COST OF CONCRETE. The cost of concrete depends upon the following: (1) the unit cost of the materials; (2) the proportions; (3) the character of the work—whether foundation work, mass concrete above ground, or reinforced-concrete building work,; (4) the magnitude of the job; (5) the cost of labor per hour; (6) the hours worked per day; (7) the character of the labor; (8) the space available for the storage and the handling of the materials; (9) the time of the year; (10) the probable weather conditions; (11) the amount of time allowed for doing the work, etc. In making an estimate of the probable cost of any proposed work, each of these items must be carefully studied; and in using published data on cost of concrete, attention should be given to the conditions under which the work was done.
The Cement. The price of cement (I 127-29) varies with the conditions of the market and with the locality, and hence it is wise to consult the dealers before making an estimate. Further, freight is a considerable part of the delivered price, and hence quota tions should be secured f.o.b. the point of delivery. The cost of wagon haul will usually vary from 15 to 20 cents per ton-mile de pending upon the locality, the season, and the character of the roads; and assuming for this purpose that a barrel of portland cement weighs 400 pounds, the wagon haul will vary from 3 to 4 cents per barrel per mile.
The amount of cement required for a cubic yard of concrete can be obtained from Table 28, page 158, and hence the cost delivered at the work can easily be computed.
The Sand. The cost of sand varies greatly with the locality, since in some places sand may be found comparatively near the work, while in others it must be transported a long distance (see f 203). If the sand is found near the wor(:, the cost of haul will be the cost of loading, which for large jobs is about one hour's labor per cubic yard and for small jobs about 1 hours per cubic yard, plus the cost of transportation, which is about 1 cent per 100 feet of distance. If the sand is hauled a few miles instead of a few hundred feet, the cost of loading is relatively small and may be included in the cost of hauling, which is from 15 to 20 cents per ton-mile. The cost of haul per unit of distance is more for short distances than for long ones because of the proportionally greater loss of time on account of the detention of the wagon or cart at the pit. For distances
under 250 to 300 feet, sand can be hauled in wheelbarrows more economically than in carts or wagons. In computing the cost of wagon haul, we may assume sand to weigh 1 tons per cubic yard; and hence the wagon haul will cost from 22 to 30 cents per cubic yard per mile. Table 28, page 158, gives the amount of sand required per cubic yard of concrete.
The Aggregate. If the aggregate is'gravel, the data in the preceding section are applicable also in this case. Broken stone is bought by the ton or by the cubic yard, and for this purpose a yard of stone may be assumed to weigh 1+ tons. For data on the price of crushed stone, see § 218.
Under this head will be included only the cost of forms for mass concrete, no reference being made to the forms employed in reinforced-concrete buildings, since that subject is too complicated to be treated in the space here available. For a little data on the cost of forms for reinforced-concrete buildings, see the left-hand side of Table 46, page 258.
The cost of the forms of mass concrete is materially affected by nearly all the items affecting the cost of the concrete (see § 412), and in addition the cost of the forms depends also upon the following: (1) the outlines of the structure, which govern the amount of labor required in erecting and removing the forms and the loss in cutting the lumber; (2) the consistency of the concrete, which determines the length of time the forms must remain in place and hence governs the amount of lumber required for any particular job; (3) the de tails of the design of the forms—whether the facing planks have square edges, beveled edges, or are tongued and grooved, or whether the forms are sectional or not, etc.; (4) the composition of the form building gang—whether all are high-priced and expert carpenters or low-priced unskilled laborers, or whether there is an economic proportion of each; (5) the care employed in taking down the forms; (6) the number of times the lumber may be used; and (7) the surface finish required on the completed concrete. The forms sometimes support the runway used in delivering the concrete, in which case part of the cost of the forms is strictly not chargeable to form-work proper.