"The scouring was done on each section of the wall immediately after the forms supporting these sections had been removed. The object was to rub this interior surface with carborundum before the surface of the concrete had taken its final set. By rubbing the concrete at this stage and at the same time applying with a brush a coating of neat cement grout, we believe the face of the concrete was made more or less impermeable, as examination shows the pores of the concrete are very largely filled up. We have no accurate figures as to the cost per square yard of this treatment, but one can readily see that this cost would be insignificant as compared with the possible improvement of the work. The carborundum brick was selected on account of its hardness. I believe practically any stone would answer the same purpose. In addition to filling the pores of the concrete, this treatment gives the surface a good smooth finish."
LINING A RESERVOIR, QUINCY, MASS.—The following methods and costs are given by Mr. C. M. Saville, M. Am. Soc. C. E., for lining the Forbes Hill Reservoir at Quincy, Mass. This reservoir is 100×280 ft. on the floor, with side slopes of 1 on 1.75, and was built by contract in 1900-1901.
Fig. 285.—Section of Reservoir Lining, Quincy, Mass.
Figure 285 is a section of the concrete lining; the bottom layer for the floor was a 1-2-5 natural cement concrete, and for the sides a 1-2½-6½ Portland cement concrete; the top layer on both floor and sides was a 1-2½-4 Portland cement concrete; 2½-in. stone was the maximum size allowed in any concrete and 1½-in. the maximum allowed in the top layer. Smaller stone was used for special surface work, as noted further on. The stone was cobbles turned up in the excavation work and had to be gathered from scattered piles and washed before crushing. A 9×15 Farrel crusher, operated by a 12 HP. engine did the crushing; it was rated at 125 tons a day, but averaged only about 40 tons. The fine dust was screened out and the remainder discharged into a 30-cu. yd., three-compartment bin, one compartment for stone less than 1½ ins., another for 1½ to 2½-in. stone and a third for returns. The stone had 46 per cent. voids and weighed 95 lbs. per cu. ft. The sand was of excellent quality. Atlas and Beach's Portland and Hoffman natural cement were used.
All concrete was mixed and placed by hand, the concrete gang consisting generally of 1 sub-foreman, 2 men measuring materials, 2 men mixing mortar, 3 men turning concrete three times, 3 men wheeling concrete, 1 man placing concrete and 2 men ramming concrete. Two gangs were ordinarily employed, each mixing and placing about 20 cu. yds. per day, or 1.43 cu. yds. per man per day. The materials (sand and stone) were measured in bottomless boxes, the following sizes being used:
| —Sand Box— | —Stone Box— | |||
| Prop. of Mix. | Size. | Vol. cu. ft. | Size. | Vol. cu. ft. |
| 1-2½-4[H] | 2'9"×2'×1'8" | 9.25 | 5'×4'5½" | 14.8 |
| 1-3-6[H] | 2'9"×2'×2' | 11.1 | 5'×6'8" | 22.2 |
| 1-2-5 | 2'9"×2'×1'4" | 7.4 | 5'×6'6⅝" | 18.5 |
| 1-2½-6½ | 2'9"×2'×1'8" | 9.25 | 5'×7'2½" | 24.05 |
[H] These mixtures were used for gate house and standpipe foundation work.
The bottom layer was placed in a continuous sheet; the top layer was laid in 10-ft. squares on the floor and in 8×10-ft. squares on the sides; these squares alternated in both directions, one-half being first laid and allowed to set. In laying the sides the surface was left 1 in. low and then before the concrete had set was brought to plane by a 1-in. layer of 1-2½-4 mixture using stone and stone dust less than ⅜ in. The concrete for the floor was mixed rather wet and rammed until it quaked; on the sides a drier mixture was necessary to prevent flow. The cost of the lining concrete was as follows:
| Bottom Layer on Floor: 1-2-5 Mixture: | |
| 1.25 bbls. natural cement at $1.08 | $1.350 |
| 0.34 cu. yd. sand at $1.02 | 0.347 |
| 0.86 cu. yd. stone at $1.57 | 1.350 |
| 4½ ft. B. M. lumber at $20 per M. | 0.090 |
| Labor, on forms | 0.100 |
| Labor mixing and placing | 1.170 |
| Labor general expenses | 0.080 |
| ——— | |
| Total | $4.487 |
| Bottom Layer on Sides: 1-2½-6½ Mixture: | |
| 1.08 bbl. Portland cement at $1.53 | $1.652 |
| 0.37 cu. yd. sand at $1.02 | 0.377 |
| 0.96 cu. yd. stone at $1.57 | 1.507 |
| Lumber for forms (about 1 ft. B. M.) at $20 | 0.016 |
| Labor, on forms. | 0.121 |
| Labor, mixing and placing | 1.213 |
| Labor, general expenses | 0.177 |
| ——— | |
| Total | $5.063 |
| Top Layer on Floor and Sides: 1-2½-4 Mixture: | |
| 1.37 bbls. Portland cement at $1.53 | $2.09 |
| 0.47 cu. yd. sand at $1.02 | 0.48 |
| 0.75 cu. yd. stone at $1.57 | 1.17 |
| 12½ ft. B. M. form lumber at $20 per M. | 0.25 |
| Labor, on forms | 0.26 |
| Labor, mixing and placing | 1.530 |
| Labor, general expenses | 0.150 |
| ——— | |
| Total | $5.93 |