The plant used in the construction of the Quebec Cantilever Bridge2 consists of a No. 5 rotary stone crusher, with a maximum capacity of thirty cubic yards per hour, discharging into a bucket conveyor which delivered the crushed stone in a small storage bin directly over the concrete mixer. The latter was of the cubical form, five feet on a side, with a capacity of two cubic yards of concrete per batch.
1 Emile Low, U. S. Asst. Engr., Engineering News, Oct. 8, 1903.
2 Engineering News, Jan. 29, 1903.
The cement warehouse and the sand supply were near the mixer. Cement and sand were hoisted to the top of the machine in boxes, with bottoms inclined at forty-five degrees, each holding a batch, and dumped into the charging hopper of the mixer as required. The mixer was elevated sufficiently to permit dumping the concrete directly in a skip on a car, the latter being run to the work. The skip was handled by guy derricks. This plant made the remarkable record of two hundred eighty-five batches in ten hours, and on one occasion turned out one hundred fifty batches in five hours, or, if all were two-yard batches, at the rate of sixty yards per hour.
For the construction of the Galveston sea wall two concrete mixing and handling machines were designed,1 each consisting of a double-deck car, on eight wheels, with two revolving derricks, one on either side for handling materials and concrete, respectively. The materials are delivered on tracks beside the mixer car track which is parallel to the sea wall. One derrick hoists the loaded skips from the material cars and deposits them on the upper deck of the mixer car, whence they are delivered in measured quantities to the Smith Rotary Mixer located on the lower deck. When mixed, the concrete is dumped into a skip, which is handled by the second derrick and dumped into the forms.
343. For work having similar requirements to that just described, namely, for retaining walls on track elevation, Chicago & Western Indiana R. R. at Chicago, the problem was met in a somewhat different manner.2 An ordinary flat car was double decked and the space between decks inclosed to protect the machinery, including the Drake Concrete Mixer. Cars containing cement, sand and stone were coupled in the rear of the mixer car. These material cars were fitted with removable wheeling platforms, making a complete runway along the sides of the cars. The materials were delivered at the mixer car in wheelbarrows and dumped into measuring boxes, and thence fed to the mixer. The concrete was delivered on a belt conveyor mounted on a boom with turntable permitting nearly half of a revolution. The outer end of the conveyor could be raised or lowered as desired, and the concrete was thus deposited where needed in the work. To permit the mixer train to move along the track, the two ends of a cable were made fast to anchorages placed about a thousand feet apart, one in front of, and the other behind, the train. As this cable had about eight turns around a winding drum on the mixer car, the train could be propelled forward or backward at will.
1 Engineering News, Jan. 15, 1903. 2 Ibid., Feb. 28, 1901.
A somewhat similar form has been used for street work, where the mixer and electric motor are mounted on a truck with a swinging conveyor for the delivery of concrete anywhere between the curbs. A pair of wheels in the rear serve to carry an inclined runway for wheelbarrows by which the materials are delivered to the mixer.
344. The data for the following items concerning the Cost of mixing concrete for culverts on railroad work are taken from an article in Engineering News.1
"The plant is located on a hillside with the crusher bins above the loading floor or platform that extends over the top of the mixer, so that crushed stone can be drawn directly from the chutes of the bins and wheeled to the mixer. The sand is hauled up an incline in one-horse carts and dumped on the floor, and is also wheeled in barrows to the mixer." The capacity of the cubical mixer used was seven-eighths cubic yard. The Cost of mixing and placing was as follows:
Cost per Day.
Cost per Cu.Yd.
One foreman assumed at $2.50 per day......
Three men supplying mixer at $1.50 per day.....
One engineman assumed at $2.00 per day......
Fuel and supplies assumed at.........
$2.50 4.50 2.00 200
Cost of mixing 40 cu. yds...........
Two men loading wheelbarrows at $1.50......
Four men wheeling wheelbarrows at $1.50......
Cost of wheeling 40 cu. yds. 100 feet.......
Four men ramming at $1.50..........
Four men wheeling in and bedding large stone in concrete at $1.50................
Total Cost mixing and placing........
1 Location and Construction of the Ohio Residency, Pittsburg, Carnegie & Western R.R., Engineering News, May 21, 1903.
It is not explained why six men are required to load and wheel forty cubic yards one hundred feet in ten hours, but it may be that these men assisted in other operations.
Another contractor on the same work used a different form of mixer with much lower loading platform and handled the mixed concrete with skips and derrick. The Cost is estimated as follows:
1 man feeding mixer............... $1.50
1 engineman assumed at ............. 2.50
1 derrick man assumed at............. 2.50
2 tagmen swinging boom and dumping....... 3.00
6 barrowmen supplying mixer........... 9.00
2 men tamping................. 3.00
Fuel, supplies, etc................ 1.50
Cost of mixing and placing 50 cu. yds. . . $23.00 Cost per cu. yd., 46 cents.