of all the columns and 10,000 ft. B. M. ÷
33,600 sq. ft. = 0.3 ft. B. M., or, say, 1/3 ft. B. M., of form lumber
was used per square foot of concrete enclosed. The cost of the forms per
1,000 ft. B. M., and, therefore, per form, was:
Lumber, 1,000 ft. B. M., at $31.75 $31.75
Labor constructing form 16.39
------
Total per 1,000 ft. B. M. $48.14
[Illustration: Fig. 228.--Channel Section Wall Column for Factory
Building.]
This gives us a cost per cubic yard of concrete for materials and labor
constructing forms of $480 ÷ 370 = $1.30, and per square foot of outside
wall area of $480 ÷ (146 × 80) = 4.1 cts.
The erection and taking down of the forms, owing to the weight of some
of the pieces, was done by means of special derricks. The footings were
brought to within ½ in. of grade and a tenon form of the exact shape of
the channel section of the column was placed on top and filled with
grout to a depth of 1 in. These tenons served as guides in setting the
column forms, and proved to be much quicker and more accurate than
points.
[Illustration: Fig. 229.--Footing for Wall Column Shown by Fig. 228.]
The forms were assembled on the ground and erected by a 35-ft. A-frame
derrick mounted on wheels. The construction is shown by Fig. 231. This
derrick had a capacity of about 4 tons and carried a Ransome friction
crab hoist driven by a 5 h.p. Meitz & Weiss kerosene oil engine. It was
the practice to set a number of forms before filling any. This enabled
the carpenter gang to be plumbing up the first form while the erecting
gang were setting others. The forms had to be very securely guyed and
braced to withstand the impact of the falling concrete. Very little
trouble was had in keeping them well lined up.
[Illustration: Fig. 230.--Form for Molding Wall Column Shown by Fig.
228.]
Two gangs were employed in assembling forms and a portion of the men in
each gang also shaped and placed the reinforcement and placed and tamped
the concrete in the forms so that no exact division of labor is
possible. The organization of these gangs and the wages paid were as
follows:
Derrick Gang:
1 foreman, at 36 cts. per hour $ 3.94
1 crabman, at 30 cts. per hour 2.70
2 topmen, at 27 cts. per hour 4.86
2 bottom men, at 23 cts. per hour 4.14
------
Total per 9-hour day $15.64
Assembling Gang:
1 boss carpenter, at 47 cts. per hour $ 4.23
2 carpenters, at 36 cts. per hour 6.48
2 carpenters, at 30 cts. per hour 5.40
2 carpenters' helpers, at 25 cts. per hour 4.50
4 men forming and placing reinforcing steel
and rethreading bolts, at 23 cts. per hour 8.28
------
Total per 9-hour day $28.89
------
Grand total $44.53
These gangs assembled and erected the molds and concreted 80 columns in
22 working days, including 2 days lost on account of cold weather, so
that 4 columns were completed per day of 9 hours. We can subdivide the
cost as follows:
Item. Per cu. yd.
Erecting forms and concreting $0.81
Assembling forms and reinforcement 1.56
-----
Total $2.37
Charging the 4 men placing reinforcement and rethreading bolts to
forming and placing reinforcement alone we can figure the cost of
fabrication and erection of reinforcement very closely. There were 160
lbs. of reinforcing steel in each column, hence $8.28 ÷ (160 × 4) = 1.3
cts., was the cost per pound of forming and placing it. This includes
handling.
The stripping of the forms was carried on by another gang using a
derrick similar to the first one described, except it could be of
lighter construction as it had to handle only the separate parts of each
form and not the forms assembled. The derrick shown in Fig. 232 was a
33-ft. A-frame, with wheels at the bottom of each leg. It had a friction
crab hoist driven by an electric motor, both of which were fastened to
the derrick frame between the shear legs.
[Illustration: Fig. 231.--Derrick for Erecting Wall Column Forms Shown
by Fig. 230.]
The operation of stripping required only four men and the crabman. The
outside flat panel was removed first, and left leaning up against the
concrete while the inside trough shaped panel was pried loose and
lowered onto the ground with its inside face uppermost. The side panels
being comparatively light, were stripped without the use of the derrick,
and these panels were assembled on the ground with the inside piece. The
derrick then picked up the outside panel again, and placed it in its
proper place. After the bolts were put in place, the assembled form was
moved on rollers to another point in the line of columns where it was
again erected. The arrangement of derricks for erecting and stripping
forms is shown in Fig. 233.
The gang stripping forms was made up as follows:
1 foreman, at 30 cts. per hour $ 2.70
1 crabman, at 27 cts. per hour 2.43
1 topman, at 27 cts. per hour 2.43
2 bottom men, at 23 cts. per hour 4.14
------
Total per 9-hour day $11.70
[Illustration: Fig. 232.--Derrick for Stripping Wall Column Forms Shown
by Fig. 230.]
This gang of five men stripped 4 columns containing 18.52 cu. yds. of
concrete each day, so that the cost of stripping was $11.70 ÷ 18.52 =
62.7 cts. per cu. yd.
_Concrete._--The concrete was mixed in a No. 2 Ransome mixer and
delivered to the work in Ransome concrete carts. These carts were pushed
along a runway which terminated in a slight incline under the derrick so
that their contents could be emptied into the derrick buckets.
The concrete was hoisted in an 8-ft. bottom dump bucket, using the
derrick described above. It was necessary to stir up the concrete
thoroughly with long-handled slicers as it was being deposited in order
to prevent segregation. This expedient combined with a wet mixture and
tight molds was found to overcome this difficulty very effectually.
The gang mixing and wheeling concrete was made up as follows:
1 mixer foreman and engineer at 27 cts. per hour $ 2.43
4 laborers charging mixer at 18 cts per hour 6.48
4 laborers wheeling concrete at 18 cts. per hour 6.48
------
Total per 9-hour day $15.39
This gang mixed and wheeled concrete for four columns, or 18.52 cu.
yds., hence the cost per cubic yard was 82.6 cts.
With cement at $1.60 per bbl., sand at $1 per cu. yd. and slag at $1.10
per cu. yd. the cost of materials per cubic yard of concrete was $3.
[Illustration: Fig. 233.--Arrangement of Derricks for Erecting and
Stripping Forms.]
Summarizing the above figures we have the following cost per cubic yard
of concrete in place:
Item. Per cu. yd.
Concrete materials $3.00
Reinforcing steel 0.73
Forms, lumber and framing 1.30
Forms, erecting and concreting 0.81
Forms, assembling and reinforcement 1.56
Forms, stripping 0.63
Mixing and wheeling concrete 0.83
-----
Total $8.86
~CONSTRUCTING ONE-STORY WALLS WITH MOVABLE FORMS AND GALLOWS FRAMES.~--In
constructing the walls for an 85×30-ft. factory building at Old Bridge,
N. J., Mr. A. E. Budell made use of movable forms and gallows frames to
construct the curtain walls and columns in one piece. Each side wall was
built its full height in successive 50-ft. lengths by depositing the
concrete between two forms which were moved upward as the concreting
progressed. Fig. 234 indicates the mode of procedure. The form was
raised and lowered by means of two gallows frames fitted with blocks and
tackle. A steel cable, with a trolley affixed, extending from one frame
to the other, provided a convenient mode of hoisting material to the
form, and the gallows frames took the place of ladders for climbing onto
the structure. No scaffolding whatever was used and only one man was
required overhead to dump the buckets and tamp the concrete into place.
[Illustration: Fig. 234.--Gallows Frame Supporting Wall Form Panels for
One-Story Building.]
[Illustration: Fig. 235.--Details of Wall Form Panel for One-Story
Building.]
The two walls were carried up simultaneously, one form being shifted
into place and filled while the other was left in place until the
concrete was sufficiently hard. It was found that 18 hours was amply
sufficient to allow the concrete to set hard, after which the form was
removed and lifted to a higher level. Thus the men were continuously
engaged in lifting and filling first one form and then the other. The
average length of time required to remove, raise and fill one form was 5
to 6 hours. Thus, two forms could be raised and filled almost every day.
The construction of the forms and of the gallows frames is shown by
Figs. 234 and 235. The cost of one set of forms and gallows frames was
as follows:
320 ft. B. M. of 2×10 in.×10 ft. plank at $34 $ 10.88
150 ft. B. M. of 3×4 in.×16 ft. spruce at $33 5.25
135½ ft. B. M. 1×8 in. yellow pine at $30 4.08
335 ft. B. M. 1¼×6 in. spruce at $33 11.05
4 posts 6×8 in.×26 ft. = 416 ft. B. M. at $30 12.48
4 sills 6×8 ins.×16 ft., 2 caps 6×6 ins.×9 ft.,
4 braces 6×6 ins.×16 ft. = 490 ft. B. M. at $30. 14.70
3 pieces 3×10 ins.×20 ft. = 150 ft. B. M. at $30 4.50
-------
Total lumber (1,996.5 ft. B. M.) $ 62.94
Accessories:
Bolts for trussing, 675 lbs. at 2 cts. $ 13.50
Iron guy rope and clips 7.00
Blocks 8.00
One coil of ¾-in. rope 28.00
-------
Total accessories $ 56.50
Labor making one outfit:
2 men, 8 days, at $2.75 per 9 hrs. $ 44.00
-------
Grand total $163.44
This sum covered the cost of forms for one side of the building 85 ft.
long and containing 150 cu. yds. of concrete, hence the cost of forms
was in round figures $1.10 per cu. yd. of concrete. Each cubic yard of
concrete required 1,997 ÷ 150 = 13-1/3 ft. B. M. of form lumber.
The concrete was a 1-2½-4½ mixture. A careful record for 15 days, showed
an average of 2.8 cu. yds. of concrete placed in 6 hours by a gang of
6.3 men. From this we can figure the cost of concrete in place to be
about as follows:
2.8 cu. yds. concrete at $3 for materials $ 8.40
6.3 men 6 hours at 15 cts. 5.67
1 foreman 6 hours at $4 per day 2.00
------
Total per cu. yd. $16.07
Thus the cost of concrete in place was $16.07 ÷ 2.8 = $5.73 per cu. yd.
Adding the cost of forms we get $5.73 + $1.10 = $6.83 per cu. yd. as the
cost for labor and materials in constructing forms and mixing and
placing concrete.
[Illustration: Fig. 236.--Detail of Column and Cantilever Column Footing
for Four-Story Garage.]
Offsets and molding decorations were easily made, although they were
quite numerous on the building in question, at least more so than would
ordinarily be the case in mill building construction. The offset of 1
ft. at every column was made very readily by sliding wooden shoulder
pieces into place on the inner face of the form, which pieces in turn
received 2-in. faced planking, the latter being slid into place from
above. Thus the entire system was collapsible and small alterations were
easily made whenever the form was shifted. Flat surfaces or offsets
could be obtained at will by either removing or setting in the shoulder
pieces. Molding effects were made on the front face of the wall by
tacking molding strips to the form wherever necessary. The entire work
was done with common labor and the finished building presented a smooth,
homogeneous surface which required very little dressing.
[Illustration: Fig. 237.--Details of Cantilever Girders for Mezzanine
Floor for Four-Story Garage.]
~FLOOR AND ROOF CONSTRUCTION FOR FOUR-STORY GARAGE.~--The building was
53×200 ft., and 4 stories high, with provision for 2 additional stories
in the design of footings and columns. Two rows of wall columns
connected by transverse girders carrying the floor and roof slabs made a
comparatively simple construction, except for a mezzanine floor carried
on cantilever beams and except for the use of cantilever footings;
these two special details are shown by Figs. 236 and 237. The amount of
concrete in the building was 1,910 cu. yds., distributed as follows:
Cu. yds.
Footings, reinforced 190
Columns, reinforced 450
Floors and roof, reinforced 1,100
Floor on ground, not reinforced 170
-----
Total 1,910
The amount of reinforcing metal used was 237 tons, distributed as
follows:
Item. Tons. Lbs. per cu. yd.
Footings 42 442
Columns 20 90
Floors and roof 175 318
--- ---
Total and average 237 272
This is equivalent to 2 per cent. of steel in 1,910 - 170 = 1,740 cu.
yds.
_Forms._--The total area of concrete covered by forms (1,740 cu. yds.)
was 94,000 sq. ft., distributed as follows:
Footings, sq. ft. 4,000
Columns, sq. ft. 20,000
Floors and girders, sq. ft. 70,000
------
Total, sq. ft. 94,000
For the work 50,000 ft. B. M. of old lumber was used and 170,000 ft. B.
M. of new lumber was bought, the cost being as follows:
50 M. ft. B. M. at $13 per M. $ 650
170 M. ft. B. M. at $26 per M. 4,420
------
220 M. ft. B. M. at $23 $5,070
This is equivalent to 126 ft. B. M. per cu. yd. of concrete. New forms
were made for each floor except the sides of the girder molds which were
re-used so far as they would fit, but the roof forms were made from
lumber used for the floors. In all no more than 20 per cent of the form
lumber was used a second time. In round figures new lumber was required
for 80,000 sq. ft. of concrete; this gives a cost for lumber of 6.4 cts.
per sq. ft. The construction of the column and floor forms is shown by
Fig. 238. A force of 15 carpenters at $4.40 per day under a foreman at
$35 per week erected and tore down forms; the carrying was done by
laborers at $1.70 per day working under a foreman at $35 per week;
carpenters worked an 8-hour and laborers a 10-hour day. Forms for one
floor were framed and erected in 8 to 10 days. The cost of forms for
1,740 cu. yds. and 80,000 sq. ft. of concrete and per M. ft. B. M. was
as follows:
Item. Per cu. yd. Per sq. ft. Per M. ft.
Lumber $2.90 $0.064 $23.00
Framing, erecting and removing. 2.00 } 15.67
} 0.057
Handling lumber 1.10 } 8.70
----- ------ ------
Totals $6.00 $0.121 $47.37
[Illustration: Fig. 238.--Column and Floor Forms for Four-Story Garage.]
The lumber had a considerable salvage value which is not allowed for in
the above figures.
_Concrete._--The concrete was a Portland cement, ¾-in. trap rock
mixture, mixed wet in two Chicago Improved Cube Mixers equipped with
charging buckets. The mixers were located on the ground floor, one at
the rear and one at the front of the building, both discharging directly
to a hoist. With a gang of 30 men at $1.70 per 10-hour day under a
foreman at $35 per week a floor was concreted in 2 days, the columns
being concreted the first day and the floor being concreted the second
day. The labor cost for mixing and placing concrete and for fabricating
and setting reinforcement was as follows:
Item. Per cu. yd.
Mixing and placing concrete $1.95
Erecting and setting steel 2.05
-----
Total $4.00
The cost of concreting includes the cost of granolithic surface for the
floor slabs. The girder reinforcement was made up into unit frames and
the frames were set as a unit, horses set over the molds being used to
suspend and lower them into place. The cost of $2.05 per cu. yd. is
equivalent to ¾ ct. per lb. Summarizing, we have the following cost for
materials and labor on forms and for labor mixing and placing concrete
and reinforcement:
Per cu. yd.
Lumber for forms $ 2.90
Labor on forms 3.10
Labor on concrete 1.95
Labor on steel 2.05
-----
Total $10.00
This $10 total does not include the cost of the concrete nor of the
steel.
CHAPTER XX.
METHOD AND COST OF BUILDING CONSTRUCTION OF SEPARATELY MOLDED MEMBERS.
This chapter deals exclusively with the methods and cost of molding and
erecting separately molded wall blocks, girders, columns and slabs. The
structural advantages and disadvantages of this type of construction as
compared with monolithic construction will not be considered. The data
given in succeeding paragraphs show how separate piece work has been
done and what it has actually cost to do it in a number of instances.
~COLUMN, GIRDER AND SLAB CONSTRUCTION.~--European engineers have developed
several styles of open web or hollow girder and column shapes, but in
America solid columns and girders have been used except in the
comparatively few cases where one of the European constructions has been
introduced by its American agents.
~Warehouses, Brooklyn, N. Y.~--In constructing a series of warehouses in
Brooklyn, N. Y., the columns and girders were molded in forms on the
ground. For molding the columns, forms consisting of two side pieces and
one bottom piece, were used, saving 25 per cent. in the amount of lumber
required for a column form, and doing away with yokes and bolts, since
only simple braces were required to hold the side forms in place. It was
found that the side forms could readily be removed in 24 to 48 hours,
thus considerably reducing the time that a considerable portion of the
form lumber was tied up. It was figured by Mr. E. P. Goodrich, the
engineer in charge of this work, that this possible re-use of form
lumber reduced the amount required another 50 per cent. as compared with
molding in place. Girders were molded like columns in three-sided forms;
the saving in form work was somewhat less than in the case of columns,
but it was material. In general, Mr. Goodrich states, the cost of
hoisting and placing molded concrete members is higher per yard than
when the concrete is placed wet. That is in mass before it is hardened.
[Illustration: Fig. 239.--Sketch Showing Forms and Reinforcement for
Visintini Girder.]
~Factory, Reading, Pa.~--In constructing a factory at Reading, Pa., an
open or lattice web type of girder invented by Mr. Franz Visintini and
extensively used in Austria was adopted; columns were molded in place in
the usual manner with bracket tops to form girder seats. The girders
were reinforced with three trusses made up of top and bottom chord rods
connected by diagonal web rods; one truss was located at the center of
the beam and one at each side. The method of molding was as follows: The
trusses were made by cutting the chord rods to length and threading the
web diagonals and verticals onto them. To permit threading the web
pieces were bent, when rods were used, with an eye at each end; when
straps were used the ends were punched with holes. The work was very
simple and was done mostly by boys in the machine shop of the company
for which the building was being erected. The girders were molded two at
a time in forms constructed as shown by the sketch. Fig. 239. A form
consisted of a center board, two side boards, two end pieces and the
proper number of cast iron cores, all clamped together by three yokes.
Triangular cast iron plates, A, were screwed to the bottom boards for
spacers. The side, center and end boards were then set up and the end
clamps were placed. The cast iron hollow cores, B, were then set over
the spacers, and the form was ready for pouring. A layer of concrete was
placed in the bottom of the mold and the first side truss was placed;
the concrete was then brought half way up and the middle truss was
placed; concreting was then continued up to the plane of the second side
truss which was placed and covered. Cores and forms were all cleaned and
greased each time they were used. The cores were removed first by means
of a lever device and generally within three or four hours after the
concrete was placed. The remainder of the form was taken down in two to
four days and the beam removed.
~Kilnhouse, New Village, N. J.~--In constructing a kiln house for a cement
works one story columns with bracket tops and 50-ft. span roof girders
were molded on the ground and erected as single pieces. The columns by
rough calculation averaged about 2 cu. yds. of concrete and 675 lbs. of
reinforcement each or about 337 lbs. of steel per cubic yard. The
girders averaged by similar calculation 5 cu. yds. of concrete and 2,260
lbs. of steel, or 452 lbs. per cubic yard of concrete. The average
weight of columns was thus not far from 41.3 tons and of girders fully
11 tons.
[Illustration: Fig. 240.--Arrangement for Molding Ten Single-Bracket
Columns.]
Several combinations of arrangements were used for molding the columns
and girders. For wall columns having one bracket the arrangement shown
by Fig. 240 was adopted. The concrete slab molding platform was covered
with paper, and on this the two outside and the middle columns were cast
in forms. When those columns had set the forms were removed, the
intervening spaces were papered and the two remaining columns were cast.
Ten columns, five sets of two columns in line, were cast on each base.
The remaining columns were cast in combination with girders as shown by
Fig. 241. The two outside lines of columns (1) were molded in forms,
allowed to stand until set and then stripped. Using a column surmounted
by a shallow side form for one side and a full depth side form for the
other side molds were fashioned for the two outside girders, Nos. 2 and
3. One full depth side form and the side of girder No. 2 formed the mold
for girder No. 4. Girder No. 5 was then molded between girders No. 3 and
No. 4.
[Illustration: Fig. 241.--Arrangement for Molding Four Four-Bracket
Columns and Four Roof Girders]
[Illustration: Fig. 242.--Forms for 50-ft. Roof Girders.]
The construction of the girder forms is shown by Fig. 242. This drawing
shows one of the four main sections making up a complete form. A full
size form of this construction contained about 1,100 ft. B. M. of
lumber, and three were built, so that 3,300 ft. B. M. of form lumber
were used for molding 20 girders, or 33 ft. B. M. per cubic yard of
concrete. A full size column form contained about 225 ft. B. M. of
lumber, and eight were constructed, so that 1,800 ft. B. M. of form
lumber were used for molding 56 columns, or about 16 ft. B. M. per cubic
yard of concrete.
The following was the cost of erecting a full column form including
lining, plumbing, bracing and yoking, but excluding lumber and original
construction:
1 carpenter, 3 hrs., at $0.25 $0.750
1 helper, 3 hrs., at $0.175 0.525
1 helper, 1 hr., at $0.175 0.175
1-5 boss carpenter, 3 hrs., at $0.30 0.180
------
Total $1.630
This gives a cost of $7.25 per M. ft. B. M. for erecting column forms.
The cost of erecting a full size girder form including lining, plumbing,
bracing and setting six bolts was as follows:
2 carpenters, 5 hrs., at $0.25 $2.50
2 helpers, 5 hrs., at $0.175 1.75
2 laborers, ½ hr., at $0.15 0.15
¼ boss carpenter, at $0.30 0.375
------
Total $4.775
This gives a cost of $4.35 per M. ft. B. M. for erecting girder forms.
The reinforcement was erected inside the forms for both columns and
girders. The cost of erection for one column was:
2 laborers, 4 hrs., at $0.15 $1.20
1/3 foreman, 4 hrs., at $0.225 0.30
-----
Total $1.50
This gives a cost of about 0.22 cts. per pound for erecting column
reinforcement, including the bending of the horizontal ties or hoops.
The girder reinforcement was erected by piece work at a cost of $1.80
per girder--or about 0.08 ct. per pound.
The concrete used was a 1-6 mixture of Portland cement and crusher run
stone all passing a ½-in. sieve and 10 per cent. passing a 200 mesh
sieve. No trouble was had in handling this fine aggregate. It was mixed
in a Ransome mixer, elevated so as to deliver the batches into cars on a
standard gage track. This track ran between the base slabs on which the
molding was done. Each car held about 3 cu. yds. and discharged through
a side gate and spout directly into the forms, the mixture being made so
wet that it would flow readily. The company used its own cement and
stone for concrete and charged up the cement at $1 per barrel and the
stone at 60 cts. per cubic yard. At these prices, and assuming that a
cubic yard of concrete of the mixture above described would contain
about 1.25 bbl. of cement and 1.5 cu. yd. of stone, we have the
following cost of materials per cubic yard of concrete:
1.25 bbls. of cement, at $1 $1.25
1.5 cu. yds. stone, at $0.60 0.90
-----
Total $2.15
The actual cost of mixing the concrete and delivering it to the cars was
as follows:
Item. Per cu. yd.
1 foreman, at 20 cts per hour $0.0300
3 men shoveling stone, at 15 cts. per hour 0.0675
3 men filling hopper, at 15 cts. per hour 0.0675
1 man bringing cement, at 18 cts. per hour 0.0225
1 man dumping cement, at 15 cts. per hour 0.0225
9 h.p., at ½ ct. per h.p. hour 0.0450
Superintendence, repairs, etc. 0.0270
-------
Total $0.2820
The cost of hauling the concrete from mixer to forms ran about 2.7 cts.
per cubic yard, so that we have a cost for concrete in place of:
Concrete materials, per cu. yd. $2.150
Mixing concrete, per cu. yd. 0.281
Hauling concrete, per cu. yd. 0.027
------
Total cost, per cu. yd. $2.458
The cost, then, per column or girder molded, assuming that it was
necessary to erect a full form, was about as follows:
Columns:
2 cu. yds. concrete, at $2.46 $ 4.92
675 lbs. steel, at 2½ cts. 16.77
Erecting steel, at 0.22 ct. per lb. 1.50
Erecting forms 1.63
------
Total $24.82
Girders:
5 cu. yds. concrete, at $2.46 $12.30
2,260 lbs. steel, at 2½ cts. 56.50
Erecting steel, at 0.08 ct. per lb. 1.80
Erecting forms 4.77
-----
Total $75.37
[Illustration: Fig. 243.--View Showing Method of Hoisting Molded
Columns.]
These figures give a unit cost of $12.41 per cu. yd. for molded columns,
and of $15.07 per cu. yd. for molded girders, The columns were erected
by a Browning locomotive crane, which lifted and carried them to the
work and up-ended them into place. To facilitate lifting the columns
from the molding bed a 1½-in. pipe 8 ins. long was cast into both ends;
pins inserted into these sockets provided hitches for the tackle. The
column was lifted off the molding bed and blocked up, then iron clamps
were attached, one at each end, as shown by Fig. 243. A gang of 1
foreman and 14 men erected from 5 to 7, or an average of 6 columns per
10-hour day. The average wages of the erecting gang were 21 cts. per
hour. The cost then of column erection was (14 × $2.10) ÷ 6 = $5.25 per
column, or $2.63 per cu. yd. of concrete.
[Illustration: Fig. 244.--Sketch Showing Sling for Erecting 50-ft. Roof
Girders.]
The roof girders had 1-in. eye-bolts 24 ins. long cast into them
vertically about 4 ft. from the ends. They were lifted off the molding
bed by tackle by the locomotive crane to these eye-bolts and blocked up
to permit the adjustment of the sling. This sling is shown by the
sketch, Fig. 244, and as will be observed acts as a truss. At first it
was used without the vertical, but the cantilever action of the
unsupported ends caused cracks. The girders were loaded onto cars by the
locomotive crane and taken to the work, where they were hoisted and
placed by a gin pole. The girder erecting gang consisted of 1 foreman
and 14 men, working a 10-hour day at 21 cts. per hour. This gang erected
four girders per day, at a cost of (15 × $2.10) ÷ 4 = $7.87 per girder,
or $1.57 per cu. yd. of concrete.
The cost of girders and columns in place was thus about as follows:
Columns: Per unit. Per cu. yd.
Molding $25.00 $12.50
Erecting 5.25 2.63
------ ------
Totals $30.25 $15.13
Girders:
Molding $75.00 $15.00
Erecting 7.87 1.57
------ ------
Totals $82.87 $16.57
[Illustration: Fig. 245.--View Showing Method of Handling Roof Slabs.]
In this same building the roof was composed of 12×6¼ ft.×4-in. slabs
molded in tiers; a slab was molded and when hard was carpeted with paper
and the form moved up and a second slab molded on top of the first. This
operation was repeated until a tier of slabs had been molded. By molding
each slab with a 3-in. overlap, as shown by Fig. 245, they could be
easily separated by lifting on hooks inserted under the overhanging
ends. Each slab contained 0.925 cu. yd. of concrete and about 116¾ lbs.
of reinforcement. The cost of molding one roof slab, including
materials, forms and labor, was as follows:
Materials: Per slab. Per cu. yd.
1 bbl. cement, at $1 $1.000 $1.081
1.06 tons stone, at $0.60 0.636 0.687
116¾ lbs. steel, at 2¼ cts. 2.647 2.862
------ ------
Total $4.283 $4.630
Forms:
Lumber and making $0.104 $0.112
92 sq. ft. paper, at 33-1/3
cts. per 500 sq. ft. 0.055 0.059
Labor erecting and removing 0.5625 0.608
------- ------
Total $0.7215 $0.779
Mixing, Hauling and Placing:
Mixing $0.222 $0.240
Hauling 0.025 0.027
Placing concrete and steel 0.170 0.183
------ ------
Total $0.417 $0.450
General Expenses:
Housing and heating $0.700 $0.757
Superintendence, power, etc. (10%) 0.612 0.661
------ ------
Total $1.312 $1.418
Grand totals $6.7335 $7.277
The roof slabs were raised from the casting beds by means of the
locomotive crane and hooks, as shown by Fig. 245, and loaded onto cars;
eight slabs made a carload. The cars were run to the work, where the gin
poles hoisted the slabs one at a time to cars running on a track built
on timbers laid on top of the roof girders. A small derrick on rafters
picked the slabs from the hand car and set them in place. A gang of 15
men erected from 18 to 20 slabs per 10-hour day. With average wages at
21 cts. per hour the cost of erection was (15 × $2.10) ÷ 19 = $1.66 per
slab, or $1.79 per cu. yd. The total cost of slabs in place was thus:
Item. Per slab. Per cu. yd.
Molding $6.73 $7.27
Erecting 1.66 1.79
----- -----
Total $8.39 $9.06
In studying these cost figures their limitations must be kept in mind.
Because of the character of the available data quantities had in several
cases to be estimated from the working drawings. The cost of lumber for
and of framing column and girder forms is not included, but this is
partly balanced at least by the assumption that each form was erected
complete for each column and girder, which was not the case, as has been
stated. Cost of plant is not included nor is cost of shoring the columns
until girders and struts were placed, nor are several minor
miscellaneous items.
~HOLLOW BLOCK WALL CONSTRUCTION.~--Three general processes of molding
hollow wall blocks of concrete are employed: (1) A dry mixture is
heavily tamped into a mold and the block is immediately released and set
aside for curing; (2) a liquid is poured into molds, where the block
remains until hard: (3) a medium wet mixture is compressed into a mold
by hydraulic presses or other means of securing great pressure. The
molds used may be simple wooden boxes with removable sides or mechanical
molds of comparative complexity. Generally mechanical molds, or concrete
block machines as they are commonly called, will be used. There are a
score or more kinds of block machines all differing in construction and
mode of operation. None of them will be described here, but those
interested may consult "Concrete Block Manufacture" by H. H. Rice or
"Manufacture of Concrete Blocks and Their Use in Building Construction"
by H. H. Rice, Wm. M. Torrance and others.
~Factory Buildings, Grand Rapids, Mich.~--The buildings ranged from one to
four stories high and altogether occupied some 74,000 sq. ft. of ground.
The owners installed a block making plant fully equipped with curing
racks, two Ideal machines, two National concrete mixers, 5 h.p. gasoline
engine, platens, tools and a Chase industrial railway.
The walls were constructed of 24-in. square pilasters of blocks arranged
as shown by Fig. 246, connected by curtain wall belt courses of single
blocks. The blocks were 8×8×16 ins., and after molding the faces were
bush hammered and the edges tooled. The pilasters, consisting of four
blocks laid around an 8×8-in. hollow space, were solidified by pouring
the 8×8-in. space and all but the three outside block cavities with wet
concrete. The interior of the building was of regulation mill
construction, and as the pilasters reached the heights for beam supports
cast iron plates with downward flanges were set in the concrete. These
plates had a cast pin projecting upward to fasten the beam end.
[Illustration: Fig. 246.--Concrete Block Pilaster for a Factory
Building.]
The materials used for the block were Sandusky Portland cement and ¾-in.
bank gravel well balanced from fine to coarse. The blocks were molded
with 1-3 mortar faces, the mortar being waterproofed by a mixture of
Medusa waterproofing compound. All concrete was machine mixed. The men
operating the block machines were paid 1 ct. for each block molded, so
that their pay depended upon the energy with which they worked. The men
handling materials and engaged in handling and curing the blocks were
paid $1.75 per day. The gravel was shoveled from the railway cars onto
the screens and from the screen piles to the mixers. The gang was
organized as follows:
Item. Per day.
8 men handling materials, at $1.75 $14.00
5 men operating molds, at 1 ct. per block 15.00
1 man mixing facing mortar, at $1.75 1.75
2 men loading blocks onto trucks, at $1.75 3.50
2 men unloading blocks from trucks, at $1.75 3.50
3 men sprinkling blocks, at $1.75 5.25
------
Total, 21 men molding and curing blocks $43.00
The average daily run was 1,500 blocks, or 300 blocks per machine.
This output was easily maintained after the gang got broken in;
sometimes it ran higher and sometimes lower, but the average was as
given. The men operating the block machines thus earned $3 each per day.
The labor cost of molding and curing per block was thus 2.87 cts. As the
blocks had about 25 per cent. hollow space, each block 8×8×16 ins.
contained 0.45 cu. ft. of concrete; a cubic yard of concrete, therefore,
made 60 blocks, so that the labor cost of making the blocks was 60 ×
2.87 cts. = $1.72 per cubic yard. This cost does not include foreman's
time, materials, interest, depreciation or general expenses. It was
estimated by the owners that the blocks cost them 9 cts. apiece cured,
or about $5.40 per cubic yard of concrete. This 9 cts. evidently
includes materials and labor alone.
Upon removal from the molds the blocks were loaded onto cars, taken to a
large shed and there unloaded onto shelving arranged to hold five rows
of blocks one above the other, two blocks opposite each other on each
shelf. The blocks were left in the shed 24 to 48 hours to get the
preliminary set, then they were loaded on small cars and taken to the
yard, where they were removed from the cars and stacked. They were
sprinkled every day for six days, being kept covered meanwhile with
oiled cotton cloth. The labor costs given above include molding,
sprinkling and handling the blocks up to this point.
To lay the blocks they were again loaded on cars and run to an elevator
in a wooden tower outside the building. The elevator lifted the car to
the floor on which the blocks were to be used, where it was run off onto
a track reaching the full length of the building. The blocks were
unloaded directly behind the masons. Where the walls were high enough
for scaffolding the blocks were unloaded directly onto the first
scaffold and, when necessary, handed up to the scaffolds above. The
masons employed were regular stone masons receiving the regular scale of
wages of $3.50 per day. The number of blocks laid by each mason was 125
per day in building pilasters and 200 per day in building plain wall.
Sometimes 250 blocks per day per man were laid in plain wall work. The
cost per block of laying above was thus 2.8 cts. pilasters and 1.75 cts.
in plain wall. This cost does not include transporting the blocks from
yard or of handling them to the scaffold behind the masons, nor does it
include the cost of materials and labor for mixing and delivering
mortar.
One of the features of this work was the method of transporting the
blocks by cars. A complete system of tracks was provided covering the
block plant and yard, the building sites and the several floors of the
buildings themselves. All blocks and other materials were transported by
cars running on these tracks, both cars and tracks being of the type
made by the Chase Foundry & Manufacturing Co. of Columbus, Ohio.
~Residence, Quogue, N. Y.~--The following record of methods and cost of
constructing a concrete block residence is furnished by Mr. Noyes F.
Palmer: A mixture of sand and pebbles was had on the site; screening was
necessary merely to sort out the odd size stones. A mixture of 1 cement
and 5 sand was really a 1-2-3 mixture, the 2 being the finest grades of
sand and the 3 being various gravel sizes--none too large, none too
small--so that the proportion was 2/5 fine sand and 3/5 gravel.
The concrete was hand mixed, and as the gravel had always just been
excavated it contained moisture and did not have to be wetted. The sand
and gravel were mixed and turned three or four times and spread out
thin, and the cement was carefully spread over them in a uniform layer.
The mass was then turned three or four times until the eye could detect
no difference in color; that is, each grain large enough for the eye to
discern seemed to be coated with cement. After this dry mixing, water
was added in a fine spray--not a deluge from a pail--but only enough to
moisten the mixture. The mass was then turned three or four times. The
mixture was then shoveled into the mold, no special face mixture being
used, so as to about half fill it, and was then tamped by two men, one
standing on each side of the machine. Altogether three layers of
material were so placed and tamped and then a shovelful of sand and
cement mixture was spread over the top to permit an even "strike-off."
As each block was molded it was carried on the working plate and set
down on skids properly spaced to fit the marks on the plate. This is an
important detail and Mr. Palmer comments on it as follows: "The writer
saw inexperienced men careless about it and who would break the backs of
many blocks by not having the skids properly placed. After the blocks
have been at rest for half an hour commence to spray them with a
revolving garden sprinkler or by carefully wetting with a sprinkling pot
on the center of the block only. The blocks should not be allowed to dry
out for at least ten days after removal from the working plate. The
removal from the working plate can be done the morning after molding and
should never be done before even if the block was made in the morning.
In removing the green block from the skids let there be cones of sand
between the rows of blocks and up-end each working plate so as to let
the end of the block come upon the sand cushion. Don't twist and turn
the block, and to remove the working plate pass a stick through the core
holes in both block and plate so that the plate will not fall when
loosened. A slight rap on the center of the plate will loosen it. As
soon as the blocks are up-ended commence the spraying and soak the sand
underneath the block. It may seem unnecessary to dwell on these points
so long, but barrels of cement and barrels of money have been wasted by
neglecting to supply the hardening block with water. Curing is just as
important as molding in making concrete blocks."
The block construction had been detailed by the architect from cellar to
roof, so that it was known beforehand how many blocks of given size were
to be made. The unit of length was 32 ins.; this afforded fractional
parts of 8 ins., 16 ins. and 24 ins., therefore all openings were in
multiples of 8 ins. Odd sizes were made, by inserting "blanks" in the
mold box, to inches or fractions of an inch if desired. This unit
length was less mortar joints, while the unit of height was 9 ins., or
the same as four ordinary bricks with joints. The floor levels were
calculated in multiples of 9 ins., so that the wall could be finished
all around where the beams were to be seated. This beam course was made
of solid blocks; that is, no cores were used in molding them. With the
machine used no change was required to mold these solid blocks except to
remove the cores. The core holes in the working plate were simply
covered with pieces of tin. The shape of the block was the same and the
same materials were used.
The best record in making blocks for this work was 30 blocks, 8×9×32
ins., in one hour, working six men, three mixing and three on the
machine, and using one barrel of cement for 16 blocks. This was a record
run, however, a fair average being 20 blocks per hour, or 200 per ten
hours, which was the day worked. We have then the cost of making blocks
as follows:
1 foreman, at $2.50 $ 2.50
5 helpers, at $2 10.00
13 barrels cement, at $2 26.00
10 cu. yds. sand and gravel, at $1 10.00
Interest and depreciation on machine 2.00
------
Total for 200 blocks $50.50
This gives a cost per block of $50.50 ÷ 200 = 25¼ cts. The displacement
in the wall of each block is 1.75 cu. ft., or the same as 30 bricks.
The cost of laying blocks is the most uncertain item in the whole
industry. Mr. Palmer states that he has known of instances where it cost
only 5 cts. per block and of other instances where, because of the
difficulty of getting help and its inexperience, it cost 15 cts. per
block. In this particular building one mason and three helpers laid 100
blocks per day. The building had no long walls, but it did have many
turns. The cost of laying, then, was as follows:
1 mason, at $4 $ 4.00
3 helpers, at $2 6.00
-----
Total for 100 blocks $10.00
This gives a cost for laying of 10 cts. per block. We have, then:
Making 2,000 blocks $505
Laying 2,000 blocks 200
----
Total $705
This gives a cost of 35¼ cts. per block for making and laying.
The use of a derrick for laying the blocks proved a considerable item of
economy in this work. This derrick cost $50 and two men could mount and
move it on the floor beams. It had a boom reaching out over the wall and
was operated by a windlass. A plug and feather to fit the center 6-in.
hole in the block was used for hoisting the blocks. By this means blocks
only seven days old were laid without trouble. It may be noted that the
walls were kept drenched with water to make sure that the blocks did not
dry out until they were at least 28 days old. In laying the blocks a
thin lath was used to keep the mortar back about one inch from the face.
This precaution will prevent much labor in cleaning the walls from
mortar slobber.
~Two-Story Building, Albuquerque, N. M.~--The following record of cost of
making 9×10×32-in. hollow blocks in a Palmer machine and of laying 2,000
of them in two-story building walls is given by Mr. J. M. Ackerman. Sand
cost 60 cts. per cu. yd., and cement cost $3 per barrel. Lime cost 30
cts. per bushel. One barrel of cement made 20 blocks, using a 1-4 sand
mixture. In making 2,000 blocks about 100 blocks, or 5 per cent., were
lost by blocks breaking in hauling from yard to building or by cutting
blocks to fit the work. The blocks were molded by piece work for 5 cts
per block, all materials, tools and plant being supplied to the molders.
Three men with one machine made from 100 to 150 blocks per day. The cost
was as follows:
Item. Per block.
Cement, at $3 per bbl. $0.15
Molding, at 5 cts. per block 0.05
Sand, at 60 cts. per cu. yd. 0.03
Carting, yard to building 0.02
Lime and sand for mortar 0.03
Laying in wall 0.10
Loss in making and cutting 0.01
-----
Total $0.39
As each block gave 9 × 32 = 288 sq. ins., or 2 sq. ft., of wall surface,
the cost of the wall per square foot was 19.5 cts. Assuming 40 per cent.
hollow space, each block contained 1 cu. ft. of concrete, which cost 23
cts., or $6.21 per cu. yd., for materials and molding. Blocks in the
wall cost $10.55 Per cu. yd. of concrete.
~General Cost Data.~--The following data are given by Prof. Spencer B.
Newberry. The average weights of three sizes of hollow blocks are as
follows:
Size, ins. P. C. Hollow Space. Weight, lbs.
8×9×32 33-1/3 120
10×9×32 33-1/3 150
12×9×32 33-1/3 180
Costs of materials are assumed as follows:
Item. Per 100 lbs.
Cement, at $1.50 per bbl. $0.40
Hydrated lime, at $5 per ton $0.25
Sand, gravel or screenings, at 25 cts. per ton $0.012
Mixed in batches of 750 lbs., sufficient for six 8-in. or four 12-in.
blocks, the cost of materials per batch and per block will be for a 1-4
mixture as follows:
Item. Per Batch. 8-in. Block. 12-in. Block.
150 lbs. cement $0.60 $0.10 $0.15
600 lbs. sand 0.072 0.012 0.018
------ ------ ------
Total $0.672 $0.112 $0.168
In general a factory producing 600 8-in. blocks per day will require 25
men to operate it. At an average wage of $1.80 per day the following is
considered as a fair estimate of cost:
Item. Per Day. Per Block.
Materials for 600 blocks $ 60 $0.10
25 men, at $1.80 45 0.075
Repairs 10 0.017
Office and miscellaneous 20 0.034
---- ------
Total $135 $0.226
This gives for 8×9×32-in. blocks a cost of about $6.78 per cu. yd. of
concrete for materials and molding or of 11.3 cts. per sq. ft. of face.
Mr. L. L. Bingham gives the following as the average cost per square
foot of face for 10-in. wall from data collected from a large number of
block manufacturers operating in Iowa in 1905:
Cement at $1.60 per bbl. 4.5 cts.
Sand 2.0 cts.
Labor at $1.83 per day 3.8 cts.
---------
Total cost per square foot 10.3 cts.
Assuming one-third hollow space, the cost for materials and molding was
$5.05 per cu. yd. of concrete not including interest, depreciation,
repairs, superintendence or general expenses.
CHAPTER XXI.
METHODS AND COST OF AQUEDUCT AND SEWER CONSTRUCTION.
Aqueducts and sewers in concrete are of three kinds: (1) Continuous
monolithic conduits, (2) conduits laid up with molded concrete blocks,
and (3) conduits made up of sections of molded pipe. Block conduits and
conduits of molded pipe are rare in America compared with monolithic
construction; examples of each are, however, given in succeeding
sections, where forms, methods of molding, etc., are described. The
following discussion refers to monolithic construction alone.
~FORMS AND CENTERS.~--Forms and centers for conduit work have to meet
several requirements. They have to be rigid enough not only to withstand
the actual loads coming on them, but to keep from being warped by the
alternate wetting and drying to which they are subjected. They have also
to be constructed to give a smooth surface to the conduit. To be
economical, they have to be capable of being taken down, moved ahead and
re-erected quickly and easily. The carpenter costs run high in
constructing conduit forms, so that each form has to be made the most of
by repeated use.
Three different constructions of traveling forms are described in the
succeeding sections. For small work, such forms appear to offer certain
advantages, but for conduits of considerable size their convenience and
economy are uncertain. The experience with the large traveling form
employed on the Salt River irrigation works in Arizona was, when all is
said, rather discouraging. The authors believe that for work of any size
where the concrete must be supported for 24 hours or more, forms of
sectional construction will prove cheaper and more expeditious than any
traveling form so far devised.
No class of concrete work, perhaps, offer so good an opportunity for the
use of metal forms as does conduit work. The smooth surface left by
metal forms is particularly advantageous, and there is a material
reduction in weight and a large increase in durability due, both to the
lack of wear and to freedom from warping. Steel forms of the Blaw type
shown by Fig. 247, have been used for conduits up to 25 ft. in diameter.
The form illustrated, Fig. 247, was for a 12-ft. 3-in. sewer; in this
case a roof form alone was used, but full circular and egg-shape forms
are made. The Blaw collapsible Steel Centering Co., of Pittsburg, Pa.,
make and lease steel forms of this type.
[Illustration: Fig. 247.--Blaw Collapsible Steel Centering for Conduit
Construction.]
Sectional wooden forms for conduits of large diameters are shown by the
drawings in several of the succeeding sections. Figures 248 and 249 show
such forms for small diameters. The form shown by Fig. 248 is novel in
the respect that after being assembled a square timber was passed
through it lengthwise, occupying the holes B and having its ends
projecting and rounded to form gudgeons. The form was mounted with
these gudgeons resting on horses, so that it could be rotated and thus
wound with a narrow strip of thin steel plate. Thus sheathed, the form
was lowered into the trench and the concrete was placed around it. When
the arch had been turned, the wedges A were driven in until the ribs
C dropped into the slots a and clear of the steel shell; the arch form
was then pulled out and finally the invert form, leaving the steel shell
in place to hold the concrete until hard. The strip of steel was then
removed by pulling on one end until it unwound like cord from the inside
of a ball of twine. Steel strips 6 ins. wide and 1/24 in. thick were
used successfully in constructing a 5-ft. egg-shaped sewer in
Washington, D. C. The forms were made in sections 16 ft. long, and were
taken out as soon as the concrete had been placed.
[Illustration: Fig. 248.--Sectional Steel Wrapped Wooden Form for
Conduit Construction.]
[Illustration: Fig. 249.--Invert Form for Conduit Construction.]
The form shown by Fig. 249, is an invert form, used in constructing the
sewer shown by Fig. 249, built at Medford, Mass., in 1902, by day labor.
The concrete was 1-3-6 gravel. The forms for the invert were made
collapsible and in 10-ft. lengths. The two halves were held together by
iron clamps and hook rods. The morning following the placing of the
concrete the hook rods were removed and turnbuckle hooks were put in
their places, so that by tightening the turnbuckle the forms were
carefully separated from the concrete. The concrete was then allowed to
stand 24 hours, when the arch centers were set in place. These centers
were made of 7/8×1½-in. lagging on 2-in. plank ribs 2 ft. apart, and
stringers on each side. Wooden wedges on the forward end of each section
supported the rear end of the adjoining section. The forward end of each
section was supported by a screw jack placed under a rib 2 ft. from the
front end. To remove the centers, the rear end of a small truck was
pushed under the section about 18 ins.; an adjustable roller was
fastened by a thumb screw to the forward rib of the center; the screw
jack was lowered allowing the roller to drop on a run board on top of
the truck; the truck was then pulled back by a tail rope until the
adjustable roller ran off the end of the truck; whereupon the truck was
pulled forward drawing the center off the supporting wedges of the rear
section. Each lineal foot of sewer required 1¼ cu. yds. of excavation
which cost 74.2 cts. per foot, and 1 cu. ft. of brick arch which cost
$12.07 per cu. yd., or 44.2 cts. per lineal foot of sewer. The invert
required 4 cu. ft. of concrete per foot, which cost as follows:
Item. Per cu. yd.
Portland cement at $2.15 per bbl. $2.292
Labor mixing and placing 3.017
Cost of forms 0.187
Labor screening gravel 0.471
Carting 0.592
Miscellaneous 0.146
------
Total $6.705
The cost of the invert was thus $1.002 per lin. ft. of sewer.
Collapsible metal forms for manholes and catch basins are made by
several firms which make block and pipe molds. A cylindrical wooden form
construction is shown by Fig. 250. The outside form consists of three
segments of a cylinder made of 2-in. lagging bolted to hoops. Bent lugs
on the ends of the hoops, were provided with open top slots and were
bolted together through 1×3/8-in. bars which extended the full length of
the form between lugs. The assembled form was collapsed by pulling up on
the bars, thus lifting the bolts out of the slots. The inner mold is
also made in three sections with strap hinges at two of the joints and
at the third joint a wedge-shaped stave. The other details are shown by
the drawing. To mold the top of the basin two cone-shaped forms are
used, an outer form made in one piece and an inner form made in
sections. Some 26 catch basins were built in Keney Park, Hartford,
Conn., by Mr. H. G. Clark, at a cost of $7 apiece for concrete in place,
and there was closely 1 cu. yd. of concrete in each.
[Illustration: Fig. 250.--Form for Circular Catch Basin or Manhole.]
~CONCRETING.~--Except for pipes of small diameter, the concreting is done
in sections, each section being a day's work. Continuity of construction
has not proved successful, except for pipes of moderate size, in the few
cases where it has been tried. Examples of continuous construction
methods are given in succeeding sections. Methods of molding and laying
cast concrete pipe are also best shown by the specific examples given
further on. In concreting large diameters, the work may be done by
molding successive full barrel sections, or by molding first the invert
and then the roof arch, each in sections. The engineer's specifications
generally stipulate which plan is to be followed. Construction joints
between sections are molded by bulkhead forms framed to produce the type
of joint designed by the engineer; the most common type is the tongue
and groove joint.
[Illustration: Fig. 251.--Cross-Section of Pinto Creek Irrigation
Conduit.]
For small diameters built with traveling forms, a comparatively dry
concrete is essential, but when the centers are left in place until the
concrete has set, a wet mixture is preferable, as it is more easily
placed and worked around the reinforcement in the thin shells. Mixers
are commonly specified even for small work, because of their generally
more uniform and homogeneous product. Portable mixers hauled along the
bank and discharging into the forms through chutes, furnish a cheap and
rapid arrangement where the section being built has a considerable
yardage. The examples given in succeeding sections present various
methods of mixing and placing concrete in conduit work.
[Illustration: Fig. 252.--Traveling Form for Pinto Creek Conduit.]
~REINFORCED CONDUIT, SALT RIVER IRRIGATION WORKS, ARIZONA.~--The pipe had
the cross-section shown by Fig. 251, and formed a syphon carrying water
under the bed of a creek. The concrete was a 1-2½-4 fine gravel mixture,
mixed by hand on boards 150 ft. apart along the line. The shell was
reinforced as shown.
The forms consisted of an outside form constructed as shown by Fig. 251,
by inserting 2½-in.×5½ ft. lagging strips in the metal ribs. The inside
form was designed to permit continuous work by moving the form ahead as
the concreting progressed. It consisted as shown by Fig. 252, of an
invert form on which an arch form was carried on rollers. The invert
form was pulled along by cable from a horsepower whim set ahead, being
steered, aligned and kept to grade by being slid on a light wooden
track. It had the form of a long half cylinder, with its forward end
beveled off to form a scoop-like snout. The arch center consisted of
semi-circular rings 2 ft. long, set one at a time as the work required.
Each ring, when set, was flange-bolted to the one behind, and each was
hinged at three points on the circumference to make it collapsible. In
operation, the invert form was intended to be pulled ahead and the arch
rings to be placed one after another in practically a continuous
process. So that the arch rings might continue supported after the
invert form was drawn out from under them, invert plates similar to the
arch plates were inserted one after another in place of the shell of the
invert form. The plan provided very nicely for continuous work, but
continuous work was found impracticable for all but about 2,500 ft. of
the 6,000 ft. of conduit built. The reason for this seems to have been
at least in a great measure, the slow setting cement made at the cement
works established by the Government, at Roosevelt. In building the first
300 ft. of conduit, a commercial cement was used and a progress of 120
lin. ft. of pipe per 24 hours was easily made. This work was done in
June. Later, but still in warm weather, using the Government cement and
70 ft. of arch plates, not more than 70 ft. of pipe could be completed
in 24 hours; if the plates were taken down sooner, patches of concrete
fell out or peeled off with them. As the weather grew colder, this
difficulty increased, until finally, the idea of continuous work was
abandoned and for some 3,500 ft. of conduit only one 8-hour shift per
day was worked. In December and January the plates had to remain in
place three days, so that the progress was only 24 ft. per day; in warm
weather this rate was increased to 40 ft. per day.
Costs were kept on two sections of one of the lines and the figures
shown in the accompanying table were obtained.
A gang consisted of a foreman at $175 per month, a sub-foreman at $3.50
per day, and the following laborers at $2.50 per day: one bending the
reinforcement rings; two placing the reinforcement; four taking down,
moving and erecting the stationary plates; four placing the concrete and
outside lagging; two wheeling concrete; six mixing concrete; one
wheeling sand and gravel; one watering the finished pipe; four laying
track for the steering apparatus, moving the superstructure and hangers,
mixing boards, runways, etc.; one pointing and finishing inside the
pipe; and one on the whim and doing miscellaneous work. The labor was
principally Mexican, and only fairly efficient.
It is important to note that the costs given in the table are labor
costs only of mixing and placing concrete and moving forms; they do not
include engineering, first cost of forms, concrete materials,
reinforcement or grading.
May, '06. July, '06.
Wages 714 1,009 Cost Per
Per Lin. Ft. Lin. Ft. Per Cu.
Day. Cost. Cost. Lin. Ft. Yd.
{ Laying track for
{ steering alligator $ 5.00 $ 71.48 $ 43.98 $0.0670 $0.16
4 men { Moving and erecting
{ superstructure 5.00 299.94 358.44 0.3821 0.93
4 men Moving plates 10.00 202.50 253.44 0.2646 0.65
Repairs to alligator 58.50 2.50 0.0354 0.08
1 man Bending rings 2.50 32.87 59.87 0.0538 0.13
2 men Placing reinforcement 5.00 126.94 138.13 0.1538 0.38
12 men Mixing and placing
concrete 30.00 709.68 949.74 0.9631 2.34
1 man Watering finished pipe. 2.50 45.00 78.27 0.0716 0.17
1 man Painting and
brush-coating inside 2.50 96.50 117.37 0.1241 0.31
Blacksmith's work 30.00 25.00 0.0319 0.08
1 man Whim 2.50 23.87 28.75 0.0306 0.07
1 man Screening and hauling
sand and gravel 2.50 183.13 300.00 0.2804 0.68
--------- --------- ------- -----
Total $1,880.41 $2,335.49 $2.4584 $5.98
~CONDUITS, TORRESDALE FILTERS, PHILADELPHIA, PA.~--At the Torresdale plant
of Philadelphia filtration system the clear water conduits are
reinforced concrete. The following description is composed from
information furnished the authors in 1904 by the Bureau of Filtration,
Mr. John W. Hill, then chief engineer. The lengths of the several
conduits are as follows: 576 ft. of 7½-ft., 782 ft. of 8-ft., 1,050 ft.
of 9-ft., and 1,430 ft. of 10-ft. horseshoe conduit. All sizes of
conduit have the same cross-sectional form--the cross-section of the
9-ft. conduit is shown by Fig. 253, and all are reinforced by expanded
metal arranged as indicated. The concrete is a 1-3-5, ¾-in. stone
mixture. The conduits were first designed with circular sections, but
before construction had been begun on these plans, experience had been
obtained in building a circular sewer that made a change to the
horseshoe section appear desirable. In the circular sewer work, great
difficulty had been found in properly placing and ramming the concrete
in the lower quarters of the circular section.
[Illustration: Fig. 253.--Section of 9-ft. Conduit, Philadelphia Filter
Plant.]
_Forms._--The forms used for the several sizes of conduit were all of
the same general type, but improvements in detail were made as
successive sizes were built. The last form to be designed was that for
the 9-ft. section and this was the best one; it is shown by Fig. 254.
The forms were built in sections from 12 ft. to 13½ ft. long. They were
covered with No. 27 galvanized sheet iron, and this covering was found
of advantage both in giving a smooth finish and in prolonging the life
of the centers. The important feature is the construction in sections
which could be set up and broken down by simply inserting and removing
the connecting bolts. Three sets of forms were made for each size of
conduit.
[Illustration: Fig. 254.--Form for 9-ft. Conduit Philadelphia Filter
Plant.]
_Procedure of Work._--The first operation in building a section of
conduit was to set to exact line and grade and the length of the form in
advance of the finished work the bulkhead shown by Fig. 255. In this
space the invert concrete was deposited and formed to a plane 1 in.
below the finished invert bottom. The two bottom sections of the form
were then assembled and located by bolting one end to the last preceding
form and inserting the other end into the bulkhead. About two tons of
pig iron were then placed on the invert form to keep it from floating
while the liquid granolithic mixture was being poured into the 1-in.
space between the form and the invert concrete. In building up the sides
a facing form was used for placing the granolithic finish. This
consisted of "boards" of sheet steel ribbed transversely on one side
with ¾-in. pipe and on the other side with 1½-in. pipe. Two boards were
used on each haunch, slightly lapping in the center, as follows: The
board was placed with the small ribs against the form and the larger
ribs kept the expanded metal just 3 ins. from the face of the form. A
6-in. depth of concrete was placed between the metal board and the
outside form or planks, then 6 ins. of granolithic was poured into the
1-in. space between the center and the board and finally the board was
raised 6 ins. and the concrete and granolithic mixture tamped together.
With the board in its new position, another layer of concrete and
granolithic was placed. Toward the crown the granolithic mixture was
made stiff and simply plastered onto the mold. The expanded metal was
cut into sheets corresponding to the length of the sides of the form and
lapped 6 ins. in all directions; the bulkhead having a slot as shown to
permit the metal to project 6 ins. from the face of the concrete in
order to tie two sections together and also having a rib which formed a
mortise in the face of the shell of concrete to key it to the succeeding
section.
[Illustration: Fig. 255.--Bulkhead Form for Conduits, Philadelphia
Filter Plant.]
All the conduits were built in sections from 12 ft. to 13½ ft. long, and
there was very little, if any, difference in the labor required to build
a section, in from eight to ten hours, of any of the three sizes. One
foreman and 18 men on the top of the trench mixed and handled the
concrete and granolithic mortar while one foreman, one carpenter and
seven men in the trench set the forms and placed and rammed the concrete
for one section in generally eight hours. About one-third of the
concrete for the whole work was mixed in a portable cubical mixer of ½
cu. yd. capacity, and the remainder was mixed by hand. Owing to the
relatively small amount of concrete used per day, about 20 cu. yds., it
was found that there was practically no difference in the cost of
machine mixing and of hand mixing. The 9-ft. conduit as an average of
the three sizes, contained 20 cu. yds. of concrete, 1,200 sq. ft. of
expanded and required 125 bags of cement for a section 13½ ft. long. The
cost of the work excluding excavation and profit, but including forms,
metal, concrete materials and labor, was about $10.50 per cu. yd.
~CONDUIT, JERSEY CITY WATER SUPPLY.~--In constructing the 8½-ft.
reinforced concrete conduit for the Jersey City water supply, use was
made of forms without bottoms. Each form was made of segmental sections
12½ ft. long of wood covered with sheet steel. They were set end to end
in the trench, resting on 6-in. concrete cubes which were finally
permanently embedded in the invert concrete. In each form there was a
scuttle about 2 ft. square at the crown, and the bottom was open between
the curves of the invert haunches. The form being set and greased and
the reinforcement placed, the concrete was deposited on the outside and
forced by means of tamping bars down the curve of the invert haunches
until it filled the whole space between the form and the earth and
appeared at the edges of the bottom opening in the form. Concrete was
then thrown through the scuttle and the invert screeded into shape. The
concreting of the sides and crown of the arch was then completed, using
outside forms except for about 5 ft. of the crown, the scuttle, of
course, being closed by a fitted cover. The centers were left in place
about 48 hours. The concrete was a 1 cement 7 sand and run of the
crusher 2-in. broken stone mixture, and was made so wet that it would
flow down an incline of 1 on 8. The mixing was done in portable Ransome
mixers, set on the trench bank alongside the work and discharging by
chute into dished shoveling boxes provided with legs to set on the
erected forms. Coal scoops were used in shoveling from the box into the
forms and were found superior to shovels in keeping the relative
proportions of water and solids constant.
~TWIN TUBE WATER CONDUIT AT NEWARK, N. J.~--In constructing the Cedar
Grove Reservoir, at Newark, N. J., two conduits side by side were built
across the bottom from gate house to tunnel outlet. A section of one of
the conduits showing the form construction and the arrangement of the
reinforcement is given by Fig. 256. The concrete was a 1-2-5 1½-in.
stone mixture and the reinforcement was No. 10 3-in. mesh expanded
metal. The method and cost of construction are given as follows, by Mr.
G. C. Woollard, the engineer for the contractors.
[Illustration: Fig. 256.--Conduit for Cedar Grove Reservoir, Newark. N.
J.]
"The particular thing that was insisted upon by both Mr. M. R. Sherrerd,
the chief engineer of the Newark Water Department and Mr. Carlton E.
Davis, the resident engineer at Cedar Grove Reservoir, in connection
with these conduits, was that they be built without sections in their
circumference, that the whole of the circumference of any one section of
the length should be constructed at one time. They were perfectly
willing to allow us to build the conduit in any length section we
desired, so long as we left an expansion joint occasionally which did
not leak.
"The good construction of these conduits was demonstrated later, when
the section stood 40 lbs. pressure to the square inch, and, in addition,
I may say that these conduits have not leaked at all since their
construction. This shows the wisdom of building the conduit all round in
one piece, that is, in placing the concrete over the centers all at one
time, instead of building a portion of it, and then completing that
portion later, after the lower portion had had an opportunity to set.
"The centers which I designed on this work were very simple and
inexpensive, as will be gathered from the cost of the work, when I state
that this conduit, which measured only 0.8 cu. yd. of concrete to the
lineal foot of single conduit, cost only $6.14 per cu. yd., built with
Atlas cement, including all labor and forms and material, and expanded
metal. The forms were built in 16 ft. lengths, each 16 ft. length having
five of the segmental ribbed centers such as are shown in Fig. 256,
viz., one center at each end and three intermediate centers in the
length of 16 ft. These segments were made by a mill in Newark and cost
90 cts. apiece, not including the bolts. We placed the lagging on these
forms at the reservoir, and it was made of ordinary 2×4 material,
surfaced on both sides, with the edges beveled to the radius of the
circle. These pieces of 2×4 were nailed with two 10d. nails to each
segment. The segments were held together by four ½-in. bolts, which
passed through the center, and 1½-in. wooden tie block. There was no
bottom segment to the circle. This was left open, and the whole form
held apart by a piece, B, of 3×2 spruce, with a bolt at each end
bolted to the lower segment on each side.
"The outside forms consisted of four steel angles to each 16 ft. of the
conduit, one on each end, and two, back to back, in the middle of each
16 ft. length. These angles were 2×3, with the 2-in. side on the
conduit, and the 3-in. side of the angle had small lugs bolted on it at
intervals, to receive the 2×12 plank, which was slipped down on the
outside of the conduit, as it was raised in height. The angles were held
from kicking out at the bottom by stakes driven into the ground, and
held together at the top by a 2½-in. tie-rod.
"The conduit was 8 ins. thick, save at the bottom, where it was 12 ins.
The reason for the 12 ins. at the bottom was that the forms had to have
a firm foundation to rest on, in order to put all the weight required by
the conduit on them in one day or at one time, without settling. We
therefore excavated the conduit to grade the entire length, and
deposited a 4-in. layer of concrete to level and grade over the entire
length of the conduit line. This gave us a good, firm foundation, true
and accurate to work from, and this is the secret of the good work which
was done on these conduits. If you examine them, you will say that they
are one of the neatest jobs of concrete in this line that has been
built, especially with regard to the inside, which is true, level and
absolutely smooth. [The authors can confirm this statement.] When the
conduit is filled with water, it falls off with absolutely no point
where water stands in the conduit, owing to its being out or the proper
amount of concrete not being deposited.
"The centers were placed in their entirety on a new length of conduit to
be built, resting upon four piles of brick, two at each end as shown.
The first concrete was placed in the forms at the point marked X and
the next concrete was dropped in through a trap door cut in the roof of
the conduit form at the point marked Y. This material was dropped in
to form the invert, and this portion was shaped by hand with trowels and
screeded to the exact radius of the conduit. The concrete was then
placed continuously up the sides, and boards were dropped in the angles
which I have mentioned, and which served as outside form holders till
the limit was reached at the top, where it was impossible to get the
concrete in under the planking and thoroughly tamped. At this point the
top was formed by hand and with screeds.
"Each 16-ft. length of this conduit was made with opposite ends male and
female respectively, that is, we had a small form which allowed the
concrete to step down at one end to 3 ins. in thickness for 8 ins. back
from the end of the section, and on the other end of the section it
allowed it to step down to 3 ins. in thickness in exactly the opposite
way, making a scarf joint. This was not done at every 16 ft. length,
unless only 16 ft. were placed in one day. We usually placed 48 ft. a
day at one end of the conduit with one gang of men. This was allowed to
set 24 hours, and, whatever length of conduit was undertaken in a day,
was absolutely completed, rain or shine, and the gang next day resumed
operations at the other end of the conduit on another 48 ft. length.
This was completed, no matter what the weather conditions were, and,
towards the close of this day the forms placed on the preceding day were
being drawn and moved ahead.
"The method used in moving these forms ahead for another day's work is
probably one of the secrets of the low cost of this work, and it is one
which we have never seen employed before. The bolt at A, Fig. 256, was
taken out, and the tie brace B thrown up. We had hooks at the points
C. A turnbuckle was thrown in, catching these hooks, and given several
sharp turns, causing the entire form to spring downward and inwards,
which gave it just enough clearance to be carried forward, without doing
any more striking of forms than pulling the bolt at A. This method of
pulling the forms worked absolutely satisfactorily, and never gave any
trouble, and we were able to move the forms very late in the day and get
them all set for next day's work, giving all the concrete practically 24
hours' set, as we always started concreting in the morning at the
furthest end of the form set up and at the greatest distance from the
old concrete possible in the 48 ft. length, as the furthest form had, of
course, to be moved first, it being impossible to pass one form through
the other.
"Six 16-ft. sections of these forms were built, and three were used each
day on each end, as shown by the diagram MN, Fig. 256, which gives the
day for the month for the completion of each of seven 48-ft. sections.
"A gang of men simply shifted on alternate days from end to end of the
conduit, although several sections were in progress at one time; and of
course, finally, when a junction was made between any division, say of
1,000 ft. to another 1,000 ft., one small form was left in at this
junction inside of the conduit, and had to be taken down and taken out
the entire length of the conduit.
"The centers for a 16-ft. length of this conduit cost complete for labor
and material, $18.30, but they were used over and over again; and, after
this conduit was completed, they were taken away for use at other
points, so that the cost is hardly appreciable, and the only charge to
centers that we made after the first cost of building the centers, was
on account of moving them daily. Part of this conduit was built double
(two 6-ft. conduits) and part single, the only difference being that,
where the double conduit was built, two forms were placed side by side,
and not so much was undertaken in one day.
"These conduits, when completed and dried out, rung exactly like a
60-in. cast-iron pipe, when any one walked through them or stamped on
the bottom."
Mr. Woollard gives the following analysis of the cost per cubic yard of
the concrete-steel conduit above described:
Per cu. yd.
1.3 bbl. cement $1.43
10 cu. ft. sand 0.35
25 cu. ft. stone 1.10
26 sq. ft. expanded metal, at 3 cts. 0.78
Loading and hauling materials 2,000 ft.
to the mixing board (team at $4.50) 0.50
Labor mixing, placing, and ramming 1.38
Labor moving forms 0.60
-----
Total $6.14
Wages were 17½ cts. per hr. for laborers and 50 cts. per hr. for
foremen. The concrete was 1-2-5, a barrel being assumed to be 3.8 cu.
ft. The concrete was mixed by hand on platforms alongside the conduit.
The cost of placing and ramming was high, on account of the expanded
metal, the small space in which to tamp, and to the screeding cost. When
forms were moved they were scraped and brushed with soft soap before
being used again.
From Mr. Morris R. Sherrerd, Engineer and Superintendent, Department of
Water, Newark, N. J., we have received the following data which differ
slightly from those given by Mr. Woollard. The differences may be
explained by the fact that the cost records were made at different
times. Mr. Sherrerd states (Sept. 26, 1904,) that each batch contains 4
cu. ft. of cement, 8 cu. ft. of sand, and 20 cu. ft. of stone, making 22
cu. ft. of concrete in place. One bag of cement is assumed to hold 1
cu. ft. He adds that a 10-hour day's work for a gang is 63 lin. ft. of
single 6-ft. conduit containing 47.4 cu. yds. of concrete and 1,260 sq.
ft. of expanded metal. This is equivalent to ¾ cu. yd. of concrete per
lin. ft. The total cost of material for one complete set of forms 64 ft.
long was $160; and there were 7 of these sets required to keep two gangs
of men busy, each gang building 63 lin. ft. of conduit a day. Since the
total length of the conduit was 3,850 ft., the first cost of the
material in the forms was 18 cts. per lin. ft.
Cost of Labor on 6-ft. Conduit:
Per day. Per cu. yd.
1 foreman on concrete $ 3.35 $0.07
1 water boy 0.75 0.01
11 men mixing at $1.75 19.25 0.39
5 men mixing at $1.50 7.50 0.16
4 men loading stone at $1.40 5.60 0.12
4 men wheeling stone at $1.40 5.60 0.12
2 men loading sand at $1.40 2.80 0.06
2 men wheeling sand at $1.40 2.80 0.06
1 man placing concrete at $1.75 1.75 0.04
6 men placing concrete at $1.50 9.00 0.19
2 men supplying water at $1.50 3.00 0.06
1 man placing expanded metal at $2. 2.00 0.04
1 man placing expanded metal at $1.50 1.50 0.03
------ -----
Total labor on concrete $64.90 $1.35
Cost of Labor Moving Forms:
Per day. Per cu. yd.
4 carpenters placing forms $13.00 $0.27
2 helpers placing forms 4.00 0.08
1 carpenter putting up boards
for outside forms 2.75 0.06
1 helper putting up boards
for outside forms 2.25 0.05
2 helpers putting up boards
for outside forms 3.50 0.07
1 team hauling timber 4.50 0.09
1 helper hauling lumber 1.75 0.04
------ -----
Total labor moving $31.75 $0.66
It will be noted that it required two men to bend and place the 700
lbs., or 1,260 sq. ft., of expanded metal required for 63 lin. ft. of
conduit per day, which is equivalent to ½c per lb., or 3 cts. per sq.
ft., for the labor of shaping, placing and fastening the metal.
~CIRCULAR SEWER, SOUTH BEND, INDIANA.~--In building 2,464 ft. of 66-in.
circular reinforced concrete sewer at South Bend, Ind., in 1906, the
method of construction illustrated in Figs. 257, 258 and 259 was
employed. The sewer has a 9-in. shell buttressed on the sides and is
reinforced every 12 ins. by a 3/16×1-in. peripheral bar in the sides and
roof and 3 ins. in from the soffit. Each bar is composed of three
pieces, two side pieces from 15 ins. below to 6 ins. above springing
lines and a connecting roof bar attached to the side bars by cotter
pins. Two grades of concrete were used, a 1-3-6 bank gravel concrete for
the invert and a 1-2-4 bank gravel concrete for the arch. The invert was
given a ½-in. plaster coat of 1-1 mortar as high as the springing lines.
[Illustration: Fig. 257.--Form for South Bend Sewer (First Stage).]
[Illustration: Fig. 258.--Form for South Bend Sewer (Second Stage).]
[Illustration: Fig. 259.--Form for South Bend Sewer (Third Stage).]
Forms and Concreting.--In constructing the sewer the trench was
excavated so as to give a clearance of 1 ft. on each side and was
sheeted as shown by Fig. 257. The sewer was built in 12 ft. sections as
follows: The bottom of the trench was shaped as nearly as possible to
the grade and shape of the base of the sewer. Four braces to each 12 ft.
section were then nailed across the trench between the lowest rangers on
the trench sheeting. A partial form consisting of a vertical row of
lagging was set on each of the outside lines of the sewer barrel as
shown by Fig. 257. Each section of this lagging was held by stakes
driven into the trench bottom and nailed at their tops to the cross
braces as shown by Fig. 258. A template for the invert was then
suspended from the cross braces by pieces nailed to the four ribs of the
template and to the cross braces as shown by Fig. 257. The concrete was
now placed and carried to the top of the template, which was then
removed. The side pieces of the reinforcing bars were then set and
fastened as shown by Fig. 258. The side forms extending up to the
springing lines were then placed. They were held in position by braces
nailed to their ribs at the tops and by other braces fitting into
notches in the ends of their ribs at the bottom. The concrete was then
carried up to the springing lines, the arch centers in two pieces were
placed; the arch bar of the reinforcement was placed and the extrados
forms erected up to the 45° lines, all as shown by Fig. 259. The placing
of the arch concrete completed the sewer barrel. The outside forms and
bracing were removed about 24 hours after the completion of the arch and
back filling the trench was begun immediately, but the inside forms were
left in place for two weeks; they were then removed by the simple
process of knocking out the notched braces. By building several lengths
of invert first and following in succession by the side wall
construction and then by the arch construction, the form erection and
the concreting proceeded without interruption by each other. It was also
found that, by making bends in the form of polygons with 10 ft. sides
instead of in the form of curves, there was a material saving in
expensive form work. To overcome the friction of the angles in such
bends an additional fall was provided at these places. All concrete was
made in a Smith mixer mounted on trucks so that it could be moved along
the bank of the trench and discharging into a trough leading to the
work.
_Labor Force and Cost._--With a gang of 12 men from 24 to 36 ft. of
sewer was built per 10-hour day, working only part of the time on actual
concreting. The disposition of the force mixing and laying concrete and
the wages were as follows:
Item. Per day.
Six wheelers, at 18.5 cts. per hour $11.10
One mixer, at 22.5 cts. per hour 2.25
One dumper, at 18.5 cts. per hour 1.85
Four placers, at 22.5 cts. per hour 9.00
------
Total $24.20
There were 0.594 cu. yd. of concrete per lineal foot of sewer and its
cost is given as follows:
Item. Per cu. yd.
Cost of gravel $0.774
Cost of sand 0.36
Cost of cement 1.50
Cost of steel reinforcement 0.84
Cost of labor, mixing and placing concrete 1.094
Cost of moving forms, templates, etc. 0.757
Cost of forms, templates, etc. 0.589
Cost of finishing, plastering, etc. 0.639
Cost of tools and general expenses 0.841
------
Total $7.394
~SEWER INVERT, HAVERHILL, MASS.~--In constructing sewers with concrete
inverts at Haverhill, Mass., in 1905, use was made of the traveling form
or mold shown by Fig. 260. The form consists of an inner and an outer
shell, the annular space between which forms the mold; in operation the
annular space is filled with concrete, then the outer shell is pulled
ahead from underneath, leaving the inner shell in place. A second inner
shell is then adjusted to the outer shell in its new position, the
annular mold is concreted and the outer shell again pulled ahead.
Continued repetition of the operations described completes the invert.
The merit of the device lies in the fact that the inner shell is not
moved until the concrete has attained some degree of rigidity; when, in
such devices, the inner mold is slid ahead on the green concrete it is
likely so to "drag" forward the material that a rough and pitted surface
results.
_Mold Construction._--Referring to the drawings of Fig. 260, A is the
outer mold of sheet steel bent to the required shape of the outer
surface of the conduit to be constructed. A rib, or angle, B, is
riveted to the inside of the mold at its front end and a diaphragm C
of plank is securely fastened to the rear side of the rib. The opposite
or rear end of the mold is open. Angles D forming tracks are riveted
inside the mold a short distance below the edges and reaching their full
length. The inner mold comprises a steel shell E curved to the form of
the inside of the conduit; inside this steel shell is a reinforcing
lagging, and at each end there is a wooden diaphragm F. Passing
through both end diaphragms and having its ends flush with the end
planes of the mold is a timber G. Rearward projecting lips e are
secured to the lagging at the rear end of the mold and on each side of
the timber G. The diaphragms F have each two arms f which project
horizontally beyond the surface of the inner mold and engage the tracks
D; locking dogs H are pivoted to the arms f so as to hook under
the track angles D and hold the inner form from rising. Setting on the
inner mold is an inverted V-shaped deflector I; its edges are flush
with the sides of the mold and its purpose is to facilitate the placing
of the concrete. There is also a movable diaphragm K, fitting loosely
inside the outer mold A and bearing against the end of the inner mold
E. The length of the inner mold E is about one-half that of the
outer mold A; as a rule several inner molds are provided with one
outer mold.
[Illustration: Fig. 260.--Traveling Invert Form for Sewer Construction.]
_Mode of Operation._--In using the device described the outer mold A
is first placed in the trench with its rear end at the end of the
trench. An inner mold E is then suspended on the tracks of the outer
mold and locked therein by the dogs H, with its rear end flush with
the rear end of the outer mold. The partition K is then placed in
position against the forward end of the inner mold and a jack J of any
suitable form is interposed between diaphragms K and C, the jack
being extended sufficiently to press diaphragm K firmly against the
front end of the inner mold. The deflector I is next placed in
position on the inner mold and the concrete is forced down with an iron
rammer between the two molds, so as to fill completely the annular
space. The deflector aids in directing the concrete into this space, as
will be obvious. After the mold has been filled and the concrete
compacted as much as possible, the jack is operated to separate the
diaphragms K and C, and as the partition K is pressed against one
end of the mass of concrete which has been laid, the opposite end of
which abuts against the end of the trench, it follows that any backward
movement of the diaphragm K will compress the concrete. This movement
will be practically inappreciable in distance, but enough to compact
thoroughly the concrete and fill any voids. The action of the jack will
also push forward the diaphragm C and the outer mold A, the latter
being withdrawn from beneath the inner mold and the newly laid concrete,
the tracks D of the outer mold being drawn from beneath the arms f
of the inner mold, leaving the latter behind resting on the freshly laid
concrete. Further compression of the concrete after it has been left by
the outer mold will fill the spaces between the inner mold and the
surface of the trench. The outer mold is moved forward in this manner a
distance equal to the length of the inner mold, and then the diaphragm
K is drawn forward and another inner mold is lowered into the outer
mold exactly as was the first one. The jack is then placed, the concrete
deposited and the outer mold again advanced exactly as before. As the
outer mold advances, the inner molds become disengaged one after another
and are set ahead; in practice, enough inner molds are provided to
enable the concrete to harden sufficiently to keep its position when it
becomes necessary to take up successively the rearmost molds and place
them ahead.
_Haverhill Sewer Work._--The work at Haverhill, Mass., previously
mentioned in which the form just described was used, was a 24-in.
circular sewer with 6-in. walls. The outer form was 36 ins. in diameter
and 6 ft. 2 ins. long; the inner form was 24 ins. in diameter and 3 ft.
long. Angle B was 3 ins. and the track angles D were 1½ ins.; diaphragm
K was made of two thicknesses of 3-in. plank and diaphragm C of one
thickness of 3-in. plank, the other diaphragms were of 2-in. plank. The
shells of the molds were of ¼-in. steel plate; the jack was an ordinary
screw jack. Eight inner molds were used.
The form used at Haverhill was built by the city carpenter, the metal
portions being made in a boiler shop. Its cost was not ascertained, but
was, it is thought, about $75. The concrete used was a 1-3-5 stone
mixture, with cement costing $2 per barrel, sand $1.50 per load of 36
cu. ft., and stone $2.50 per load of 36 cu. ft. The men were paid 25
cts. per hour. Records kept on 265 ft. of invert, or, theoretically,
19.3 cu. yds. of concrete, gave the following figures:
Per Per
lin. ft. cu. yd.
Labor, setting and moving
forms, 42 hours, at 25 cts. $0.05 $0.67
Labor, mixing, placing and wheeling
concrete, 179 hours, at 25 cts. 0.16 2.19
----- -----
Total labor cost $0.21 $2.86
With the ordinary 1-3-5 mixture the cost of materials would run about as
follows:
Per cu. yd.
Cement, 0.96 bbl., at $2. $1.92
Sand, 0.47 cu. yd., at $1.13 0.53
Stone, 0.78 cu. yd., at $1.88 1.47
-----
Total cost materials $3.92
Two men were worked in the trench, one alternately ramming the concrete
into place and working the jack, and the other shaping the trench ahead
and assisting in bringing the rear forms ahead.
The form described was invented by Mr. Robert R. Evans, of Haverhill,
Mass., and has been patented by him.
~29-FT. SEWER, ST. LOUIS, MO.~--The following account of the method and
cost of constructing 162 ft. of very large sewer section at St. Louis,
Mo., is compiled from information furnished by Mr. Curtis Hill.
The cross-section of the sewer is given by Fig. 261, which also shows
the arrangement of the reinforcing bars. Johnson corrugated bars, old
style, are used for reinforcement. The sections of the various
reinforcing bars are: Longitudinal bars, 0.18 sq. in.; invert bars, 0.7
sq. in., and arch bars, 0.7 sq. in. The spacing of the bars and the
arrangement of the splices are indicated on the drawings of Fig. 261.
All splices have a lap of 36 ins. Some gravel concrete has been used in
the invert, but most of the concrete has been crushed limestone and
Mississippi River channel sand. The proportions were 1-3-6 in the invert
and 1-2-5 in the arch. The arch was computed by Prof. Greene's method.
The ultimate strength of concrete in compression was taken as 2,000 lbs.
per sq. in. and the working strength at 500 lbs. per sq. in. The elastic
limit of the reinforcing bars was taken at 50,000 lbs.
[Illustration: Fig. 261.--Harlem Creek Sewer, St. Louis, Mo.]
The trenching was done by wheel scrapers to the amount of waste. Then a
cableway was erected spanning the entire length of the section and the
remainder of the material taken out. The last 4 or 5 ft. in depth were
in limestone and the excavated rock was taken by cableway to dump carts
which took it to the crusher and returned with crushed rock to be used
for concrete. This rock foundation was taken advantage of to reduce the
amount of invert concrete.
In constructing the sewer proper the invert was first concreted to
template to the height shown in Fig. 262. The arch forms were then
placed as shown in Fig. 262, and the roof arch concreted. Both templates
and arch forms were constructed of wood. The arch forms were moved ahead
on iron rails and jacked into place. The ribs were 2×10-in. pieces and
were spaced 4 ft. on centers; the lagging was 2-in. tongue and grooved
stuff and was smeared with crude oil. The reinforcing bars shown in Fig.
261 were bent to proper radius by means of a wagon tire bender and were
held in place by templates. The concrete was all mixed by two Chicago
Improved Cube mixers operated by electric power.
[Illustration: Fig. 262.--Center for Harlem Creek Sewer.]
The cost records of constructing the section of 29-ft. sewer so far
built are not susceptible of complete analysis, but the following
figures can be given. The prices of materials were as follows:
Cement, per barrel $1.80
Sand, per cubic yard 0.75
Broken stone, per cubic yard 1.00
Reinforcing bars, per pound 0.02
Vitrified brick, per 1,000 12.00
The wages paid different classes of labor were:
Per hour.
Firemen $0.50
Laborers 0.175
Laborers 0.20
Laborers 0.25
Laborers 0.28
Laborers 0.3025
Bricklayers 0.66 2/3
Helpers $0.25
Carpenters 0.55
Engineers 0.50
Timekeepers 0.25
Watchmen 0.175
Hostlers 0.175
Teams 0.60
Taking up the several items of work in order, the excavation amounted to
21,400 cu. yds., of which 1,400 cu. yds. were rock excavation. The cost
of excavation was as follows:
Total. Per cu. yd.
Earth, excavation $7,640 $0.38
Earth bracing 2,000 0.10
Rock excavation 1,400 1.00
Rock, dynamite, tools, etc. 560 0.40
The cost of crushing the excavated rock and returning it to the mixer
was $1 per cu. yd.
The cost of the concrete work was as follows:
Per cu. yd.
1.30 bbl. cement at $1.80 $2.34
.044 cu. yd. sand at 75 cts. 0.33
1 cu. yd. broken stone at $1 1.00
-----
Total concrete materials $3.67
There were 1,600 cu. yds. of concrete placed at a cost of for:
Total. Per cu. yd.
Mixing and placing $1,180 $0.7375
Forms 2,000 1.25
Moving forms 400 0.25
------ -------
Total for forms and labor $3,580 $2.2375
For reinforcing the concrete 86,600 lbs. of steel, or about 55 lbs. per
cu. yd. were used. The cost of placing and bending this steel was as
follows:
Total. Per lb.
Cost of placing $172 0.1986 ct.
Cost of bending 52 0.06 ct.
We can now summarize the cost of the concrete work proper of this sewer
as follows:
Items. Per cu. yd.
Cement, sand and stone $3.67
55 lbs. steel at 2 cts. 1.10
Forms, labor and materials 1.25
Mixing and placing concrete labor 0.74
Placing steel at 0.1986 ct. per lb. 0.11
Bending steel at 0.06 ct. per lb. 0.03
Moving forms 0.25
-----
Total labor and materials $7.15
To get the total cost of the sewer proper we must add the cost of the
vitrified brick invert paving. There were 71 cu. yds. of this paving and
its cost was as follows:
Per cu. yd.
0.6 bbls. cement at $1.80 $1.08
0.25 cu. yd. sand at 75 cts. 0.19
450 bricks at $12 per M. 5.40
Labor laying, 71 cu. yds. at $180.33 2.54
-----
Total $9.21
None of the preceding figures includes the plant charges. The plant cost
$12,000 and the cost of running it during the work described was $2,000.
In explanation it should be noted that the plant served for building
some 1,340 lin. ft. of 27-ft. sewer as well as for the section
described.
~SEWER AT MIDDLESBOROUGH, KY.~--In constructing an oval sewer 4 ft. high
at Middlesborough, Ky., two steel forms in 10-ft. sections were used. As
shown in Fig. 263, T-iron ribs were spaced 5 ft. apart, fastened
together at the top by longitudinal angle irons, and at the bottom by a
sheet of steel 22 ins. wide, forming the bottom of the invert. The
lagging for the sides consists of movable 5-ft. lengths of channel iron,
secured by sliding bolts. After the bottom of the trench has been
roughly shaped with concrete, a 10-ft. section of invert forms is
lowered and suspended by the cross-beams, and the space beneath packed
with concrete; then a channel iron is slid into place and bolted, and
concrete packed behind it, and so on until the invert is made. The next
10-ft. section is then built while the first is hardening. Upon the
completion of the second section, the channel iron sides of the first
section are removed, and then the rib framework is lifted out. Wood arch
centers are then put in place and an inch of 1:2 plaster spread over the
lagging before placing the concrete for the arch, which is 6 ins. thick.
[Illustration: Fig. 263.--Invert Form for Sewer Construction.]
The cost per 100 ft. of this sewer was as follows (prices being assumed
for cement and labor):
Bottom concrete. Cost per 100 ft.
18.5 bbls. cement, at $1.50 $ 27.75
2.7 cu. yds. sand, at $1.00. 2.70
15 cu. yds. stone, at $1.00 15.00
17 days labor, at $1.50 25.50
Bottom concrete. Cost per 100 ft.
25.25 bbls. cement, at $1.50 37.85
7.5 cu. yds. sand, at $1.00 7.50
22 days labor, at $1.50 33.00
Sewer Arch.
26 bbls. cement, at $1.50 39.00
3.9 cu. yds. sand, at $1.00 3.90
13.6 cu. yds. stone, at $1.00 13.60
21 days labor, at $1.50 31.50
-------
Cost per 100 ft. $237.30
[Illustration: Fig. 264.--Sewer at Cleveland, Ohio.]
~INTERCEPTING SEWERS, CLEVELAND, O.~--An intercepting sewer some 3½ miles
long, of the form and construction shown in Fig. 264, was built at
Cleveland, Ohio, in 1904. The construction consists of a plain concrete
invert lined with two courses of shale bricks, and having two rows of
anchor bars set in the side walls so that the bars of one row are
staggered with respect to those of the other row. The anchor bars are
2×½-in. steel, and are spaced 30 ins. apart in each row. To the anchor
bars are bolted arch reinforcing bars arranged as shown, and these arch
bars have bolted to them eight lines of 1½×¼-in. longitudinal bars. A
natural cement concrete is used for the invert and side walls. The arch
is Portland cement concrete of normally a 1-3-7½, 1½-in. screened stone
mixture, but where the voids in the broken stone exceeded 40 per cent.,
it is a 1-3-6 mixture. The invert bricks are laid in Portland cement
mortar and the arch has a mortar lining and is waterproofed with 1-in.
of mortar on top.
_Forms._--Separate forms were used for the invert and for the arch ring.
Regarding these, the engineer, Mr. Walter C. Parmley, remarks:
One of the first forms used in the sewer was like a piece of segmental
arch centering inverted, and with the lagging nailed fast to the ribs.
The trouble with this form is that it is difficult to tamp concrete
under the bottom portion of the form, and hence a very rough surface is
produced. Much better results were obtained by omitting the lagging
boards on the bottom and at the sides till a point was reached where the
inclination of the concrete surface was about 45°. The concrete for the
bottom could then be worked down between the ribs, thorough tamping
done, and a good surface obtained. The ribs serve as a guide, so that
the workman produces the proper shape. From this point up to the
vertical, good results can be secured with the ribs attached to the
lagging. Some contractors found it more convenient to use ribs that were
connected with each other by a skeleton framework only, and then to slip
the lagging in, one piece at a time. For some of the sewers, in which
the brick lining was not carried quite up to the spring line, a separate
side form of skeleton ribs and loose lagging was set upon brace legs
bearing on the bottom of the invert. This form carried the concrete from
about 2 ft. below to about 2 ft. above the springing line. The arch ribs
then became segmental and rested upon the middle braces. This method has
the advantage of using ribs that are lighter and more easily handled
than those that are semi-circular. For arch centering, it is necessary
and convenient to use independent ribs and loose lagging, for the
centers can then be carried forward piece-meal, the falsework upholding
the green arch and re-erected at the advance end of the work. In these
matters each contractor prefers to use his own ingenuity, and so long as
the work is properly built, the engineer can well give him considerable
latitude as to use of methods. One thing, however, the engineer must
insist upon--that all centering and falsework be as nearly rigid as
possible. Even a slight settlement of the centers at the crown under the
load of concrete and back-fill will cause the arch to kick out at the
quarters, and if the green concrete arch is not cracked at the crown, it
will be crushed on the inside, about half way between the crown and
springing line. A reinforced arch is no more immune to this danger than
is a plain concrete arch. However, with a few days of hardening,
although the damage may be serious, the danger of actual collapse is
less. A point to be guarded against, especially in reinforced
construction, is any foolish act on the part of contractor or workman,
due to his overconfidence in the strength of the structure because it
contains embedded steel.
The mode of procedure in constructing the arch ring was to erect the
centers with lagging complete. The lagging was then covered with
building paper waterproofed with paraffine. The arch reinforcing bars
were then bolted to the anchor bars and the longitudinals connected up.
The lining of Portland cement mortar was first laid on the lagging.
Before this mortar had set, concrete was rammed in between it and the
sheeting to a height of 18 ins. above the springing line, and then the
remainder of the concrete placed without outside forms. The top of the
arch ring was finally finished with a 1-in. mortar coat. In regard to
the concrete, Mr. Parmley remarks:
"Concrete will flush up to the forms and produce a better surface, and
the voids in the stone will be much better filled if it is so wet as to
require but little tamping; moreover there is less danger of obtaining a
weak, porous wall should a workman neglect thorough tamping, than there
is where only a moist mixture is used. It is also to the contractor's
interest to use wet concrete for much less labor is required in mixing
and placing it. Small broken stone or gravel is preferable in concrete
for sewers. The walls being comparatively thin, unless there be a
considerable excess of mortar, if coarse stones are used, the concrete
will be honeycombed with voids. The stones should be well graded in size
from large to fine, but the largest fragments should not exceed 1½ ins.
in greatest dimension."
_Cost._--A number of records of cost of constructing short sections of
the sewer described are given by Mr. Parmley, as follows:
Labor placing anchor bars. Per day.
1 man, at $3.50 $3.50
1 man, at $1.75 1.75
4 hours carrying steel at 20 cts. 0.80
-----
$6.05
The anchor bars were placed for 40 lin. ft. of sewer, or about 1,504
lbs. of metal at a cost of 0.4 ct. per lb.
The concreting gang for the sides consisted of:
5 men wheeling and mixing at $1.75 $8.75
1 man tamping 1.75
2/3 time man lowering brick and concrete at $2.25 1.50
1 man carrying concrete 1.75
------
$13.75
This gang built the side wall for 40 ft. of sewer daily, or 13 cu. yds.
Cost of labor per cu. yd. was, therefore, $1.06. The concrete was tamped
behind the brick lining as the latter was built up by the mason.
Cost of single ring brick lining at sides:
2 masons at 70 cents per hour $1.20
1 man mixing mortar 2.25
1/3 time man lowering at $2.25 0.75
3 men wheeling sand, filling buckets and dumping 5.25
------
Total labor for 40 lin. ft. of sewer $19.45
Quantity of brick masonry laid, cu. yd. 6.38
Labor per cu. yd. 3.05
An account was kept of labor performed on 85 lin. ft. of arch work, or
14 1-6 ft. daily. The force was as follows:
1 man putting mortar lining on centering $1.75
2 men mixing mortar, screening and wheeling sand 3.50
1 man tamping concrete 1.75
8 men on mixing board at $1.75 14.00
------
$21.00
No. cu. yd. placed daily 25.64
Labor per cu. yd. 0.82
Placing centering and arch bars:
2 men at $1.75 $3.50
1 man at $3.50 3.50
-----
$7.00
Costs, for 14 1-6 ft. daily, $0.49 per lin. ft.
As nearly as could be judged, about two-thirds of the labor was used in
erecting the centering and one-third in putting the steel in place. The
amount of steel placed daily was 785 lbs., at cost, therefore, of 0.3 of
a cent per lb., and the cost of erecting and moving centers, $0.33 per
lin. ft. of arch.
Another record of 39.27 ft. on a curve, gave for the cost of the brick
work at sides the same result as above, but the inspector's record of
men working on concrete backing at sides showed a less cost, as follows:
4 men mixing at $1.75 $7.00
2/3 time man lowering at $2.25 1.50
1 man in bottom 1.75
-----
$10.25
They placed 12.7 cu. yd. at a cost of $0.81 per cu. yd. This figure
probably more nearly represents the average cost than the $1.06 reported
in the first instance.
The cost of placing the anchor bars on straight sewer, representing
average progress, at another time, was found to be:
1 man $3.50
1 man 1.75
-----
$5.25
They placed the steel for 44 ft. of sewer or 1,650 lb. at a cost of 0.32
of a cent per lb.
Further notes for 6 days' work, when it seemed to represent as nearly as
possible the general average for the whole were:
Labor on arch concrete:
Daily progress was 13 1-6 ft.
The force employed was:
7 men making concrete, at $1.75 $12.25
1 man plastering the center 1.75
1 man mixing mortar 2.00
1 man tamping 1.75
-----
$17.75
On straight arch work they placed 24.1 cu. yd. daily at a cost of $0.74
per cu. yd. In three days' work on a curve, the same gang placed 26.37
cu. yd. daily at a cost of $0.675 per cu. yd.
On centering and steel for arch, three men kept up with the regular
progress of the arch-concreting gang. The cost, therefore, is:
1 man $3.50
2 men at $1.75 3.50
-----
$7.00
They averaged 13 ft. daily, or at a total cost of about $0.54 per lin.
ft. of sewer.
Two-thirds of this labor was on the centering or $0.36 per lin. ft. of
arch; $0.18 per lin. ft. placed the steel ready for embedding, or about
55.5 lb. per ft. of arch, at a cost of 0.32 of a cent per lb.
For the double ring brick lining at the bottom, the regular daily rate
of progress was 28 ft. or 11.15 cu. yd. with:
2 bricklayers $11.20
5 men at $1.75 8.75
1 man at $2.25 2.25
-----
$22.20
or at a cost of $1.98 per cu. yd. This is given only because it is of
interest in connection with the cost of the concrete.
Other observations on cost of placing steel skeleton and concrete did
not vary materially from the figures given. It will be observed that no
charge for superintendence or anything for the general expenses is
included in the estimates of cost. These charges were, of course,
impossible to obtain. On another contract with machine mixing, as high
as 36 lin. ft. of 13 ft. 6 in. arch were built in a day, but no data as
to cost were taken, though it was evidently less than for the work with
hand-mixed concrete.
~REINFORCED CONCRETE SEWER AT WILMINGTON, DEL.~--Records of a notable job
of sewer construction at Wilmington, Del., in 1903, are furnished by Mr.
T. Chalkley Hatton. The sewer was built by day labor for the city; its
cross-section at various points is shown by Fig. 265. The cross-section
of sewers in trenches deep enough to cover the arch are marked "deep
cutting"; the sections where the arch projects above the ground surface
are marked "light cutting." The section through the marsh was 700 ft.
long, the cutting being 8 ft. deep, and at high tide the marsh was
flooded 1 to 4 ft. The material was a soft mud that would pull a tight
rubber boot from a workman's foot. The cost of this marsh excavation
including cofferdams, underdraining, pumping, etc., was $4.60 per cu.
yd. For 1,100 ft. the 9¼ ft. sewer was through a cut 22 to 34 ft. deep,
the material being clay underlaid by granite. A Carson-Lidgerwood
cableway was used. Although the crown of the arch was but 8 ins. thick,
it withstood the shock of dumping 1 cu. yd. buckets of earth and rock
from heights of 3 to 10 ft.; and the weight of 25 ft. of loose filling
caused no cracks in the concrete.
Concrete was placed in 4-in. layers (the depth of the lagging) and well
rammed, since it was found that "wet" concrete left small honeycombed
spaces on the inner surface. Concrete for the invert was 1-2-6, the
stone being 1½-in. and smaller, and the sand being crusher dust. The
arch was 1-2-5.
The reinforcing metal used in the 9½-ft. sewer was No. 6 expanded metal,
6-in. mesh, in sheets 8×5½ ft., supplied by Merritt & Co., of
Philadelphia. A single layer was placed around the sewer, 2 ins. from
the inner surface, its position being carefully maintained by the men
ramming, and with but little difficulty as the sheets were first bent to
the radius of the circle. Each sheet was lapped one mesh (6 ins.) over
its neighbor at both ends and sides, and no sheets were wired except the
top ones, which were liable to displacement by men walking over them.
[Illustration: Fig. 265.--Cross-Sections of Sewer at Wilmington, Del.]
The metal used on the rest of the work was a wire-woven fabric furnished
by the Wight-Easton-Townsend Co., of New York. This fabric comes in
rolls 5½ ft. wide and 100 ft. to the roll. The wire is No. 8, with a
6×4-in. mesh. This fabric was placed by first cutting the sheets to the
required length to surround the sewer entirely, embedding it in the
concrete as fast as concrete was placed, in the same manner as was done
with the expanded metal except over the center where, on account of its
pliability, the fabric was held the proper distance from the lagging by
a number of 2-in. blocks which were removed as the concrete was placed.
The wire cloth, being all in one sheet, can be placed a little more
expeditiously than expanded metal, but, on the other hand, the expanded
metal holds its position better in the concrete, since it is more rigid.
We quote now from Mr. Hatton's letter: "The major portion of concrete
was mixed by machine at a cost of 66 cts. per yard, including wheeling
to place, coal and running of mixing machine, wages being $1.50 per day
of 8 hrs, Stone was delivered alongside of machine and all material had
to be wheeled in barrows upon the platform, and after mixing to the
sewer. Placing and ramming concrete around the forms cost 39 cts. per
cu. yd., additional. Setting forms in invert cost 2 cts. per cu. yd.,
setting centers 7 cts. per cu. yd. Cost of setting forms and centers
includes placing steel metal. Each lineal foot of 9¼ ft. sewer contained
1 cu. yd. of concrete, although the section only calls for 0.94 cu. yd.
The excess was usually wasted by falling over sides of forms or being
made too thick at crown.
"This yard of 1-2-5 concrete cost in place as follows (record taken as
an average of several-days' run):
Cement, 1.31 bbls. at $1.30 $1.703
Stone, 0.84 cu. yds. at $1.21 1.016
Stone dust, 0.42 cu. yd. at $1.21 0.508
Labor at 18¾ cts. per hour 0.987
Labor setting forms and setting metal 0.045
Cost of forms (distributed over 1,800 ft. of sewer) 0.082
40 sq. ft. expanded metal at 4¼ cts. 1.700
Labor plastering invert 0.070
------
Cost per ft., or per cu. yd. $6.111
"The forms for the invert were made of 2-in. rough hemlock boards cut
out 4 ins. less diameter than the diameter of the sewer, except for 18
ins. at the bottom of the form which coincided with the inside form of
sewer. The bottom of the sewers was laid to the bottom of this form
before it was set. Then the lagging, consisting of 2×6-in.×16-ft.
hemlock planed, was placed against each side of the form, one at a time,
and the concrete brought to the line of this top in 6-in. layers until
the whole invert was finished. These forms were set in 16-ft. sections,
five to each section.
"The centers consisted of seven ribs of 2-in. hemlock upon which was
nailed 1½-in. lagging, 2 ins. wide, tongued and grooved, and were 16 ft.
long, non-collapsible, but had one wing on each side, 9 ins. wide, which
could be wedged out to fit any inaccuracies in the invert. We used four
of these centers setting two at each operation and worked from two ends.
We left the centers in for 18 hours before drawing.
"The cost of the concrete on the smaller sewers was the same as are the
larger sewers, but the steel metal cost less, as it was wire woven metal
that cost 2½ cts. per sq. ft. It was much easier handled and cut to no
waste as it came in long rolls and was very pliable.
"After training our men, which occupied about one week or 10 days, we
had no difficulty in getting the concrete well placed around the metal,
preserving the proper location of the latter, which, however, bore
constant watching, as a careless workman would often take the temporary
supporting blocks and allow the metal to rest against the wooden center,
in which case the metal would show through the surface inside of the
sewer. The metal was kept 2 ins. away from the inside forms and the
arch. To keep it at this location we had several 2-in. wooden blocks cut
which were slipped under the wire or expanded metal and as soon as some
concrete was pushed under the wire at this point the block was removed.
"After the forms were removed the invert needed plastering, but the arch
was practically like a smoothly plastered wall except where it joined
the invert, where it frequently showed the result of too much hurry in
depositing the first loads of concrete on the arch. We remedied this by
requiring less concrete to be deposited at the start, thus giving the
rammers time to place the material properly.
"An interesting result was obtained in the smoothness of the inside
surface by using a mixture of different sized stones. When ¾-in. stones
or smaller were used in the arch, the inside was honeycombed; but, where
1 to 1½-in. stones (nothing smaller) were used, the inside was perfectly
smooth, and the same was true of the invert, showing that the use of
larger stones is an advantage and secures more monolithic work. When the
run of the crusher from 1½ to ¾-in. stones was used the work was not at
all satisfactory.
"The difference in cost of mixing by hand and machine is practically
nothing on this kind of work. As the moving of the machine to keep pace
with the progress of the work equals the extra cost of mixing by hand
when the mixing can be done close to the point where the cement is being
placed."
The total cost of the sewers, including excavation, etc., was:
Cost per lin. ft.
9¼-ft. sewer through marsh $32.00
9¼-ft. sewer in cut averaging 24½ ft. 24.00
6½-ft. sewer in cut averaging 12 ft. 10.00
5-ft. sewer in cut averaging 11½ ft. 6.70
~SEWER WITH MONOLITHIC INVERT AND BLOCK ARCH.~--The following records of
construction for a sewer built at Coldwater, Mich., in 1901, are given
by Mr. H. V. Gifford. The sewer had a monolithic invert and a block
arch.
The sewer was circular, having an inner diameter of 42 ins., the
thickness of the invert and the arch alike was 8 ins. Figure 266 is a
cross-section. The concrete was 1 of Portland cement to 6 of gravel.
There were 11 concrete blocks in the ring of the arch, each block being
24 ins. long, 8 ins. thick, 8 ins. wide on the outside of the arch and
5¾ ins. wide on the inside of the arch. A block weighed 90 lbs. which
was too heavy for rapid laying; blocks 18 ins. long would have been
better. Some 8,500 blocks were made. Molds were of 2-in. lumber, lined
with tin, for after a little use it was found the concrete would stick
to the wood when the mold was removed. The four sides of the mold formed
the extrados, the intrados, and the two ends of the block; the other two
sides being left open. When put together the mold was laid upon a 1-in.
board, 12×30 ins., reinforced by cleats across the bottom. The sides of
the molds were held together with screws or wedge clamps. When the
blocks had set, the sides of the molds were removed, and the blocks were
left on the 12×30-in. boards for 3 days, then piled up, being watered
several times each day for a week.
A gang of 14 men made the blocks; 2 screening gravel through 1-in. mesh
screen; 4 mixing concrete; 4 molders; 3 shifting and watering blocks,
and 1 foreman. With a little practice each molder could turn out 175
blocks a day; and since each block measured ¾ cu. ft., the output of the
14 men was 19½ cu. yds. a day. Mr. Gifford informs us that the wages
were $1.50 a day for all the men, except the foreman. The daily wages of
the 14 men were $22, so that the labor of making the blocks was $1.10
per cu. yd.
[Illustration: Fig. 266.--Sewer with Monolithic Invert and Block Arch.]
Each batch of concrete, containing ½ bbl. of Portland cement costing
$1.35 per bbl., made 18 blocks. (1 bbl. per cu. yd.) Since the gravel
cost nothing, except the labor of screening it, the total cost of each
block was 11 to 12 cts., which includes 0.85 cent for use of molds and
mold boards, which were an entire loss. At 12 cts. per block the cost
was $4.32 per cu. yd.
The contract price was $3 per lin. ft. of this sewer, as against a bid
of $3.40 per ft. for a brick sewer.
When the trenching had reached to the level of the top of the invert,
two rows of stakes were driven in the bottom, stakes being 6 ft. apart
in each row, and rows being a distance apart ¼-in. greater than the
outer diameter of the sewer. These stakes were driven to such a grade
that the top of a 2×4-in. cap or "runner" set edgewise on top of them
was at the proper grade of the top of the invert. The excavation for the
invert was then begun, and finished to the proper curve by the aid of a
templet drawn along the 2×4-in. runners. In gravel it was impossible to
hold the true curve of the invert bottom. Concrete was then placed for
the invert. To hold up the sides of the invert concrete, a board served
as a support for the insides, but regular forms were more satisfactory
in every respect except that they were in the way of the workmen. A form
was tried, its length being 6 ft. It was built like the center for an
arch, except that the sheeting was omitted on the lower part of the
invert. It was suspended from the cross-pieces resting on the "runners."
After the concrete had been rounded in place, the form was removed and
the invert trued up. This form worked well in soil that could be
excavated a number of feet ahead, so that the forms could be drawn ahead
instead of having to be lifted out; but in soil, where the concreting
must immediately follow the excavation for the invert, the form is in
the way. The invert was trued up by drawing along the runners a
semi-circular templet having a radius of 21½ ins. Then a ½-in. coat of
1-2 mortar was roughly troweled on the green concrete. Another templet
having a 21-in. radius was then drawn along the runners to finish the
invert.
When the plaster had hardened, two courses of concrete blocks were laid
on each shoulder of the invert, using a 1-2-¼ mortar, the ¼ part
being lime paste. The lime made the mortar more plastic and easier to
trowel. Then the form for the arch was placed, and as each 8-ft. section
of the arch was built, a grout of 1-1 mortar was poured over the top
to fill the joints. Earth was thrown on each shoulder and tamped, and
the center moved ahead.
Common laborers were used for all the invert work, except the plastering
which was done by masons who were paid 30 cts. per hr. Masons were also
used to lay the concrete blocks in the arch. Mr. Gifford states that two
masons would lay at the rate of 100 lin. ft. of arch per day, if enough
invert were prepared in advance. As there were 11 blocks in the ring of
the arch, this rate would be equivalent to 7½ cu. yds. of arch laid per
mason per day.
[Illustration: Fig. 267.--Concrete Block Manhole.]
~COST OF BLOCK MANHOLES.~--The following costs of constructing concrete
block manholes for electric conduit at Rye, N. Y., were recorded by Mr.
Hugh C. Baker, Jr. The arrangement of the blocks, their size and shape
and the dimensions of the completed manholes are shown by Fig. 267. The
blocks were molded of 1-2-5¾-in. broken stone concrete in 30 wooden
molds made by a local carpenter at a cost of from $3.50 to $12 each. The
concrete was placed in the molds very wet, with very little tamping, and
was allowed to set for seven days before the blocks were moved to the
work. The molds were left in place from 24 to 36 hours. With the
facilities at hand six complete sets of top blocks were made each day by
four men, when no wall blocks were being made, and half a set (15) wall
blocks and two sets of top blocks were made each day by four men. The
cost of the block manholes complete was as follows, per manhole:
30 wall blocks, 2½ cu. yds. $21.00
6 cover blocks, 1½ cu. yds. reinforced 4.27
I-beams for cover, in place 5.40
Supervision, freight, hauling 5.6 tons concrete 9.38
Labor placing cover, 3 hrs. at 15 cts. 0.45
Labor placing walls, 20 hrs. at 15 cts. 3.00
------
Total, exclusive of iron cover $43.50
~CEMENT PIPE, CONSTRUCTED IN PLACE.~--In constructing 8-in. cement sewer
for the Foster Armstrong Piano Co.'s works at Rochester, N. Y., a gang
of seven men averaged 300 ft. of pipe per 10-hour day, using a Ransome
pipe mold. The mold is shown by Fig. 268. It is made of sheet steel,
with an inner core 10 ft. long, the front end of which is surrounded
with a sheet steel shell that serves as an outer form for the pipe. The
mortar mixed rather dry was packed into the annular space between core
and shell by one man, using a short wooden rammer. A second man kept the
mold slowly moving forward by operating the lever, which by means of a
ratchet and drum winds up a wire rope stretched ahead to a deadman in
the trench bottom. As the mold moves ahead it leaves behind it the
cement pipe. A third man carefully filled under the invert and over the
haunches of the green pipe with earth to give it support. The following
was the itemized cost per day, 300 ft. of pipe laid:
6 men at $1.70 per 10-hour day $10.20
1 foreman 3.00
3 bbls. cement at $1.25 3.75
3.3 cu. yds. sand at 85 cts. 2.80
Water 0.15
------
Total for 300 lin. ft. $19.90
This is equivalent to 6.63 cts. per lin. ft. of pipe.
[Illustration: Fig. 268.--Ransome Continuous Mold for Concrete Pipe
Construction.]
In Trans. C. E., Vol. 31, 1894, p. 153, James D. Schuyler gives the cost
of cement pipe made by the Ransome system for the Denver Water Works.
There is a wrought iron shell of the size of the inner diameter of the
pipe forming the inner mold. To this shell is attached a "leader" and
"saddle" of larger diameter forming the outer mold. These molds are
drawn slowly along the trench by a cable and horse whim, and the
concrete is shoveled continuously into the core space between the molds
and rammed on a long incline. The top half, or arch, of the pipe is
supported by sheet iron plates (2 ft. wide), placed one after another on
the forward end of the mold; and, being clamped together at the top and
sides, remain in position after the mold is slid out from under them.
After the mold has passed along, these iron plates are supported by
upright sticks and by horizontal clamping rods. The plates are left in
place for 24 to 48 hrs. The concrete, made 1-3½, river sand and gravel,
was machine mixed. A gang of 30 men mixed, wheeled, shoveled and tamped
the concrete, attended to the plates, cleaning and greasing them, etc.
This gang would make short runs at the rate of 900 lin. ft. of pipe a
day, but counting stoppages, the average rate was 300 ft. a day. The
inner diameter of the pipe was 38 ins., and its bottom was molded flat
for a width of 18 ins. The concrete shell was 2½ to 3 ins. thick. The
pipe was washed with pure cement grout, applied with brushes after
removing the iron plates. With cement at $3.75 per bbl., gravel at $1.25
per cu. yd., and labor at $1.75 to $2 per day, the cost of this pipe was
$1.35 to $1.50 per ft., after the gang was well organized.
~PIPE SEWER, ST. JOSEPH, MO.~--In constructing extensions to 36-in.,
42-in., 48-in. and 72-in. sewers at St. Joseph, Mo., reinforced concrete
pipe of the form shown by Fig. 269 was employed. The thickness of shell
for the various sizes was 4 ins., 4½ ins., 5 ins., and 7 ins. All sizes
were made in 3-ft. lengths, one end of which is rebated and beveled to
form a spigot and the other end of which is chamfered on the inner edge
to receive the bevel of the spigot. This jointing leaves a
circumferential groove, into which the hooked ends of the longitudinal
reinforcing bars project in such a way that a circular hoop can be
threaded through them to connect successive lengths. The reinforcement
is of the same form for all sizes of pipe, but seven longitudinals were
used in the 72-in. size and five for all smaller sizes; the
circumferential bars were in all cases spaced one 9 ins. from each end.
The pipe, as described, is the standard pipe made by the Reinforced
Concrete Pipe Co., of Jackson, Mich., and is covered by patents. The
practice of this company is to manufacture the pipe itself on the ground
and furnish it to the contractor. It does not contract to build sewers
nor does it dispose of rights to manufacture to contractors.
[Illustration: Fig. 269.--Jackson Concrete Sewer Pipe.]
_Pipe Molding._--The pipe is molded endwise. A bottom plate so shaped as
to form the hub or receiving end of the pipe is set up. On the upper or
inner flange of this cast iron bottom plate is set the core defining the
inside diameter of the pipe; this core is in four segments of sheet
steel. The longitudinal reinforcing bars are next inserted in slots in
the bottom plate and the outside form of sheet steel is then set up on
the lower and outer flange of the bottom plate. Spacing clips on the top
edge of the outer shell hold the tops of the reinforcing bars in
position. The concrete is then shoveled into the annular mold and tamped
until it reaches the level for the first circumferential reinforcing
bar; this is then placed by removing the spacing clips, threading the
hoop over the longitudinal bars and sliding it down to position. Filling
and tamping then proceeds until the second hoop is to be placed; this is
placed exactly like the first, and filling and tamping then proceeds
until the mold is filled. At the St. Joseph work a 1-2-3 mixture, with
crushed limestone aggregate ranging from pea size to 1-in. stone was
used. The molding was done in tents which were heated by coke fires in
salamanders in freezing weather.
_Pipe Laying._--In laying, the pipes are handled and lowered into
position just as are cast iron water pipe. Successive lengths are placed
by inserting the spigot ends into the chamfered hub ends and then
threading the tie hoop through the hooked ends of the projecting
longitudinal reinforcing bars. A strip of galvanized iron is then passed
under the pipe and bent up so as to girdle the circumferential groove
except for a space at the top; the groove is then poured with a wet 1-2
cement mixture, which, when hardened, completes the joint.
~COST OF MOLDING SMALL CEMENT PIPE.~--Mr. Albert E. Wright gives the
following account of the method and cost of molding and laying 6 to
12-in. cement pipe for irregular work at Irrigon, Ore.: The pipe was 6
to 12 ins. inside, made of Portland cement and clean, sharp sand of all
sizes up to very coarse. The mortar was mixed rather dry, but very
thoroughly, using 14.1 cu. ft. of sand to 1 bbl. of cement, or very
closely a 1 to 4 mixture. From six to seven buckets of water were used
to each barrel of cement, except for the 6-in. pipe, for which the
mortar had to be made somewhat stiffer in order to remove the inner
form, which was not made collapsible as in the larger sizes.
The forms were sheet iron cylinders with a longitudinal lap joint that
could be expanded after molding the pipe, and removed without injuring
the soft mortar. The inner form was self-centering, so that there was
little variation in the thickness of the pipe.
Four men were required in making cement pipe by hand; one mixed the
mortar, and wheeled it to the place of work; another threw it into the
form a little at a time with a hand scoop; a third rammed it with a
tamping iron, and a fourth kept the new pipe sprinkled, and applied a
coat of neat cement slurry to the inside when it was sufficiently hard.
In molding, the form of the bell at the bottom was secured by an iron
ring that was first dropped into the form, and the reverse or convex
form at the top was made with a second ring. While still in its form
the pipe was rolled or lifted into its place in the drying yard, and the
form was then carefully removed. A very slight blow in removing the form
would destroy the pipe, and a considerable number, especially of the
larger sizes, collapsed in this way, and had to be remolded. To avoid
handling, the pipe was stacked on end a few feet from the place of
mixing, the form being moved as the yard filled with pipe. One crew of
four men could make about 250 joints or 500 lin. ft. of pipe a day.
As soon as hard enough, the pipe was turned end for end, and was then
kept wet for several weeks before being laid. The coating of neat cement
on the inside was applied with a short whitewash brush, and was a small
item in the cost.
In laying, the trench was carefully finished to grade in order to have
the joints close nicely, and the ends were well wet with a brush. The
mason then spread mortar, mixed 1 to 2, on the end of the pipe, and laid
a bed of mortar at the bottom of the joint. He then jammed the section
into place, and swabbed out the inside of the joint with a stiff brush,
to insure a smooth passage for the water. A band or ring of mortar was
spread round the outside of the joint as an additional reinforcement.
One barrel of cement would joint about 300 sections of pipe. The
materials cost as follows: Portland cement, per bbl., $4.45; labor, per
day, $2; foremen, per day. $2.50 to $3; hauling, per load mile (1 cu.
yd.), 20 cts.; sand, free at pit; water, free.
The pipe was all of a 1-4 sand and cement mortar, and the amount of
cement in one foot of pipe was arrived at by assuming that where the
sand has voids in excess of the cement used, the mortar will occupy 1.1
(see Chapter II) times the space of the dry sand, which yields the
following formula:
Where--
c = cost per bbl. of cement, or $4.45.
n = cu. ft. in one bbl. (taken at 3.5 here).
s = ratio of sand to cement, or 4.
d = inside diameter in inches.
t = thickness of pipe in inches.
l = length of pipe considered, or 1 ft. here.
Then:
c × l × [pi] × (dt + t²)
Cement-cost per foot = --------------------------,
n × s × 1.1 × 144
which gives here =
4.45 × 1 × 3.142(dt + t²)
------------------------------- = 0.00631(dt + t²).
3.5 × 4 × 1.1 × 144
This gave the following cement costs per lineal foot:
Diameter, Thickness, Cost
ins. ins. per foot.
6 1¼ $0.0571
8 1¼ 0.0730
10 1-3/8 0.0998
12 1½ 0.1278
The sand cost was based on 15 cts. per cubic yard for loading, and a
haul of two miles of 1 cu. yd. to the load, making five trips per day,
at $4 for man and team. It bears a constant ratio to cement cost, being
11.2 per cent. of the cement cost. The labor cost of making was based on
the foreman's estimate that a foreman, tamper, mortar mixer, and water
man should finish 250 joints a day of 6 or 8-in. pipe. For the 10 and
12-in. pipe, the labor was assumed to be greater in proportion to the
material. The foreman was taken at $3, one man at $2.50 and two at $2.
The cement for painting the inside was neglected. Hauling the pipe to
place was taken at twice the cost of hauling the sand per mile, and a
haul of 4 miles was assumed. The cost of laying was based on a foreman's
estimate of 2 cts. per foot for trench, and that one man to lay, one man
to plaster the joints, one helper and one man to back-fill would lay 600
ft. per day of 6 or 8-in. pipe. The larger sizes were assumed to cost
more in proportion to their material.
These various costs gave the following results for small size pipe:
--Cost per foot for--
6-in. 8-in. 10-in. 12-in.
pipe. pipe. pipe. pipe.
Cement $0.057 $0.073 $0.099 $0.128
Sand 0.006 0.008 0.011 0.014
Labor 0.019 0.019 0.026 0.034
Hauling 0.024 0.032 0.044 0.056
Laying 0.024 0.024 0.032 0.042
Trench 0.020 0.020 0.020 0.020
------ ------ ------ ------
Totals. $0.15 $0.176 $0.232 $0.294
The above costs show that the pipe in place costs about twice as much as
pipe in the yard, even with cement at $4.45.
[Illustration: Fig. 270.--Bordenave Pipe for Swansea, England, Water
Works.]
~MOLDED PIPE WATER MAIN, SWANSEA, ENGLAND.~--As a good example of foreign
practice in molded pipe conduit work a water main constructed at
Swansea, England, has been selected. This pipe line had to operate under
a head of 185 ft.; it was constructed under the patents of the French
engineer, Mr. R. Bordenave, who has built many miles of the same type of
conduit on the Continent.
Fig. 270 shows the construction of the pipe, the drawing being a part
longitudinal section through the shell at the joint. The pipe consists
of an inner and an outer reinforcement separated by a sheet steel tube
and all embedded in a 1-2 mortar. Both inner and outer reinforcements
consists of longitudinal bins of cruciform (+) section wound by a spiral
bar of the same section wired to them at every intersection. Only the
outer reinforcement and the steel tube are considered in calculating the
strength of the pipe, the inner reinforcement being considered as simply
supporting the mortar.
_Fabrication of Reinforcement_.--The steel tube is made of 1 mm. (0.04
in.) thick sheets of steel bent to a cylinder and jointed longitudinally
by welded butt joints, welded by a blow pipe using acetylene and oxygen.
Tests of this welded joint by R. H. Wyrill, Waterworks Engineer,
Swansea, showed it to be quite as strong as the unwelded steel cut from
the shell. The circumferential joints of the tube were made by turning
up the edges of the sheets and welding them; this gives a flexible
watertight joint. The tube was made in lengths of 9 ft. 9½ ins. and its
ends were turned up all around; just back from the turned-up ends a
vertical sheet steel collar was welded to the tube to form a strip end
for the external coating. These details are shown in Fig. 270. When the
tube for a length of pipe is completed the inside shell reinforcement
previously made is slipped into it and the outside shell reinforcement
is formed on it as a mandril, as shown by Fig. 271.
[Illustration: Fig. 271.--Applying External Reinforcement to Bordenave
Pipe.]
[Illustration: Fig. 272.--Casting Bordenave Pipe at Swansea, England.]
_Molding._--When the three positions of the steel skeleton were
completed, as shown by Fig. 271, they were set on curved wooden curbs
made to the exact shape necessary to center them and preserve the
correct thickness of cement coating. A collapsible core was lowered into
position in the inside, and a two-part sheet steel mold was erected
outside; the space between core and mold was then poured with a thin
mortar of one part Portland cement to two parts clean river sand. During
the process of pouring, the outer steel mold is sharply struck with
wooden mallets to facilitate the escape of air bubbles. The mortar was
mixed on an elevated traveling platform which is shown in Fig. 272,
which also shows a completed pipe, a core being withdrawn, a filled mold
and a section of reinforcement set up. The difficult feature of the
molding process was found to be the determination of the time for
withdrawing the core and removing the exterior mold; the time of setting
of the mortar was different in warm and in cool weather and varied with
the wetness of the mixture, the brand of cement, etc. By using a single
brand of cement that ran very uniform in quality and time of setting it
was possible, however, for the workmen, after a little practice, to gage
very accurately the correct time for removing the molds. With four sets
of molds a gang of eight men would curb 16 pipes per day under favorable
conditions, but when the temperature was low it was not possible to make
more than six or eight pipes. The pipes were allowed to stand four or
five days after the removal of the mold; they could then be removed by a
crane and laid in stock until used. It was found advisable to let the
pipes age about four weeks before laying; by this time, it is stated,
they would stand as much rough usage as cast iron pipe.
_Laying_.--The pipes were laid much in the same way as cast-iron pipes
are laid; they were each 9 ft. 9½ ins. long and weighed each about 12
cwt., and were handled by ordinary tackle. In laying, the pipes were
adjusted end to end and the joint enclosed by a temporary steel ring
inside which the bitumen seal, Fig. 270, was run and allowed to set when
the steel ring was removed. The joint was then encircled by a collar of
similar construction to the pipe itself and the space between collar and
pipe was poured with cement mortar. About ten lengths of pipe were laid
per day by one gang of men, one jointer and his assistant making all the
cement and bitumen joints as fast as the gang could lay the pipes.
CHAPTER XXII.
METHODS AND COST OF CONSTRUCTING RESERVOIRS AND TANKS.
Floor, wall and roof work of structurally very simple character sum up
the task of the constructor in reservoir and tank construction. The only
intricacy involved lies in form design and construction for cylindrical
tank work. Several examples of such work are given in this chapter, and
in each the construction and handling of the forms are described. To
repeat details here would serve no purpose, but one general instruction
may be enunciated. No care is too great which ensures rigidity and
invariable form, both in the construction of the individual form units
and in the assembling of these units into the complete form. This is
particularly true of cylindrical tank work and especially high
cylindrical tank work where the forms are moved upward as the work
progresses. To the designer it may be suggested that any beauty he may
gain by giving the walls of his standpipe a batter is paid in the extra
cost of form work.
Concreting in tank work is expensive. The reasons are two. The work has
to be done in a narrow space, commonly pretty well filled with a network
of steel rods or bars. Again the work has to be done uniformly well, not
only for appearance sake but because of the necessity of watertightness.
Making a reservoir watertight is, when all things are said, the one
difficult constructional task in tank work and the contractor who
accepts the task lightly courts trouble. Exceptionally good concreting
is essential in tank work if watertightness is to be secured.
The illustration of these general admonitions will be found in the
specific examples of tank and reservoir work which follow.
~SMALL COVERED RESERVOIR.~--The reservoir was designed to hold 75,000
gallons of water for fire purposes. As it is of a type which is certain
to be frequently constructed and as we have personal knowledge of the
costs recorded we describe the work in some detail. The specifications
stipulated that the reservoir must be absolutely watertight and that the
roof should be capable of sustaining a load of 300 tons evenly
distributed and a live load of 5,000 lbs. on two wheels. Figure 273
shows a plan, Fig. 274 a longitudinal section, Fig. 275 a transverse
section and Fig. 276 the column construction.
[Illustration: Fig. 273.--Sectional Plan of 75,000-Gallon Reservoir.]
_Quantities of Work._--The excavation called for the removal of 579 cu.
yds. of earth. There were 83 cu. yds. of concrete in the structure,
although the plans called for less, the additional amount being used in
increasing the two 4-in. walls to 6-in. and increasing the bottom and
top, on one end, so as to give perfect drainage. The yardage was
divided as follows:
Cu. yds.
Footings 3.5
Columns 6.8
Sides 22.6
Girders 11.0
Top 20.0
Floor 19.1
----
Total 83.0
[Illustration: Fig. 274.--Longitudinal Section of 75,000-Gallon
Reservoir.]
A manhole had to be put in the top and a sump in the bottom. Several
pipes also had to be placed in the concrete. None of these details is
shown on the plan. The structure had to be waterproofed.
_Excavation._--The excavation was made with pick and shovel and the
material hauled away in carts, the distance to the dump being 700 ft.
The top was shoveled directly into the carts, while the rest was handled
two and three times. When the reservoir was finished dirt had to be
filled in around the sides and puddled.
_Wages._--The following rates of wages were paid on the job:
Foreman $3.00
Carpenter 3.50
Carts and driver 3.50
Laborers 1.50
The carpenters worked 8 hours a day and were paid time and a half for
overtime. The rest worked ten hours per day and were paid regular rates
for overtime.
[Illustration: Fig. 275.--Transverse Section of 75,000-Gallon
Reservoir.]
_Forms._--Carpenters framed and erected the forms, but laborers did all
the carrying for them. Laborers also tore down the forms. For the
girders and columns 2-in. boards were used, but for the sides 1-in.
boards with 3×4-in. scantlings were used. The props for supporting the
girder and top forms were 3×4. Except for columns and girders and some
props, all the forming was used three times. The lumber cost:
400 ft. B. M. at $24 $ 9.60
8,000 ft. B. M. at $18 144.00
-------
Total $153.60
[Illustration: Fig. 276.--Column Construction for 75,000-Gallon
Reservoir.]
This makes an average price per 1,000 ft. of about $18.30, which price
we shall use in giving costs.
The cost of framing and erecting the forms was $167.27 for the sides,
columns, girders and top. In the forms for the sides, forming was only
used on one side of the concrete for two sides, the earth bank being
used for the other side of the forms, but on the other two sides the
banks had caved in, and forming was used on both sides of the wall. The
cost per cubic yard for forms was:
Lumber $2.54
Framing and erecting 2.77
Tearing down .54
-----
Total $5.85
This cost is for the yardage of 60.4 on which forms were actually used.
For the total yardage in the tank the cost was:
Lumber $1.85
Framing and erecting 2.01
Tearing down .40
-----
Total $4.26
The common labor cost of assisting to erect the forms was 15 per cent of
the total. Nothing is allowed for foreman, for the contractor acted as
his own foreman.
The cost of forms per 1,000 ft. for the amount of lumber purchased was:
Lumber $18.30
Framing and erecting 19.90
Tearing down 4.00
------
Total $42.20
As the lumber was used three times, the cost per thousand for all work
and materials on the forms would be just one-third of this--namely:
$14.06.
Since the framing, erecting and tearing down cost $19.90 plus $4, or
$23.90 per M. ft. B. M. purchased, and since the lumber was used three
times, the labor cost nearly $8 per M. each time that the lumber was
used. It will be noted that 8,400 ft. B. M. were required for the 83 cu.
yds. of concrete, or a trifle more than 100 ft. B. M. per cubic yard.
It will be of interest to see the labor costs of forms for the various
parts of the structure.
For the sides the cost of framing and erecting the forms was $4.19 per
cubic yard. Of this cost 4 per cent. was for common labor and the rest
for carpenters. The tearing down cost 47 cts. per cubic yard. For the
columns the erecting was $2.35, of which 1 per cent. was for common
labor. The tearing down cost 47 cts. For the girders and top the
erecting cost $1.83, of which 35 per cent. was common labor. The tearing
down cost 61 cts. per cubic yard. A summary would show:
Girders
Sides Columns and
per per top per
cu. yd. cu. yd. cu. yd.
Framing and erecting $4.19 $2.35 $1.83
Tearing down .47 .47 .61
----- ----- -----
Total $4.66 $2.82 $2.44
The greater cost of the columns forms over the girders and top was due
to the fact that the columns forms were handled almost exclusively by
the carpenters, and also in setting them great care and much time had to
be used to get them plumb and in line. The cost of the forms for the
sides was about twice as great as that for the top and girders. The
reasons for this are evident. The walls had forms on both sides, while
the top needed forming only underneath it, the area covered on the forms
being about 2,200 sq. ft. as compared to 1,000 sq. ft. The side forms
had to be set plumb and kept so. The framing was done ahead, but nearly
half of the lumber in the sides was erected as the concrete was being
put in place. The forms for the top were all put in place before any
concreting was done on the top, and the carpenters discharged. A much
larger per cent. of common labor could be used in placing forms for top
and girders than on the sides. The props were nearly all put in place
by laborers. The extra cost of tearing down the forms for the top was
due to the fact that the lumber all had to be handled one piece at a
time through a small manhole in the top, and carried about 150 ft. to be
piled.
To all the costs for forming should be added 6 cts. per cubic yard for
nails, wire and lines used on the forms.
_Concrete._--The mixtures varied for the different members. The cost of
materials was as follows:
Cement, 110 bbls. @ $1.12 $123.20
¾-in. stone, 80 cu. yds., @ $1.86 148.80
Gravel, 3 cu. yds., @ $1.33 4.00
Sand, 42 cu. yds., @ $1.20 50.40
The sides were first put in place, then the center columns were built,
following which the bottom was placed. Then the forms were erected for
the top and the girders, and these cast. In building the sides, one side
and half of the two ends were built at one time, and then forms erected
for the other half of the sides. For the sides the mixing was done in
the bottom of the reservoir. For the rest of the structure it was done
on the ground, the mixing board being along side of the reservoir. The
labor cost of the concrete work for the various members and the average
per cubic yard was as follows:
Columns
and
Sides. Footings. Bottom. Girders. Top. Average.
Cubic yards 22.6 10.3 19.1 11 20.0 83.
Preparing and cleaning up $0.166 $0.060 $0.095 $0.065
Handling materials 1.022 .306 $0.070 .198 $0.187 .404
Cleaning out forms .040 .070 .053 .032
Mixing and placing 1.542 .728 .353 .792 1.080 .952
Ramming 1.090 .540 .455 .450 .597 .673
Handling steel .890 .020 .395 .083 .324
------ ------ ------ ------ ------ ------
Total $4.750 $1.654 $0.878 $2.000 $2.000 $2.450
The total cost of labor was $203.35. The mixing was done entirely by
hand. Some plastering was done to the walls after the forms were taken
off, and the sides and bottom were washed with a brush with cement and
water. The plastering cost $6.60, including a barrel of cement and the
washing or grouting, two coats, cost $9.10, including a barrel of
cement. This added a cost of 19 cts. per cubic yard to the concrete
work, making the total cost per cubic yard $2.65.
It was a mistake to have mixed the concrete for the sides in the bottom
of the reservoir, as it made two handlings of the materials and
compelled all the concrete to be raised by hand to place it in the
forms. This accounts for the high cost of these two items.
The handling of the steel was high for the side walls, as it was all
separated and put into piles for the different panels and members in
getting it out of the pile for the sides. The rammers not only rammed
the concrete but they also bent down the prongs of the steel to get them
in place in the narrow forms, and afterwards had to pull out these
prongs. This had to be done for every piece of steel used, and readily
doubled the cost of ramming. The high cost of ramming the top was caused
by the fact that the 6 ins. of concrete had to be placed in three layers
and each rammed. The steel handling was high on account of the prongs
entangling the pieces with others, making them hard to handle. The cost
of handling steel per ton was about $4, or 0.2 ct. per pound. The steel
was all handled by common laborers.
The stock piles of material had to be made along a street and alley and
thus caused the material to be handled in wheelbarrow several hundred
feet.
The preparing to mix concrete, the cleaning up afterwards and the
cleaning out of forms are items that are seldom kept separate from the
others.
The cost of mixing and placing is high, owing to the fact that working
space was small and the mixers had to wait until the concrete was taken
off the board and placed in the forms before starting another batch.
This also meant an increased cost in the ramming, as the rammers were
idle some time waiting for a new batch to be mixed.
The total cost of concrete, including labor and materials, per cubic
yard on a basis of the 83 cu. yds. was:
Per cu. yd.
Cement, 1-1/3 bbls., @ $1.12 $ 1.49
Stone, 1 cu. yd. 1.86
Sand ½ cu. yd. .60
Steel 4.76
Forms, 100 ft. B. M., @ $18.30 1.85
Labor on forms 2.41
Labor on concrete and steel 2.65
------
Total $15.62
The cost of a foreman is not included in this, as the contractor looked
after the men himself.
_Waterproofing._--The waterproofing of the structure proved a serious
problem. It was thought at first that the concrete itself would be
nearly water tight, but the tank leaked like a sieve. After considering
several methods, an agent of a European waterproofing mixture prevailed
upon those interested to try his compound. To apply it, the walls had to
be dry, so a large coal burning stove was put in the reservoir and a
fire kept up day and night. While this drying process was going on
several light falls of snow occurred, and this had to be cleared away to
make the walls and roof dry. Two coats of the mixture were applied
according to the agent's instructions, and the reservoir was tested. The
water fell nearly half a foot in an hour's time.
Then a waterproofing contractor agreed to make the reservoir water tight
with paper and tar, by applying it on the inside. Three thicknesses of
paper were laid on the bottom and run well up on the sides, each layer
of paper being well covered with a preparation of tar. Upon testing it,
it was found that the leaking had been reduced about 50 per cent. A
preparation of asphalt was then placed over this, but upon a third test
the tank still leaked. As the sub-contractor had verbally agreed to make
it water tight for $125, only this amount was paid him. After this last
test he refused to do any more work.
After these attempts the sides of the reservoir were exposed on the
outside by excavating around it, and a one-brick-wall built up a few
inches from the concrete. This space was filled in with rich cement
mortar and the ground once more filled in around the structure. This
work and the materials used in it cost $1,240. Upon a fourth test the
reservoir was found to be water tight. Thus more than a third of the
cost of the entire work was in waterproofing the structure, and this
made the contract a money losing one, as this heavy cost was not
anticipated.
Several items of miscellaneous work are listed in the total cost of the
reservoir, such as filling in and puddling around reservoir and
replacing cobble paving. The top of the structure was used as a bin for
the storage of coal. For this purpose eight I-beams were embedded in
concrete around the top to be used as posts for the sides of the bin.
The cost of placing these is given.
_Total Cost._--The cost of the structure without any profits was:
579 cu. yds. excavation @ $.896 $ 529.65
Steel 395.00
Crushed stone 148.80
Gravel 4.00
Sand 50.40
Cement 123.20
Lumber 153.60
Labor on forms 200.09
Labor on concrete 203.35
Plastering 6.60
Sides and bottom 9.10
Nails, wire, etc. 4.98
Bailing water 21.19
Building temporary fence 1.65
Extra excavation for forms, footings, etc. 13.90
Setting I-beams in concrete 17.65
Filling in and pudding around reservoir 34.47
Replacing cobble paving 4.30
Hauling tools 3.60
Heating reservoir and handling snow 14.50
Waterproof mixture 29.00
Labor applying it 9.74
Applying paper and tar, labor and materials 125.00
Labor and materials of final waterproofing 1,240.00
Tools 48.75
General expense 210.00
---------
Total $3,602.52
~COVERED RESERVOIR, AT FORT MEADE, SOUTH DAKOTA.~--The following account
of the method and cost of constructing a 500,000-gallon reservoir is
compiled from information furnished by Mr. Samuel H. Lea, M. Am. Soc. C.
E. As shown by Fig. 277, the reservoir consists of two equal
compartments, each 50×60 ft. inside dimensions, with rounded corners.
Both compartments are covered with a 3-in. slab roof carried on the
walls and interior columns.
The concrete was a 1-2-4 Portland cement, sand and broken stone mixture,
mixed by hand on a movable platform. A concrete gang consisted of four
men who were each paid $2.75 per day. They wheeled the materials from
the supply piles to the mixing platform, mixed the concrete and
deposited it in place. During the construction of the footings and floor
two concrete gangs were employed, but after the walls were started, one
gang only was required for concrete work; the other gang was then put to
work assisting the carpenters.
[Illustration: Fig. 277.--Reservoir at Ft. Meade, S. D.]
The sand and stone were wheeled to the platform in iron wheelbarrows of
2½ cu. ft. capacity. The cement was in ¼-bbl. sacks and each sack was
taken as 1 cu. ft. Each batch of concrete contained the following
quantity of material:
2½ sacks of cement 2½ cu. ft.
2 wheelbarrows of sand 5 cu. ft.
4 wheelbarrows of stone 10 cu. ft.
The quantities of sand and stone were adjusted so as to form the proper
proportion for making a dense concrete. From time to time, as the work
progressed, experiments were made to determine the percentage of voids
both in the sand and the crushed stone; and, in this way, uniformity in
composition was secured. The mixture was made quite wet in order to
insure a free flow around the reinforcing bars. On account of the narrow
space inside the forms and the number of reinforcing bars therein care
was taken to cause the mixture to be well distributed throughout. The
wet concrete was well spaded in an effort to secure a smooth surface
next to the forms. This was generally accomplished, but some rough
places which showed after the removal of the forms required patching up.
In constructing the footings some concrete was first deposited in place
and the metal reinforcement was embedded therein. For the floor
reinforcement the lower bars were carefully embedded in the concrete
after it had been brought to a suitable height; the upper bars were then
placed crosswise upon the lower ones and kept in position until the
remainder of the concrete had been deposited around and over them. In
the wall footings a depression or groove, several inches deep, was left
under the wall space for its entire length. This ensured a good bond
between the wall proper and the footing.
The concrete floor in each compartment was built in one continuous
operation, the object being to secure a practically monolithic
construction. The lower reinforcing bars in the floor were embedded at
the proper depth in the fresh concrete and the upper bars were then
placed crosswise upon the lower ones; the two sets were then wired
together at a sufficient number of places to prevent displacement while
the remaining concrete was being deposited around and over them.
The reinforcement for the walls and columns was erected in place upon
the footings and formed a steel skeleton around which the forms were
erected. The upright bars in the walls were held together and at the
proper distance apart by means of templates consisting of wooden strips
in which holes were bored at suitable intervals to receive the bars. The
templates were maintained in a horizontal position and were moved upward
as the concrete advanced in height. The horizontal reinforcing bars
were wired in place to the upright bars; they were placed in position
ahead of the concreting as the wall was built up.
The corrugated bars in beam and girders were placed in position in the
forms and held up by blocks which were removed as the forms were filled
with concrete. The expanded metal reinforcement for the roof slab was
placed so as to be close to the lower face of the slab, but far enough
up to be entirely enveloped in the concrete.
The wall forms were made of 2-in. planks, surfaced on the inner side and
placed horizontally on edge. They were held in place by 4×4-in. posts
spaced at intervals of about 4 ft., in pairs on opposite sides of the
wall. The posts were firmly braced on the outside; they were prevented
from spreading by connecting wires passing through the wall space
between the edges of adjacent planks. At the rounded corners of the
reservoir the pairs of posts were spaced about two feet apart and the
curve was made by springing thin boards into place to fit the curve and
nailing them to the posts. The posts were high enough to reach to the
top of the wall; the siding was built up one plank at a time as the
concrete work progressed. Column forms were made of 2-in. planks on end,
extending from floor to girder. Three sides were enclosed and one side
was left open to receive the concrete; this side was closed up as the
concreting advanced in height.
The beam and girder forms were open troughs of the required dimensions,
made of 2-in. plank, surfaced on inner faces. The form of centering for
the roof slab consisted of a smooth, tight floor of 2-in. planks,
extending between the open tops of column, beam and girder forms over
the entire area between enclosing walls of the reservoir. The centering
and the beam and girder forms were supported by 6×6-in. posts resting
upon the floor below.
The regular carpenter gang consisted of a foreman carpenter at $5 per
day, a carpenter at $3.50 per day, and two helpers at $2.75 per day.
During the early concrete work of making footings and floor, where forms
were not required, the carpenter force was employed in erecting the
steel skeleton for the walls. The upright bars were placed in position
and secured by temporary wooden stays extending from the upper portion
of bars to the surface of ground outside of excavation. These stays were
removed after concreting had advanced to a sufficient height to hold the
steel securely in place.
The wages paid the concrete gang which mixed and placed all the concrete
and the carpenter gang which constructed and erected the forms and
placed the reinforcement have been given above. The costs of
construction materials on the site were:
Cement, per barrel $2.57
Sand, per cu. yd. 1.80
Stone, per cu. yd. 3.15
Lumber, per M. ft. B. M. 27.50
The quantities in the completed concrete structure were as follows:
Total volume of concrete in reservoir 704.71 cu. yds.
Total volume of steel reinforcement in reservoir. 5.57 cu. yds.
------
Total volume of material in completed structure. 710.28 cu. yds.
The steel was, therefore, about 0.8%.
Volume of material in structure exclusive of roof slab 648.35 cu. yds.
Volume of material in roof slab 61.93 cu. yds.
------
Total 710.28 cu. yds.
The cost of the structure per cubic yard of concrete, exclusive of the
roof slab, was as follows:
Item. Per cu. yd.
Crushed stone $ 3.168
Sand .842
Cement 3.859
Reinforcement 4.959
Labor, mixing and placing concrete 1.721
Forms, labor and material 2.960
-------
Total $17.509
In constructing the roof slab the expanded metal reinforcement raised
the unit cost. For this portion of the work the costs were:
Item. Per cu. yd.
Expanded metal reinforcement $ 5.241
Other items, same as above 12.550
-------
Total $17.791
The floor and the inside surface of reservoir walls were covered with a
coating of cement mortar composed of one part Portland cement and one
part sand. The wall plastering was from ½ in. to ¾ in. thick; it was
applied in two coats. The floor finish was laid in alternate strips
about 1 in. thick and 3 ft. wide. After the strips first laid had
hardened the remaining strips were laid, the edges being grouted to
ensure tight joints.
The outside of walls and roof was covered with a coating of tar which
was heated in an open kettle to a temperature of about 360º F. and then
applied with a brush or mop.
The cost of wall and floor plastering was 44.4 cts. per square yard,
itemized as follows:
Cement 26.4 cts.
Sand 2.6 cts.
Labor 15.4 cts.
-----
Total 44.4 cts.
The cost of outside waterproofing was 4 cts. per square yard,
distributed as follows:
Material 2.5 cts.
Labor 1.5 cts
---
Total 4.0 cts.
While some of the cost items are apparently high when compared with the
cost of similar work in other places, it should be remembered that the
isolated locality and the local conditions were unfavorable for low
cost. Owing to the isolated location of the reservoir with respect to
large markets and also to local sources of supply the cost of material
and labor was quite high. All construction material, except some of the
stone for crushing, had to be hauled over a mountain road from 3 to 4
miles to the top of the hill selected for the reservoir site. Labor was
scarce and commanded a wage of $2.50 per day for ordinary work; the
laborers mixing concrete were paid $2.75 per day. Another source of much
relative expense was the high cost of lumber and carpenter work on the
forms. On account of the thinness of the walls and roof, the cost of
lumber and labor required per cubic yard of concrete was considerable. A
part of the lumber was used the second time in forms, but it was found
impracticable to delay the work by waiting for the concrete to harden
before beginning the new portions of the walls. This lumber was sold
after the completion of the work, but the salvage was inconsiderable,
amounting to less than 10 per cent. of the original cost.
[Illustration: Fig. 278.--Reservoir Forms. Bloomington, Ill.]
~CIRCULAR RESERVOIR, BLOOMINGTON, ILL.~--An open circular reinforced
concrete reservoir was constructed in 1905-6 for the water-works of
Bloomington, Ill. This reservoir is 300 ft. in diameter, 15 ft. deep at
the circular wall and 25 ft. deep at the center of the spherical bottom.
The wall construction is shown clearly by Fig. 278, and the floor is a
6-in. spherical slab reinforced by a mat of ¼-in. round rods placed 6
ins. on centers in both directions. The wall reinforcement is corrugated
bars. Neither the wall nor the bottom has expansion joints.
_Concrete._--The specifications required not less than 1 part Portland
cement to 2 parts sand and 5 parts clean gravel, and stipulated that
there should always be more than enough cement to fill the voids in the
sand more than enough mortar to fill the voids in the gravel. The
proportions were varied, depending on the character of the available
material and on the location the concrete was to occupy. The
stipulations regarding the minimum quantities of cement and mortar were,
however, always at least fulfilled. A 1-3-4 mixture of cement, broken
stone and gravel was largely used in the footing and wall. The gravel
was fine and contained 40 to 50% of sand; the broken stone was the
crusher-run, with the dust screened out, and the maximum-sized pieces
not larger than those which would pass a 2-in. screen. The mortar facing
on the front face of the wall was made of 1 part cement to 4 parts fine
gravel, containing sand. Some gravel from the excavation was used in the
concrete for the floor. This gravel was so fine that about one-quarter
of it was replaced with broken stone and the mixture made 1-6. Both
faces of the wall were painted with a 1-1 mixture of cement and sand;
the inner face was also painted with a 1-1 mixture of waterproof Star
Stettin Portland cement and sand. The sidewalk finish on the surface of
the floor consisted of 1-1½ mortar.
_Mixing and Handling._--The concrete mixing plant was set up outside of
the site of the reservoir along a side track from the railroad. The
concrete materials were delivered on the side track, except some gravel
from the excavation that was used. A Foote portable continuous mixer was
used in making the concrete for the wall footings and the wall. It was
mounted so it could discharge into dump cars on a service track laid on
the ground. A double hopper was built up over the mixer, one compartment
for sand and one for broken stone. The end of a service track leading
from the side track was laid on an inclined trestle up to a floor level
with the top of this double hopper, the materials being hauled in dump
cars from the side track to the hopper. The service track from the mixer
extended entirely around the wall, and 10 ft. from it, on the
embankment made there with earth from the trench for the wall-footing.
The concrete was dumped from the cars on the service track to portable
shoveling platforms near the point where work on the wall was in
progress. It was shoveled by hand from these platforms to place in the
forms as the presence of the reinforcement bars in the narrow forms
precluded dumping in large quantities. The footing was built without
forms up to the right-angle joint between it and the base of the wall at
the front, and to the top of the 45° slope on its rear face. A layer of
concrete 2.5 in. thick was first placed in the completed trench. The
reinforcement bars near the bottom were then laid on this green
concrete, the vertical bars near the front face of the wall usually
being erected at the same time. The concrete in the toe of the footing
and in the footing proper up to the top layer of reinforcement was then
laid. After the top layer of reinforcing bars had been laid, the footing
was completed, except for a top layer about 2 ins. thick at the base of
the front face of the wall and 15 ins. thick at the toe of the footing.
This left a strip of surface about 6 ft. wide, sloping at about 1 in 6
from the wall toward the center of the reservoir, and furnished the
widest and best possible bond for the joint which had to be made when
floor was laid.
_Location and Construction of Forms and Wall._--The design of the wall
of the reservoir, although simple in itself, required unusually accurate
work in the location and construction of the forms for it. The location
was made with very little difficulty, however, by an arrangement devised
by the contractor which enabled the foreman, without the aid of an
engineer, to set the necessary grade and reference stakes. A post, 10
ins. in diameter, was set very accurately and firmly in the ground at
the center of the reservoir. This post was sawed off squarely on top so
that the line of collimation of an engineer's transit set on it without
a tripod would be exactly at the grade of the top of the completed wall
of the reservoir. A 200-ft. steel tape was used to measure the radial
distance from a nail in the center post to the posts of the back, or
outside forms for the wall. In the form for the back face of the wall
2×6-in. posts, spaced one one-hundredth of the circumference apart, were
set considerably in advance of any concrete work, and were made the
basis of all measurement in building the forms. The forms as originally
planned are shown in Fig. 278.
The wall, when started, was built continuously in both directions from
the starting point. The back forms consisted of planks for lagging
nailed to vertical posts, which were accurately set and firmly braced.
The front forms were made in lengths equal to one one-hundredth of the
circumference of the reservoir, and when set up were fastened to the
back forms. Twenty-one of these front form sections were built and all
set up at once. Concrete was filled in between the front and back forms,
starting at the central form, and was rammed in inclined layers,
sloping, at about 1 on 6, both ways towards the end forms. This method
was adopted in order that the concrete might be laid continuously and
without joints. The lagging of 1-in. boards on the vertical portion of
the sections was nailed to the vertical posts, and was carried up just
ahead of the concrete filling.
When the concrete had reached the top of the central one of the 21
sections of the forms, and the concrete in that section had set
sufficiently, the section was broken up and removed, leaving two sets of
10 sections of the forms. Subsequently the other forms could be removed
in turn as desired without being broken up. As the filling-in proceeded
between the two sets of 10 forms each, the form in each set nearest the
starting point was removed, carried forward, and put in place at the
other end of its set of forms. Twelve men were required to take down and
transport one of the front form sections.
In setting up a front form, its inner toe was firmly supported by a
stake driven into the ground and by the horizontal board, nailed
transversely under the bottom 4×4-in. horizontal stringers, which rested
on the ground. The upper part of the form was then securely fastened to
the 2×6-in. posts of the back forms by temporary wooden connecting
strips, which were removed as the concrete filling was carried up. The
sections of the front forms were also securely tied to each other.
A facing of gravel concrete, rich in cement and with no pebbles larger
than ½-in. was placed on the front face of the wall, extending from the
back edges of the vertical reinforcing bars to the surface. A sheet-iron
plate, about 8 ins. wide by 5 ft. long, was placed vertically just back
of those bars. The concrete was shoveled in loose to the top of these
iron plates, and then the mortar was poured in between the latter and
the front face forms from buckets. The iron plates were next drawn by
handles attached to them, and the mortar and concrete tamped together
before either had set. In making joints, the old concrete surfaces were
always brushed and wet down, and, if necessary slushed with a grout of
neat cement before new concrete was laid on them.
_Construction of Floor._--The excavation over the site of the reservoir
floor was brought accurately to grade 6 ins. below the surface of the
finished concrete by hand after the scoop-bucket excavator had passed
over. In making the excavation the levels were given on radial lines
drawn from the ends of the 10-ft. sections of the wall to the center. A
rod, on which the elevations of the sub-grade at every 10 ft. from the
wall to the center of the reservoir were clearly marked, was used in
connection with a transit on the center post in locating the elevations
of different points in the reservoir floor. By using this method the
elevations required were easily found by the foreman in charge without
the assistance of an engineer. When the work approached the center, the
post was removed and the transit was placed on a portable pedestal which
was set on points of known elevation on the finished concrete.
The slanting surface left on the top of the footing inside the wall
formed, together with the projecting reinforcement rods, an excellent
bond between the concrete of the wall and that of the floor, when the
latter was laid. A circular strip of the floor, 16 ft. wide, was put
down next to the wall first, and the remainder of the floor was laid
according to the progress of the excavation. The lower 3½ ins, of the
concrete was usually first spread out over an area 12 or 16 ft. square,
then the reinforcement was placed, and after that the top 2 ins. of
concrete and a ½-in. sidewalk finish surface were laid.
[Illustration: Fig. 279.--Standpipe at Haverhill, Mass.]
The ¼-in. rods in the bottom are 6-ins. on centers in both directions.
They were in 12 and 16-ft. lengths and were partly woven together in
mats before being placed. The rods in one direction were all laid out
and woven with four or five of those in the other direction, the joints
being tied with small wire. The remaining cross rods were laid after the
mat had been placed. The mats were overlapped 1 ft. This method of
placing proved economical and efficient, giving at the same time
something permanent on which to lay the remaining concrete.
~STANDPIPE AT ATTLEBOROUGH, MASS.~--The stand pipe was 50 ft. in diameter
and 106 ft. high inside, with walls 18 ins. thick at the bottom and 8
ins. thick at the top. Figure 279 shows the general arrangement of the
reinforcement. Round bars of 0.4 carbon steel were used; the bars came
in 56½-ft. lengths, so that three lengths with laps of 30 ins., made a
complete ring around the tank. The concrete was a 1-2-4 mixture of ¼ to
1½-in. broken stone with screenings used as portion of sand.
The floor was built first, and on it was erected a tower to a height of
60 ft. and a derrick with a 40-ft. boom was set on its top. The derrick
was operated by an engine on the ground which also had a revolving gear
attached. When the work had reached the top of this tower, the tower was
raised to 110 ft. in height and the derrick shifted to the new
elevation. The forms were convex and concave sections 7½ ft. high and
about 11 ft. long. The concave or outside forms were made in 16 panels,
with horizontal ribs and vertical lagging; two complete rings of panels
were used. The panels were joined into a ring by clamps across the
joints, this clamping action and the friction of the concrete holding
them in place. The inside forms consisted of vertical ribs carrying
horizontal lagging put in place a piece at a time as the filling
proceeded. They were supported by staging from the derrick tower. The
remaining plant comprised a Sturtevant roll jaw crusher feeding to
screens which discharged fines below ¼-in. into one bin, medium stone
into another bin and coarse stone into a third bin. These bins fed to
the measuring hopper of a Smith mixer, which discharged into the derrick
bucket.
The mode of procedure was as follows: The reinforcing rings were erected
to a height of 7½ ft. The bars were bent by being pulled through a tire
binder and around a curved templet by a steam engine. The bending gave
some trouble, due, it was thought, to the stiffness of the high carbon
steel. Vertical channels 4 ins. deep were set with webs in radial planes
or across wall at four points in the circumference. The flanges of these
channels were punched exactly to the vertical spacing of the reinforcing
rings. Through the punched holes were passed short bars on the opposite
ends of which the reinforcing rings were supported and wired. The three
sections of rod of which each ring was composed, were lapped 30 ins. and
connected by Crosby clips. Considerable difficulty was had in holding
the reinforcing rings in line by the method employed; it is stated by
the engineer that a greater number than four channels would have been
much better.
The reinforcement being in place, an inside and an outside ring of forms
was erected. Concreting was then carried on simultaneously from four
points on the circumference and a ring 7½ ft. high was concreted in one
operation. Several facts were brought out in the concreting; careful and
conscientious spading was necessary to get a smooth dense surface; a too
wet mixture allowed the stone to settle and segregate; care was
necessary in this thin wall containing two rings of bars to keep the
stone from wedging among and around the bars and thus causing voids. The
engineer states that for this reason the substitution of mortar for
concrete in tank walls is worth considering. He estimates that in this
work, costing $35,000, that the use of a 1-2 mortar in place of the
1-2-4 concrete would have increased the cost by $2,300, a 1-2½ mortar by
$1,500, and a 1-3 mortar by $750. It was also found that there was
danger from a movement of the reinforcement in the concrete and of the
forms in placing the concrete.
When a ring of wall 7½ ft. high had been concreted, the reinforcement
was placed as before described for another ring. The two rings of forms
below those just filled were removed from the wall, hoisted up and set
in place on top. These two operations of placing reinforcement and
setting forms for another ring of wall took three days, so that the top
surface of the wall to which new concrete was to be added, had become
hard. This hard surface was very thoroughly washed and then coated with
neat cement immediately before depositing the fresh concrete. Water was
admitted to the tank as the work progressed, being kept about 20 ft.
below the work in progress. Numerous small leaks developed, but only two
were large enough for the water to squirt beyond the face of the wall.
These leaks appeared to grow smaller as time went on. To do away with
them entirely, the inside wall was plastered. The first coat of plaster
was not successful in stopping the leaks, so the standpipe was emptied
and replastered, five coats being used in the lower 20 ft. This did not
serve so resort was had to a Sylvester wash. A boiling hot solution of
12 ozs. to the gallon of water of pure olive oil castile soap was
applied to the dry wall. In 24 hours this was followed with a 2 ozs. to
the gallon solution of alum applied at normal temperature. Four coats of
each solution were applied, which reduced the leakage to a small amount.
To do away with all leakage another four-coat application of Sylvester
wash was used.
Details of the cost of the work are not available. There were 770 cu.
yds. of concrete in the walls and 185 tons of steel bars. Altogether
3,000 Crosby clips, costing $1,100 were used. The cost of the concrete
in place was about as follows:
Cement, per cu. yd. of concrete $ 4.80
Sand and stone, per cu. yd. of concrete 3.90
Mixing, per cu. yd. of concrete 0.40
Placing, per cu. yd. of concrete 2.20
Forms, per cu. yd. of concrete 2.65
------
Total per cu. yd. of concrete $13.95
~GAS HOLDER TANK, DES MOINES, IOWA.~--The tank was 84 ft. in diameter and
21 ft. 5 ins. deep. It had a horizontal floor 16 ins. thick 5 ft. below
ground level and a wall 21 ft. high, 18 ins. thick at base and 12 ins.
thick at top under coping and with alternate pilasters and piers around
the outside. The concrete for the floor was a 1-2½-5 2-in. stone mixture
and the concrete for the walls was a 1-2-4 1-in. stone mixture. The
floor was constructed first, with a circular channel for the wall
footing, and then the wall was constructed.
Piles were driven in the bottom and their heads cut to level and filled
around with tamped cinders. Two circumferential rows of posts were
driven around the edge so that a pair of posts, one inner and one outer,
came on each radius through a wall pilaster or pier. These posts served
primarily to carry the frames for the wall forms and secondarily for
holding the forms for the circular wall footing channel as shown by the
sketch Fig. 280. The floor concrete was put in in diamond-shaped panels
between forms, whose top edges were set to floor level. Each form was
designed to make a groove in the edge of the slab so that adjacent slabs
would bond with it. The concrete was wheeled to place in barrows,
thoroughly tamped, roughly floated to surface and finally given a trowel
finish.
[Illustration: Fig. 280.--Forms for Constructing Channel for Wall in
Reservoir Floor.]
To construct the walls, the posts before mentioned, were cut off to
exact level 6 ins. above the finished floor. A bent for the wall forms
was then erected on each radial pair as shown by Fig. 281. The bents
were erected by hand and carefully plumbed and lined up, both radially
and circumferentially. The pier and pilaster forms were then erected
across wall opposite each bent as shown by Fig. 281. The forms for the
wall between pilasters and piers consisted of panels 4 ft. high.
[Illustration: Fig. 281.--Frame for Forms for Circular Reservoir Wall.]
[Illustration: Fig. 282.--Form Panels for Circular Reservoir Wall.]
A panel for the inner face of the wall is shown by Fig. 282, the panel
for the outer face was similar in construction but was, of course,
concave instead of convex. Enough panels of each kind were made to reach
entirely around the tank. The inside panels were bolted at the ends to
the uprights of the bents; the outside panels were similarly lag screwed
to the uprights of the pier and pilaster forms; Fig. 281 shows the holes
for bolts and lag screws. The spaces between ends of inside panels in
front of the bents was closed by a ½×6-in. steel plate the full height
of the wall; this plate was bolted to the bents and had anchor bolts
every 3 ft., reaching into the wall. This anchoring of the plate to the
wall permitted the diagonal bracing of the bents to be removed to allow
runways to be laid on the cross-pieces, since the plate held firmly the
bent post to which it was bolted as indicated by Fig. 283. A complete
circle of inside and outside forms was erected and filled, then the
forms were raised 3 ft. by block and tackle from cross timbers across
wall between bent and pilaster form, and this depth concreted and the
forms raised again. The forms were oiled on the faces coming against the
concrete. It took about half a day to raise and set a complete circle of
forms. The concrete was mixed outside the tank and was wheeled up
inclines and dumped onto runways laid on the cross pieces of the bents
and then loaded and wheeled to place. The runway was raised to
successive horizontals as the work progressed.
[Illustration: Fig. 283.--Sketch Showing Filler for Joint Between Form
Panels.]
Only a few general cost figures are available. The labor for mixing and
placing concrete was as follows:
For floor, per cu. yd. 3.4 hrs.
For walls, per cu. yd. 5.2 hrs.
For cornice, per cu. yd. 5.4 hrs.
The cost of unloading the reinforcing steel from cars and placing it in
the structure was $7 per ton, or 0.35 ct. per lb. The cost of form
lumber, framing, erecting and taking down forms was 9 cts. per square
foot of wall covered.
~GAS HOLDER TANK, NEW YORK CITY.~--The tank for the Central Union Gas
Co.'s gas holder at 136th St. and Locust Ave. has an interior diameter
of 189 ft. and a depth of 41 ft. 6 ins. The exterior wall is 42 ft. 6
ins. deep, 5 ft. 6 ins. thick at the base and 4 ft. 6 ins. thick at the
top; concentric with it and 11 ft. 6 in. away is the interior wall 166
ft. in external diameter and 16 ft. 6 ins. high with a uniform
thickness of 2 ft. 6 ins. The bottom of the tank enclosed by the
interior wall is a truncated cone whose base is at the level of the wall
top. Fig. 284 shows the arrangement.
It was specified that the diameter of this tank should not vary more
than 2 ins. and that the exterior wall should not vary more than 1 in.
from the vertical. The main form was a circular drum whose exterior face
formed the inner face of the main wall. Its framework consisted of 40
vertical trusses or radial frames 6 ft. deep and 42 ft. high set
equidistant around the tank, these trusses being braced together on both
edges by circumferential timbers. Radial horizontal pieces nailed across
the radial frames and projecting beyond their faces carried vertical
iron guide strips against which the movable panels of lagging were
seated. These panels were cylindrical segments 5 ft. high and long
enough to span between two radial frames or 14 ft. 11-5/8 ins. The
panels were adjusted radially by wedges to give 1/8 in. clearance in
respect to inner face of wall; enough of them were made to form a
complete circle and they were set with 1-in. clearance between vertical
edges of adjacent panels to allow for swelling when wetted.
[Illustration: Fig. 284.--Section of Gas Holder Tank, New York City.]
The concrete bottom of the annular space between walls was first
constructed. On this floor were set 6×6-in.×8-ft. sills for the radial
frames; these were located accurately by transit. The radial frames were
then set on the sills by a derrick, adjusted to exact radial position by
a measuring wire swiveled to the center point of the tank and plumbed
by transit. A complete circle of lagging panels was then adjusted to the
frames at the bottom of the trench. For concreting, the wall was divided
circumferentially into three sections. These sections were separately
concreted to the top of the lagging panels, that is to a height of 5 ft.
After the concrete had set 48 hours the panels were hoisted 4 ft., so
that their lower edges still overlapped the concrete 12 ins., and
another ring of wall was concreted. This procedure was repeated until
the wall was completed. The back of the wall was formed against the side
of the trench where possible and in other places against rough board
lagging held in position in any convenient way.
For handling the concrete, four equidistant panels of the form framework
were converted into double compartment elevator shafts providing for two
balanced cars controlled by a sheave provided with a friction brake.
Three mixers supplied concrete to these elevators. Considering a single
elevator, two barrows of concrete were wheeled from the mixer onto the
car at the top of the elevator frame, the friction brake was released
and the loaded car descended to the work hoisting at the same time its
twin car loaded with two empty barrows. The elevators distributed to
wheeling platforms cantilevered out from the outer face of the framework
and located successively 5 ft., 15 ft., 20 ft., etc., above the bottom
of the trench. On these platforms the concrete was distributed as
required, the maximum wheeling distance being never over one-eighth the
circumference of the tank. The concrete was mixed very wet and deposited
in 6-in. layers.
The inner and outer surfaces of the wall were both painted with two
coats of stiff cement grout neat, and in addition the inner surface was
rubbed smooth by carborundum brick. Regarding this finishing work Mr.
Howard Bruce, Engineer of Construction, writes:
"The scouring was done on each section of the wall immediately after the
forms supporting these sections had been removed. The object was to rub
this interior surface with carborundum before the surface of the
concrete had taken its final set. By rubbing the concrete at this stage
and at the same time applying with a brush a coating of neat cement
grout, we believe the face of the concrete was made more or less
impermeable, as examination shows the pores of the concrete are very
largely filled up. We have no accurate figures as to the cost per square
yard of this treatment, but one can readily see that this cost would be
insignificant as compared with the possible improvement of the work. The
carborundum brick was selected on account of its hardness. I believe
practically any stone would answer the same purpose. In addition to
filling the pores of the concrete, this treatment gives the surface a
good smooth finish."
~LINING A RESERVOIR, QUINCY, MASS.~--The following methods and costs are
given by Mr. C. M. Saville, M. Am. Soc. C. E., for lining the Forbes
Hill Reservoir at Quincy, Mass. This reservoir is 100×280 ft. on the
floor, with side slopes of 1 on 1.75, and was built by contract in
1900-1901.
[Illustration: Fig. 285.--Section of Reservoir Lining, Quincy, Mass.]
Figure 285 is a section of the concrete lining; the bottom layer for the
floor was a 1-2-5 natural cement concrete, and for the sides a 1-2½-6½
Portland cement concrete; the top layer on both floor and sides was a
1-2½-4 Portland cement concrete; 2½-in. stone was the maximum size
allowed in any concrete and 1½-in. the maximum allowed in the top layer.
Smaller stone was used for special surface work, as noted further on.
The stone was cobbles turned up in the excavation work and had to be
gathered from scattered piles and washed before crushing. A 9×15 Farrel
crusher, operated by a 12 HP. engine did the crushing; it was rated at
125 tons a day, but averaged only about 40 tons. The fine dust was
screened out and the remainder discharged into a 30-cu. yd.,
three-compartment bin, one compartment for stone less than 1½ ins.,
another for 1½ to 2½-in. stone and a third for returns. The stone had 46
per cent. voids and weighed 95 lbs. per cu. ft. The sand was of
excellent quality. Atlas and Beach's Portland and Hoffman natural cement
were used.
All concrete was mixed and placed by hand, the concrete gang consisting
generally of 1 sub-foreman, 2 men measuring materials, 2 men mixing
mortar, 3 men turning concrete three times, 3 men wheeling concrete, 1
man placing concrete and 2 men ramming concrete. Two gangs were
ordinarily employed, each mixing and placing about 20 cu. yds. per day,
or 1.43 cu. yds. per man per day. The materials (sand and stone) were
measured in bottomless boxes, the following sizes being used:
--Sand Box-- --Stone Box--
Prop. of Mix. Size. Vol. cu. ft. Size. Vol. cu. ft.
1-2½-4[H] 2'9"×2'×1'8" 9.25 5'×4'5½" 14.8
1-3-6[H] 2'9"×2'×2' 11.1 5'×6'8" 22.2
1-2-5 2'9"×2'×1'4" 7.4 5'×6'6-5/8" 18.5
1-2½-6½ 2'9"×2'×1'8" 9.25 5'×7'2½" 24.05
[Footnote H: These mixtures were used for gate house and standpipe
foundation work.]
The bottom layer was placed in a continuous sheet; the top layer was
laid in 10-ft. squares on the floor and in 8×10-ft. squares on the
sides; these squares alternated in both directions, one-half being first
laid and allowed to set. In laying the sides the surface was left 1 in.
low and then before the concrete had set was brought to plane by a 1-in.
layer of 1-2½-4 mixture using stone and stone dust less than 3/8 in. The
concrete for the floor was mixed rather wet and rammed until it quaked;
on the sides a drier mixture was necessary to prevent flow. The cost of
the lining concrete was as follows:
Bottom Layer on Floor: 1-2-5 Mixture:
1.25 bbls. natural cement at $1.08 $1.350
0.34 cu. yd. sand at $1.02 0.347
0.86 cu. yd. stone at $1.57 1.350
4½ ft. B. M. lumber at $20 per M. 0.090
Labor, on forms 0.100
Labor mixing and placing 1.170
Labor general expenses 0.080
------
Total $4.487
Bottom Layer on Sides: 1-2½-6½ Mixture:
1.08 bbl. Portland cement at $1.53 $1.652
0.37 cu. yd. sand at $1.02 0.377
0.96 cu. yd. stone at $1.57 1.507
Lumber for forms (about 1 ft. B. M.) at $20 0.016
Labor, on forms. 0.121
Labor, mixing and placing 1.213
Labor, general expenses 0.177
------
Total $5.063
Top Layer on Floor and Sides: 1-2½-4 Mixture:
1.37 bbls. Portland cement at $1.53 $2.09
0.47 cu. yd. sand at $1.02 0.48
0.75 cu. yd. stone at $1.57 1.17
12½ ft. B. M. form lumber at $20 per M. 0.25
Labor, on forms 0.26
Labor, mixing and placing 1.530
Labor, general expenses 0.150
------
Total $5.93
The side finish with 1-2½-4 concrete of 3/8-in. stone cost $0.154 per
sq. yd. 1 in. thick. This work was done by a gang of 3 plasterers and 3
helpers.
The layer of plaster between the concrete layers was put down on 4-ft.
strips and finished similarly to the surface of a granolithic walk. This
layer consisted of 1-2 mortar finished with a 4-1 mortar. To keep the
plaster from cracking it was covered with strips of coarse burlap soaked
in water; this precaution was not entirely successful, some cracks
appeared and had to be grouted. Three gangs, each consisting of 1
plasterer and 1 helper, did the plastering, each gang laying about 700
sq. yds. per day. The cost of the plaster layer was as follows:
Item. Per 100 sq. ft. Per sq. yd. Per cu. yd.
Cement at $1.53 $1.15 $0.103 $7.42
Sand at $1.02 0.13 0.012 0.86
Burlap 0.02 0.002 0.14
Labor 0.92 0.083 6.00
----- ------ ------
Totals $2.22 $0.200 $14.42
It will be noted that it took over 5 bbls. of cement per cubic yard, and
that the labor cost was $6 per cubic yard.
~RELINING A RESERVOIR, CHELSEA, MASS.~--The following account of relining
the Powder Horn Hill Reservoir at Chelsea, Mass., is taken from a paper
by Mr. C. M. Saville. This reservoir which holds about 1,000,000 gallons
is oval in shape, 98×175 ft. at the top, 68×148 ft. at the bottom and 15
ft. deep, with side slopes about 1 on 1. The work was done by day labor.
For sake of completeness the costs of excavation and back-filling are
given here as well as the concrete costs.
The top of the bank was too narrow to allow the use of carts and an
18-in. gage railroad was decided upon as most convenient for handling
materials. A 65-ft. boom derrick with a 70-ft. mast was used for
removing the excavated material and for depositing concrete. The derrick
was operated by a 15-h.p. double drum hoisting engine, was held in place
by six wire guy ropes, and had a reach such that only one moving was
necessary after it was placed. The engine and derrick were set up on the
floor of the reservoir, and the work of excavation was begun at about
the middle of the south side. In order to facilitate the work, a
platform supported on A frames was set up. These frames were spaced
about 15 ft. apart and rested on the bottom and slope of the reservoir,
being held in place by bolts driven into the floor.
The paving blocks on the top of the slope were removed and piled up to
be taken away. The old lining and the material excavated from the bank
were shoveled into the scale pan of the derrick, hoisted to the cars on
the top of the bank, and then run by gravity to a dump a short distance
down the hillside. Here the cars were run out on a rough trestle, the
load dumped, and the empties hauled back to the work by a rope carried
through pulleys to the winch head on the hoisting drum of the engine.
For the storage of some of the materials, two small portable storehouses
were set up--one 8×10×7 ft., the other 11×16 x 7 ft. The bulky portions,
such as cement, sand, and stone, were delivered as necessary, a few
days' supply only being kept on hand. A branch from the railroad was so
arranged that it passed the storehouses and stone piles, while the sand
was piled close to the concrete mixing board. The intention on the work
was to do nothing by hand that could possibly be done by steam, except
that all of the concrete was mixed by hand. As great a proportion of
water was used as could be done without causing the material to slide
when rammed in place.
The lower layer of concrete was of the proportion by volume of 1 cement,
2½ sand, and 6½ crushed stone (sizes from ¾ to 1½ ins.). This was rather
a lean mixture, and as it could not be rammed enough to flush all over,
the surface was finished where necessary by a thick mortar made in the
proportion of 1 cement to 6 sand, and applied with heavy brushes. Before
placing any of the concrete, the bank back of the old concrete left in
place was thoroughly rammed with iron railroad tampers, and the edge of
the old concrete was scrubbed with water and a stiff brush and then
coated with 1 to 4 grout, which was allowed to fill in the angle between
the concrete and the slope. Just before placing the concrete the earth
bank was well wet in order that moisture might not be drawn from the
concrete while it was soft.
In order to make the new lining as waterproof as possible, a layer of
asphalt was placed on top of the lower layer of concrete and brought up
on the exposed edge of the old layer at the bottom of the new work.
This, it was expected would make an elastic and watertight joint between
the new and the old work.
Venezuela asphalt, "Crystal Brand," was used, being poured upon the top
of the concrete layer and allowed to run down the slope, care being
taken that the concrete was entirely and perfectly covered. After the
first layer of asphalt was cool, a second layer was similarly applied,
and the resulting sheet was about ¼ in. thick. Any inclination to crawl
down the slope when exposed to the sun was readily stopped by throwing
on a pailful of cold water. A most particular part of this work was to
get the asphalt as hot and liquid as possible and yet not burn it. All
of the concrete was protected from the sun and kept damp by being
covered with strips of burlap, which were moistened by sprinkling.
The upper layer of concrete was composed of a much richer mixture of
concrete than that used in the bottom layer, the proportions by volume
being 1 cement, 1¼ sand, 1¼ stone dust, and 4 broken stone of the sizes
mentioned above. On account of the steep slope it was possible to do
only a little ramming, and the material was laid as wet as possible. To
make this layer more impervious and also to obtain a smooth surface, the
concrete was left about an inch below and a finish coat applied by
expert granolithic finishers. This coating was applied as soon as it was
possible to do so after the main layer was in place, but on account of
the steepness and the liability of the wet concrete to flow, care had to
be taken not to begin work too soon.
The top finishing coat was made in the proportion of 1 part cement,
1-2/3 part sand, and 3-1/3 parts stone dust. In order to help in
bonding, the last ramming on the concrete was done with rammers studded
with pieces of iron about 1 in. long and ½ in. deep.
The finishing was done in three operations: The material was spread on
the concrete and thoroughly worked into it by the finishers, using rough
wooden floats; after this it was gone over and partially smoothed down
with a thin steel float; and finally it was worked to give the finished
appearance and an impervious surface.
The under layer of concrete was placed in a continuous sheet. The upper
layer was put down in alternate strips, 10 ft, long (the whole length of
the layer) and 5 ft. wide. These blocks were built up in forms, which
were not removed until the concrete had set. Finally, the back or edge
of the block toward the bank was well wet and thoroughly plastered, to
prevent, as far as possible, the infiltration of any water. The plaster
was mixed in the proportion of 1 part cement to 4 parts sand. When the
forms were wholly removed, the space between the concrete and the bank
was refilled, to within about 6 ins. of the top, with a clayey material
previously excavated, and the space was filled and graded to the top of
the bank with loam. During the work two holidays intervened; the men
were also transported to and from the work. Charges were made for these
items, amounting to $209.77, and this sum, together with the cost of
installing the plant ($716.03) are proportionally charged against the
work as follows:
Per cent. Total. Per cu. yd.
Excavation 70.3 $651 $2.17
Lower concrete 12 111 1.16
Upper concrete 15.4 143 1.11
Back fill 2.3 21 .28
The detailed cost of repairing the reservoir lining is given in the
following tabulations:
Excavation.
Rate. Per cu. yd.
Foreman 9 5/9 days $4.00 $0.13
Engineman 12 3/9 days 3.00 .12
Carpenter 2 days 2.67 .02
Laborers 9 6/9 days 2.25 .07
Laborers 110 2/9 days 2.00 .73
Laborers 46 5/9 days 1.75 .27
Derrick 12 3/9 days 3.75 .15
Rails and cars 11 2/9 days 0.40 .02
Stove coal 3.05 tons 6.50 .07
Egg coal .95 tons 6.25 .02
----
Total, 300 cu. yds. 1.60
Estimated proportionate charge for plant
installation and holidays 2.17
----
Grand total 3.77
Lower Layer Concrete.
Rate. Per cu. yd.
Foreman 3-7/9 days $4.00 $0.16
Engineer 2-3/9 days 3.00 0.07
Carpenters 7 days 2.67 0.20
Laborers 1-7/9 days 2.25 0.06
Laborers 89 days 2.00 1.87
Laborers 4 days 1.75 0.07
Derrick and engine 2-3/9 days 3.75 0.08
Rails and cars 2-2/9 days 0.40 0.01
Cement 106-3/8 bbls. 1.35 1.50
Sand 37.4 cu. yds. 1.10 0.43
Broken stone 117.9 tons 1.35 1.67
Egg coal .41 tons 6.25 0.03
Lumber 1.3 M. ft. 21.00 0.28
----
Total, 95.5 cu. yds. $6.43
Estimated proportionate charge for
plant installation and holidays 1.16
----
Grand total $7.59
Upper Layer Concrete.
Rate. Per cu. yd.
Foreman 6-7/9 days $4.00 $0.21
Engineer 1-8/9 days 3.00 0.04
Carpenter 18-5/9 days 2.67 0.38
Laborers 1-7/9 days 2.25 0.03
Laborers 119-5/9 days 2.00 1.85
Derrick and engine 1-8/9 days 3.75 0.05
Rails and cars 8-3/9 days 0.40 0.03
Cement 176½ bbls. 1.35 1.86
Sand 30.2 cu. yds. 1.10 0.26
Stone dust 41.6 tons 1.50 0.48
Broken stone 122.8 tons 1.35 1.28
Egg coal .2 tons 6.25 0.00
Lumber 4 M. ft. 21.00 0.65
Burlap 300 yds. 0.04½ 0.10
Nails 170 lbs. 0.05 0.03
----
Total, 129.2 cu. yds. $7.25
Estimated proportionate charge for
plant installation and holidays 1.11
----
Grand total $8.36
Back Plaster.
Rate. Per cu. yd.
Plasterer 3-8/9 days $5.40 $0.08½
Plasterer 8/9 days 6.00 0.02
Plasterer 5-5/9 days 4.50 0.09
Laborers 9-3/9 days 2.25 0.08½
Laborers 3/9 days 2.00 0.00
Cement 6 bbls. 1.35 0.03
Sand 3.3 cu. yds. 1.10 0.01
----
Total, 262 sq. yds. 0.32
Surfacing.
Rate. Per cu. yd.
Plasterer 7-6/9 days $5.40 $0.09
Plasterer 2-1/9 days 6.00 0.03
Plasterer 9-4/9 days 4.50 0.09
Laborers 12-8/9 days 2.25 0.06
Laborers 2-4/9 days 2.00 0.01
Cement 22¼ bbls. 1.35 0.06
Sand 5.07 cu. yds. 1.10 0.02
Stone dust 14 tons 1.50 0.04
----
Total, 460 sq. yds. $0.40
Asphalt.
Rate. Per cu. yd.
Foreman 1/9 day $4.00 $0.00
Asphalt man 11 days 2.00 0.05
Laborers 6 days 2.00 0.02½
Asphalt kettle 11 days 1.50 0.03½
Asphalt 3.9 tons 30.00 0.25
Asphalt mops 3.00 0.01
----
Total, 464 sq. yds. $0.37
Back Filling.
Rate. Per cu. yd.
Foreman 1-3/9 days $4.00 $0.07
Laborers 23-3/9 days 2.00 0.62
Laborers 9 days 1.75 0.21
Rails and cars. 2-2/9 days 0.40 0.02
Loam 27-5/9 cu. yds. 1.25 0.46
-----
Total, 75 cu. yds. $1.38
Estimated proportionate
charge for installing plant and holidays $0.28
-----
Grand total $1.66
Installing Plant.
Total.
Foreman 15-4/9 days $4.00 $61.78
Sub-foreman 1 day 3.00 3.00
Engineer 8-4/9 days 3.00 25.33
Carpenter 3 days 2.67 8.00
Watchman 42 days 2.00 84.00
Laborers 17-4/9 days 2.25 38.36
Laborers 149-8/9 days 2.00 299.78
Double team 10½ days 5.00 52.50
Single team 6 days 2.00 12.00
Single team 1 day 3.50 3.50
Teaming (total) 53.00
Derrick and engine. 11-4/9 days 3.75 49.92
Rails and cars 8-2/9 days 0.40 3.29
Broken stone 7.05 tons 1.35 9.52
Egg coal .6 ton 6.25 3.75
Kerosene 30 gal. 0.11 3.30
Oil 4 gal. 0.25 1.00
Spikes 220 lbs. 0.05 11.00
-------
Total $723.03
The cost of the concrete work in the lower and upper layers can be still
further detailed as shown below:
Lower Layer Concrete.
95.5 cu. yds., 1-2½-6½ concrete.
Materials: Rate. Per cu. yd.
Atlas cement 1.11 bbl. $1.35 $1.50
Sand .39 cu. yd. 1.10 0.43
Broken stone (.97 cu. yd.) 1.23 tons 1.35 1.66
Miscellaneous, plant, coal, etc. 1.28
Labor:
Mixing and placing $2.09
Carpenter work on forms at $24.00 per M. .34
-----
Total per cu. yd. in place $7.30
Upper Layer Concrete.
129.2 cu. yds., 1-1¼-1¼-4 concrete.
Materials: Rate. Per cu. yd.
Atlas cement 1.37 bbl. $1.35 $1.85
Sand .24 cu. yd. 1.10 0.26
Stone dust (.25 cu. yd.) .32 ton 1.50 0.48
Broken stone (.75 cu. yd.) .96 ton 1.35 1.30
Lumber 0.31 M. ft. 21.00 0.65
Miscellaneous, plant, etc. 1.32
Labor:
Mixing and placing 1.85
Carpenter work on forms at $21.00 per M. 0.66
-----
Total per cu. yd. in place $8.37
The following approximate labor costs are also given: Transporting,
erecting and removing derrick, $260.85. Equivalent time: Foreman, 6
days; engineer, 4 days; laborer, 85 days.
Transporting, laying and removing track, $125.03. Equivalent time:
Foreman, 4 days; laborer, 40 days.
Caring for dump and disposing of surplus by rough grading, $70.28.
Equivalent time: Foreman, 1 day; laborer, 33 days.
The total cost of the work was $3,503.66, divided up as follows:
Excavation $ 480.79
Lower layer concrete 614.15
Upper layer concrete 937.94
Back plaster 84.73
Surfacing 186.04
Asphalting 170.94
Back filling 103.27
Installing plant 716.03
Transportation and holidays 209.77
---------
Grand total $3,503.66
~LINING JEROME PARK RESERVOIR.~--The bottom of the reservoir that was
lined covered 250 acres, and the concrete lining was 6 ins. thick. The
lining was laid in alternate strips 16 ft. wide between forms set to
grade. The concrete was mixed in 18 Ransome mixers provided with
charging hoppers and mounted on trucks without boilers. Steam was
supplied to the mixer engines from the boilers of the contractor's
locomotives. One locomotive supplied steam for three or four mixers.
Tracks were laid in parallel lines across the reservoir bottom from 150
to 200 ft. apart. Sand and stone were hauled in on these tracks. The
sand was dumped in stock piles at intervals; the stone was shoveled from
the cars directly into the charging hopper and the sand was delivered by
wheelbarrows to the same hopper. Four men shoveled the stone for each
mixer. To deliver the concrete from the mixer to the work required six
men with wheelbarrows. Two men leveled off the concrete discharged by
the barrows and two other men floated the surface by means of a
straight-edge spanning the 16-ft. strips and riding on the forms. By
using a wet but not sloppy concrete and moving the straight-edge back
and forth a good surface was secured. The gang mixing and placing
consisted of 20 men for each mixer and 18 gangs laid approximately 1½
acres per 10-hour day. The gang organization and wages were as follows:
Item. Per 10 hours.
4 men shoveling stone at $1.50 $ 6.00
2 men wheeling sand at $1.50 3.00
2 men delivering cement at $1.50 3.00
1 man dumping mixer at $1.50 1.50
1 man tending engine and water at $1.50 1.50
6 men wheeling concrete at $1.50 9.00
2 men spreading concrete at $1.50 3.00
2 men leveling concrete at $1.50 3.00
1 foreman 3.00
------
Total per day $33.00
These costs do not include the fraction of a day's labor for fireman or
the cost of fuel.
~RESERVOIR FLOOR, CANTON, ILL.~--The following costs are given by Mr. G.
W. Chandler for lining the bottom of a 160×80-ft. reservoir with corners
of 20-ft. radius and vertical brick sidewalls. A 1-3½-7½ crushed stone
concrete was used; it was mixed by hand in batches of 2.7 cu. ft.
cement, 9 cu. ft. sand and 20¼ cu. ft. stone. The sand and stone were
measured separately, the sand and cement mixed dry, then shoveled into a
pile with the rock, well wetted, shoveled over again and then shoveled
into wheelbarrows. The stone had 40 per cent. voids and the sand 30 per
cent. voids. The lining was 10 ins. thick including a ¾-in. coat of 1-2¼
mortar spread and worked smooth with a trowel. The cost per cubic yard
of the lining in place was as follows:
0.856 bbl. cement at $2.50 $2.14
10.1 bu. sand (100 lbs. per bu.) at 5¾ cts 0.58
0.857 cu-yd-stone at $2.17 1.86
Labor, mixing and placing at 19 cts. per hr. 0.80
-----
Total $5.38
~RESERVOIR FLOOR, PITTSBURG, PA.~--The following methods and costs of
laying a reservoir floor are given by Mr. Emile Low, M. Am. Soc. C. E.,
for the Hiland Reservoir constructed at Pittsburg, Pa., in 1884, by
contract. There were 7,681 cu. yds. of concrete in the floor which was 5
ins. thick and laid on a clay puddle foundation.
Natural cement costing $1.35 per barrel was used. The broken stone
varied in weight from 147 to 152 lbs. per cu. ft.; it was quarried and
hauled 20 miles by rail and then unloaded into small cars and hauled ½
mile to the reservoir. The cost of the stone per cubic yard delivered
was:
Quarrying, per cu. yd. $0.45
Breaking, per cu. yd. 0.35
Transporting, per cu. yd. 0.50
Total $1.30
The sand was obtained on the site at the cost of excavation, or 1¼ cts.
per bushel.
The method of proportioning and mixing the concrete was as follows:
Platforms 10×16 ft. of 2-in. plank were laid on the puddle foundation
and by these were set 5×4×1½-ft. boxes on legs. Into these boxes 1 bbl.
of cement and 2 bbls. of sand were emptied and thoroughly mixed dry,
then mixed with water to a thin grout. Five barrels of stone were placed
on the platform and thoroughly wetted; the grout was then emptied over
the stone and the two turned over three times with shovels. The concrete
was rammed until the mortar flushed to the surface. The following costs
cover various periods as follows:
Two Days Work (101 cu. yds.): Total. Per cu. yd.
27 laborers, 2 days, at $1.25 $72.90 $0.7217
1 foreman, 2 days, at $2.50 5.00 0.0495
------ -------
Total $77.90 $0.7712
One Month's Work (1,302 cu. yds.):
642 days, laborers, at $1.35 $ 866.70 $0.6649
17 days, water boy, at $0.60 10.20 0.0078
22 days, foreman, at $2.50 55.00 0.0421
------ -------
Total $931.90 $0.7148
Two Days Work (101 cu. yds.): Total. Per cu. yd.
27 laborers, 2 days, at $1.25 $72.90 $0.7217
1 foreman, 2 days, at $2.50 5.00 0.0495
------ -------
Total $77.90 $0.7712
One Month's Work (1,302 cu. yds.):
642 days, laborers, at $1.35 $ 866.70 $0.6649
17 days, water boy, at $0.60 10.20 0.0078
22 days, foreman, at $2.50 55.00 0.0421
------ -------
Total $931.90 $0.7148
Total Work (7,861 cu. yds.):
Quarrying stone $0.45
Transporting stone 0.50
Breaking stone 0.35
1-1/3 bbl. natural cement 1.80
8 bu. sand 0.10
Water 0.05
Labor mixing and laying at $1.25 0.75
Incidentals 0.05
-----
Total $4.05
The contract price was $6 per cu. yd.
[Illustration: Fig. 286.--Form for Constructing Silo.]
~CONSTRUCTING A SILO.~--The form construction shown in Fig. 286 was
employed in building a silo 28 ft. high, 22 ft. 3 ins. interior
diameter, and having 6-in. walls. The bottom of the silo was made 9 ins.
thick and set 2 ft. below the surface. The reinforcement consisted of
ten 2½×3/16-in. rings spaced equally in the lower half and of woven wire
fencing in the upper half. The iron rings were hoops removed from an old
wooden silo. The concrete was a 1-6 mixture of Portland cement and sandy
gravel. Figure 286 is a section through the forms. There were twenty
T-shaped posts, which extended perpendicularly from the ground to a
height of 28 ft., being secured at top and bottom by a system of guy
ropes and posts. The rings, of which there are four, two inside and two
outside, were built of weather boards with their edges reversed. Four
thicknesses of board were used in each ring. The curbing consisted of
2×8-in. sticks 4 ft. long. Wedges driven between the vertical posts and
the rings held the latter in place. When the forms were to be removed
the wedges were knocked out and the rings sprung enough to permit the
removal of the curbing. The rings were then pushed up and fastened in
place for another section. The average rate of progress was one 4-ft.
section per day. The forms were filled in the afternoon and moved up the
following forenoon. Five-foot sections could have been built just as
readily.
The work was all done by farm laborers hired by the month and 100
man-days of such labor were required, excluding seven days work of a
mason brushing and troweling the surface. The cost of the work, not
including the old hoop iron or the old lumber used in forms, was as
follows:
Item. Total. Per cu. yd.
Cement $100.00 $2.62
Gravel and sand 35.00 0.92
1 20-rod roll of fencing 5.20 0.01
New lumber 18.00 0.47
100 days labor at $1.75 175.00 4.60
7 days mason troweling at $3.50 24.50 0.64
------- -----
Total, 38.2 cu. yds. $357.70 $9.26
The external area of the silo is 1,950 sq. ft., which makes the cost of
brushing and troweling 1¼ cts. per sq. ft. There were about 2,300 ft. B.
M. of lumber used in the forms, or about 61 ft. B. M. per cu. yd. of
concrete.
~GROINED ARCH RESERVOIR ROOF.~--The following data are given by Mr. Allen
Hazen and Mr. William B. Fuller, in Trans. Am. Soc. C. E. 1904. The
concrete was mixed in 5-ft. cubical mixers in batches of 1.6 cu. yds. at
the rate of 200 cu. yds. per mixer day. One barrel of cement, 380 lbs.
net, assumed to be 3.8 cu. ft., was mixed with three volumes of sand
weighing 90 lbs. per cu. ft., and five volumes of gravel weighing 100
lbs. per cu. ft. and having 40 per cent voids. On the average 1.26 bbls.
of cement were required per cu. yd. The conveying plant consisted of two
trestles (each 900 ft. long) 730 ft. apart, supporting four cableways.
The cables were attached to carriages, which ran on I-beams on the top
of the trestles. Rope drives were used to shift the cableways along the
trestle. Three-ton loads were handled in each skip. The installation of
this plant was slow, and its carrying capacity was less than expected.
It was found best to deliver the skips of concrete to the cableway on
small railway track, although the original plan had been to move the
cableways horizontally along the trestle at the same time that the skip
was traveling.
The cost of mixing and placing the concrete was as follows:
Per cu. yd.
Measuring, mixing and loading $0.20
Transporting by rail and cables 0.12
Laying and tamping floors and walls including setting forms 0.22
-----
Total $0.54
The cost of laying and tamping the concrete on the vaulting was 14 cts.
per cu. yd. The vaulting is a groined arch 6 ins. thick at the crown and
2½ ft. thick at the piers.
The lumber of the centering for the vaulting was spruce for the ribs and
posts, and 1-in. hemlock for the lagging. The centering was all cut by
machinery, the ribs put together to a template, and the lagging sawed to
proper bevels and lengths. The centers were made so that they could be
taken down in sections and used again. The cost of centering was as
follows:
Labor on centers covering 62,560 sq. ft.
Foreman, 435 hrs. at 35 cts. $ 152.25
Carpenters, 4,873 hrs. at 22½ cts. 1,096.42
Laborers, 3,447 hrs. at 15 cts. 517.05
Painters, 577 hrs. at 15 cts. 86.55
Teaming, 324 hrs. at 40 cts. 121.60
---------
Total labor building centers, 313 M. at $6.37 $1,973.87
Materials for centers covering 62,560 sq. ft.
313,000 ft. B. M. lumber, at $18.20 $5,700.00
3,700 lbs. nails, at 3 cts. 111.00
8 bbls. tar, at $3 24.00
---------
Total $5,835.00
These centers covered two filters, each having an area of 121-1/3×258
ft. There were six more filters of the same size, for which the same
centers were used. The cost of taking down, moving and putting up these
centers (313 M.) three times was as follows:
Foreman, 2,359 hrs. at 35 cts. $ 825.65
Carpenters, 12,766 hrs. at 22½ cts. 2,872.35
Laborers, 24,062 hrs. at 15 cts. 3,609.30
Team, 430 hrs. at 40 cts. 172.00
3,000 ft. B. M. lumber, at $20 60.00
3,000 lbs. nails, at 3 cts. 90.00
---------
Total cost of moving centers to cover 196,660 sq. ft. $7,629.30
[Illustration: Fig. 287.--Forms for Constructing Grain Elevator Bins.]
The cost of moving the centers each time was $8.10 per M., showing that
they were practically rebuilt; for the first building of the centers, as
above shown, cost only $6.37 per M. In other words, the centers were not
designed so as to be moved in sections as they should have been.
Although the centers were used four times in all, the lumber was in fit
condition for further use. The cost of the labor and lumber for the
building and moving of these centers for the 8 filter beds, having a
total area of 259,220 sq. ft., was $15,438, or 6 cts. per sq. ft.
~GRAIN ELEVATOR BINS.~--In constructing cylindrical bins 30 ft. in
diameter and 90 ft. high for a grain elevator the forms shown by Fig.
287 were used. For the inside wall a complete ring of lagging 4 ft. high
nailed to circular horizontal ribs of 2×8-in. planks was used. For the
outside wall two, three or four segments fitting the clear spaces
between adjoining tanks were used, these panel segments being also 4 ft.
high. The inside and outside rings were held together by yokes
constructed as shown, and bolted to the inner and outer ribs. A staging
built up inside the tank carried jack screws, on which were seated the
inner legs of the yokes.
CHAPTER XXIII.
METHODS AND COST OF CONSTRUCTING ORNAMENTAL WORK.
The safest rule for ornamental work is to leave its construction to
those who make a specialty of such work. This is perfectly practicable
in most concrete structures having ornament. Bridge railings can be and
usually are made up of separately molded posts, balusters, bases and
rail. Ornamental columns in building work, keystones, medallions,
brackets, dentils, rosettes, and cornice courses can be similarly molded
and placed in the structure as the monolithic work reaches the proper
points. The general constructor, therefore, can readily delegate these
special parts of his concrete bridge or building to specialists at
frequently less cost to himself and nearly always with greater certainty
of good results than if he installed molds and organized a trained gang
for doing the work.
Good concrete ornament is not alone a matter of good design. It is also
a matter of skilled construction. Nearly anyone can mold an ornament,
but few can mold an ornament which is durable. To produce clean, sharp
lines and arises which will endure, the molder must have special
knowledge and familiarity with the action of cement and of concrete
mixtures, both in molding and on exposure to the elements. This is
knowledge that the general concrete worker rarely possesses but which
the ornament molder does possess if he knows his business. Special work
is always best left to the specialist.
While the more intricate ornamental work is best done by sub-contract,
so far at least as the actual molding of the ornaments is concerned,
there is a large amount of simple paneling and molding which the general
practitioner not only can do but must do. Knowledge of the best methods
of doing such work is essential and it is also essential that the
constructor should know in a general way of the special methods of
molding intricate ornaments.
~SEPARATELY MOLDED ORNAMENTS.~--The cement for ornamental work must be
strong and absolutely sound. Where an especially light color is wished a
light colored cement is desirable. So called white cements are now being
manufactured. Lafarge cement, a light colored, non-staining cement made
in France, gives excellent results. Of American cements, Vulcanite
cement has a light color, and next to it in this respect comes Whitehall
cement. A light colored ornament can, however, be secured with any
cement by using white sand or marble or other white stone screenings.
Some authorities advocate this method of securing light colored blocks
as always cheaper and usually superior to the use of special cements.
The choice between the two methods will be governed by the results
sought; where as nearly as possible a pure white is desired it stands to
reason that a white or nearly white cement will give the better results.
In the matter of sand and aggregate for ornamental work, the kinds used
will ordinarily be the kinds that are available. They must conform in
quality to the standard requirements of such materials for concrete
work. Where special colors or tints are wanted they can be secured by
using for sand and aggregate screenings from stones of the required
color. This is in all respects the best method of securing colored
blocks, as the color will not fade and the concrete is not weakened. A
great variety of pigments are made for coloring concrete; these colors
all fade in time, and with few exceptions they all weaken the concrete.
The mixtures used in ornamental work will depend upon the detail of the
ornament and upon whether color is or is not required. Generally a rich
mixture of cement and sand or fine stone screenings will be used for the
surface and will be backed with the ordinary concrete mixture. A surface
mixture of fine material is necessary where clear, sharp lines and edges
or corners are demanded.
The molds used for ornament are wooden molds, iron molds, sand molds and
plaster of Paris and special molds. Each kind has its field of
usefulness, and its advantages over the others. They will be considered
briefly in the order named.
~Wooden Molds.~--Wooden molds are perhaps the best for general work where
plain shapes and not too delicate ornamentation are wanted. They give
the best results only with a quite dry and rather coarse grained surface
mixture. If a wet mixture is used such water as flushes to the surface
cannot escape and small pits and holes are formed, which necessitates
grout or other finishing. The following are examples of wooden mold
work:
In constructing a five-span reinforced concrete arch bridge at Grand
Rapids, Mich., in 1904, the railings and ornamental parts of the bridge,
such as keystones, brackets, consols, dentiles and panels, were cast in
molds and set in place much as cut stone would be. Special molds were
employed for each of these different shapes. These molds were plastered
with an earth damp mortar composed of 1 part cement and 2½ parts fine
sand, which was followed up with a backing of wet concrete composed of 1
part cement, 2 parts sand and 3 parts broken stone passing a ¾-in. ring.
The facing mortar was made 1½ ins. thick. The castings cannot be told
from dressed stone at a few feet distance.
The part elevation and sections in the drawings of Fig. 288 show the
arrangement of the various castings to form the completed railing,
coping, etc. To specify, A is the arch ring, B the brackets, C the
coping, and D, E, F, respectively, the base, balusters and rail of
the bridge railing. The blocks G and H show the keystone and railing
post. The forms or molds for each of these parts are shown by the other
drawings of Fig. 288. A description of each of these forms follows:
The keystones were molded in wooden forms, consisting of one piece, a,
forming the top and front; of two side pieces, f, of a bottom
consisting of two parts, b and c; and of a back piece, g. The back
and side pieces are stiffened with 2×3½-in. pieces, and the front, sides
and back are held together by yokes or clamps. The front of the mold was
the only portion calling for particular work, and this was made of
boards laminated together.
The bracket molds consisted of two side pieces provided with grooves for
receiving the front and back pieces, and with slots for tie rods
clamping the whole mold together. It will be noted also that the side
pieces had nailed to them inside a beveled strip to form a groove in
each side of the cast block. The purpose of this groove was to provide a
bond to hold the bracket more firmly in the adjoining concrete of the
wall. The bottom of the mold was formed by a 2-in. plank, and when the
concrete had been tamped in place the forms were removed, and the
bracket was left on the bottom to set. It may be noted here that a
goodly number of the brackets showed a crack at the joint marked x
caused by tamping at the point y. In construction the bracket castings
were set at proper intervals on the spandrel walls, which had been
completed up to the level of the line X Y. The coping course was then
built up around the bracket blocks to the level of the bottom of the
railing base.
[Illustration: Fig. 288.--Molds for Railings and Ornaments for Concrete
Arch Bridge.]
The mold or form for the coping course was designed to build the coping
in successive sections, and was built up around the bracket blocks, and
supported from the centers as shown by the drawings. To form the
expansion joints in the coping course there were inserted across the
mold at proper intervals a short iron plate ¼ in. thick, cut to fit. The
cutting of this plate was found to be a slow operation.
The forms for the base of the railing (Section D) consisted of 1¾-in.
stock for the sides, and ¾-in. stock for the slopes. They extended
across the arch, and were held together by a very simple though very
efficient clamp. This consisted of two 2×3×33-in. pieces nailed to a
2×3×17-in. piece by means of galvanized iron strips. About half-way down
the long pieces, a ½-in. rod was run through, and secured up against
blocks, h, placed about 56 ins. apart. These blocks were removed as
the concrete was put in place. It will be noticed from the cross-section
of the railing that the balusters are set into sockets formed in the top
of the base course. These sockets were formed by means of the mold shown
at W and Z.
In casting the balusters, Section (E), a 3/8-in. cast iron mold,
consisting of four iron sides and an iron top, was used. Originally
there were two end plates of iron, but it was found more convenient to
have the bottom one of wood and allow the cast spindle to stand and set.
The mold was held together by ½-in. bolts. It would have been more
practical to have had the side casting composed of two parts.
The form for the railing is built up around the tops of the spindles.
The bottom piece is 1×9 ins., to which 4¼-in. ogee molding is nailed.
The sides are of 1-in. stock, and are clamped together. The top is
finished off with a trowel.
The mold for the posts is made in four parts, which fit together at the
top and bottom by a bevel joint, as shown in the one-fourth section. The
broad sides rest against the narrow ones, and are held against the same
by means of ½-in. rods running through 2×3-in. stock: 2-in. projections
of the broad sides facilitate the removal of the form from the completed
post.
[Illustration: Fig. 289.--Molds for Ornamental Railing Posts for
Concrete Facade for Bridge.]
In constructing a concrete facade for a plate girder bridge at St.
Louis. Mo., the railing above the base was constructed of separately
molded blocks as follows: The balusters were cast in plaster molds. To
make these molds a box square in plan and the height of the baluster
was constructed of wood and cut vertically into three sections. The
inside lateral dimensions of this box were made 6 ins. greater than the
largest dimension of the baluster. A full size wooden pattern of the
baluster was set up and the three sections of the box were set around
it. Sheets of thin galvanized metal, with their inner edges cut to
conform to the curves of the baluster, were inserted in the joints of
the assembled box so as to divide the vacant space between the pattern
and the box into vertical sections.
[Illustration: Fig. 290.--Railing for Arch Bridge.]
[Illustration: Fig. 291.--Form for Lattice Panels Shown by Fig. 290.]
A mixture of 1 part Portland cement and 1 part plaster of Paris, made
wet, was then poured around the pattern until the box was filled. When
this mixture had become hard, the box was taken down, leaving a plaster
and cement casing separated into three parts by the sheets of galvanized
metal. This casing was separated from the pattern and given a coat of
shellac on the inside. Four or five molds of this description were cast.
To cast a baluster, the sections were assembled and a ½-in. corrugated
bar was set vertically in the center. A mixture of 1 part Portland
cement and 3 parts sand was then poured into the mold and allowed to
harden. The molds for the urns on the railing post and the balls on the
end posts were made in exactly the same manner as the baluster molds.
The construction of the railing posts is shown by the drawings of Fig.
289. Referring first to the end posts, it will be seen that they were
molded in place in seven sections marked A, B, C, E, F, and G. The
construction of the mold for each section is shown by the
correspondingly lettered detail. The intermediate posts were built up of
the separately molded pieces I, K and H. The costs of molding the
several parts were: Balusters, 60 cts. each; hand rail, 40 cts. per lin.
ft. The six intermediate posts cost $12 each, and the four end or newel
posts cost $75 each.
[Illustration: Fig. 292.--Form for Hand Rail Shown by Fig. 290.]
In constructing the 72-ft. span-ribbed arch bridge over Deer Park Gorge,
near La Salle, Ill., a hand railing of the design shown by Fig. 290, was
used. In constructing this railing, the posts were molded in place, but
the open work panels between posts and the hand rail proper were molded
separately and set in place between the posts as indicated. For molding
the panels a number of boxes constructed as shown by Fig. 291, were
used. These were simple rectangular boxes on the bottom boards of which
were nailed blocks of the proper shape and in the proper position to
form the openings in the railing. The bottom of the form was first
plastered with mortar, then the concrete was filled in and plastered on
top. As soon as the concrete had begun to set the blocks were removed so
that final setting could take place without danger of cracking. When the
concrete had set so that the panel could be safely handled, it was
removed from the form and stored until wanted. The hand rail for each
side was molded in two pieces in forms constructed as shown by Fig. 292.
The total cost of the railing in place was about $2 per lineal foot.
The concrete was a 1-2-4 mixture of screenings and 7/8-in. broken stone.
~Iron Molds.~--Iron molds have the same disadvantages as wooden molds in
the use of wet mixtures. They can be made to mold more intricate
ornaments, and in the matter of durability, are, of course, far superior
to wood. Iron molds can be ordered cast to pattern in any well equipped
foundry. Many firms making block machines also make standard column,
baluster, ball and base, cornice, and base molds of various sizes and
patterns. These molds are made in two, three or more sections which can
be quickly locked together and taken apart. A column mold, for example,
will consist of a mold for the base, another for the shaft, and a third
for the capitol, each in collapsible sections. Where the pattern of the
shaft changes in its height, two shaft molds are commonly used, one for
each pattern. Prices of iron molds are subject to variation, but the
following are representative figures: Plain baluster molds 14 to 18 ins.
high, $7.50 to $10 each; fluted square balusters, 14 to 18 ins. high,
$10, each; ball and base, 10 to 18-in. balls, $15 to $25 each; fluted
Grecian column, base, capitol and one shaft molds, $30; Renaissance
column, base, capitol and two shaft molds, $45.
~Sand Molding.~--Molding concrete ornaments in sand is in all respects
like molding iron castings in a foundry. Sand molding gives perhaps the
handsomest ornament of any kind of molding process, the surface texture
and detail of the block being especially fine. It is, however, a more
expensive process than molding in wooden or iron molds, since a separate
mold must be made for each piece molded. The process was first employed
and patented in 1899, by Mr. C. W. Stevens, of Harvey, Ill., and for
this reason it is often called the Stevens process. Sand molded
ornaments and blocks are made by a number of firms to order to any
pattern. The process as employed at the works of the Roman Stone Co., of
Toronto, Ont., is as follows: The stone employed for aggregate, is a
hard, coarse, crystalline limestone of a light grey color, being
practically 97 per cent. calcium carbonate, with a small percentage of
iron, aluminia and magnesia. Nothing but carefully selected quarry
clippings are used and these are crushed and ground at the factory and
carefully screened into three sizes, the largest about the size of a
kernel of corn. Daily granulometric tests are made of the crusher output
to regulate the amount of each size got from the machines. It has been
found that next in importance to properly graded aggregates is the
gaging of the amount of water used in the mixture. This is done by an
automatically filled tank into which lead both hot and cold water and in
which is fixed a thermometer to properly regulate the temperature. In
gaging the mix about 20% of water is used, but of course when the cast
is made the surplus is immediately drawn off into the sand, where it is
retained and serves as a wet blanket to protect the cast and supply it
with the proper amount of water during crystallization. Experiments seem
to indicate that about 15% by weight gives the greatest amount of
strength of mortar at the age of six months, while, giving less strength
at shorter time tests than mortar gaged with a smaller percentage of
water.
The method of handling the mix and casting is quite simple and almost
identical with the practice in iron foundries. The mixture is made in a
batch mixer to about the same consistency as molasses, from which it is
poured into a mechanical agitator and carried about the foundry by a
traveling crane. This agitator is so constructed that it keeps the
materials in motion constantly and prevents their segregation. In each
cast is inserted the proper reinforcing rods, lifting hooks and tie
rods, and the casts are allowed to remain for a proper period in the wet
sand after they are poured; they are then taken to the seasoning room
which is kept at as constant a temperature as it is practical to
maintain. Each cast is marked with the number which determines its
location in the building and the date it was cast, and it is then kept
in the storage shed a fixed time before shipping.
Records are kept of each cast made and the company is able to get, as in
mills rolling structural steel, the exact number and location of all
casts made from the same mix. Careful records are always kept of the
tests of cement and material, and test cubes are made from each
consignment of cement so tested; in this way all danger of defective
stone through inferior cement is eliminated. The patterns used in
making the molds and the method of molding are quite similar to ordinary
iron foundry practice except that the sand used is of special nature.
The finish of the stone is generally tooled finish molded in the sand,
the different textures of natural stone being produced by the veneering
of the pattern with thin strips of wood which are run through a machine
producing the different finishes. Each stone is provided with setting
hooks cast in the blocks which take the place of the ordinary lewis
holes used in cut stone.
~Plaster Molds.~--Plaster of Paris molds are made from clay, gelatin or
other patterns in the usual manner adopted by sculptors. They are
particularly adapted to fine line and under cut ornaments. The concrete
is poured into the plaster mold and after the cement has become hard,
the plaster is broken or chiseled away, leaving the concrete exposed.
Two examples of excellent work in intricate concrete ornaments are
furnished by the power house for the Sanitary District of Chicago, and
by the State Normal School building, at Kearney, Neb. In the power
house, the ornamental work consisted of molded courses, cornice work;
and particularly of heavy capitals for pilasters. These capitals were
very heavy, being 7½ ft. long and of the Ionic design. These were made
from plaster molds; made so as to be taken apart or knocked down and to
release in this way, perfectly. There were also scrolls, keystones and
arches in curved design over all of the 40 windows. None of this
ornament was true under cut work. In building the Normal School
building, Corinthian capitals, in quarters, halves, corners and full
rounds were made in plaster molds. There were some 30 of these capitols.
They were made in solid plaster molds; the molds having been cast in
gelatine molds, one for each capitol. Into these, the concrete was
tamped, made very wet, and after the concrete had hardened, the plaster
cast was chiseled away. This was very easily accomplished. These
capitols were true Corinthians, having all the floriation and under-cut
usually seen in such capitols.
~ORNAMENTS MOLDED IN PLACE.~--Molding ornaments in place is usually, and
generally should be, confined to belt courses, cornices, copings and
plain panels. Relief work, like keystones, scrolls or rosettes, can be
molded in place if desired, by setting plaster molds in the wooden forms
at the proper points. This method is often advantageous in bridge work,
where comparatively few ornaments are required, such as keystones.
[Illustration: Fig. 293.--Spandrel Wall Mold for Arch Bridge.]
The construction of forms for ornamental work in place is best described
by taking specific examples. Figure 293, shows the face form for the
arch ring, spandrel wall and cornice or coping course of the Big Muddy
River Bridge on the Illinois Central R. R. The section is taken near the
crown of the arch. The lagging only is shown; this was, of course,
backed with studding. The point to be noted in this form is the
avoidance of any approach to under cut work; there are, in fact, very
few straight cut details. This brings up a point that must be carefully
watched if trouble is to be avoided, namely, the construction of the
form work in sections which can be removed without fracturing the
ornament. To illustrate by an assumed example, supposing it is required
to mold the wall and cornice shown by Fig. 294. It is clear that if the
backing studs are in single pieces, notched as shown, the forms cannot
be removed without fracturing at least the corner A. If the studs and
lagging be constructed in two parts, separated along the line a b, the
form is possible of removal if great care is used without damage to the
concrete. The construction shown by this sketch does not greatly
exaggerate matters. Figure 295 shows a wall form that has been given
several times as a presumably good example in which, as will be seen it
is impossible to remove the board a, without breaking the concrete
even if the narrow face were not broken by the swelling of the lumber
before ever it became time to take down the forms.
[Illustration: Fig. 294.--Diagram Illustrating Details of Mold
Construction.]
[Illustration: Fig. 295.--Example of Poor Wall Form Construction.]
This matter of making provision for the swelling of the forms is another
point to be watched. Referring again to Fig. 294 it will be seen that
the swelling of the lagging, even if the cornice instead of being under
cut at A were straight cut on the line c d, is liable so to crowd
the lagging into the corner A and B that the concrete is cracked
along the lines e f or g h. A suggested remedy for this danger is
shown by Fig. 296. At a distance of every 3 or 4 ft. insert a narrow
piece of lagging a and behind these lagging strips cut notches b in
the studs. When the concrete has got its initial set pull back the
lagging strip a into the notches b, leaving an open joint to provide
for expansion due to swelling.
[Illustration: Fig. 296.--Notched Studding for Removal of Lagging Board
to Permit Swelling.]
[Illustration: Fig. 297.--Form for Concrete Facade Shown by Fig. 298.]
[Illustration: Fig. 298.--Concrete Facade for Plate Girder Bridge.]
[Illustration: Fig. 299.--Forms for Curved Concrete Abutments.]
[Illustration: Fig. 300.--Cornice Form.]
[Illustration: Fig. 301.--Method of Supporting Cornice Form Shown by
Fig. 300.]
In constructing a concrete facade for a plate girder bridge at St.
Louis, Mo., the form shown by Fig. 297 was used. The completed facade is
shown by Fig. 298. The ceiling slab was first built and allowed to set
and then the forms were erected for the frieze and coping. After these
were molded the forms were continued upward as shown for the base of the
railing. Above this point the several parts were separately molded as
shown by Fig. 285 previously described. Molded in this manner the
ceiling cost 25 cts. per sq. ft.; the frieze and coping cost $2 per lin.
ft., and the railing base cost 45 cts. per lin. ft. In constructing the
concrete abutments of this same structure use was made of the forms
shown by Fig. 299. These abutments had curved wing walls and for molding
these girts cut to the radii of the curves were fastened to the studs
and vertical lagging was nailed to the girts. All the lagging was tongue
and groove stuff.
[Illustration: Fig. 302.--Cornice and Balustrade for Arch Bridge.]
In constructing an open spandrel arch bridge at St. Paul, Minn., the
cornice form shown by Fig. 300, supported as shown by Fig. 301, was
used. The particular feature of this form was the use of a lath and
plaster lining to the lagging. This lining was used for all exposed
surfaces of the bridge. So called patent lath consisting of boards with
parallel dovetail grooves and ridges was used. This was plastered with
cement mortar and the concrete was deposited directly against the
plaster after smearing the plaster surface with boiled linseed oil. This
lining is stated to have given an excellent surface finish to the
concrete. It cost 55 cts. per sq. ft. for materials and labor. A section
of the balustrade and cornice is shown by Fig. 302. The posts, balusters
and railing were molded separately. The balusters were molded in zinc
molds. At first some trouble was had in getting good casts on account
of air pockets. This was largely done away with by filling the mold as
compactly as possible and then driving a ¾-in. iron rod through the
center vertically; this rod crowded the concrete into all parts of the
mold and also served to strengthen the baluster. The baluster molds were
made in two parts; this proved a mistake--three parts would have been
better.
CHAPTER XXIV.
MISCELLANEOUS DATA ON MATERIALS, MACHINES AND COSTS.
The following cost data comprise such miscellaneous items as do not
properly come in the preceding chapters. They are given not as including
all the miscellaneous purposes for which concrete is used but as being
such items of costs as were secured in collecting the more important
data given in preceding sections.
[Illustration: Fig. 303.--Device for Drilling Green Concrete.]
~DRILLING AND BLASTING CONCRETE.~--Concrete is exceedingly troublesome
material in which to drill deep holes, and this statement is
particularly true if the concrete is green. The following mode of
procedure proved successful in drilling 1½-in. anchor bolt holes 6 ft.
and over in depth in green concrete. The apparatus used is shown by Fig.
303, re-drawn from a rough sketch made on the work by one of the
authors, and only approximately to scale. The drill is hung on a small
pile driver frame, occupying exactly the position the hammer would
occupy in a pile driver, and is raised and lowered by a hand windlass.
By this arrangement a longer drill could be used than with the ordinary
tripod mounting and less changing of drills was necessary. A wide flare
bit was used, permitting a small copper pipe to be carried into the hole
with the drill; through this pipe water was forced under pressure,
carrying off the chips so rapidly that no wedging was possible. By this
device drilling which had previously cost over 25 cts. a hole was done
at a cost of less than 5 cts. a hole.
In removing an old cable railway track in St. Louis, Mo., holes 8 ins.
deep were drilled in the concrete with a No. 2 Little Jap drill, using a
1¼-in. bit and air at 90 lbs. pressure. A dry hole was drilled, the
exhaust air from the hollow drill blowing the dust from the hole keeping
it clean. The concrete was about 18 years old and very hard. Two holes
across track were drilled, one 10 ins. inside each rail; lengthwise of
the track the holes were spaced 24 ins. apart, or four pairs of holes
between each pair of yokes.
Common labor was used to run the drills and very little mechanical
trouble was experienced. Three cars were fitted up, one for each gang,
each car being equipped with a motor-driven air compressor, water for
cooling the compressors being obtained from the fire plugs along the
route. The air compressors were taken temporarily from those in use in
the repair shops, no special machines being bought for the purpose.
Electricity for operating the air compressor motors was taken from the
trolley wire over the tracks. The car was moved along as the holes were
drilled, air being conveyed from the car to the drills through a
flexible hose. Two drills were operated normally from each car. One of
the air compressors was exceptionally large and at times operated four
drills. The total number of holes drilled in the reconstruction of the
track was 31,000. The total feet of hole drilled was 20,700 ft.
With the best one of the plants operating two to three drills 30 8-in.
holes, or 20.3 ft. of hole, were drilled per hour per drill at a labor
cost of 2.7 cts. per foot.
For blasting, a 0.1-lb. charge of 40 per cent. dynamite was used in each
hole. A fulminating cap was used to explode the charge, and 12 holes
were shot at one time by an electric firing machine. The dynamite was
furnished from the factory in 0.1-lb. packages, and all the preparation
necessary on the work was to insert the fulminating cap in the dynamite,
tamp the charge into the hole and connect the wires to the firing
machine. In order to prevent any damage being done by flying rocks at
the time of the explosion, each blasting gang was supplied with a cover
car, which was merely a flat car with a heavy bottom and side boards.
When a charge was to be fired, this car was run over the 12 holes and
the side boards let down, so that the charge was entirely covered. This
work was remarkably free from accidents. There were no personal accident
claims whatever, and the total amount paid out for property damages for
the whole six miles of construction was $685. Most of this was for glass
broken by the shock of explosion. There was no glass broken by flying
particles. The men doing this work, few of whom had ever done blasting
before, soon became very skillful in handling the dynamite, and the work
advanced rapidly. The report made by the firing of the 12 holes was no
greater than that made by giant fire-crackers.
For the drilling and blasting the old rail had been left in place to
carry the air compressor car and the cover car. After the blasting, this
rail was removed and the concrete, excavated to the required depth. In
most cases the cable yokes had been broken by the force of the blast.
Where these yokes had not been broken, they were knocked out by blows
from pieces of rail. The efficacy of the blasting depended largely upon
the proper location of the hole. Where the holes had been drilled close
to the middle of the concrete block, so that the dynamite charge was
exploded a little below the center of gravity of the section, the
concrete was well shattered and could be picked out in large pieces.
Where the hole had been located too close to either side of the concrete
block, however, the charge would blow out at one side and a large mass
of solid concrete would be left intact on the other side. The total
estimated quantity of concrete blasted was 6,558 cu. yds., or 0.2 cu.
yd. of concrete per lineal foot of track. The cost of the dynamite
delivered in 0.1 lb. packages was 13 cts. per pound. The exploders cost
$0.0255 each.
The cost of drilling and blasting was as follows:
Item. Per mile. Per lin. ft. Per cu. yd.
Labor, drilling $ 89.76 $0.017 $0.085
Blasting labor and materials. 285.12 0.054 0.268
------- ------ ------
Total drilling and blasting. $374.88 $0.071 $0.353
[Illustration: Fig. 304.--Bench Monument, Chicago, Ill.]
The cost of blasting with labor and materials, separately itemized, was
as follows, per cubic yard:
Dynamite and exploders $0.192
Labor 0.076
------
Total $0.268
Two cubic yards of concrete were blasted per pound of dynamite.
~BENCH MONUMENTS, CHICAGO, ILL.~--The standard bench monuments, Fig. 304,
used in Chicago, Ill., are mostly placed in the grass plot between the
curb and the lot line, so that the top of the iron cover comes just
level with the street grade or flush with the surface of the cement
walk. The monument consists of a pyramidal base 6 ft. high and 42 ins.
square at the bottom, with a ¼-in.×2-ft. copper rod embedded, and of a
cast iron top and cover constructed as shown by the drawing. Mr. W. H.
Hedges, Bench and Street Grade Engineer, Department of Public Works,
Chicago, Ill., gives the following data regarding quantities and cost.
The materials required for each monument are: 1.78 cu. yd. crushed
stone, 0.6 cu. yd. torpedo sand, 1½ bbls. cement, 60 ft. B. M. lumber,
one ¼×24-in. copper rod, one top and cover. A gang consisting of 1
foreman, 4 laborers and 2 teams construct from one to three monuments
per day, the average number being two per 8-hour day. In 1906 the
average cost of the monuments was $24.12 each, based on above material
and labor charges.
[Illustration: Fig. 305.--Base for Wooden Pole.]
[Illustration: Fig. 306.--Mile Post, Chicago & Eastern Illinois Ry.]
~POLE BASE.~--Figure 305 shows a concrete base for transmission line poles
invented by Mr. M. H. Murray, of Bakersfield, Cal., and used by the
Power Transit & Light Co. of that city. These bases are molded and
shipped to the work ready for placing. They weigh about 420 lbs. each.
One base requires 37½ lbs. of 2×¼-in. steel bar, 40 lbs. of Portland
cement, 3 cu. ft. of broken stone or gravel and enough sand to fill the
form or mold, which is 10×10 ins. by 4½ ft. Unskilled labor is employed
in the molding and two men can mold ten bases per 8-hour day. The cost
of molding is as follows per base:
2 men at $2 per day $0.40
Brace irons per set 2.50
1-9 cu. yd. stone at $4.05 0.45
40 lbs. cement at 1½ cts. 0.60
Sand 0.15
-----
Total cost $4.10
Two men at $2 per day each set five bases in eight hours, making the
cost of setting 80 cts. per base. The bases were sunk to a depth of 3
ft. 3 ins. In many cases they were placed under poles without
interrupting service by sawing off the pole, dropping it into the
ground, placing the new base and setting the sawed-off pole on it and
bolting up the straps.
~MILE POST, CHICAGO & EASTERN ILLINOIS R. R.~--The dimensions of the post
are shown by Fig. 306. Each post weighs 498 lbs. They are made when
other concrete work is being done. The form is laid flat, with the molds
for the letters on the bottom, and bottom and sides are plastered with
mortar, which is backed up with a 1-1-2 stone concrete. The cost of the
post is given as follows:
¼ barrel of cement at $2 $0.50
267 lbs. crushed stone 0.01
133 lbs. sand 0.01
1-1/3 hours labor at 15 cts. 0.20
1/3 hour carpenter changing letters at 25 cts. 0.08
Coloring cement 0.02
-----
Total $0.82
~BONDING NEW CONCRETE TO OLD.~--Concrete which has set hard has a surface
skin or glaze to which fresh concrete will not adhere strongly unless
special effort is made to perfect the bond. Various ways of doing this
are practiced. The most common is to clean the hardened surface from all
loose material and give it a thorough wash of cement grout against which
the fresh concrete is deposited and rammed before the grout has had time
to set. Washing the old surface with a hose or scrubbing it with a brush
and water improves the bond, as does also the hard tamping of the
concrete immediately over the joint. Mortar may be used in place of
grout. The thorough cleansing of the surface is, however, quite as
essential as the bonding coat, in fact in the opinion of the authors it
is more essential. As a rule, a good enough joint for ordinary purposes
can be got by tamping the fresh concrete directly against the old
concrete, without grout or mortar coating, if the surface of the latter
is thoroughly cleaned by scrubbing and flushing. The secret of securing
a good bond between fresh concrete and concrete that has set lies
largely in getting rid of the glaze skin and the slime and dust which
forms on it. Washing will go far toward doing this. The glaze skin can
be removed entirely by acid solutions, but the acid wash must be flushed
free from the surface before placing the fresh concrete. Ransomite, made
by the Ransome Concrete Machinery Co., Dunellen, N. J., is a prepared
acid wash which to the authors' knowledge has given excellent success in
a number of cases. The glaze coat can also be removed by picking the
hardened surface, but the picking should be followed by washing to
remove all loose chips and dust.
~DIMENSIONS AND CAPACITIES OF MIXERS.~--In planning plant lay-outs it is
often desirable to know the sizes, capacities, etc., of various mixers
in order to make preliminary estimates. Tables XXII to XXXIII give these
data for a number of the more commonly employed machines. The Eureka,
the Advanced and the Scheiffler mixers are continuous mixers and the
others are batch mixers.
Table XXII--Sizes, Capacities and Weights of Advanced Mixers.
Cement Machinery Co., Jackson, Mich.
Height ground to hopper top 3' 6"
Width over all 3' 6"
Length over all on trucks 10' 6"
Capacity per hour, cu. yds. 25 to 75
Horsepower, engine 2
Weight:
On trucks, without power, lbs. 1,700
On trucks, steam engine 2,000
On trucks, gas engine 2,200
On trucks, steam engine and boiler 2,500
Table XXIII--Sizes, Capacities and Weights of Scheiffler Proportioning
Mixers. The Hartwick Machinery Co., Jackson, Mich.
Mixer Number. No. 2. No. 2½. No. 3.
Dimensions of hopper, ins. 55×33 53×33 60×40
Height, from ground to top of hopper, ins. 43 43 48
Width over all on trucks, ins. 46 46 46
Length over all on trucks, ins. 126 126 132
Hourly capacity in cubic yards 5-6 8 12-15
Horsepower required, gasoline engine 2 3 4
Horsepower required, steam engine. 3 4
Weights:
On trucks, without power, lbs. 2,400 2,900 3,300
On trucks, gasoline engine, lbs. 3,000 3,600 4,500
On trucks, steam engine, lbs. 2,800 3,330 4,000
On trucks, steam engine and boiler, lbs. 3,500 3,700 4,800
Table XXIV--Sizes, Capacities and Weights of Eureka Mixers.
Eureka Machine Co., Lansing, Mich.
-----------------------------------------------------------------
| | | |
Mixer Number | No. 81 | No. 82 | No. 83 |
-------------------------------|----------|----------|----------|
_ | | | |
| Sand | 18"×25½" | | |
Size hoppers, ins. | Cement | 17"×25½" | do | do |
|_ Stone | 30"×25" | | |
Height, ground to hopper top | 49" | 49" | 49" |
Width over all on trucks | 40" | 40" | 40" |
Length over all on trucks | 12'-9" | 10'-0" | 10'-0" |
Capacity per hour, cu. yds. | 10 to 18 | 10 to 18 | 10 to 18 |
Engine horsepower | 3 stm. | 3 stm. | 3½ gas |
Boiler horsepower | 4 | | |
Weight on trucks, no power | 1,980 | 1,980 | 1,980 |
Weight trucks steam engine | 2,800 | | |
Weight trucks gas engine | | | 2,300 |
Weight trucks, eng. and boiler | 3,000 | | |
-------------------------------|----------|----------|----------|
-----------------------------------------------------------------
| | |
Mixer Number | No. 84 | No. 25 | No. 23
-------------------------------|------------|----------|----------
_ | | |
| Sand | 18"×25½" | 18"×25½" | 18"×25½"
Size hoppers, ins. | Cement | 17"×25½" | 17"×25½" | 17"×25½"
|_ Stone | 30"×25" | |
Height, ground to hopper top | 49" | 49" | 49"
Width over all on trucks | 40" | 40" | 40"
Length over all on trucks | 10'-0" | 8'-0" | 8'-0"
Capacity per hour, cu. yds. | 10 to 18 | 10 to 18 | 2 to 4
Engine horsepower | 3 el. motr | Pulley. | Hand.
Boiler horsepower | | |
Weight on trucks, no power | 1,980 | 1,400 | 1,400
Weight trucks steam engine | | |
Weight trucks gas engine | | |
Weight trucks, eng. and boiler | | |
-------------------------------|------------|----------|----------
Table XXV--Sizes, Capacities and Weights of Snell Mixers.
R. Z. Snell Mfg. Co., South Bend, Ind.
Mixer Number. No. 0. No. 1. No. 2. No. 3.
Size batch, cu. ft. 3 7 11 24
Capacity per hour, cu. yds. 2½ 5 8 20
Speed revs. per min. 30 30 25 19
Weight on Skids:
With pulley, lbs. 480 800 900 2,000
With engine, lbs. 800 1,550 2,050 3,500
With eng. and boiler, lbs. 2,170 2,900 4,000
Weight on Wheels:
With engine, lbs. 1,100 2,200 3,450 4,700
With engine and boiler, lbs. 3,570 4,750 5,200
Engine:
Size cylinder, ins. 4×6 3½×4½ 4×5 5×6½
Rated horsepower 1½ 4 5 6
Boiler:
Size, ins. 24×60 26×60 30×60
Rated horsepower 5 6 8
Outside dimensions on skids 2'9"×4' 3'4"×5'6" 4'×6' 6'×9'
Total height on skids 3'8" 4'6" 5' 5'6"
Table XXVI--Sizes, Capacities and Horsepower of Ransome Mixers.
Ransome Concrete Machinery Co., Dunellen, N. J.
Mixer number. No. 1. No. 2. No. 3. No. 4.
Size batch, cu. ft. 10 to 14 20 30 40
Capacity per hr., cu. yds. 10 20 30 40
Speed, Revs. per min. 16 15 14½ 14
Weight on Skids:
Pulley or gear, lbs. 3,300 3,650 5,900 7,400
With engine, lbs. 4,600 5,050 7,700 9,250
With engine and boiler, lbs. 6,450 8,700 12,200 14,700
Weight on Wheels:
With engine, lbs. 5,100 5,550 8,200 9,750
With engine and boiler, lbs. 6,950 9,200 12,700 15,000
Engines:
Size cylinder, ins. 6×6 7×7 8×8 9×9
Rated horsepower 7 10 14 20
Boiler:
Size, ins. 36×69 42×75 42×87 48×93
Rated horsepower 10 15 20 30
Table XXVII--Sizes, Capacities and Horsepowers of Chicago Improved Cube
Mixers. Municipal Engineering and Contracting Co., Chicago, Ill.
Mixer No. No. No. No. No. No.
number. "Handy." 6. 11. 17. 22. 33. 64.
Size batch, cu. ft. 2½ 6 11 17 22 33 64
Capacity per hr., cu. yds. 5½ 13 24 40 50 70 120
Speed, revs. per min. 24 20 18 17 16 15 12
Weight on Skids:
Pulley or gear, lbs. 1,000 1,900 2,800 5,000 7,000 9,600 19,000
With engine, lbs. 2,500 3,600 6,100 8,200 12,000
With eng. and boiler, lbs. 3,100 4,300 7,800 10,000 16,000
Weight on Wheels:
With engine, lbs. 1,400 3,200 4,500 7,100 9,500 15,000
With eng. and boiler, lbs. 4,000 6,000 8,800 10,300 17,000
Engine:
Size cylinder, ins. 4×4 6×6 6½×7 7×8 8×9
Rated horsepower 2 3 6 8 12 15 30
Boiler, rated horsepower 4 8 10 15 18 35
Width over all 4'-5" 5'-10" 7'-1" 7'-8" 8'-6" 9'-8"
Length over all 4'-10" 6'-9" 8'-0" 8'-10" 10'-2" 13'-6"
Height bot. sill to
charging hopper 3'-4¼" 3'-5" 3'-10" 4'-7" 5'-0" 5'-9"
Additional height on
wheels 9-7/8" 1'-5-1/8" 1'-5-1/8" 6-3/8" 5½"
Table XXVIII--Sizes, Capacities and Horsepowers of Cropp Mixers.
A. J. Cropp, Concrete Machinery, Chicago, Ill.
Mixer number. No. 0. No. 1. No. 2. No. 3. No. 4.
Size batch, cu. ft. 7 to 8 10 13 16 20
Cap. per hr., cu. yds. 15 20 25 30 40
Speed, revs. per min. 12 10 10 10 10
Weight on Skids:
With engine, lbs. 1,375 1,650 1,700 1,975 2,100
With eng. and boiler, lbs. 2,575 2,950 3,000 3,775 3,900
Weight on Wheels:
With engine, lbs. 1,775 2,050 2,200 2,475 2,600
With eng. and boiler, lbs. 2,900 3,350 3,400 4,250 4,350
Engine:
Size cylinder, ins. 4×4 5×5 5×5 6×6 6×6
Rated horsepower 3 5 5 7 7
Boiler:
Size inside 24"×4' 24"×6' 24"×6' 30"×6' 30"×6'
Rated horsepower 4 6 6 9 9
Out. dimensions on skids 40" 40" 40" 48" 48"
Total height 50" 56" 56" 56" 62"
Height fr. ground on trucks:
Charging, ins. 20 20 20 20 20
Discharging, ins. 30 30 30 30 30
TABLE XXIX--SIZES, CAPACITIES AND HORSEPOWERS OF CHICAGO CONCRETE MIXERS.
Chicago Concrete Machinery Co., Chicago, Ill.
Number of mixer. No. 00. No. 0. No. 1. No. 2.
Standard charge in cu. ft. cement ½ 1 1 2
" " Sand 1½ 2½ 4 8
" " stone 3 5 8 16
Total unmixed batch in cu. ft 5 8½ 13 26
Mixed concrete per batch, loose in cu. ft. 3½ 6 9 18
Cubic yards of unmixed material per hour,
45 batches per hour 8 14 21 42
Cubic yards of mixed concrete per hour,
45 batches per hour 6 10 15 30
Minimum horsepower required 2 4 6 8
Revolutions of driving pulley per min 200 190 185 170
Revolutions of drum per min 20 18 15 13
Diameter and face of driving pulley 20×3½ 20×4½ 24×5½ 28×6½
Weight:
On skids with pulley, lbs. 1,550 2,150 2,900 4,850
On truck with pulley or gears, lbs. 1,800 2,550 3,500 5,150
On skids with st. engine only, lbs. ... 2,400 3,400 4,600
On truck with st. engine only ... 2,900 4,000 5,300
On skids with st. eng. and boiler, lbs. ... 2,800 4,700 6,000
On truck with st. eng. and boiler, lbs. 2,400 4,200 5,750 7,850
On skids with gasoline engine, lbs. 2,000 3,500 5,000 6,500
On truck with gasoline engine, lbs. 2,400 4,300 5,800 7,800
TABLE XXX--SIZES, CAPACITIES AND HORSEPOWERS OF KOEHRING MIXERS.
Koehring Machine Co., Milwaukee, Wis.
Mixer number. No. 0-B. No. 1-B. No. 2-B. No. 3-B.
Capacity per charge, in cu. ft 7 11 22 27
Capacity per hour in cu. yds 7 14 25 30
Horsepower, steam engine 4 6 8 10
Horsepower, steam boiler 5 8 10 14
Horsepower, gasoline engine 4 6 10 12
Horsepower, electric motor 5 6 7½ 10
Speed of drum 20 17 15 15
Speed of intermediate shaft 132 108 75 75
Weight of mixer on skids 1,800 2,800 5,200 5,500
Weight of mixer on skids, with steam eng. 2,300 3,550 6,500 7,000
Weight of mixer on skids, with steam
engine and boiler 3,300 5,000 8,000 9,300
Weight of mixer on skids, gasoline
engine and housing 3,000 4,400 7,500 8,600
Weight of trucks with pole 400 600 850 950
Weight of automatic loading bucket
complete 500 700 1,000 1,100
Weight of mixing through complete 200 250 400 400
TABLE XXXI--SIZES, CAPACITIES AND HORSEPOWERS OF SMITH MIXERS.
Contractors' Supply & Equipment Co., Chicago, Ill.
Mixer number. No. 0. No. 1. No. 2. No. 2½. No. 4. No. 5.
Stand. charge cu. ft. Cement 1 1 2 2 3 4
" " " " Sand 2½ 4 6 7½ 10½ 14
" " " " Stone 5 8 12 15 21 28
Total unmixed per batch,
cu. ft. 8½ 13 20 24½ 34½ 46
Mixed material per batch
(loose), cu. ft. 6 9 13½ 16½ 22 30
Cubic yards mixed per
hour, up to 9 20 30 39 46 62
Power required--H.P. 4 6 8 10 15 19
Revs. per minute of
driving pulley 218 180 173 162 160 125
Diameter and face of
driving pulley, ins. 20×4½ 24×5½ 28×5½ 28×6½ 36×6½ 48×7½
Weight on skids with
pulley only, lbs. 1,740 2,500 3,600 4,400 6,200 7,900
Weight on truck with
pulley or gears, lbs. 2,200 3,650 4,750 5,500 7,400 ....
Weight on truck with
steam eng. & boil., lbs. 3,750 5,600 7,200 8,600 11,400 ....
Weight on truck with
gasoline engine, lbs 4,000 5,100 7,400 9,300 .... ....
TABLE XXXII--SIZES, WEIGHTS AND CAPACITIES OF POLYGON MIXER.
Waterloo Cement Machinery Co., Waterloo, Iowa.
Mixer number. No. 4. No. 5. No. 6. No. 7.
Maximum charge, cu. ft. 6 10 12 16
Cubic yards mixed per day (10 hrs.) up to 60 190 130 180
Weight on skids with pulley (approx.) 1,600 2,200 3,500 4,000
Weight on skids with steam engine and
boiler (approx.) 3,100 3,900 5,500 6,200
Weight on skids with gasoline engine
(approx.) 2,900 3,900 5,100 5,700
Weight on trucks with steam engine and
boiler (approx.) 3,600 4,600 6,000 7,000
Weight on trucks with gasoline engine
(approx.) 3,400 4,650 5,700 6,750
~DATA FOR ESTIMATING THE WEIGHT OF STEEL IN REINFORCED
CONCRETE.~--Architects' and engineers' plans record the steel used in
reinforced concrete in various ways. Sometimes complete schedules of
shapes, dimensions and weights of the various reinforcing elements are
drawn up and submitted to bidders with the plans. In such cases the
estimating is usually a simple problem for the contractor. In other
cases the amount of steel that will be required is stated as a
percentage of the volume of the concrete. In still other cases the
detail drawings merely show the number, location and dimensions of the
reinforcing bars, stirrups, etc., and the contractor has to compile from
them his own schedule of quantities. The following tables and discussion
will aid the contractor in making his estimates. Before proceeding with
these data, however, the authors would strongly advise that to
facilitate rapid estimating the contractor should keep accurate records
of all reinforced concrete structures in such form as to show the
percentages of steel used. In doing this, however, he should be careful
to separate the foundations, etc., which are not reinforced from the
superstructure which is reinforced. A reinforced concrete arch bridge,
for example, usually rests on piers and abutments which are not
reinforced. Do not lump together all the concrete in recording the
weight of reinforcement used, but separate the reinforced arch from the
unreinforced portions.
~Method of Computing Weight from Percentage of Volume.~--In a cubic yard
of concrete there is 1 per cent. of 27 cu. ft. or 0.27 cu. ft. of steel
if the reinforcement is 1 per cent. Now a cubic foot of steel weighs 490
lbs., but for all practical purposes we can call it 500 lbs. Hence
reinforced concrete containing 1 per cent. of steel has 0.27 × 500 = 135
lbs. per cubic yard. Table XXXIII has been computed in this manner;
knowing the price of steel it is a matter of simple multiplication to
estimate from the table the cost of steel for any percentage of
reinforcement.
~Weights and Dimensions of Plain and Special Reinforcing Metals.~--Steel
for reinforcement is used in the shape of plain round and square bars,
deformed bars, woven and welded netting and metal mesh of various sorts.
Tables XXXIV to XXXVII show the weights, dimensions, etc., of these
various metals.
TABLE XXXIII--SHOWING WEIGHT OF STEEL PER CUBIC FOOT AND PER CUBIC YARD OF
CONCRETE FOR VARIOUS PERCENTAGES OF REINFORCEMENT.
Per cent Lbs. steel Lbs. steel
of steel. Per cu. ft. Per cu. yd.
0.20 1.00 27.0
0.25 1.25 33.8
0.30 1.50 40.5
0.35 1.75 47.3
0.40 2.00 54.0
0.45 2.25 60.8
0.50 2.50 67.5
0.55 2.75 74.3
0.60 3.00 81.0
0.65 3.25 87.5
0.70 3.50 94.5
0.75 3.75 101.3
0.80 4.00 108.0
0.85 4.25 114.8
0.90 4.50 121.5
0.95 4.75 128.3
1.00 5.00 135.0
TABLE XXXIV--WEIGHTS OF ROUND AND SQUARE BARS OF DIMENSIONS COMMONLY
USED FOR REINFORCING CONCRETE.
Thickness or Weight of square Weight of round
diameter in inches bars. Lbs. per ft. rods. Lbs. per ft.
1/16 0.013 0.010
1/8 0.053 0.042
3/16 0.119 0.094
¼ 0.212 0.167
5/16 0.333 0.261
3/8 0.478 0.376
7/16 0.651 0.511
½ 0.850 0.668
9/16 1.076 0.845
5/8 1.328 1.043
11/16 1.607 1.262
¾ 1.913 1.502
7/8 2.608 2.044
1 3.400 2.670
1-1/8 4.303 3.380
1¼ 5.312 4.172
1½ 7.650 6.008
1¾ 10.404 4.178
2 13.600 10.68
TABLE XXXV--DIMENSIONS AND WEIGHT OF EXPANDED METAL.
Mesh, Sectional area sq. Weight, lbs.
inches. ins. per ft. width. per sq. ft.
Standard ½ 0.209 0.74
Standard ¾ 0.225 0.80
Standard 1½ 0.207 0.70
Standard 2 0.166 0.56
Standard 3 0.083 0.28
Light 3 0.148 0.50
Standard 3 0.178 0.60
Heavy 3 0.267 0.90
Extra heavy 3 0.356 1.20
Standard 3 0.400 1.38
Standard 3 0.600 2.07
Old style 4 0.093 0.42
Standard 6 0.245 0.84
Heavy 6 0.368 1.26
TABLE XXXVI--DIMENSIONS AND WEIGHT OF KAHN RIB METAL.
Size Section area Weight per
No. per ft. width sq. ins. sq. ft. lbs.
2 0.54 2.13
3 0.36 1.43
4 0.27 1.08
5 0.22 0.87
6 0.18 0.72
7 0.15 0.62
8 0.14 0.55
TABLE XXXVII--WEIGHTS OF DEFORMED BARS OF DIMENSIONS COMMONLY USED FOR
REINFORCED CONCRETE.
Size. Weight, lbs. Area. Size Weight, lbs. Area
ins. per ft. sq. ins. ins. per ft. sq. ins.
[Illustration: Ransome Twisted Bar.] [Illustration: New Style Corrugated Bar.]
¼ 0.212 0.063 ¼ 0.24 0.06
½ 0.85 0.25 ½ 0.85 0.25
5/8 1.32 0.319 5/8 1.33 0.39
¾ 1.91 0.563 ¾ 1.91 0.56
7/8 2.6 0.765 7/8 2.60 0.77
1 3.4 1.000 1 3.40 1.00
1¼ 5.3 1.563 1¼ 5.30 1.56
[Illustration: Diamond Bar.] [Illustration: Universal Corrugated Bar.]
½ 0.85 0.25 ¼×1 0.73 0.19
5/8 1.33 0.39 5/16×1¼ 1.18 0.32
¾ 1.91 0.56 3/8×1-3/8 1.35 0.41
7/8 2.60 0.76 3/8×1¾ 1.97 0.54
1 3.40 1.00 3/8×2 2.27 0.65
1¼ 5.31 1.56 3/8×2½ 2.85 0.80
--No. 1 Mill-- [Illustration: Thatcher Bulb Bar.] --No. 2 Mill.--
¼ 0.16 0.047 ... ... ...
½ 0.61 0.18 ½ 0.58 0.17
5/8 0.95 0.28 5/8 0.92 0.27
¾ 1.39 0.41 ¾ 1.34 0.39
7/8 1.87 0.55 7/8 1.79 0.53
1 2.42 0.71 1 2.32 0.68
1¼ 3.74 1.10 1¼ 3.55 1.04
1½ 5.30 1.56 1½ 5.20 1.53
1¾ 7.07 2.08 .... .... ....
2 9.02 2.65 .... .... ....
[Illustration: Monolith Bar.] [Illustration: Twisted Lug Bar.]
0.4 0.55 0.25 ¼ 0.222 0.625
½ 0.85 0.32 ½ 0.87 0.250
... .... .... 5/8 1.35 0.3906
... .... .... ¾ 1.94 0.5625
0.8 2.18 0.64 7/8 2.64 0.7656
1 3.37 1.00 1 3.45 1.00
... .... .... 1¼ 5.37 1.5625
1½ 7.75 2.25 1½ 7.70 2.25
[Illustration: Cup Bar]
3/8 0.48 ....
½ 0.86 ....
5/8 1.35 ....
¾ 1.95 ....
7/8 2.65 ....
1 3.46 ....
1-1/8 4.38 ....
1¼ 4.51 ....
~RECIPES FOR COLORING MORTARS.~--The following recipes for coloring cement
mortar have been found reliable; the weights given being weight of
coloring matter per bag of cement and for a 1-2 mortar:
_Brown Stone_: 4 to 5 lbs. brown ochre or ½ lb. best quality roasted
iron oxide.
_Buff Stone_: 4 lbs. yellow ochre.
_Red Stone_: 5 lbs. raw violet iron oxide.
_Bright Red Stone_: 5½ to 7 lbs. English or Pompeiian red.
_Blue Stone_: 2 lbs. ultramarine blue.
_Dark Blue Stone_: 4 lbs. ultramarine blue.
_Slate_: Lamp black ½ lb. light slate; 4 lbs. dark blue slate.
_Light Terra Cotta_: 2 lbs. Chattanooga iron ore.
CHAPTER XXV.
METHODS AND COST OF WATERPROOFING CONCRETE STRUCTURES.
Resistance to penetration by water is desirable in all concrete
structures, and is essential in such structures as tanks, reservoirs,
vaults, subways, basements and roofs. Concrete, as it is ordinarily
made, is pervious to water, hence to secure concrete structures through
which water will not penetrate some method of waterproofing the concrete
must be employed. Many methods have been proposed and are being used;
none of these methods is without faults, the best one of them has not
yet been determined, and the evidence available as to their comparative
merits is biased and conflicting. For these reasons any discussion of
waterproofing for concrete is at the present time bound to be
unsatisfactory.
Methods of waterproofing may be roughly classified as follows: (1) Use
of mixtures so proportioned as to be impervious; (2) admixture of
substances designed to produce impermeability; (3) use of waterproof
coatings, washes or diaphragms. In succeeding sections enough examples
of each method are given to indicate current practice; no attempt has
been made to catalog all the waterproofing substances and systems being
promoted--there are too many of them.
The art of waterproofing concrete is in a transition stage. Outside of
the manufacturers of waterproofing material the art has received serious
study by comparatively few persons. No comparative tests by independent
investigators are available. Practical experience with most of the
materials used has not extended over a long enough period of time to
permit true conclusions to be drawn. Students of the subject are not
even agreed upon the broad questions whether it is better to work toward
developing an impervious concrete or toward perfecting a waterproof
covering for concrete. On the minor subdivisions there is no agreement
at all.
In the present state of the art one can lay fast hold to only three
things. The first is that waterproofing is one component of a system of
drainage; the second is that structures must, to get the best results,
be designed with the fact in mind that waterproofing is a component
structural element, and the third is that skilled and conscientious
workmanship are essential elements in the success of all waterproofing
materials and methods.
~IMPERVIOUS CONCRETE MIXTURES.~--The compounding of the regular concrete
materials so as to produce an impervious concrete has been made the
subject of numerous experiments. The most elaborate of these experiments
were those conducted over a period of five years by Mr. Feret, of the
Boulogne (France) Laboratory of the Ponts et Chaussees. Feret's
experiments led him to the following conclusions:
"That in all mortars of granulometric composition the most permeable are
those which contain the least quantity of cement.
"Of all mortars of the same richness, but of varying granulometric
composition, those which contain very few fine grains are much more
permeable. They are the more so where, with equal proportions of the
fine grains, the coarse grains predominate more in relation to the
grains of medium size.
"The minimum permeability is found in mortars where the proportion of
medium-sized grains is small, and the coarse and fine grains are about
equal to each other."
Mr. Feret also found that permeability decreased with time and that wet
mixtures were less permeable than dry mixtures.
Tests made by Messrs. J. B. McIntyre and A. L. True at the Thayer School
of Civil Engineering in 1902 gave the following results:
All the specimens composed of 1-1 mortar in the proportions of 30, 35,
40 and 45 per cent. of the whole mass were impermeable. Some of the
specimens composed of 1-2 mortar in the proportions of 40 and 45 per
cent. were also impermeable, as well as the 1-2-4 and 1-2½-4 mixtures.
All other mixtures leaked at the high pressure (80 lbs. per sq. in.) and
in a general way exhibited a degree of imperviousness in direct
proportion to the proportion of mortar in them, with the lower
pressures from 20 lbs. per sq. in. up as well as for the 80-lb.
pressure.
Other tests confirm those cited. In general we may conclude that those
mixtures richest in cement and mortar are the most impervious. It is
doubtless practicable by exercising proper care to proportion, mix and
place a concrete mixture which will be so nearly impervious that visible
leakage will be small. The task, however, is one difficult to perform in
actual construction work, and its accomplishment is never certain.
~STAR STETTIN CEMENT.~--Star Stettin cement is a Portland cement made by
grinding a clinker which has been "impregnated" with substances which
impart waterproofing properties to the ground product. The process is
the invention of Richard Liebold, and the cement is made by the Star
Stettin Portland Cement Works, Stettin, Germany. It is asserted that a
1-4 fine sand mortar made with this cement is impervious. To use it the
ordinary precautions adopted in the employment of Portland cement are
necessary, and in addition the following: The cement must be mixed with
moist instead of dry sand before the water is added; the sand should be
clean, sharp and fine of grain; the mortar must be more perfectly mixed
than ordinarily, and somewhat more water should be used than is
ordinarily used. Perfectly even mixing is essential to the best results.
~MEDUSA WATERPROOFING COMPOUND.~--This compound is a dry powder which is
mixed with the cement in proportions of from 1 per cent. to 2 per cent.
by weight, or from 4 lbs. to 8 lbs. per barrel of cement. The compound
costs 12 cts. per lb., so that its addition increases the cost from 48
to 96 cts. per barrel of cement. Thorough mixing of the compound with
the cement is of the utmost importance, otherwise none but the ordinary
precautions in the use of Portland cement is necessary. Absorption tests
on concrete blocks treated and untreated with the compound and nine
months old have shown the absorbtion of treated blocks to be about
one-fourth or one-fifth that of untreated blocks. The compound is made
by the Sandusky Portland Cement Co., Sandusky, Ohio.
~NOVOID WATERPROOFING COMPOUND.~--This compound is a dry powder which is
mixed dry with the cement in the proportion of 1 to 2 per cent. by
weight or about 1 to 2 lbs. per bag of cement. The compound costs 12
cts. per pound or about from 48 to 96 cts. per barrel of cement.
Directions for making waterproofing mortar are: To 100 lbs. of Portland
cement add 2 to 2½ lbs. of compound and 200 lbs. of clean and sharp sand
and mix the materials dry and very thoroughly. The water is then added
in the proportion necessary to make a good working mortar and the mortar
mixed and applied in the ordinary manner. Used as a wash 2 lbs. of
compound are thoroughly mixed dry with a bag of cement. Any portion of
the mixture is then mixed with water to produce a creamy grout, which is
applied to a thoroughly wet surface with a brush. This compound is made
by The Abbey-Dodge-Brooks Concrete Co., Newark, N. J.
~IMPERMEABLE COATINGS AND WASHES.~--The most common means employed for
rendering concrete structures waterproof is to coat or wash the surface
with some substance itself impervious to water or having the property of
closing the pores of the surface skin of concrete so that water cannot
penetrate.
~Bituminous Coatings.~--Bituminous coatings of one composition or another
are among the most commonly used of impermeable coatings. The bituminous
compound is used both alone and in combination with layers of a fabric
of some sort to form the coating. Where bituminous coatings are used on
surfaces exposed to the sun and frost attention must be given to the
fact that a compound of different properties is required where the range
of temperature is great than is required where this range is smaller.
Asphalt, for example, should have a flow point of 212° F. and a brittle
point of -15° F. when exposed directly to sun and frost as compared with
say a flow point of 185° F. and a brittle point of 0° F. when covered
from the direct action of sun and frost. Another point to be kept in
mind particularly in using exterior coatings is that the concrete
surface must be properly prepared to receive the coating or else it
will peel off. The following are examples from actual practice of
waterproofing with bituminous coatings.
The following method of waterproofing with asphalt coating is given by
W. H. Finley: The asphalt used must be of the best grade, free from coal
tar or any of its products, and must not volatilize more than 0.5 per.
cent, under a temperature of 100° F. for 10 hours. It must not be
affected by a 20 per cent. solution of ammonia, a 35 per cent. solution
of hydrochloric acid, a 25 per cent. solution of sulphuric acid, or a
saturated solution of sodium chloride. For structures underground a flow
point of 185° F. and a brittle point of 0° F. shall be required. If the
surface cannot be made dry and warm it should first be coated with an
asphalt paint made of asphalt reduced with naphtha. The asphalt should
be heated in a kettle to a temperature not exceeding 450° F. It has been
cooked enough when a piece of wood can be inserted and withdrawn without
the asphalt clinging to it. The first coat should consist of a thin
layer poured from buckets on the prepared surface and thoroughly mopped
over. The second coat should consist of a mixture of clean sand and
screenings, free from earthy admixtures, previously heated and dried,
and asphalt, in the proportion of 1 of asphalt to 3 or 4 of sand or
screenings by volume. This is to be thoroughly mixed in the kettle and
then spread out on the surface with warm smoothing irons, such as are
used in laying asphalt streets. The finishing coat should consist of
pure hot asphalt spread thinly and evenly over the entire surface, and
then sprinkled with washed roofing gravel, torpedo sand, or stone
screenings, to harden the top. The thickness of the coating will depend
on the character of the work and may vary from ¾ in. to 2 ins. in
thickness.
Several firms manufacture and sell ready made priming paints and mastics
for waterproofing concrete by substantially the above method. Sarco
compounds made by the Standard Asphalt & Rubber Co., of Chicago, Ill.,
are examples. Sarco waterproofing is a compound analyzing 99.7 per cent.
pure bitumen and having a range of ductility of 200° F. In waterproofing
large car barn roofs of concrete in Chicago, the concrete was first
swept clean and a coat of priming compound was thoroughly brushed in. On
the priming coat was mopped a coat of waterproofing compound, applied
hot, and covered with a layer of fine sand. The thickness of the
completed coating was 1/16 in. Where a heavier waterproofing is
necessary the waterproofing compound is covered with one or more 5/8-in.
coats of Sarco mastic.
The following bituminous coatings have been used in waterproofing
concrete fortifications by the U. S. Army Engineers:
_Mobile, Ala._--The top of the concrete was covered with a thin coat of
1-2 cement mortar and given a rough trowel finish. As soon as the
surface was dry it was covered with a layer of asphalt mastic 1 in.
thick and rubbed down to a finish with dry sand and cement in equal
parts. To prepare the mastic take 500 lbs. of Diamond T asphalt mastic,
broken into small pieces, 30 lbs. of Diamond T asphalt flux, and 5 lbs.
of petroleum residuum oil. When thoroughly melted add 400 lbs. clean,
dry torpedo gravel previously heated. Stir gravel and asphalt until
thoroughly mixed at a temperature of about 375° F.
_Key West, Fla._--The top of the concrete was covered with smooth
plaster, proper slope for drainage being given. Above this two layers of
asphalt of an aggregate thickness of ¾ in. were applied. The composition
of the asphalt was as follows: 440 lbs. rock asphalt mastic, 3 gallons
coal tar, and 5 gallons silicious sand.
_Delaware River Defenses._--The concrete was waterproofed with coal tar
and sand. The tar was made hot and applied to the surfaces with rubber
squeegees and then sanded. Joints were filled with the hot tar. A
surplus of sand was left on for a few days and then swept off. One
barrel of coal tar covered 2,279 sq. ft. with one coat and cost $4.25
per barrel delivered. The cost including material and labor was 0.74 ct.
per sq. ft.
_San Francisco Harbor._--The roof had a pitch of about 3 in 20 and was
covered with an earth fill. The concrete was troweled to a fairly smooth
surface, was mopped with a heavy coat of roofing asphaltum, or mastic,
then covered with the heaviest grade roofing felt laid 3 ply, starting
at the coping of the parade wall and made 4 ply in the gutter. On this
assumed watertight surface 3-in. book tile was laid with joints normal
to the gutter and cemented. The purpose of the tile was to afford a free
passage for the water as soon as it met the roof. The expectations were
fully realized and no water, or even a sign of moisture, has appeared in
this battery, or at another of the same type since built, after a fair
test of time.
The total cost of the work, including mastic, felt and tile, was 17 cts.
per sq. ft. for 6,200 sq. ft. covering three roofs.
In conclusion it may be noted that any of the methods of constructing
impermeable diaphragms can be used for constructing impermeable
coatings.
~Szerelmey Stone Liquid Wash.~--This wash has been used in England for
waterproofing and preserving masonry for some 20 years. It is a thin
liquid compound which is applied to the surface with a brush. The stone
or concrete surface is required to be dry and thoroughly clean, with all
scale and loose particles removed. The standard treatment is three
coats; 1 gallon of liquid is in most cases sufficient for treating
(three coats) 25 sq. yds., but in exceptionally bad cases 1 gallon for
15 sq. yds. has been found necessary. The precautions necessary for the
successful use of the liquid are: It must be well stirred; it must be
applied to a perfectly dry, clean surface, and it must be well rubbed
into the masonry. The American agency for the liquid is Szerelmey & Co.,
Washington, D. C.
~Sylvester Wash.~--Waterproofing with Sylvester wash consists in applying
alternately to the concrete surface a soap solution wash and an alum
solution wash. The soap solution is applied first, and it must be
applied hot and to a dry surface; the alum solution is applied second
and 24 hours after the soap solution and is applied cold. This
constitutes one treatment. After 24 hours a second treatment may be
given, and as many treatments may be given as necessary. In some cases
as many as six treatments have been employed. The proportions of the
solutions used in practice vary. In waterproofing the standpipe
described in Chapter XXII the soap solution consisted of 12 oz. pure
Castile olive oil soap per gallon of water, and the alum solution
consisted of 2 oz. of alum per gallon of water. In repairing the bottom
of a reservoir lined with 4 to 6 ins. of concrete the following
solutions were used: ¾ lb. Olean soap to 1 gallon of water and ½ lb.
alum to 4 gallons of water. Both alum and soap were well dissolved and
the soap solution was boiled. The boiling hot soap solution was applied
on the clean, dry concrete; 24 hours later the alum wash was applied
cold. This treatment was repeated after 24 hours. Two men applied the
solutions, using whitewash brushes, while a third man carried pails of
the solution. In making the soap solution two men attended four kettles,
one man kept up fires, two men carried solution to men applying it. The
alum solution required fewer men, being made cold in barrels. After
applying the second soap wash to the concrete slopes, the men had to be
held by ropes to keep from slipping. The rope was placed around two men,
who started work at the top of the slope, a third man paying out the
rope. The work was done in 8½ days and cost as follows:
Labor:
1,140 hours labor at 15 cts. $171.00
83 hours foreman at 30 cts. 24.90
83 hours waterboy at 6 cts. 4.98
Add for superintendence 15% 30.13
-------
Total labor $231.01
Materials:
900 lbs. Olean soap at 4-1/3 cts. $ 39.00
210 lbs. alum at 3 cts. 6.30
6 10-in. whitewash brushes at $2.25 13.50
6 stable brushes at $1.25 7.50
-------
Total materials $ 66.30
Total labor and materials $297.31
This covered 131,634 sq. ft., hence the cost of the two coats of soap
and alum was $2.26 per 1,000 sq. ft., or 0.23 ct. per sq. ft.
The ordinary Sylvester wash, as described above, has been modified with
success on Government fortification work as follows: To 2 gals. of water
add 1 lb. concentrated lye and 5 lbs. alum and mix until completely
dissolved. This is a concentrated stock solution. In use 1 pt. of
solution and 10 lbs. of cement are mixed with enough water to make a
mixture that will lather freely under the brush. Two coats of this wash
are applied, the second at any time after the first is dry, and the
first as soon as the forms are removed from the concrete. The wash
should be applied to a wet surface, if the concrete is dry it should be
wet down with a brush ahead of the wash.
~Sylvester Mortars.~--In this class of coatings the alum and soap are
added to the mortar which is used for facing. A successful recipe for
such a mortar is given as follows: To 1 part cement and 2 parts sand add
¾ lb. of pulverized alum for each cubic foot of sand and mix these
ingredients dry; then add the proper quantity of water, in which has
been dissolved ¾ lb. of soap to the gallon, and mix the mortar
thoroughly. Such a mortar is but slightly inferior in strength to
ordinary mortar of the same proportions. In plastering a clear water
well to prevent leaking a 1-2 mortar was made as follows: 1¼ lbs. of
soap were dissolved in 15 gallons of water and 3 lbs. of powdered alum
were mixed with 1 bag of cement. Two coats of plaster of an aggregate
thickness of ½ in. were applied and completely stopped the leaking. The
cost of this treatment was as follows:
2 lbs. soap (with 24 gals. water) at 7½ cts. $0.15
12 lbs. alum at 3½ cts. 0.42
------
Total per barrel of cement $0.57
In lining a new reservoir near Wilmerding, Pa., a mortar was made as
follows: A stock solution of 2 lbs. caustic potash and 5 lbs. alum to 10
quarts of water was made in barrel lots, from which 3 quarts were taken
for each batch of 2 bags of cement and 4 bags of sand. A batch of mortar
covered an area 6×8 ft. with a 1-in. coat. The extra cost of the
waterproofing was:
100 lbs. caustic potash at 10 cts. $10.00
70 lbs. caustic potash at 9 cts. 6.30
960 lbs. alum at 3½, 3¾ and 4 cts. 34.38
60 hours mixing at 15 cts. 9.00
Freight, express and haulage 11.50
------
Total for 74,800 sq. ft. $71.18
This gives a cost of 95 cts. per 1,000 sq. ft., or less than 0.1 ct. per
sq. ft. It was found that if less than 2 parts of sand to 1 part of
cement was used the mortar cracked badly in setting. Clean sand was
imperative, as any organic impurities soon decomposed, leaving soft
spots. Do not use an excess of potash; a slight excess of alum, however,
does not decrease the strength of the mortar.
~Hydrolithic Coating.~--This waterproofing is a dry mortar composed by
mixing a cementing compound with sand, and sold dry in sacks containing
96 lbs. each. The dry mortar is mixed with water to proper consistency
for plastering, and is applied as a plaster to the surfaces to be
waterproofed. The dry mortar is mixed with water to a grout of the
consistency of thick cream and then this grout is stiffened to the
proper consistency by adding more dry mortar. Thoroughness of mixing is
absolutely essential. The concrete surface is prepared by picking and
scoring sufficiently to get a fresh surface and washing away all chips,
dust and loose material, or instead of picking in new work the outer
skin may be removed by a 1 to 9 muriatic acid solution and then washed
free of all acid and scrubbed with wire brushes. After preparing the
fresh surface it is well wetted; in fact water soaked, so that, while
not oozing moisture it will absorb no more water. The mixed mortar is
then applied with a trowel in a workmanlike manner. In mixing, no more
than 8 gallons of water per barrel of mortar should be used. The
coatings used are 3/8 to 5/8 in. for walls and ½ to ¾ in. for floors.
The following estimate of cost is made by the manufacturers, the E. J.
Winslow Co., Chicago, Ill. The figures are presented with the
understanding that they are to be considered merely as average costs for
waterproofing, without special construction, and subject to change in
accordance with local conditions, and to the time of year when the work
will need to be performed:
Per sq. ft.
To prepare surfaces to receive "coating" may
cost the contractor 5½ cts.
The coating material, f. o. b. Chicago, may
cost the contractor 4½ cts.
The labor of application may cost the contractor 7½ cts.
Administration and incidental expenses may
cost the contractor 7½ cts.
--------
25 cts.
The lowest price yet asked for work was 20 cts., and the highest, 55
cts., these two prices representing the opposite extremes of conditions
that different jobs will present.
~Cement Mortar Coatings.~--Rich cement mortar mixtures offer considerable
resistance to penetration by water and when well made may be used with a
fair degree of success to waterproof ordinary concrete. European
engineers make wide use of mortar coatings for waterproofing tanks and
reservoirs and appear to have good success with them. The experience in
this country is that no great reliance can be placed on them, where the
pressures are at all large. Records of work done show both successes and
failures, with no apparent reason for either so far as composition of
mortar or quality of workmanship goes. A rich mortar plaster will reduce
leakage, and may prevent it entirely, but it is uncertain how far it
will prove water tight.
~Oil and Paraffin Washes.~--The theory of the use of oil and paraffin
washes is that the material soaks into the concrete and closes the
surface pores against the penetration of water. Paraffin has been quite
widely used for preserving stone masonry walls for buildings. It is
applied hot, and in the best practice is applied to a dry heated
surface. Concerns doing such work on buildings have portable devices for
heating the masonry. Oil is sometimes applied hot but is more often
flushed onto the surface and allowed to soak in as it will.
~IMPERMEABLE DIAPHRAGMS.~--The most generally employed method of
waterproofing concrete structures, with the possible exception of
painting and coating methods, is to embed in the wall, roof and floor
slabs a diaphragm that is impervious to water. Such diaphragms are
usually composed of layers of waterproof felt or paper cemented together
and to the concrete by asphalt, coal tar pitch or patented cementing
compound. Another construction consists of a layer of asphaltic compound
between two layers of cement mortar. In some cases also the combination
felt and cementing compound diaphragm is further strengthened by placing
it between layers of mortar. In wall work the diaphragm is frequently
applied to the face of a single layer brick wall and the concrete filled
against it. The brick wall may be further waterproofed by laying the
brick in hot asphalt instead of in mortar.
Within the last few years a number of firms have devoted their efforts
to producing special fabrics (felts or papers) and special cementing
compounds designed to be used with the fabrics for waterproofing
concrete. These fabrics and cements are in most cases superior in
toughness, flexibility, ease of application, etc., to the ordinary
roofing and waterproofing fabrics designed originally for general
building purposes.
~Long Island R. R. Subway.~--In constructing the Long Island R. R. subway
the roof was waterproofed according to specifications as follows: After
the roof concrete was crowned, brought to a smooth surface and
thoroughly dried, it was swabbed over with hot melted "medium hard" coal
tar pitch to an even thickness of not less than 1-16 in. Immediately
upon the first coat of pitch and while it was still melted was laid a
covering of single-ply roofing felt, with the sheets lapping 4 ins. on
all cross joints and 12 ins. on longitudinal joints. This felt was in
turn mopped with pitch, and upon that again was laid another layer of
roofing felt, which was given a final coating of pitch. The pitch used
was of a grade somewhat softer than that used for roofing purposes, or
such as would soften at a temperature of 60° F. and melt at a
temperature of 100° F. The felt used consisted of pure wood paper pulp
or asbestos pulp, which had been thoroughly treated and soaked in
refined coal tar and which weighed for single ply at least 15 lbs. per
100 sq. ft.
After the waterproofing with pitch and felt had thoroughly hardened it
was plastered over with a trowel with a 1-in. layer of Portland cement
mortar, laid in uniform squares, in every respect similar to the plaster
on top of granolithic pavement. The dimensions of the squares were 5×5
ft. Their purpose was to take up expansion and contraction in the
coating.
During the year 1903, there were laid 9,056 sq. yds. of the
waterproofing described. The labor cost of placing the two layers of
felt and the three coats of pitch was as follows: 206 days labor at a
cost of $498 (or an average of $2.41 per day) for the 9.056 sq. yds.,
which is equivalent to 5½ cts. per sq. yd. for labor. Since this is for
two layers of felt the labor cost was 2¾ cts. per sq. yd. of single
layer. The labor cost of mixing and placing the 1-in. mortar covering
was as follows: It required 589 days at a cost of $1,306 (or an average
of $2.22 per day) to place 9,056 sq. yds., which is equivalent to 14½
cts. per sq. yd. The total cost of labor for two layers of tar felt and
the layer of cement mortar was, therefore, 20 cts. per sq. yd.
~New York Rapid Transit Subway.~--The waterproofing consisted of alternate
layers of asbestos felt and asphalt laid on the concrete and covered
with concrete. A coat of hot asphalt was laid on the concrete and on
this a layer of felt, then another coat of asphalt and another layer of
felt, and so on until the required number of layers of felt, from 2 to
6, were laid with asphalt between and on top and bottom. Natural asphalt
containing not less than 95 per cent bitumen was specified. The felt was
required to weigh 10 lbs. per 100 sq. ft. In constructing sidewalls the
alternative was allowed of placing the waterproofing layer between a
4-in. outside wall of brick laid in asphalt and the concrete lining. On
two sections of the work the actual cost of waterproofing was as
follows:
98,074 sq. yds. Single-Ply Felt. Per sq. yd.
Labor laying $0.05
Materials and plant 0.10
------
Total $0.15
1,337 cu. yds. Brick in Asphalt: Per cu. yd.
Labor laying $6.32
Materials and plant 11.48
------
Total $17.80
INDEX.
A
Page
Abutment Construction
Cost of
Bridges Over City Streets 254
Ernst St. Bridge, Cincinnati, O. 257
Kansas City Outer Belt & Electric Ry. 253
Lonesome Valley Viaduct 256
Railway Bridge 106
Methods of
Bridges over City Streets 253
Illinois & Mississippi Canal 196, 197
Lonesome Valley Viaduct 254, 255
Railway Bridge 105, 250
Summary of 230
Aggregates
Balanced, Value of 14
Broken Stone 13
Cinders 14
Cost of 15
Gravel 14
Heating (See Heating Aggregates)
Kinds Used 13
Measuring, Methods of 42
Open Box 42, 50
Trump Automatic Measurer 44
Quantities in Concrete, Test Determinations 192
Screened or Crusher Run, Stone for 15
Sizes Used 15
Slag 14
Voids in 25
Weighing, Apparatus for 102
Aqueduct Construction
Cost of
Cedar Grove Reservoir 549, 550
Salt River Irrigation Work 540
Methods of
Cast Pipe Swansea, England 584
Cedar Grove Reservoir 545
Jersey City Water Supply 544
Salt River Irrigation Works 538
Torresdale Filters 540
Asphalt Concrete
Definition of 108
Furnace for Heating 109, 110
Machine Mixing of 111
Asphalt Concrete Construction
Cost of
Base for Mill Floor 110, 111
Slope Paving for Dam 109
Methods of
Base for Mill Floor
Slope Paving for Dam 108, 109
B
Bags (See Cement Bags)
Depositing Concrete Under Water 89, 90
Barrels (See Cement Barrels)
Belt Conveyors
Capacity of 65
Gas Works Foundations, Astoria, N. Y. 64
Horse Power Required 65
Bench Monuments
Construction of 656
Cost of 657
Blasting Concrete 655
Bonding New Concrete to Old 659
Breakwater Construction
Cost of
Buffalo, N. Y. 214
Marquette, Mich. 209, 212
Methods of
Buffalo, N. Y. 212, 214
Marquette, Mich. 208, 212
Bridge Centers (See Centers)
Bridge Construction
Cost of
Arch Viaduct 373
Connecticut Ave. Bridge 392, 397
Elkhart, Ind., Arch 398
Five Span Arch 407
Girder Highway 377, 379
Grand Rapids Bridge 410, 413
Molded Slab Girders 387
Plainwell, Mich., Arch 399
Railway Bridge 375
Methods of
Connecticut Ave. Bridge 387
Elkhart, Ind., Arch 397
Five Span Arch 400
Girder Highway 367, 377
Grand Rapids, Mich., Arch 407
Molded Slab Girders 384
Plainwell, Mich., Arch 398
Bridge Pier Construction
Cost of
Calf Killer River Bridge 243, 245
City Island Bridge 236
Miami River Bridge 257
Steel Cylinder 241
Viaducts, Cincinnati, O. 258
Williamsburg Bridge 230, 231
Methods of
Calf Killer River Bridge 241, 245
City Island Bridge 235
K. C., M. & O. Ry. 245, 250
Lonesome Valley Viaduct 254, 255
Miami River Bridge 256
Nova Scotia Railways 108
Railway Bridge 231, 235
Scottish Railways 107, 108
Summary of 230
Tharsis & Calamas Ry. 106, 107
Williamsburg Bridge 237, 241
Broken Stone
Crushing (See Stone Crushing)
Quarrying (See Quarrying)
Rocks for, Best 13
Shoveling (See Shoveling)
Screened or Crusher Run 15
Voids in
Amount of 29, 30
Effect of Granulometric Composition 30
Effect of Hauling 33, 34
Effect of Loading 29
Variation, Causes of 28
Weight no Index 32
Weight of 32, 33
Building Construction
Cost of
Four-Story Garage 510
Wall Columns for Power Station 490
Walls for Factory Building 507
Divisions of Work 433
Methods of
Four-Story Garage 509
One-Story Car Barn 495
Six-Story Building 491
Wall Columns 488
Walls for Factory Building 505
C
Cableways
Capacity of 64
Construction of Bridge Work 369
Cost of 64
Fortification Work 186
Retaining Wall Work 269
Cars
Mixer Charging 72
Carts (See Concrete Carts, Horse Carts)
Cement
Classification of 1
Natural Definition of 2
Portland, Definition of 1
Quantity in Concrete
Formula for Computing 37
Rule for Figuring 40
Tables Showing 39, 40, 41
Quantity in Mortar
Formula for Computing 36
Tables Showing 38
Test Determinations 40, 41
Theory of 35
Shrinkage by Wetting 35
Slag, Definition of 2
Weight 2, 4
Cement Bags
Capacity of 2
Packing for Shipment 3
Rebate on 3
Storage House for 3
Cement Barrels
Capacity of 2, 3, 4
Dimensions of 4
Cement Specifications 4
Cement Testing, Cost of 4
Centers
Computation of
Luten Arch 566
Construction of
Conditions Governing 363
Cocket, 50 ft. Span 364
Connecticut Ave. Bridge 392
Five Span Arch 400
Grand Rapids Bridge 408
Luten Arch 365
Mechanicsville Bridge 365
Parabolic Arch 366
Supported, 50 ft. Span 364
Walnut Lane Bridge 368
Cost of
Connecticut Ave. Bridge 392, 393
Deflection of
Test Determinations 367
Types of 363
Charging Barrows
Ransome, Description 71
Sterling, Description 71
Charging Buckets
Wheeled 74
Charging Mixer
Cost of 270, 272
Gravity from Bins 69
Methods of
Car Plants 72
Charging Barrows 70, 71
Derricks and Buckets 73
Elevating Charging Hoppers 70
Enumeration 68
Gravity from Bins 68, 69
Shoveling 72, 73
Wheelbarrows 70
Wheeled Bucket for 74
Chutes
Cement Bag, Construction of 65
Concrete. Examples of 66, 67, 68
Working Gradients 65, 66
Cinders 15
Cofferdam Construction
Cost of Bridge Pier 232
Coloring Concrete, Recipes for 666
Colors for Mortar, Recipes for 666
Concrete
Asphalt (See Asphalt Concrete)
Definition of 1
Depositing (See Depositing Concrete)
Mixers (See Mixers)
Mixing (See Mixing Concrete)
Proportioning, Methods of 25
Concrete Bucket
Side Dumping 486
Subaqueous
Cyclopean 87
O'Rourke 86
Stuebner 88
Concrete Block
Molding (See Molding Concrete Blocks)
Sling for Handling 216
Concrete Cars
Lock Work, Coosa River 195
Concrete Carts
Hand, Capacity of 53, 54
Horse, Briggs 298
Ransome Two-Wheeled 53
Culvert Construction
Characteristics of 414
Cost of
Arch 26 ft. Span 425
Arch, N., C. & St. L. Ry. 418, 419, 422
Kalamazoo, Mich. 430
Kansas City Outer Belt & Electric Ry. 252
Pennsylvania R. R. 424
Methods of
Arch, N., C. & St. L. Ry. 417
Arch, Wabash Ry. 422
Box, C., B. & Q. R. R. 414
Kalamazoo, Mich. 427
Pennsylvania R. R. 423
Curb and Gutter Construction
Cost of
Champaign, Ill. 326
Estimating 321
Ottawa. Ont. 324
Methods of
Champaign, Ill. 325
General Discussion 321
Kinds of 318
Ottawa, Ont. 321
Curbing, Wood for Shafts 160, 161
D
Dam Construction
Cost of
Hemet 104
Richmond, Ind. 224
Rock Island, Ill. 225
Spier Falls 103
Methods of
Barossa Dam 101
Boonton, N. J., Dam 103
Boyds Corner Dam 105
Chaudiere Falls, Quebec 228
Chattahoochee River Dam 100
Hemet Dam 103, 104
McCall Ferry, Pa. 225, 228
Richmond, Ind. 223
Rock Island, Ill. 224, 225
Spier Falls Dam 103
Water Works Reservoir 104
Depositing Concrete
Subaqueous
Bags
Bridge Foundations 91
Marquette Breakwater 209, 210
Peterhead Pier 89, 90
Buckets
Marquette Breakwater. 208, 209
Pier Construction 222
Characteristics of 86
Closed Buckets 86, 87, 88
Tremie
Charlestown Bridge Foundations 92, 93
Masonry Bridge Foundations, France 93, 94
Harvard Bridge Foundations 91
Nussdorf Lock Foundations 94, 95
Drilling Concrete, Drill Mounting for 653
Dumping Concrete
Cost of
Wheelbarrows 55
Methods of
Chutes 55
Wheelbarrows 55
Dump Wagons for Transporting Concrete 54
E
Efflorescence
Causes of 126
Preventing, Methods of 126, 127
Removing, Cost of 127
Ejecters for Washing Sand 7
Erecting Derrick
Cost of Bridge Pier 232
Erecting Forms
Derrick for 501
Directions for Building Work 460
Erecting Molded Columns
Cost of 520
Methods of 520
Erecting Molded Roof Slabs
Cost of 522
Excavating Cofferdams
Cost of 232, 244, 250
F
Fabricating Reinforcement
Bending Machine for 468
Bending Tables for 466
Methods of
Building Work 464
Five Span Arch Bridge 402
Falseworks in Form Construction 144
Finishing Concrete Surfaces
Methods of
Acid Etching and Washing 133
Careful Mixing and Placing
Concrete 125, 126
Coloring 135
Form Construction 124, 125
Grout Washing 130
Mortar Facing 128, 129
Plastering 128
Scrubbing and Washing 131, 132, 133, 134
Spading and Troweling 127, 128
Special Facing Mixtures 130
Stuccoing 128
Tooling 133, 134
Washed Gravel or Pebble 134
Form Construction
Cost of
Aqueduct, Cedar Grove Reservoir 550
Arch Culverts 418, 419, 422, 425, 430
Battery Emplacement 188
Bridge Abutment 257
Bridge 233, 235, 250
Bridge Pier Work 243
Building Work 493, 496, 501, 503, 507, 511
Connecticut Ave. Bridge 392, 393
Dam Rock Island, Ill. 225
Effect of Design on 137
Estimating, Method of 146, 147, 148, 149
Girder for Separate Casting 517
Girder Highway Bridge 377, 380, 382
Grand Rapids Bridge 412
Guard Lock, Ill., & Miss. Canal 201
Gun Emplacements 185
Lock, Coosa River 196
Lock, Ill. & Miss. Canal 202, 206, 207
Mortar Battery Platform 187
Permanent Way Structures 252
Piers for Taintor Gates 198
Pier Superior Entry, Wis. 222
Reservoir for Fire Protection 591, 592, 593
Retaining Walls 273, 275
Retaining Wall Work 270, 272
Slab and I-Beam Floors 450
Subway Lining 362
Economics of 136
Falseworks and Bracing 144, 145
Methods of
Aqueduct, Cedar Grove Reservoir 546
Aqueduct Torresdale Filters 541
Arch Culvert 427
Arch Culverts 421
Blocks for Lake Pier 216
Blocks Molded Under Water 217-219
Box Culverts 417
Bridge Piers 255
Building Work 492, 495
Cement Pipe Molded in Place 577
Circular Columns 445
Columns 434
Connecticut Ave. Bridge 392
Coping for Walls 264
Culvert Pipe 431
Curb and Gutter 319, 321, 323
Dam Abutments 196
Dam, Rock Island, Ill. 228
Five Span Arch Bridge 400
Gasholder Tank 612
Girder for Separate Casting 516
Guard Lock, Ill. & Miss. Canal 200
Lock, Coosa River 195
Lock, Ill. & Miss. Canal 201, 203
Manhole Hartford, Conn. 536
Marquette Breakwater 211, 212
Ornamental Columns 446, 447
Piers for Taintor Gates 198
Polygonal Columns 443, 444
Rectangular Columns 435, 443, 490, 492, 511
Reservoir Bloomington, Ill. 605
Reservoir, Ft. Meade, S. Dak. 600
Retaining Wall, C., B. & Q. R. R. 262
Retaining Wall, Chicago Drainage Canal 275
Retaining Wall, Grand Central Terminal 281
Retaining Walls, N. Y. C. & H. R. R. R. 261, 262
Salt River Aqueduct 539
Sewer, Cleveland, O. 564
Sewer Invert, Haverhill, Mass. 554
Sewer, Invert, Medford, Mass. 535
Sewer, Invert, Middlesborough, Ky. 561
Sewer, South Bend, Ind. 551
Sewer, Wilmington, Del. 572
Sidewalks 309
Six-Story Building 492
Slab and Girder Floors 450, 456, 492
Slab and I-Beam Floors 448, 450
Slab Girders 385
Steel for Conduits 533
Steel, McCall Ferry Dam 227, 228
Steel Sheathed Collapsible for Conduits 533
Tunnel Centers 335, 341, 352, 358
Tunnel Sidewalls 330, 335, 340, 351, 358
Wall 456, 460, 505
Wall Columns for Factory 498
Computation, Methods of 140, 141
Design
Considerations in 141
Details Entering 142, 143
Lubrication, Methods of 144
Lumber
Dressing, Purpose of 138
Finish and Dimensions 138, 139
Kinds Suitable 138
Mortar Facing 129
Pile
Round 179
Rectangular Pier
Cost of, Rule for Calculating 14
Removing, Time of, Directions for 145, 146
Unit Construction, Purposes of 143
Steel, Opportunity for Development 136
Fortification Construction
Cost of
Battery Emplacement 188, 189, 190
Gun Emplacements 185
Mortar Battery Platform 187
Methods of
Battery Emplacement 187, 189
Gun Emplacements 185
Mortar Battery Platform 186
Foundation Construction
Street Railway
Cost of Continuous Mixer 301
Methods of Continuous Mixer 300, 301
Freezing Weather, Laying Concrete in 112
G
Grain Elevator Bins
Construction, Methods of 635
Gravel
Characteristics of 14
Commercial Sizes of 22
Screening and Washing Plants 23
Screening (See Screening Gravel)
Voids in
Amount of 30, 31
Effect of Granulometric Composition 29, 30
Weight no Index 32
Amount of 31, 32
Grouting Under Water
Hermitage Breakwater 96
Tests of Efficiency of 95
H
Heating Aggregates
Efficiency of 114
Methods of
Bridge Work, Plano, Ill. 118
Chicago, Burlington & Quincy R. R. 118
Hot Water Tanks 120
Huronian Power Co.'s Dam Work 118
Portable Combination Heater 115
Stationary Bin Outfits 115, 116
Steam Box 119
Steam Jets 119
Wachusett Dam Work 117
Water Power Plant, Billings, Mont. 116, 117
Hoists
Gallows, Frame and Horse 54
Ransome 476
Wallace-Lindesmith 474
Housing Concrete Work
Methods of
Chicago, Burlington & Quincy R. R. 119
Dam, Chaudiere Falls, Quebec 120, 121
Portable Unit System for Buildings 122, 123
I
Inclines
Grades of 62
L
Laying Concrete Blocks
Cost of 526, 529
Loading Concrete
Characteristic Features 53
Rate of 53
Loading Materials
Cost of
Shoveling into Wheelbarrows 47
Rate of 6
Lock Construction
Cost of
Coosa River 196
Ill. & Miss. Canal 200, 202, 205, 207
Cascades Canal 190, 191, 192, 193
Coosa River 194, 195
Ill. & Miss. Canal 200, 207
Lock Foundation 207
M
Manhole Construction
Cost of
Rye, N. Y. 577
Methods of
Rye, N. Y. 576
Mixers
Batch
Chicago 662
Chicago Improved Cube 75, 661
Cropp 661
Forms of 75
Koehring 662
Polygon 663
Ransome 75, 661
Rate of Output 83, 84
Smith 77, 662
Snell 660
Charging (See Charging Mixers)
Continuous
Advanced 660
Eureka Automatic Feed 78, 660
Forms of 78
Foote 297
Scheiffler 660
Efficiency of
Rating, Methods of 84, 85
Gravity
Forms of 79
Gilbreth Trough 80
Hains, Fixed Hopper 80, 81
Hains, Telescoping Hopper 81
Output
Conditions Affecting 83, 84
Hains Gravity 83
Types of 74
Mixing Concrete
Hand
Cost of
Abutment Construction 197
Culvert Work 428, 430
Fortification Work 189
Girder Highway Bridge 380, 382
Lock, Cascades Canal 192
Marquette Breakwater, 209, 210, 212
Retaining Wall, Allegheny 284
Superintendence, 57, 58
Cost of, 52, 59
Methods of Abutment Construction, 196, 197
Examples from Practice, 49
Fortification Work, 189
Lock Foundation, 207
Marquette Breakwater, 209
Retaining Wall, Allegheny, 283, 284
Rates of, 50, 51, 52
Specific Directions, Necessity, 51, 52
Machine
Cost of, 361, 362, 518
Buffalo Breakwater, 214
Building Work, 504, 507, 511
Dam Work, Rock Island, Ill., 225
Fortification Work, 190
Hains Gravity Mixer, 83
Lock, Cascades Canal, 193
Lock, Ill. & Miss. Canal, 206, 207
Pier, Superior Entry, Wis., 222
Retaining Wall, Allegheny, 284
Retaining Wall Work, 270, 273, 275
Methods of
Bridge Abutment Work, 253, 254
Building Work, 471
Fortification Work, 189
Hains Gravity Mixer, 82, 83
Operations Enumerated, 61
Piers in Caissons, 165, 166
Mixing Plants
Construction
Battery Emplacement, 187, 188
Bridge Construction, 369, 371, 372, 374, 386, 389, 403.
Culvert Work, 415, 416, 418, 420, 422, 423
Dam, McCall Ferry, Pa., 226
Lock, Cascades Canal, 190, 191
Lock Work, Coosa River, 194
Lock Work, Ill. & Miss. Canal, 198, 199, 204
Pier Work, Superior, Wis., 221
Retaining Wall, Grand Central Terminal, 277
Scow, Port Colborne Harbor, 216, 217
Traveling, Chaudiere Falls Dam, 228
Traveling, Chicago Track Elevation, 267
Traveling, Galveston Sea Wall, 268
Cost of
Lock Work, Ill. & Miss. Canal, 199
Retaining Walls, Chicago Drainage Canal, 274
Mixing Water
Reducing Freezing Point
Methods of, 112
Salt (Sodium Chloride), 113
Solutions for, Composition of, 113
Molding Blocks
Cost of, 524, 528, 530, 531
Marquette Breakwater, 211
Connecticut Ave. Bridge, 395
Separate Casting, 519
Methods of, 523, 526
Connecticut Ave. Bridge, 393
Marquette Breakwater, 211
Pier, Port Colbourne Harbor, 215
Separate Casting, 513, 515
Molding Cement Pipe
Cost of
Irrigon, Ore., 584
Ransome Mold, 577, 579
Methods of
Irrigon, Ore., 581
Ransome Mold, 577
Molding Culvert Pipe
Cost of
Chic. & En. Ill. R. R., 432
Methods of
Chic. & En. Ill. R. R., 430
Molding Girders
Cost of
Separate Casting, 519
Methods of
Separate Casting, 513, 514, 515
Molding Piles
Forms for (See Forms)
Methods of
Corrugated Polygonal, 176
Round, 179
Plant Arrangements for, 169
Cost of, 522
Molding Roof Slabs
Methods of, 521
Mortar Facing
Cost of
Lock, Ill. Miss. Canal, 206
Forms for, 129
N
Natural Cement (See Cement)
O
Ornament Construction
Methods of
Iron Molds, 644
Molding in Place, 647
Plaster Molds, 646
Sand Molding, 644
Wooden Molds, 637
P
Pavement Base Construction
Cost of
Batch Mixer, 306
Batch Mixer and Wagon Haulage, 302
Brick, Champaign, Ill., 296
Continuous Mixers, 298, 300, 305
Miscellaneous Examples 294, 295, 296
New Orleans 293
Stone Block, New York 292
Toronto, Ont. 293
Traction Mixer 304
Methods of
Batch Mixer 305
Batch Mixer and Wagon Haulage 302
Continuous Mixers 297-300, 304
Hand Mixing 290
Machine Mixing 290, 291
Traction Mixer 303
Mixtures Employed 288
Organization for 288
Stock Pile Distribution 289
Pavement Construction
Cost of
Fortification Work 186
Richmond, Ind. 318
Windsor, Ont. 317
Methods of
Richmond, Ind. 318
Windsor, Ont. 316
Pier Construction
Cost of
Lonesome Valley Viaduct 255
Superior Entry, Wis. 222, 223
Taintor Gates 198
Methods of
Port Colborne Harbor 215-217
Superior Entry, Wis. 217-223
Piers in Caissons
Construction of
Methods of 159-168
Cost of 168, 169
Pile Construction. (See Molding Piles, Pile Driving.)
Cost of
Ocean Pier 173, 174
Raymond Process 152, 154, 155
Methods of
Building Foundation Work 174, 175, 178, 179
Compressed Process 158, 159
Enumeration of 151
Molding in Forms 161-170, 172, 179, 180
Molding in Place 151
Ocean Pier 172, 173
Raymond Process 152
Rolling Process 181
Simplex Process 155, 156, 157
Spread Footing Process 157, 158
Track Scales 181
Pile Driving
Conditions Requisite for
Cost of
Ocean Pier 173, 174
Methods of
Corrugated Polygonal 177, 178
Hammer 179, 180, 181
Water Jetting 172, 177
Pile Driving Caps 177, 178, 180
Pile Rolling Machine 182
Piles (See Molding Piles)
Construction
Compressol Process 158, 159
Octagonal 180
Rolling Process 181
Round Piles 178, 179
Spread Footing Process 157, 158
Square 179, 180
Cost of
Rolling Process 183
Driving (See Pile Driving)
Handling, Sling for 175
Raymond
Construction, Method of 151, 152
Cost of 152, 154, 155
Simplex
Construction, Methods of 155, 156, 157
Placing Concrete
Cost of
Bags, Under Water 210
Belt Conveyors 275
Buckets Under Water 209
Buffalo Breakwater 214
Car and Trestle Plant 196, 201, 202, 206, 207, 244
280, 422
Cars and Chute 193
Cars and Derrick 285
Derricks 192, 233, 235
Port Colborne Harbor 217
Pneumatic Caissons 230
Retaining Wall Work 270, 272
Steel Cylinder Pier 241
Subaqueous Buckets 223
Wheelbarrows 189, 197, 198, 257, 285, 418, 419, 423
Methods of
Building Work 486
Locks Coosa River 194
Pneumatic Caissons 237, 238
Retaining Wall Work 266
Sewer Work 537
Placing Reinforcement
Cost of
Building Work 494
Directions for 470
Permanent Way Structures 252
Pole Base, Cost of 658
Portland Cement (See Cement)
Proportioning Concrete (See Concrete)
Q
Quarrying
Cost of
Limestone 18, 276
Trap Rock 17
Methods of
Limestone 18
Trap Rock 17
R
Ramming Concrete (See also Placing Concrete)
Cost of 423
Conditions Governing 56
Examples from Practice 56, 57
Pavement Base 292, 294
Methods of
Piers, Lonesome Valley Viaduct 255
Specific Directions, Necessity of 57
Raymond Piles (See Piles)
Reinforcement
Weight in Concrete
Tables for Estimating, 663-665
Removing Forms
Derrick for, 502
Methods of
Building Work, 461
Time for
Building Work, 462
Reservoir Construction
Cost of
Covered for Fire Protection, 594, 595
Ft. Meade, S. Dak., 601
Methods of
Bloomington, Ill., 603
Covered for Fire Protection, 588
Fort Meade, S. Dak., 597
Reservoir Lining
Cost of
Canton, Ill., 629
Chelsea, Mass., 623
Jerome Park, 628
Pittsburg, Pa., 630
Quincy, Mass., 619
Methods of
Chelsea, Mass., 620
Jerome Park, 628
Quincy, Mass., 617
Reservoir Roof, Cost of 632
Retaining Wall Construction
Cost of, 286
Chicago Drainage Canal, 273-277
Footing for Masonry, 283
Grand Central Terminal, 280
Railway Yard, 282
Methods of
Allegheny Track Elevation, 283
Chicago Drainage Canal, 272-277
Grand Central Terminal, 277-281
Subway in Trench, 269, 270
Retaining Walls
Comparison of Plain and Reinforced, 260, 261
Types of, 259
Rubble Concrete Construction
Cement, Saving in, 98
Cost of
Abutment, Railway Bridge, 106
Hemet Dam, 104
Spier Falls Dam, 103
Economy, Limitations to, 98, 99
Methods of
Abutment, Railway Bridge, 105
Barossa Dam, 101
Boonton Dam, 103
Bridge Piers, Nova Scotia, 108
Bridge Piers, Scotland, 107, 108
Bridge Piers, Spain, 106, 107
Chattahoochee River Dam, 100
Dams for Waterworks, 104, 105
Hemet Dam, 103, 104
Spier Falls Dam, 103
Percentages Rubble Stone, 100, 101, 103, 105, 108
Shape of Stones for, 99
Runway Construction, Methods of, 48
S
Salt
Percentages in Mixing Water, 114
Sand
Balanced, Value of, 6
Cleanness, Value of, 5
Cost of
Excavating and Loading, 6
Granulometric Composition, 28
Prices Charged for, 6
Sharpness, Value of, 5
Substitutes for, 5
Voids in
Amount of, 26, 28
Conditions Affecting, 25
Effect of Moisture, 25
Effect of Size of Grains, 27
Volume in Concrete, 5
Weight of, 6, 26
Sand Washing
Cost of
Ejector Method, 10
Hose Method, 7
Tank Method, 13
Methods of
Ejectors, 7
Hose, 7
Tank, 10
Rate of
Ejector Method, 9
Hose Method, 7
Tank Method, 10, 12, 13
Water Required
Ejector Method, 9
Sand Washing Plants, 7-13
Screening Gravel
Cost of
L. S. & M. S. Ry., 22
Stewart-Peck Sand Co., 24
Methods of
Handwork, 19
Lock, Cascades Canal, 191
Scraper into Wagons, 21
Stewart-Peck Sand Co, 23
Sewer Construction
Cost of
Cleveland, O., 566
Coldwater, Mich., 574
Haverhill, Mass., 557
Medford, Mass., 535
Middlesborough, Ky., 562
St. Louis, Mo., 560, 561
South Bend, Ind., 554
Wilmington, Del., 571, 573
Methods of
Cleveland, O., 563
Coldwater, Mich., 573
Haverhill, Mass., 554
Medford, Mass., 535
Middlesborough, Ky., 561
Pipe, St. Joseph, Mo., 579
St. Louis, Mo., 558
South Bend, Ind., 551
Wilmington, Del., 569
Shoveling
Cost of
Concrete into Barrows, 197
Rate of
Broken Stone from Piles, 46
Broken Stone from Shoveling Boards, 46
Broken Stone from Cars, 45
Gravel Against Screens, 21
Sand into Wheelbarrows, 46
Shoveling Boards Wooden, for Broken Stone, 46
Sidewalk Construction
Cost of
Estimation of, 311, 312
Quincy, Mass., 314
San Francisco, Cal., 315
Toronto, Ont., 313
Methods of
Bonding Wearing Surface to Base, 310
Edger for, 310
General Discussion, 307
Points for, 310
Prevention of Cracks, 311
Protection from Weather, 311
Quincy, Mass., 314
Toronto, Ont., 313
San Francisco, Cal., 314
Silo Construction
Cost of, 632
Methods of, 631
Slag, 14
Slag Cement (See Cement)
Specific Gravity, Stone, Various, 32, 33
Spreading Concrete
Cost of, 197
Effect of Method of Dumping on, 55
Standpipe Construction
Cost of
Attleborough, Mass., 611
Methods of
Attleborough, Mass., 609
Stock Piles
Capacity of, 46
Distribution, Pavement Work, 289
Purposes of, 45
Stone
Specific Gravity, 32, 33
Stone Crushing
Cost of
Cobblestone, 20
Limestone, 18, 225, 273, 276
Trap Rock, 17
Methods of
Cobblestone, 19
Limestone, 18
Trap Rock, 17
Stone Crushing Plant
Construction
Lock Work. Ill. & Miss. Canal, 200
Stone Dust, Value for Mortar, 5
Storing Materials, Cost of, 185, 225
Subway Lining
Cost of
Long Island R. R., 361
New York Rapid Transit Ry, 357, 358
Methods of
Long Island R. R., 361
New York Rapid Transit Ry., 356
Superintendence
Cost of, 57, 58, 185, 193, 197, 210, 211, 212, 273, 275, 397
T
Tamping Concrete
Cost of, 197
Lock, Ill. & Miss. Canal, 206, 207
Method of
Lock, Ill. & Miss. Canal, 204
Tank Construction
Methods of
Gas Holder, Des Moines, Ia., 609
Gas Holder, New York, 614
Tooling Concrete
Cost of, 394, 396
Transporting Concrete
Cost of
Cableways, 270
Cars, 280
Chutes, 67
Cars and Derricks, 285
Car and Trestle Plant, 63, 210, 212, 222
Wheelbarrows, 53, 189, 197, 272, 285, 293, 294, 296
Methods of
Belt Conveyors (See also Belt Conveyors), 64-65
Bucket Hoists, 474
Building Work, 472
Cableways, 64, 186, 289, 369, 370
Cars, 404, 421
Cars and Chute, 191, 192
Car and Trestle, 63, 243, 246, 377
Chutes (see also Chutes), 66, 67, 68
Derricks, 479
Dump Wagons, 54
Effect on Placing, 54
Enumeration of, 52
Hand Costs, 53
Hoist and Cars, 372
Platform Hoists, 479
Pulley and Horse, 489
Traveling Derrick Plant, 374
Trestle Runways, 54
Wheelbarrows, 53
Transporting Materials
Cars for, 45
Cost of
Bridge Pier Work, 243
Cars, 275
Car and Trestle Plant, 222
Dam, Rock Island, Ill., 225
Horse Carts, 49, 270, 273
Lock, Ill. & Miss. Canal, 206, 207
Wheelbarrows, 47, 48, 189, 197, 214, 280, 292, 293, 294, 296, 419
Methods of
Belt Conveyors (see also Belt Conveyors), 64-65
Cableways, 64, 269
Carrying in Shovels, 47
Chutes (see also Chutes), 46, 65, 66
Hand Carts, 48
Horse Carts 48
Indians 62
Shoveling to Derrick Buckets 46
Trestle and Car Plants 63
Wheelbarrows 47
Trestle Runways, Cost of 54, 55
Trestles
Car, Cost of 63
Structural Details 63
Tunnel Construction (See Tunnel Lining)
Tunnel Lining
Backfilling Machine for 330
Cost of
Cascade Tunnel 338
Gunnison Tunnel 355
Hodges Pass Tunnel 345
Mullan Tunnel 333
Peekskill Tunnel 336
Short Railway 344
Methods of
Burton Tunnel 347
Capitol Hill, Washington, D. C. 329
Cascade Tunnel 336
General Discussion 328
Gunnison Tunnel 353
Hodges Pass Tunnel 338
Mullan Tunnel 332
Peekskill, N. Y. 333
Mortar Car for 333
Removing Old, Methods of 332
Traveling Derrick for 330
Traveling Platform for 337, 350
U
Unloading Materials
Cost of
Grab Buckets 62
Methods of
Grab Buckets 62
V
Voids (See also Gravel, Sand, Stone)
Conditions Governing 25
W
Wall Ties
Construction of 265
Washing Gravel
Cost of
L. S. & M. S. Ry. 22
Stewart-Peck Sand Co. 24
Washing Gravel
Methods of
Lock, Cascades Canal 191
Stewart-Peck Sand Co. 23
Water
Quantity in Concrete
Rule for Figuring 42
Waterproofing
Cost of
Hydrolithic Coating 677
Long Island R. R. Subway 679
New York Subway 680
Sylvester Mortar 675
Sylvester Wash 674
Methods of
Bituminous Coatings 670
Covered Reservoir for Fire Service 596
Hydrolithic Coating 676
Impervious Mixtures 668
Long Island R. R. Subway 678
Medusa Compound 669
Moisture Coatings 677
New York Subway 679
Novoid Compound 670
Oil and Paraffin Washes 677
Star Stellen Cement 669
Sylvester Mortar 675
Sylvester Wash 673
Szerelmey Wash 673
Wheelbarrows
Loads for 47
End of the Project Gutenberg EBook of Concrete Construction, by
Halbert P. Gillette and Charles S. Hill
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