6 BULLETIN 906, U. S. DEPARTMENT OF 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 
