Fig. 107.—End Elevation of Traveling-Mixer, Galveston Sea Wall.
Placing the concrete in the forms is generally required to be done in layers; with wet mixtures this means little more than distributing the concrete somewhat evenly along the wall and slicing and puddling it to get rid of air and prevent segregation. Where mortar facing is required the face form described in Chapter VIII may be used. A reasonably good surface can be secured without mortar facing by spading the face. With dry concrete, placing and ramming in layers, calls for such care as is necessary in dry concrete work everywhere. Where new concrete has to be placed on concrete placed the day before, good bond may be secured and the chance of efflorescence be reduced by the methods described in Chapter VIII.
WALLS IN TRENCH.—In canal excavation, in subway work in cities, and the like, it is often necessary to dig trenches and build retaining walls in them before excavating the core of earth between the walls. The following examples of such work are taken from personal records:
Example I.—A Smith mixer was used, the concrete being delivered where wanted by a Lambert cableway of 400 ft. span. The broken stone and sand were delivered near the work in hopper-bottom cars which were dumped through a trestle onto a plank floor. Men loaded the material into one-horse dump carts which hauled it 900 ft. to the mixer platform. This platform was 24×24 ft. square, and 5 ft. high, with a planked approach 40 ft. long and contained 7,300 ft. B. M. The stone and sand were dumped at the mouth of the mixer and shoveled in by 4 men. Eight men, working in pairs, loaded the broken stone into the carts, and 2 men loaded the sand. Each cart was loaded with about 70 shovelfuls of stone on top of which 35 shovelfuls of sand were thrown. It took 3 to 5 minutes to load on the stone and 1 minute to load the sand. The carts traveled very slowly, about 150 ft. a minute—in fact, all the men on the job, including the cart drivers, were slow. After mixing, the concrete was dumped into iron buckets holding 14 cu. ft. water measure, making about ½ cu. yd. in a batch. The buckets were hooked on to the cableway and conveyed where wanted in the wall. Steam for running the mixer was taken from the same boiler that supplied the cableway engine. The average output of this plant was 100 cu. yds. of concrete per 10-hour day, although on many days the output was 125 cu. yds., or 250 batches. The cost of mixing and placing was as follows, on a basis of 100 cu. yds. per day:
| Per day. | Per cu. yd. | |
| 8 men loading stone into carts | $12.00 | $ .12 |
| 2 men loading sand into carts | 3.00 | .03 |
| 1 cart hauling cement | 3.00 | .03 |
| 8 carts hauling stone and sand | 24.00 | .24 |
| 4 men loading mixer | 6.00 | .06 |
| 1 man dumping mixer | 1.50 | .01 |
| 2 men handling buckets at mixer | 3.00 | .03 |
| 6 men dumping buckets and ramming | 9.00 | .09 |
| 12 men making forms at $2.50 | 30.00 | .30 |
| 1 cable engineman | 3.00 | .03 |
| 1 fireman | 2.00 | .02 |
| 1 foreman | 6.00 | .06 |
| 1 waterboy | 1.00 | .01 |
| 1 ton coal for cableway and mixer | 4.00 | .04 |
| ——— | —— | |
| Total | $107.50 | $1.07 |
In addition to this cost of $1.07 per cu. yd. there was the cost of moving the whole plant for every 350 ft. of wall. This required 2 days, at a cost of $100, and as there were about 1,000 cu. yds. of concrete in 350 ft. of wall 16 ft. high, the cost of moving the plant was 10 cts. per cu. yd. of concrete, bringing the total cost of mixing and placing up to $1.17 per cu. yd. As above stated, the whole gang was slow.
The labor cost of making the forms was high, for such simple and heavy work, costing $10 per M. of lumber placed each day. The forms were 2-in. sheeting plank held by 4×6-in. upright studs 2½ ft. apart, which were braced against the sides of the trench. The face of the forms was dressed lumber and all cracks were carefully puttied and sandpapered.
The above costs relate only to the massive part of the wall and not the cost of putting in the facing mortar, which was excessively high. The face mortar was 2 ins. thick, and about 3½ cu. yds. of it were placed each day with a force of 8 men! Two of these men mixed the mortar, 2 men wheeled it in barrows to the wall, 2 men lowered it in buckets, and 2 men put it in place on the face of the wall. If we distribute this labor cost on the face mortar over the 100 cu. yds. of concrete laid each day, we have another 12 cts. per cu. yd.; but a better way is to regard this work as a separate item, and estimate it as square feet of facing work. In that case these 8 men did 500 sq. ft. of facing work per day at a cost of nearly 2-½ cts. per sq. ft. for labor.
Example II.—The building of a wall similar to the one just described was done by another gang as follows: The stone and sand were delivered in flat cars provided with side boards. In a stone car 5 men were kept busy shoveling stone into iron dump buckets having a capacity of 20 cu. ft. water measure. Each bucket was filled about two-thirds full of stone, then it was picked up by a derrick and swung over to the next car which contained sand, where two men filled the remaining third of the bucket with sand. The bucket was then lifted and swung by the derrick over to the platform of the mixer where it was dumped and its contents shoveled by four men into the mixer, cement being added by these men. The mixer was dumped by two men, loading iron buckets holding about ½ cu. yd. of concrete each, which was the size of each batch. A second derrick picked up the concrete bucket and swung it over to a platform where it was dumped by one man; then ten men loaded the concrete into wheelbarrows and wheeled it along a runway to the wall. One man assisted each barrow in dumping into a hopper on the top of a sheet-iron pipe which delivered the concrete. The two derricks were stiff-leg derricks with 40-ft. booms, provided with bull-wheels, and operated by double cylinder (7×10-in.) engines of 18-HP. each. About 1 ton of coal was burned daily under the boiler supplying steam to these two hoisting engines. The output of this plant was 200 batches or 100 cu. yds. of concrete per 10-hr. day, when materials were promptly supplied by the railroad; but delays in delivering cars ran the average output down to 80 cu. yds. per day.