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~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.

~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.

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.

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.

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.

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.

Introduction--Lowering the Freezing Point of the Mixing Water; Common Salt :--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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

Introduction--Separately Molded Ornaments: Wooden Molds; Iron Molds; Sand Molding; Plaster Molds--Ornaments Molded in Place: Big Muddy Bridge; Forest Park Bridge; Miscellaneous Structures.

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

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 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 of cement to the barrel, and the regulation cloth sack weighs 1 1/2 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 3 1/2 . 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- 3/4 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.

"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, 19 1/2 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 2 1/2 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 0 to 0. Such a laboratory can be operated by two or three men at a salary charge of from 0 to 0 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 to 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 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.

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."

~COST OF SAND.~--A very common price for sand in cities is 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.

~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 3/4 -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 .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.

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