In the mixing of concrete there arise many economic problems, most of which are apparently of such minor importance as not to be worthy of consideration. For small jobs of work this may be true enough, but on large ones, involving great yardage of concrete, every little item of economy is well worth while.

There are two main points of view from which this question may be considered—that of the contractor and that of the engineer—the latter, of course, acting for the best interests of his client. The contractor generally is paid for concrete in place at so much per cubic yard; but there are often several unit prices arranged to cover varying conditions. Sometimes these conditions are variations in the composition of the mixture, but often they relate to the differing costs of placing and formwork. Be this as it may, though, in ordinary specifications there is nothing to induce the contractor to try to produce the strongest and best concrete practicable. This is the duty of the engineer; and he accomplishes it by stating clearly in his specifications the qualities of all the materials employed, the compositions of the different classes of concrete, how the components thereof are to be mixed, how the fresh concrete is to be placed, and how the finished work is to be protected until the mass hardens and dries—also by carefully inspecting the materials for quality, the mixing, the placing, and the protection, so as to ensure that the specifications are fully complied with.

Ordinarily there are not many legitimate major ways in which the contractor may economize in his concrete-work, as he is confined mainly to purchasing the materials as cheaply as possible, doing the mixing economically, and placing the mixture expeditiously; but occasionally he is given an opportunity to economize on the quantity of cement by the engineer's having made it proportional to the volume of voids in the aggregate, and by being permitted to use one-man stones in the mass.

There are, however, many minor ways in which the contractor may legitimately economize in the making of concrete, principally by the application of forethought in the receiving and storing of materials promptly; locating the bins in the most favorable places for expediting the work; establishing the best practicable scheme for transportation from bins to mixers and from mixers to points of deposit; substituting machinery for man-power wherever it will facilitate the work and reduce cost; designing and building forms that are not too expensive, that can be placed and removed expeditiously,  and  that  have  some  salvage  value;  and installing

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