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Raw material selection dictates base concrete expenditure

Quarrying and crushing stone locally yields lower unit costs than shipping processed aggregates long distances. Sand requires careful washing using hose sprays or tank ejectors to strip silt and vegetable matter down to under five percent volume. Barrels of Portland cement must be inspected for uniform weight before mixing begins. Sand and stone grading directly affects the total volume of cement paste needed.

M. Am. Soc. C. E.; M. Am. Inst. M. E.

Well-balanced aggregate sizes drastically reduce cement paste requirements

Naturally crushed stone contains fine screenings that fill spaces between larger particles, minimizing empty gaps. Adding sand to unscreened crusher-run rock creates a dense mixture without requiring excess costly cement. Washing river sand in specialized flume tanks removes up to thirty percent loam while holding labor costs down to fifteen cents per cubic yard. Using boiler cinders or blast furnace slag reduces total concrete weight for specialized structural floors.

CHAPTER II.

Dense particle packing minimizes expensive void spaces

Shaking and ramming broken limestone reduces internal air voids from forty-three percent down to thirty-seven percent. Mixing equal parts of river gravel and crushed trap rock creates a combined aggregate with lower voids than either stone used alone. Specific gravity measurements reveal whether dense minerals like basalt will produce heavier concrete than light sandstones. Long wagon hauls settle loose stone, reducing volume by several percent before reaching the mixing board.

Table VI.—Specific Gravity of Stone.

Systematic water ratios ensure strength without sacrificing speed

Dry concrete mixtures achieve superior early strength under heavy tamping, but wet mixtures flow quickly around steel rebar with minimal puddling labor. Calculating water content requires multiplying sand parts by eight, adding twenty-four, and dividing by total mortar parts. Standardizing measurement units prevents costly errors, as loose cement barrels hold more volume than packed bags. A single cubic yard of standard concrete requires exact water gallon calculations based on cement weight.

CHAPTER III. → CHAPTER IV.

Mechanized transport lowers batch delivery expenses

Operating double-track timber trestles and dump cars allows five laborers to move two hundred cubic yards of concrete daily at low labor cost. Cableways spanning eight hundred feet move mixed batches across wide river beds and dam sites with great speed. Belt conveyors running under storage bins transport sand, gravel, and cement bags directly to mixer platforms. Inclined rails worked by steam locomotives handle loaded cars on grades up to five percent efficiently.

CHAPTER V.

Subaqueous placement requires sealed buckets to prevent washouts

Lowering concrete through open water without protection washes cement out of the aggregate, weakening the finished structure. Self-dumping bottom-opening buckets like the Cyclopean keep batches sealed until reaching the sea floor. Specially keyed canvas bags lowered by divers allow exact placement against underwater rock ledges before tripping open. Paper bags filled with dry concrete can be placed in bridge footings where water dissolves the paper after positioning.

CHAPTER VI.

Salt additives prevent concrete damage during severe freezing

Adding common salt to mixing water lowers the freezing point, permitting concrete placement during winter conditions. Tetmajer's rule specifies adding one percent salt by weight of water for every degree Fahrenheit below freezing. Cold weather retards setting time, requiring forms to remain standing longer than in summer construction. Heating sand and water in enclosed sheds allows concrete to set fully before frost attacks the green masonry.

CHAPTER VII. → CHAPTER IX.

Reusable form design generates maximum lumber economy

Framing formwork with reusable wooden panels reduces timber waste across large multistory building jobs. Floor forms must be calculated for allowable deflection rather than breaking strength to prevent sagged beam profiles. Skilled carpenters minimize nail usage, relying instead on timber clamps and wedges that assemble and detach easily. Training dedicated labor crews to strip and carry forms lowers carpenter costs on successive floor pours.

CHAPTER X.

Centralized plant layouts streamline foundation shaft concreting

Excavating deep building caissons for structures like the Cook County Court House relies on elevated rope-driven hoists over each pit. Portable tripods allow rapid shifting between caisson rows while continuous tracks carry clay directly to disposal tunnels. Central mixing plants positioned below street-level storage hoppers feed concrete directly into pit cars. Laborers dump concrete straight down the caisson wells, spading the mixture in continuous layers without using tremies.

CHAPTER XI.

Temporary service bridges survive heavy river floods

Building the McCall Ferry Dam required a temporary fifty-foot wide concrete arch service bridge carrying four railway tracks across the river. Robust temporary concrete arches resist flood waters better than cheap wooden trestles that wash away repeatedly. Cockburn screw-feed mixers at Rock Island Arsenal discharged concrete into two-foot plank skips for derrick handling. Counterfort dam walls built in high vertical sections require heavy through-rods to anchor front and back forms.

CHAPTER XII.

Track-mounted delivery cars simplify bridge pier extensions

Extending old bridge piers for the Calf Killer River line utilized narrow-gauge cars rolling down main tracks by gravity. Water pumped from river beds fed elevated storage tanks supplying a gasoline-powered cubical batch mixer. Zig-zag chutes with removable ten-foot wooden arms delivered concrete into deep cofferdam forms cleanly. Using blast furnace slag as aggregate provided cheap local bulk while maintaining required structural compressive strengths.

CHAPTER XIII.

Crane-lifted wall panels accelerate large terminal projects

Constructing massive retaining walls for the New York Central Terminal relied on fifty-one-foot form panels shifted by locomotive cranes. Automatic continuous mixers like the Foote model eliminate manual measuring by feeding set ratios of stone and sand. One-horse concrete dump carts move batches rapidly from street mixers to pavement foundation sites. Thorough spading along form faces produces smooth two-inch mortar surfaces without requiring post-pour plastering.

CHAPTER XIV. → CHAPTER XV.

Monolithic curb construction outperforms assembled two-piece units

Casting street curbs and water table gutters as single monolithic units prevents joint separation caused by frost action. Continuous wooden side planks held by iron stakes allow rapid concrete placement along city street grades. Steel partition plates placed every twelve feet create clean expansion joints when pulled before final mortar finishing. Rich surface mortars applied over coarse concrete foundations produce durable pavements capable of carrying heavy city traffic.

CHAPTER XVI.

Gravity mixing systems lower material handling expenses

Delivering raw materials into overhead bins allows concrete ingredients to flow downwards through gravity mixers into car hoppers. Belt conveyors transporting gravel to elevated hoppers significantly reduce manual shovel labor compared to ground mixing operations. Batch mixers consume slightly more labor than continuous gravity systems but ensure precise control over rich structural proportions. Efficient rail car delivery down track inclines lowers overall labor costs for tunnel lining operations.

CHAPTER XVII.

Precast railway slabs eliminate field form erection overhead

Molding heavy reinforced concrete bridge slabs in ground yards allows exact quality control and avoids working at high elevations. Precast track slabs weighing thirty-six tons are lifted into place on abutments using high-capacity wrecking cranes. Rich one-to-four gravel mixtures provide dense cover over corrugated reinforcing bars to resist weather exposure. Detailed labor records show hand-mixing costs rise when rich cement proportions require handling additional small batches per yard.

Table XIX.—Showing Cost of Tooling Concrete Ornamental Blocks…

Simple wooden jigs speed up steel bar bending

Bending long steel reinforcing rods for five arch bridge spans was accomplished by pulling straight bars around curved spiked boards. Three men manually bent forty-six thousand pounds of steel rods in two days at sixty cents per ton. Light timber bents lined with one-by-six sheeting formed smooth arch centers without significant mortar leakage through cracks. Reusing arch form lumber across building projects reduces net form costs to eighty cents per cubic yard.

CHAPTER XVIII.

Compact cube mixers maintain rapid culvert batching cycles

A small gasoline-driven cube mixer turned out concrete batches every seventy-eight seconds during peak culvert construction on rail lines. Over-straddling trestle tracks allowed drop-bottom cars to dump concrete into both side walls of arch culverts simultaneously. Hillside crushing plants discharge crushed stone through bin chutes directly into mixer charging wheelbarrows without hoisting labor. Sump-mounted skip hoists fed by low platforms allow derrick cranes to move concrete skips efficiently.

CHAPTER XIX.

Octagonal form yokes eliminate complex corner blocking

Clamping octagonal column forms with alternating pairs of timber yokes simplifies framing and eliminates internal triangular corner blocks. Circular steel forms assembled in vertical sections provide superior alignment for columns compared to heavy wooden stave molds. Wrapping wire mesh around column rebar spirals creates self-contained molds that hold moderately dry concrete without exterior wood casing. Plaster of Paris inserts screwed inside wooden staves cast ornamental fluted columns in place.

FABRICATION AND PLACING OF REINFORCEMENT.

Fabricated bar frames guarantee accurate reinforcement placement

Assembling reinforcing bars into rigid unit frames before installation ensures correct spacing and prevents bar displacement during pouring. Bottom support chairs hold beam steel off lower form boards, guaranteeing full concrete encasement around main tension rods. Positioning batch mixers directly under building forms minimizes horizontal wheelbarrow haulage across floor spans. Final bar inspections just prior to pouring prevent structural failures caused by missing stirrups or shifted splices.

MIXING, TRANSPORTING AND PLACING CONCRETE.

Multistory form reuse drastically reduces total building costs

Reusing timber forms three times across six building floors drops form lumber charges to under two dollars per cubic yard. Small mixing gangs supported by electric hoists place two hundred cubic yards of floor concrete per seven-day cycle. Reinforcing floor slabs with thin rods and beam stirrups adds about one hundred forty pounds of steel per cubic yard. Detailed cost summaries demonstrate that form framing and carpenter labor exceed mixing costs in building work.

CHAPTER XX.

Precasting structural members on ground beds simplifies assembly

Casting fifty-foot roof girders and octagonal columns on ground slabs eliminates high scaffolding and dangerous form erection work. A Browning locomotive crane lifts precast twenty-four-ton columns into place, completing six column erections per day. Concrete made from fine crusher-run stone flows easily through car spouts into flat ground molds. Internal pipe sockets cast into column ends provide secure attachment points for crane hoisting tackle.

CHAPTER XXI.

Collapsible iron cores enable rapid pipe section molding

Molding concrete sewer pipes vertically around four-piece sheet steel cores allows rapid stripping without damaging fresh pipe walls. Circumferential iron hoops threaded over vertical rods during tamping reinforce small-diameter cement pipe against soil pressures. Hand-tamped mortar pipes made with one-to-four sand mixtures provide inexpensive irrigation conduits when properly cured with water sprays. Pouring wet cement grout into chamfered hub joints bonds precast pipe lengths into watertight lines.

CHAPTER XXII.

Layered concrete linings protect repaired reservoir basins

Repairing cracked water reservoir linings requires laying a dense lower base concrete followed by an asphalt-waterproofed upper layer. Plastering exposed slab joints with rich cement mortar creates smooth, impervious surfaces resistant to continuous water pressure. Derrick cranes operating dump cars handle excavated debris and concrete materials across steep reservoir embankments. Itemized labor tracking shows surface plastering and asphalt mopping consume a minor fraction of repair costs.

CHAPTER XXIII.

Plaster pattern boxes produce delicate ornamental rail castings

Casting bridge parapet balusters in three-piece wooden boxes lined with plaster molds reproduces intricate architectural shapes cleanly. Split cast-iron molds held by wedges produce solid concrete railing spindles efficiently in field casting yards. Building coping forms directly over arch bracket blocks ensures exact alignment along long bridge facades. Standard batch mixer performance tables help contractors size plant machinery to match required hourly yardage outputs.

CHAPTER XXIV. → CHAPTER XXV.

Book

Concrete Construction: Methods and Costs

Master early twentieth-century civil engineering through precise unit costs, field methods, and concrete techniques.

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