6 BULLETIN 906, U. S. DEPARTMENT OE AGRICULTURE. 



by adopting better methods of molding, tamping, curing, and laying. 

 There is to-day in successful operation a large mileage of unrein- 

 forced pipe from 6 to 24 inches in diameter under heads of 25 to 40 

 feet, while other lines are under heads of 40 to 100 feet. One pipe 

 line 16 inches in diameter is successfully operating under a head of 

 80 feet. 



REINFORCED CONCRETE PIPE. 



Reinforced concrete pipe, 12 to 72 inches in diameter, is made in 

 yards or temporary sites by means of collapsible forms, the larger 

 sizes being made frequently near the point of laying to lessen the 

 cost and difficulties of transportation. The forms may be of either 

 wood or steel, or the inside form of steel and the outside of wood. 

 Either wire mesh or steel hoops may be used for reinforcing material, 

 the size and spacing of the reinforcing depending on the head to be 

 exerted against the pipe. Most reinforced pipe is made by placing 

 a cage of reinforcing wire mesh between the inside and outside forms 

 and then pouring in a wet mixture of concrete. The concrete is 

 tamped into place. The molds are removed in about 24 hours, the 

 pipe being kept moistened while curing. Most manufacturers of 

 reinforced pipe aim to use enough steel to take all tension in the pipe, 

 the concrete acting as an impervious shell only. It has been found 

 that poured concrete has a lower tensile strength than a drier mixture 

 that is well tamped, but it is difficult to tamp pipe well when wire 

 mesh reinforcing is used. 



Reinforced pipe is laid in a trench as is done with ordinary concrete 

 pipe. The joints are usually poured by the use of special forms for. 

 the purpose. Some firms put out a special lock joint, which ties the 

 longitudinal reinforcing wires of one joint to the next. It is not 

 usual however, to provide enough longitudinal wires to take all 

 stresses due to contraction, and for this reason some pipe firms have 

 provided frequent expansion joints made from a thin, crimped sheet 

 of copper. In the latter case very few, if any, longitudinal wires 

 are needed. 



Partially reinforced pipe may be made by dropping welded wire 

 rings into hand-tamped pipe while the pipe is being made. Enough 

 rings may be inserted to take all the tension, or two or three rings 

 may be used in every length, which are expected to prevent a crack 

 from one pipe being transmitted to another. 



There are several methods of constructing continuous reinforced 

 pipe one of which is shown in figure 2. This is usually done by 

 using a collapsible inner form which is moved along the trench as the 

 pipe is being made. An outside form may be used on the sides and 

 top, or the trench may be cut so as to act as the outside form. 



The Whittier Water Co., of Whittier, Calif., has laid considerable 

 quantities of continuous reinforced concrete pipe. One installation 



