Concrete Mixing.—The proportions of the subaqueous concrete were 1-2½-5 by volume, or 1-2.73-5.78 by weight, cement being assumed to weigh 100 lbs. per cu. ft.; the proportions of the superaqueous concrete were 1-3.12-6.25 by volume, or 1-3.41-7.22 by weight. The dry sand weighed 109.2 lbs. per cu. ft., the voids being 35.1 per cent.; the pebbles weighed 115.5 lbs. per cu. ft., the voids being 31 per cent.
The pebbles for the concrete were delivered by contract and were unloaded from scows by clam-shell bucket into a hopper. This hopper fed onto an endless belt conveyor which delivered the pebbles to a rotary screen. Inside this screen water was discharged under a pressure of 60 lbs. per sq. in. from a 4-in. pipe to wash the pebbles. From the screen the pebbles passed through a chute into 4-cu. yd cars which were hauled up an incline to a height of 65 ft. by means of a hoisting engine. The cars were dumped automatically, forming a stock pile. Under the stock pile was a double gallery or tunnel provided with eight chutes through the roof and from these chutes the cars were loaded and hauled by a hoisting engine up an inclined trestle to the bins above the concrete mixer. The sand was handled from the stock pile in the same manner. The cement was loaded in bags on a car in the warehouse, hauled to the mixer and elevated by a sprocket chain elevator.
Chutes from the bins delivered the materials into the concrete mixer, which was of the Chicago Improved Cube type, revolving on trunnions about an axial line through diagonal corners of the cube. The mixer possessed the advantage of charging and discharging without stopping. It was driven by a 7×10-in. vertical engine with boiler. The mixer demonstrated its ability to turn out a batch of perfectly mixed concrete every 1⅓ minutes. It discharged into a hopper provided with a cut-off chute which discharged into the concrete buckets on the cars.
Labor Force and Costs.—In the operation of the plant 55 men were employed, 43 being engaged on actual concrete work and 12 building molds and appliances for future work. The work was done by day labor for the government and the cost of operation was as follows for one typical week, when in six days of eight hours each, the output was 1,383 cu. yds., or an average of 230 cu. yds. per day. The output on one day was considerably below the average on account of an accident to the plant, but this may be considered as typical.
| Pebbles from Stock Pile to Mixer— | Per cu. yd. |
| 4 laborers at $2 | $0.0348 |
| 1 engineman at $3 | 0.0131 |
| Coal, oil and waste at $1.03 | 0.0043 |
| Sand from Stock Pile to Mixer— | |
| 5 laborers at $2 | $0.0434 |
| 1 engineman at $2.50 | 0.0109 |
| Coal, oil and waste at $0.82 | 0.0035 |
| Cement from Warehouse to Mixer— | |
| 5 laborers at $2 | $0.0434 |
| Mixing Concrete— | |
| 1 engineman at $2.50 | $0.0109 |
| 1 mechanic at $2.50 | 0.0108 |
| Coal, oil and waste at $1.29 | 0.0056 |
| Transporting Concrete— | |
| 4 laborers at $2 | $0.0348 |
| 1 engineman at $3 | 0.0130 |
| Coal, oil and waste at $0.66 | 0.0028 |
| Depositing Concrete in Molds— | |
| 4 laborers at $2 | $0.0348 |
| 1 engineman at $3 | 0.0130 |
| 1 rigger at $3 | 0.0130 |
| Coal, oil and waste at $1.18 | 0.0051 |
| Assembling, Transporting, Setting and Removing Molds— | |
| 4 laborers at $2 | $0.0347 |
| 1 engineman at $3.25 | 0.0141 |
| 1 carpenter at $3 | 0.0130 |
| 1 mechanic at $2.50 | 0.0109 |
| Coal, oil and waste at $1.39 | 0.0060 |
| Care of Tracks— | |
| 1 laborer at $2 | $0.0086 |
| 1 mechanic at $2.50 | 0.0109 |
| Supplying Coal— | |
| 3 laborers at $2 | $0.0260 |
| Blacksmith Work— | |
| 1 laborer at $2 | $0.0086 |
| 1 blacksmith at $3.25 | 0.0141 |
| 1 waterboy at $0.75 | 0.0032 |
| ——— | |
| Total per cubic yard | $0.4473 |
| Add 75% of cost of administration | 0.1388 |
| ——— | |
| Total labor per cu. yd. | $0.5861 |
The total cost of each cubic yard of concrete in place was estimated to be as follows:
| Per cu. yd. | |
| Ten-elevenths cu. yd. pebbles at $1.085 | $0.9864 |
| Ten-twenty seconds cu. yd. sand at $0.00 | 0.0000 |
| 1 26 bbls. cement at $1.77 | 2.2302 |
| Labor as above given | 0.5861 |
| Cost of plant distributed over total yardage | 0.8400 |
| ——— | |
| Total | $4.6427 |
It will be noted that the sand cost nothing as it was dredged from the trench in which the pier was built, and paid for as dredging. The cost of the plant is distributed over this south pier and over the proposed north pier work on the basis of only 20 per cent. salvage value after the completion of both piers. It is said, however, that 80 per cent. is too high an allowance for the probable depreciation.
DAM, RICHMOND, INDIANA.—The dam shown in cross-section in Fig. 89 was built at Richmond, Ind. It was 120 ft. long and was built between the abutments of a dismantled bridge. The concrete was made in the proportion of 1 bbl. Portland cement to 1 cu. yd. of gravel; old iron was used for reinforcement. The foundations were put down by means of a cofferdam which was kept dry by pumping. On completion it was found that there was a tendency to scour in front of the apron and accordingly piling was driven and the intervening space rip-rapped with large stone. Labor was paid as follows per day: Foreman, $3; carpenter, $2.50; cement finisher, $2; laborers, $1.50. The concrete was mixed by hand and wheeled to place in wheelbarrows. The cost of the work was as follows: