Concrete Construction: Methods and Costs

by Halbert Powers Gillette; Charles Shattuck Hill

Fig. 269.—Jackson Concrete Sewer Pipe.

Pipe Molding.—The pipe is molded endwise. A bottom plate so shaped as to form the hub or receiving end of the pipe is set up. On the upper or inner flange of this cast iron bottom plate is set the core defining the inside diameter of the pipe; this core is in four segments of sheet steel. The longitudinal reinforcing bars are next inserted in slots in the bottom plate and the outside form of sheet steel is then set up on the lower and outer flange of the bottom plate. Spacing clips on the top edge of the outer shell hold the tops of the reinforcing bars in position. The concrete is then shoveled into the annular mold and tamped until it reaches the level for the first circumferential reinforcing bar; this is then placed by removing the spacing clips, threading the hoop over the longitudinal bars and sliding it down to position. Filling and tamping then proceeds until the second hoop is to be placed; this is placed exactly like the first, and filling and tamping then proceeds until the mold is filled. At the St. Joseph work a 1-2-3 mixture, with crushed limestone aggregate ranging from pea size to 1-in. stone was used. The molding was done in tents which were heated by coke fires in salamanders in freezing weather.

Pipe Laying.—In laying, the pipes are handled and lowered into position just as are cast iron water pipe. Successive lengths are placed by inserting the spigot ends into the chamfered hub ends and then threading the tie hoop through the hooked ends of the projecting longitudinal reinforcing bars. A strip of galvanized iron is then passed under the pipe and bent up so as to girdle the circumferential groove except for a space at the top; the groove is then poured with a wet 1-2 cement mixture, which, when hardened, completes the joint.

COST OF MOLDING SMALL CEMENT PIPE.—Mr. Albert E. Wright gives the following account of the method and cost of molding and laying 6 to 12-in. cement pipe for irregular work at Irrigon, Ore.: The pipe was 6 to 12 ins. inside, made of Portland cement and clean, sharp sand of all sizes up to very coarse. The mortar was mixed rather dry, but very thoroughly, using 14.1 cu. ft. of sand to 1 bbl. of cement, or very closely a 1 to 4 mixture. From six to seven buckets of water were used to each barrel of cement, except for the 6-in. pipe, for which the mortar had to be made somewhat stiffer in order to remove the inner form, which was not made collapsible as in the larger sizes.

The forms were sheet iron cylinders with a longitudinal lap joint that could be expanded after molding the pipe, and removed without injuring the soft mortar. The inner form was self-centering, so that there was little variation in the thickness of the pipe.

Four men were required in making cement pipe by hand; one mixed the mortar, and wheeled it to the place of work; another threw it into the form a little at a time with a hand scoop; a third rammed it with a tamping iron, and a fourth kept the new pipe sprinkled, and applied a coat of neat cement slurry to the inside when it was sufficiently hard. In molding, the form of the bell at the bottom was secured by an iron ring that was first dropped into the form, and the reverse or convex form at the top was made with a second ring. While still in its form the pipe was rolled or lifted into its place in the drying yard, and the form was then carefully removed. A very slight blow in removing the form would destroy the pipe, and a considerable number, especially of the larger sizes, collapsed in this way, and had to be remolded. To avoid handling, the pipe was stacked on end a few feet from the place of mixing, the form being moved as the yard filled with pipe. One crew of four men could make about 250 joints or 500 lin. ft. of pipe a day.

As soon as hard enough, the pipe was turned end for end, and was then kept wet for several weeks before being laid. The coating of neat cement on the inside was applied with a short whitewash brush, and was a small item in the cost.

In laying, the trench was carefully finished to grade in order to have the joints close nicely, and the ends were well wet with a brush. The mason then spread mortar, mixed 1 to 2, on the end of the pipe, and laid a bed of mortar at the bottom of the joint. He then jammed the section into place, and swabbed out the inside of the joint with a stiff brush, to insure a smooth passage for the water. A band or ring of mortar was spread round the outside of the joint as an additional reinforcement. One barrel of cement would joint about 300 sections of pipe. The materials cost as follows: Portland cement, per bbl., $4.45; labor, per day, $2; foremen, per day. $2.50 to $3; hauling, per load mile (1 cu. yd.), 20 cts.; sand, free at pit; water, free.

The pipe was all of a 1-4 sand and cement mortar, and the amount of cement in one foot of pipe was arrived at by assuming that where the sand has voids in excess of the cement used, the mortar will occupy 1.1 (see Chapter II) times the space of the dry sand, which yields the following formula: