Fig. 68.—Sketch Plans of Concrete Making Plant for Mortar Battery Platform.
Mortar Battery Platform, Tampa Bay, Fla.—The platform contained 8,994 cu. yds. of concrete composed of a mixture of Portland cement, sand, shells and broken stone. The broken stone and cement were brought in by vessel and the sand and shells were obtained from the beach near by. The plant for the work was arranged as shown by the sketch, Fig. 68. Sand, stone and shells were stored in separate compartments in the storage bins. Box cars, divided into compartments of such size that when each was filled with its proper material, the car would contain the proper proportions for one batch of concrete, were pushed by hand under the several compartments of the bin in succession until charged; then they were hooked to a cable and hauled to the platform over the mixer and dumped. The charge was then turned over with shovels and shoveled into the hopper of a continuous mixer, located beneath. Two cars were used for charging the mixer, running on separate tracks as shown. The mixer discharged into buckets set on flat cars, which were hauled by mules under the cableway, which then lifted and dumped the bucket and returned it empty to the car. By using three bucket cars, one was always ready to receive the mixer discharge as soon as the preceding one had been filled, so that the mixer operated continuously. The cableway had a working span of 270 ft., the cable being carried by traveling towers 69 ft. high; the cableway was very easily operated back and forth along the work. The cableway complete, with 497 ft. of six-rail track for each tower, cost $4,700. The cost of materials and labor for the 8,994 cu. yds. of concrete was as follows:
| Per cu. yd. | |
| 1 bbl. cement at $2.46 | $2.46 |
| 0.89 cu. yd. stone, at $2.95 | 2.622 |
| 0.315 cu. yd. shells, at $0.45 | 0.142 |
| 0.51 cu. yd. sand, at $0.12 | 0.062 |
| Mixing and placing | 0.693 |
| ——— | |
| Total | $5.979 |
The above batch tamped in place to 30 cu. ft., or 1-1/9 cu. yds., which gives the cost as follows:
| Per cu. yd. | |
| Cost of concrete tamped in place | $5.381 |
| Cost of form work | 0.370 |
| ——— | |
| Total cost | $5.751 |
In the preceding prices of cement and stone, 59 cts. and 29 cts. per cubic yard, respectively, are included for storage. The costs of sand and shells are costs of screening and storing. Rough lumber for forms cost $10.25, and dressed lumber $12.75 per M. ft. B. M.
Emplacement for Battery, Tampa Bay, Fla.—The emplacement contained 6,654 cu. yds. of Portland cement, sand, shells and broken stone concrete. The plant arrangement is shown by Fig. 69. The sand and shells were got near the site, using an inclined cableway running from a 40-ft. mast near the mixer to a deadman at the shell bank. All the sand for the fill around the emplacement was obtained in the same way. The other materials were brought by vessel to a wharf, loaded by derrick onto cars operated by an endless cable, and taken to the work. The storage bins and mixing plant were operated much like those for the mortar battery work, previously described. A cube mixer was used, and the concrete was handled from it to the work by a crane derrick covering a circle of 100 ft. in diameter. The cost of materials and concrete was as follows:
| Cement, plus 7 cts. for storage per bbl. | $ 2.532 |
| Stone, plus 38 cts. for storage per cu. yd. | 3.047 |
| Shells, excavating and storage. | 0.481 |
| Sand, excavating and storage. | 0.250 |
| Lumber, rough per M. ft. B. M. | 10.25 |
| Lumber, dressed per M. ft. B. M. | 12.75 |
