Assessment of shrinkage and bond behaviour of high performance cement-based composites as a repair mortar

Abstract

There is a need to develop innovative repair materials which can overcome the challenges of cement-based repair mortars being relatively prone to shrinkage effects. In practice, free shrinkage of repair mortar is often considered as an indicator for potential cracking and delamination of applied repair mortars due to restrained shrinkage effects. As it is hard to measure restrained shrinkage directly, a restraint factor (R) can be used to correlate both. This study investigates the shrinkage characteristics of strain-hardening cementitious composites (SHCC), making use of polyvinyl-alcohol (PVA), high-density poly-ethylene (HDPE), or short glass fibres, for the repair and strengthening of existing concrete structures. Along with drying shrinkage and autogenous shrinkage, restrained shrinkage has been characterized with respect to the concrete substrate. Furthermore, pull-off tests were performed to assess the bond properties of these repair mortars. The results show around 65% higher autogenous shrinkage in high strength SHCC mixes while there was a decrease in drying shrinkage compared to the reference mix. In contradiction to what was initially expected, an increase in fibre content from 1.5 to 2.0 vol% resulted in a significant increase in autogenous shrinkage, especially in the high strength SHCC mixes. The restraint factor for all repair mortars was determined and was found to be in the range of 0.82–0.94. The pull-off tests showed an overall excellent bond behaviour of all studied mortars.