"Concrete" Proof of Clay's Durability - December 2002
ANN ARBOR, Mich. – A sewer pipe rehabilitation project on the campus of the University of Michigan at Ann Arbor proved to be a major test of not only the pipe's longevity, but particularly its durability, and once again clay was up to the challenge.
Inside a 150-ft. span of the pipe system, it was discovered that concrete ranging in depth from 2" to 12" was creating a massive obstruction. The source of the concrete was believed to be from a construction crew that had recently poured concrete floors in a nearby building. In addition, this 18" clay pipe sanitary sewer, originally installed between 1917 and 1927, had additional soil deposited over the pipe and was now withstanding weight that should have caused the pipe to fail. But a closed-circuit television inspection revealed that although it was seriously obstructed, the pipe was not in any threat of collapsing.
Samuel Winger, who eventually oversaw the successful attempt at removing the concrete, stated there was the equivalent of "two full truckloads of finely grained concrete" causing this obstruction. Winger is a field engineer for HydroChem Industrial Services, Inc.
Prior to the successful removal of the concrete by using acid, the clay sewer pipe had been subjected to a number of other unsuccessful methods. Initially, another company used a high-pressure water blaster in an attempt to remove the concrete, but the process was slow, and it was difficult to direct the energy into the concrete. Therefore, another method had to be implemented.
After other attempts failed, HydroChem came onto the scene using a hydrochloric acid removal process. Dow Chemical had experienced success with this process, but it was relatively new to the sewer industry. As lab tests had predicted, HydroChem's process dissolved the concrete, while the clay resisted the effects and remained unharmed.
"We blocked off two ends of the pipe so that we could recirculate the acid and test it in given intervals," said Winger. "We used extremely high concentrations of the hydrochloric acid to completely dissolve the concrete. Just as our lab tests had predicted, the acid successfully restored the flow, but had absolutely no effect on the clay pipe."
Pete Perala, utilities engineer, Field Services Division for the city of Ann Arbor, was the site engineer for the project. "The high-strength concrete, combined with the pipe depth and its proximity to other utilities, made this an extremely difficult project," stated Perala. "When we realized we needed to chemically dissolve the obstruction, it was our good fortune that the sewer pipe was clay. Due to clay's inert composition and its chemical resistance, a challenging situation did not become disastrous."
The vitrified clay allowed for the concrete to be successfully dissolved. Then, after evaluating several different options for the completion of the project, a CIPP liner was placed in this particular portion of the sewer, and the rehabilitation project was finished.
The hydrochloric acid method of removing the concrete did not require digging up and replacing the sewer pipe, so it saved the university a substantial amount of time and money. If the pipe had not been made from clay, the resolution of the problem would have been much more costly and time consuming.
"This is another prime example of not only the longevity of clay pipe but the durability as well," stated Dan DeFillipi, representative for The Logan Clay Products Company. "There are many advantages to using clay. It's environmentally safe, and in terms of chemical degradation, it is nearly impervious, which is very important when talking about corrosion. Today's clay is the best way for tomorrow."