The cost per cubic yard was thus $6.26. Wages were $1.75 per day.
METHOD AND COST OF MOLDING CULVERT PIPE, CHICAGO & ILLINOIS WESTERN R. R.—During 1906, the Chicago & Illinois Western R. R., Mr. O. P. Chamberlain, Chief Engineer, built a number of culverts of concrete pipe with an interior diameter of 4 ft., and 6-in. shells. Fig. 176 shows the forms in which the pipe was molded. Both forms are of ordinary wooden tank construction. The inner form has one wedge-shaped loose stave which is withdrawn after the concrete has set for about 20 hours, thus collapsing the inner form and allowing it to be removed. The outer form is built in two pieces with 2×⅝-in. semi-circular iron hoops on the outside, the hoops having loops at the ends. The staves are fastened to the hoops by wood screws 1¾ ins. long driven from the outside of the hoop. When the two sides of the outer form are in position, the loops on one side come into position just above the loops on the other side, and four ¾-in. steel pins are inserted in the loops to hold the two sides together while the form is being filled with concrete and while the concrete is setting. After the inner form has been removed, the two pins in the same vertical line are removed and the form opened horizontally on the hinges formed by the loops and pins on the opposite side. The inner and outer forms are then ready to be set up for building another pipe.
Fig. 176.—Form for Molding Culvert Pipe.
The concrete used in manufacturing these pipes was composed of American Portland cement, limestone screenings and crushed limestone that has passed through a ¾-in. diameter screen after everything that would pass through a ½-in. diameter screen had been removed. The concrete was mixed in the proportions of one part cement to three and one-half parts each of screenings and crushed stone. All work except the building of the forms was performed by common laborers. In his experimental work Mr. Chamberlain used two laborers, one of whom set the forms, and filled them and the other of whom mixed the concrete. The pipes were left in the forms till the morning of the day after molding. The two laborers removed the forms filled the day before, the first thing in the morning, and proceeded to refill them. The average time the concrete was allowed to set before the forms were removed was 16 hours. Mr. Chamberlain believes that with three men and six forms the whole six forms could be removed and refilled daily. Based on the use of only two forms with two laborers removing and refilling them each day, and on the assumption that a single set of forms costing $40 can be used only 50 times before being replaced, Mr. Chamberlain estimates the cost of molding 4-ft. pipes as follows:
| 2 per cent, of $40 for forms | $0.80 |
| 1.1 cu. yds. stone and screenings at $1.85 | 2.04 |
| 0.8 bbls. cement at $2.10 | 1.68 |
| 10 hours' labor at 28 cts. | 2.80 |
| —— | |
| Total per pipe | $7.32 |
This gives a cost of $1.83 per lineal foot of pipe or practically $7 per cu. yd. of concrete. The pipe actually molded cost $2.50 per lin ft., or $9.62 per cu. yd. of concrete, owing to the small scale on which the work was carried on—the laborers were not kept steadily at work.
The pipes were built under a derrick and loaded by means of the derrick upon flat cars for transportation. At the culvert site they were unloaded and put in by an ordinary section gang with no appliances other than skids to remove the pipes from the cars. As each four-foot section of this pipe weighs about two tons, it was not deemed expedient to build sections of a greater length than 4 ft., to be unloaded and placed by hand. On a trunk line, however, where a derrick car is available for unloading and placing the pipes, there is no reason why they should not be built in 6 or 8-ft. sections.