The mixture can be rammed into the molds by hand or machine. A machine-made pipe is preferable as it produces a more even and stronger product. There are two types of machines for this purpose. One type consists of a number of tamping feet which deliver about 200 blows to the minute with a pressure of about 800 pounds per square inch of area exposed. In the other type a revolving core is drawn through the pipe, packing and polishing the concrete as it is pulled through, with special provision for packing the bell of the pipe. The tamping machines can make 1,500 feet of small size pipe to 300 feet of 24–inch pipe in a day. Machines of the second type can make 750 feet of 8–inch to 200 feet of 30–inch pipe in 30–inch lengths in 9 hours. The inside and outside forms for a 24–inch pipe are shown in Fig. 74 as used with the tamping machines. The forms are swabbed with oil before being filled in order to facilitate their removal. In making a Y-branch or other special, a hole is cut in the pipe or mold the size of the joining pipe which is then set in place and the joint wiped smooth with cement.
| TABLE 38 | |||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Properties of Cement Concrete Sewer Pipe | |||||||||||||
| 1917 Specifications of American Society for Testing Materials, with Subsequent Revisions | |||||||||||||
| Internal Diameter, Inches | Laying Length, Feet | Diameter at Inside of Socket, Inches | Normal Annular Space, Inches | Depth of Socket, Inches | Taper of Socket | Minimum Thickness of Barrel, Inches | Limits of Permissible Variations | Minimum Crushing Strength, Pounds per Linear Foot at End of Diameter | Maximum Absorption, Per Cent | ||||
| Length, Inch per Foot (-) | Internal Diameter, Inches | Depth of Hub (-) Inches | Thickness of Barrel (-) Inches | ||||||||||
| Spigot (±) | Socket (±) | ||||||||||||
| 6 | 2, 2½, 3 | 8¼ | ½ | 2 | 1 : 20 | ⅝ | ¼ | 3 16 | 3 16 | ¼ | 1 16 | 1430 | 8 |
| 8 | 2, 2½, 3 | 11 | ⅝ | 2¼ | 1 : 20 | ¾ | ¼ | ¼ | ¼ | ¼ | 1 16 | 1430 | 8 |
| 10 | 2, 2½, 3 | 13¼ | ⅝ | 2½ | 1 : 20 | ⅞ | ¼ | ¼ | ¼ | ¼ | 1 16 | 1570 | 8 |
| 12 | 2, 2½, 3 | 15⅝ | ⅝ | 2½ | 1 : 20 | 1 | ¼ | ¼ | ¼ | ¼ | 1 16 | 1910 | 8 |
| 15 | 2, 2½, 3 | 19¼ | ⅝ | 2½ | 1 : 20 | 1¼ | ¼ | ¼ | ¼ | ¼ | 3 32 | 1960 | 8 |
| 18 | 2, 2½, 3 | 22¾ | ⅝ | 2¾ | 1 : 20 | 1½ | ¼ | ¼ | ¼ | ¼ | 3 32 | 2200 | 8 |
| 21 | 2, 2½, 3 | 26½ | ¾ | 2¾ | 1 : 20 | 1¾ | ¼ | 5 16 | 5 16 | ¼ | ⅛ | 2590 | 8 |
| 24 | 2, 2½, 3 | 30¼ | ¾ | 3 | 1 : 20 | 2⅛ | ⅜ | 5 16 | 5 16 | ¼ | ⅛ | 3070 | 8 |
| 27 | 3 | 34 | ⅞ | 3¼ | 1 : 20 | 2¼ | ⅜ | 5 16 | ⅜ | ¼ | ⅛ | 3370 | 8 |
| 30 | 3 | 38 | 1 | 3½ | 1 : 20 | 2½ | ⅜ | ⅜ | ⅜ | ¼ | ⅛ | 3690 | 8 |
| 33 | 3 | 41½ | 1 | 4 | 1 : 20 | 2¾ | ⅜ | ⅜ | ⅜ | ¼ | 3 16 | 3930 | 8 |
| 36 | 3 | 45½ | 1¼ | 4 | 1 : 20 | 3 | ⅜ | ½ | ½ | ¼ | 3 16 | 4400 | 8 |
| 39 | 3 | 49 | 1¼ | 4 | 1 : 20 | 3¼ | ⅜ | ½ | ½ | ¼ | 3 16 | 4710 | 8 |
| 42 | 3 | 53 | 1½ | 4 | 1 : 20 | 3½ | ⅜ | ½ | ½ | ¼ | 3 16 | 5030 | 8 |
After the removal of the mold the pipe may be cured by the water or the steam process. Hanson states:
By the former the pipe are simply set on the floor of the plant and as soon as they are sufficiently strong so that they can be sprinkled with water without falling down; sprinkling is commenced and continued at such intervals for 6 or 7 days that the pipe will be moist at all times. This is a slower process than steam curing. It is also less uniform and less subject to control than where the product is cured by steam.
In the steam process the pipe is exposed to low-pressure steam with plenty of moisture in a closed receptacle for 24 hours, or until hardened. It has been found by tests that pipes sprinkled for 28 days are as strong as steam-cured pipes.
The dimensions of cement concrete sewer pipe as recommended by the Am. Society for Testing Materials are shown in Table 38.
The following has been abstracted from the description of the manufacture of one form of concrete pipe by G. C. Bartram.[[53]] All pipe are manufactured in 4–foot lengths near the site at which they are to be installed because of their great weight, for example, 36–inch pipe weighs one ton. The plant for the manufacture of the pipe consists of cast-iron bottom and top rings for each size to be used on the job, and inside and outside steel casings. There are three bases for each steel casing as the pipes stand on the bases for 72 hours and the steel casing remains on for only 24 hours after the concrete has been poured. The pipes are then lifted off the bases and stored for aging. The pipes are cast with the spigot end up.
The concrete is ordinarily mixed in the proportions of 1 : 2 : 4. The materials are placed in the mixer in the following order: first, the stone, then the sand, then the cement, and finally the water. Sufficient water is added to make the concrete flow freely. In cold weather or for a hurry-up job the molds are covered with canvas and are steamed for 2 or 3 hours immediately after the concrete is poured. The molds are then removed but the pipe should be steamed before use. Otherwise they are allowed to stand 72 hours, as explained above. In cold weather the steam is used to prevent freezing and not to hasten the completion of the pipe.
Fig. 75.—Triangle Mesh Reinforced Concrete Pipe.
As made by the Am. Concrete Pipe and Pile Co., Chicago.