8 BULLETIN COG, U. S. DEPARTMENT OF AGRICULTURE. 



The cost of lajdng is estimated at about 1 cent per foot for each 

 inch of diameter of pipe, but conditions may arise where it may be 

 much more, especially if siphons are installed. 



MANUFACTURE OF PLAIN CONCRETE PIPE. 



Plain concrete pipe may be divided into two general classes — 

 hand-tamped and machine-made pipe. Hand-tamped pipe is made by 

 tamping concrete between inside and outside collapsible forms. The 

 forms usually run from 6 inches to 36 inches inside diameter. The 

 pipe is made for the most part in 2-foot lengths, although some is 

 made 30 inches in length. In making hand-tamped pipe, the forms 

 are set up vertically on the ground or on a platform. Concrete is 

 then poured between the forms by one man while another tamps. 

 When the pipe is finished it is reamed off on top with a special 

 reamer. The inside form is first removed by collapsing it and the 

 pipe carried to the proper place in the yard, where the outside form 

 is removed and the pipe allowed to set. Pipe should always be 

 kept thoroughly moist for at least 10 days before it is cured. If 

 the concrete is moist enough when the pipe is tamped the outside 

 form may be stripped, i. e., pulled off vertically, without loosening 

 the jacket. If so-called dry pipe is made, the forms can not be 

 stripped, but the outside form must be loosened before lifting it off. 

 The tongue and groove ends of the pipe are made to assist in lay- 

 ing. The groove end, which is usually a simple inside taper on the 

 bottom of the pipe, is made by dropping a cast-iron ring between 

 the forms. This ring is beveled to conform to the groove of the 

 pipe, and is allowed to remain on the bottom of the pipe until the 

 concrete has set sufficiently to move the pipe. (Fig. 3.) The tongue 

 end of the pipe is made when the pipe is finished, and is accom- 

 plished by whirling the reamer over the top before the forms are 

 removed. Some hand-tamped pipe is made with bell and spigot 

 ends similar to the ordinary clay sewer pipe. When pipe is made in 

 this way, the outside form is split so that the forms can be removed 

 laterally. 



Pipe machines 2 are roughly classified as tamping machines and 

 troweling machines. Some tamping machines tamp the pipe very 

 similarly to the hand-tamping process. The mechanism of most of 

 these machines causes the pipe to revolve under the tamper while 

 the concrete is poured in between the forms. A pneumatic air tamper 

 may be used to tamp the pipe. The apparatus operating the air 

 tamper is suspended over the forms, the air tamper being guided 

 around the shell of the pipe by one man, while another feeds the 

 concrete. The pneumatic hammer delivers about 700 blows a minute 



2 Arizona State Experiment Station Bulletin No. 86, by G. E. P. Smith. 



