Thermo-Cyclic Degradation Evaluation of Sewer CIPP Resin by ASTM Standard Tests and Raman Spectroscopy

This paper presented the study of potential degradation due to prolonged moist elevated thermo-cyclic loading on thermosetting resins that are used in cured in place pipe (CIPP) liner systems. Coupon samples were prepared from four different resins (high and low temperature vinyl esters, epoxy, and polyester) that were subjected to the thermo-cyclic loading. Mechanical strength evaluation tests were performed on the samples following ASTM D638-14 and ASTM D790-15e2 standards. The ASTM results showed decreased tensile and bending strength and an increased bending and tensile modulus for three of the resins (epoxy, polyester, and low temperature vinyl ester), which indicated as resin embrittlement/degradation, whereas the high temperature vinyl ester did not show any significant change in all three mechanical properties. Raman spectroscopic characterization of the three embrittled resins from the thermal cycling showed a significant decrease in the Raman band intensities, while the high temperature vinyl ester spectrum remained unchanged, also showing a correlation between the Raman spectra and resin degradation. The ASTM F1216-16 standard does not presently include a thermal loading factor, indicating a possible need for introduction of this into the current design equation for CIPP liner systems.