The Effect of Porosity and Degree of Cure in Needled Felt CIPP on Short-Term and Long-Term Flexural Properties

Abstract

The life extension capabilities of CIPP for pipe rehabilitation are well established. The measured long-term flexural modulus creep retention factor (CRF) of CIPP has been employed to design numerous installations where the actual life extension has later been demonstrated. The CRF is determined by the CIPP system manufacturer through type testing of the resin/felt material. Accepted industry consensus is that field prepared CIPP samples can exhibit lower short-term flexural properties than the short-term flexural properties which are determined by CIPP system suppliers during type testing. Factors such as installation conditions or crew experience can contribute to flexural properties of field samples occasionally falling below the specified design minimums. This characteristic of CIPP field installations has been referred to as natural variation. Two commonly observed anomalies which can be related to lower short-term flexural properties in CIPP field samples are ineffective resin saturation of the needled felt and incomplete curing. Since in needled felt CIPP systems, the resin itself is responsible for achieving the ultimate flexural properties, failure to fully saturate the voids within the felt with resin or for the resin to fully cure can result in lower flexural performance. Current design practice assumes that CIPP field samples which exhibit short-term flexural properties lower than those determined during type testing will nonetheless exhibit long-term creep performance which is similar to the creep behavior originally determined by the system supplier during type testing.