Page 183 - Trenchless Technology Piping Installation and Inspection

148 Cha pte r F o u r

move differentially with respect to the adjacent length. RCCP, on
the other hand with their longer joint lengths are checked for longi-
tudinal beam strength.
The susceptibility of concrete pipe to both internal and external
corrosion has also come to the forefront in recent years. For sanitary
sewers where the possibility of hydrogen sulfide generation is a
possibility, many engineers and city authorities now require con-
crete pipes to be internally lined because of their experience with its
deterioration. Studies suggest that unlined RCP can show signs of
deterioration in as little as 5 years after installation. Failures owing
to hydrogen sulfide attacks and internal microbiological-induced
corrosion at the crown of RCP have also been a topic of study in
recent years. In pressure applications, the loss of prestress as a result
of reinforcement wire corrosion and breakage in PCCP can lead to
pipe failures in high-pressure lines. Research to assess the risks of
such failures has been undertaken by various engineers and enti-
ties. The preceding discussion about hydrogen sulfide corrosion is
obviously not an issue in storm sewer applications.

Asbestos-Cement Pipe
With the asbestos-related litigations of the 1980s, bans were placed
on all construction materials that used asbestos. Pipe was no excep-
tion. In 1986, the U.S. EPA published a proposed regulation on the
commercial uses of asbestos in which a ban on the manufacture and
installation of asbestos-cement (AC) pipe was proposed; this pro-
posal was later carried out. Many AC manufacturing plants relo-
cated to other countries, and production in the United States came
to a complete stop. In the early 1990s, the ban on the pipe was
lifted, but today AC pipe is no longer manufactured in the United
States. Many countries of the world, including Mexico, continue to
specify and install asbestos-cement pipe for both water and sewer
applications.
Worldwide usage of AC pipe increased from 200,000 miles in the
1950s to 2 million miles in 1988. In the United States, it was estimated
that by 1988, over 300,000 miles of AC pipe was in service in water
systems. According to the Association of Asbestos Cement Product
Producers, AC pipe is still used in the southwestern United States,
but it must be imported from Mexico. However, this usage is cer-
tainly an anomaly. The hazards of asbestos inhalation are increased
during removal of the pipe, so utilities have chosen to keep them
in the ground. These pipes are regularly tapped and maintained,
so a working knowledge of the material is helpful. There are no
known instances of trenchless municipal piping construction with
AC pipe.

Manufacturing Asbestos-cement water and sewer pipe is a fiber-
reinforced, cementitious product, composed of an intimate mixture