Concrete was placed in 4-in. layers (the depth of the lagging) and well rammed, since it was found that "wet" concrete left small honeycombed spaces on the inner surface. Concrete for the invert was 1-2-6, the stone being 1½-in. and smaller, and the sand being crusher dust. The arch was 1-2-5.
The reinforcing metal used in the 9½-ft. sewer was No. 6 expanded metal, 6-in. mesh, in sheets 8×5½ ft., supplied by Merritt & Co., of Philadelphia. A single layer was placed around the sewer, 2 ins. from the inner surface, its position being carefully maintained by the men ramming, and with but little difficulty as the sheets were first bent to the radius of the circle. Each sheet was lapped one mesh (6 ins.) over its neighbor at both ends and sides, and no sheets were wired except the top ones, which were liable to displacement by men walking over them.
Fig. 265.—Cross-Sections of Sewer at Wilmington, Del.
The metal used on the rest of the work was a wire-woven fabric furnished by the Wight-Easton-Townsend Co., of New York. This fabric comes in rolls 5½ ft. wide and 100 ft. to the roll. The wire is No. 8, with a 6×4-in. mesh. This fabric was placed by first cutting the sheets to the required length to surround the sewer entirely, embedding it in the concrete as fast as concrete was placed, in the same manner as was done with the expanded metal except over the center where, on account of its pliability, the fabric was held the proper distance from the lagging by a number of 2-in. blocks which were removed as the concrete was placed. The wire cloth, being all in one sheet, can be placed a little more expeditiously than expanded metal, but, on the other hand, the expanded metal holds its position better in the concrete, since it is more rigid.
We quote now from Mr. Hatton's letter: "The major portion of concrete was mixed by machine at a cost of 66 cts. per yard, including wheeling to place, coal and running of mixing machine, wages being $1.50 per day of 8 hrs, Stone was delivered alongside of machine and all material had to be wheeled in barrows upon the platform, and after mixing to the sewer. Placing and ramming concrete around the forms cost 39 cts. per cu. yd., additional. Setting forms in invert cost 2 cts. per cu. yd., setting centers 7 cts. per cu. yd. Cost of setting forms and centers includes placing steel metal. Each lineal foot of 9¼ ft. sewer contained 1 cu. yd. of concrete, although the section only calls for 0.94 cu. yd. The excess was usually wasted by falling over sides of forms or being made too thick at crown.
"This yard of 1-2-5 concrete cost in place as follows (record taken as an average of several-days' run):
| Cement, 1.31 bbls. at $1.30 | $1.703 |
| Stone, 0.84 cu. yds. at $1.21 | 1.016 |
| Stone dust, 0.42 cu. yd. at $1.21 | 0.508 |
| Labor at 18¾ cts. per hour | 0.987 |
| Labor setting forms and setting metal | 0.045 |
| Cost of forms (distributed over 1,800 ft. of sewer) | 0.082 |
| 40 sq. ft. expanded metal at 4¼ cts. | 1.700 |
| Labor plastering invert | 0.070 |
| ——— | |
| Cost per ft., or per cu. yd. | $6.111 |