Manufacture; of Cement Pipe 93 



curs, he should not try for a record output until he first learns how 

 to make pipe of high quality. 



The proportions used with hand molds are 1 of cement to 3 or 4 

 of sand and gravel or broken stone, the richer mixture being used 

 for pipe to be placed under some pressure or where sand alone is 

 used for the aggregate. In one instance recently, near Tucson, a 

 contractor made pipe with a 1 : Ayz mixture instead of 1:3 as had 

 been directed. The pipe was weak and very porous. With hand 

 molds much coarser aggregates are allowable than with the Mc- 

 Cracken pipe machine, gravel even up to on"e-half the thickness of 

 the pipe being permissible. Such particles do not interfere with 

 hand tamping, but they do prevent the formation of the desirable 

 "polished" surface with the revolving packer-head. The advantage 

 of including small gravel is that the same strength can be obtained 

 with a smaller proportion of cement. 



The greatest advantage of the hand-made pipe is that it can 

 always be made at or near the place where it is to be used. Usually 

 sand of suitable quality can be found within a moderate distance and 

 the wagon haul for sand and cement is not expensive. On the 

 other hand, machine-made pipe presupposes a factory at some cen- 

 tral location for supplying the demand for pipe in an irrigated or 

 drainage district. Only on large contracts would it be profitable to 

 move a large machine to the work. A portable Pomona machine 

 obviates this difficulty to some extent. A freight charge on the pipe 

 plus the cost of a long wagon haul might increase the cost of the 

 pipe to a point where the superior qualities of the machine-made 

 pipe would be more than offset by its greater cost. Therefore, there 

 will always be a field, small jobs and in isolated locations, where the 

 hand-made pipe will be employed. 



WET-POURED CONCRETE PIPE 



Wet-poured pipe, also, can be considered as hand-made, though 

 it differs materially from that described above. The fact that the 

 concrete is poured wet makes it necessary to leave the pipe in the 

 molds until the concrete is thoroughly set. This requires many sets 

 of forms and the investment in forms is so great that wet-poured 

 pipe is used only for large sizes. Usually, too, wet-poured pipe is 

 for pipe lines under considerable hydraulic pressure, and the pipe 

 usually is reinforced. 



Two large contracts for wet-poured pipe have been executed at 

 Tucson, one for the water-supply main from the city's supply wells 

 four miles south of Tucson to the main pumping plant on Osborne 



