wide) for highway loading cost $25 to $33 per lineal foot, depending on 
the span. This cost includes all labor and materials necessary for 
final positioning and securing of the span. On the basis of cost per 
cubic yard, it appears that precast reinforced concrete is roughly two- 
thirds that of cast-in-place for simple and small structures. Pre- 
stressed, precast concrete costs roughly twice that of reinforce concrete. 
Fabrication of Cylindrical Elements 
Standard Technique. A successful and efficient technique for 
fabricating large prestressed concrete pipe is presently being used in 
the California State Water Project. Pipe sections 20 feet in outside 
diameter with walls 20 inches thick are fabricated at a temporary plant 
located on a 45-acre site near the Castaic Dam, fifty miles north of 
Los Angeles. 
The fabrication technique consists of two basic steps. First, 
concrete is placed into vertical, cylindrical steel forms and vibrated. 
A relatively thin steel membrane is imbedded in the resulting concrete 
"core'' to give the final product complete impermeability to seepage in 
either direction. 
After a short period of curing, the core has gained sufficient 
strength to be transported and placed vertically on a large turn-table 
where it is rotated rapidly while prestressing wire is wrapped around 
the circumference. The prestressing tension in the wire can be as high 
as 170,000 pounds per square inch. After the first layer of wire is 
finished, a layer of concrete is applied, allowed to dry, and a second 
layer of wire is wrapped. A final coating of concrete follows. Up to 
16 miles of prestressing wire have been installed in a single pipe section. 
The pipe sections are made in 20-foot lengths and weigh 150 tons. 
To handle and position these large objects, two special pieces of equip- 
ment were designed and built. One, called the "Liftmobile" is a large 
traveling frame, towed by a standard rubber-tired caterpiller tractor, 
which can lift, transport, and accurately position the sections onto 
the prestress and cement mortar coating turn-tables. When the pipe is 
ready for installation, the Liftmobile tips it on its side where it 
can be picked up by a second vehicle, the ''Pipemobile.'' The Pipemobile 
is a 63-foot long, 20-foot high rubber-~tired machine which can be backed 
through a pipe section, lift it, and move at 12 miles per hour to the 
final installation point (Figure 5.4). The Pipemobile operator can 
position the 150-ton sections to within the 1/8-inch tolerance specified 
for the project. 
High quality concrete is used for the pipe section. Depending on 
the location of the section, compressive strengths vary from 4,500 to 
6,000 psi. The production rate varies from about 350 to 700 cubic 
yards per day. The entire batching system is automated and no difficulties 
in quality control have been encountered. 
With two eight-hour shifts and a total payroll of 60, the factory 
comfortably produces eight 20-foot sections per day. Construction costs 
529) 
