A pilot study for retrospective evaluation of cured-in-place pipe (CIPP) rehabilitation of municipal gravity sewers

Abstract Pipe rehabilitation and trenchless pipe replacement technologies have seen a steadily increasing use over the past 30–40 years. Despite the massive public investment in the rehabilitation of the US water and wastewater infrastructure, there has been little formal and quantitative evaluation of whether rehabilitation technologies are performing as expected and whether rehabilitation is indeed cost-effective compared to replacement. This paper describes the results of a pilot project for the retrospective evaluation of cured-in-place pipe (CIPP) liners. The pilot testing used CIPP samples from both large and small diameter sewers in two cities: Denver, CO and Columbus, OH. Testing on the liners included: thickness, annular gap, ovality, density, specific gravity, porosity, flexural strength, flexural modulus, tensile strength, tensile modulus, surface hardness, glass transition temperature, and Raman spectroscopy. In addition, environmental data was gathered as appropriate to each retrieval process including: external soil conditions and pH, and internal waste stream pH. Summaries of the test results and a discussion of their implications for CIPP performance are provided in this paper. All of the samples retrieved from the four locations involved in the pilot study testing were in excellent condition after being in use for 25 years, 23 years, 21 years and 5 years, respectively. Overall, it is concluded that there is no reason to anticipate that the liners evaluated in this pilot study will not last for their intended lifetime of 50 years and perhaps well beyond.