Influence of elevated temperatures on the bond behaviour between concrete and NSM-CFRP strips

Abstract

This paper presents an experimental and numerical study about the effects of elevated temperatures on the bond behaviour between concrete and carbon fibre reinforced polymer (CFRP) strips installed according to the near-surface mounted (NSM) technique. In the first part of this study, single-lap shear tests were performed on concrete prisms strengthened with CFRP strips inserted into slits pre-cut in the concrete cover and bonded with an epoxy-based adhesive. The specimens were first heated up to the target temperature (from 20 to 270 °C, measured in the bonding adhesive) and then loaded up to failure. The results obtained show that with increasing temperatures (i) the bond strength is significantly reduced, (ii) the strain distribution along the bonded length becomes closer to linear, and (iii) the failure mode changes from CFRP tensile failure at 20 °C and 50 °C to adhesive failure in the CFRP-adhesive interface at higher temperatures. In the second part of this study, based on the results obtained in the experiments, a numerical procedure was developed to determine the local bond-slip laws at different elevated temperatures. In general, the stiffness and maximum bond stress of the obtained laws decreased with increasing temperatures; in addition, the predicted load vs. slip curves fit well the experimental counterparts.