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:
| Body Concrete—— | 12-in., per cu. yd. | 6-in., per 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 |