Short-Term and Long-Term Mechanical Properties of CIPP Liners

Abstract

Cured In-Place Pipe (CIPP) is a well-established method used for rehabilitation of underground pipelines. Within North America, CIPP liners used for rehabilitation of gravity pipelines are typically designed according to the design methodology provided in the non-mandatory Appendix (X1) of ASTM F1216. In the design equations provided in the standard, there are two parameters, liner long-term time-corrected modulus of elasticity and long-term time-corrected flexural strength, which are related to the CIPP long-term creep behavior. However, ASTM F1216 does not specify any methodology for characterizing the material long-term physical properties. Common industry practice has been to adopt a creep retention factor of 0.5 for all CIPP materials. With all the new CIPP product varieties that have entered the gravity pipeline renovation market since Insituform’s patent expiry, a creep retention factor of 0.5 may not apply. This thesis provides a comparison between the ASTM D2990 methodology used for the prediction of 50-year physical properties for four CIPP resins used within the City of Toronto sewers and reported in the CATT Report (2005) and the hydrostatic buckling test methodology used for long-term behavior characterization of various lining systems reported in TTC Report 302 (1994). Based on the comparison of reported results, ASTM D2990 test procedures is recommended and used for characterizing the long-term mechanical properties of nine different reinforced CIPP products used for pressure pipe. Short-term tensile and flexural properties of the nine CIPP liners are also studied. CIPP liners are typically tested for a period of 10,000 hours to evaluate the liner long-term behavior. In this thesis, long-term test analyses conducted for CIPP products used within the City of Toronto sewers based on 10,000 hours (about 1.2 years) and 96,000 hours (about 11 years) of test data are also compared. The results of this research provide a better understanding of CIPP liners short-term and long-term mechanical properties. This work also demonstrates the importance of proper and consistent interpretation of long-term test results.