Hygrothermal conditioning of wet-layup CFRP-concrete adhesive joints modified with silane coupling agent and core-shell rubber nanoparticles

The adhesive bond between externally bonded fiber-reinforced polymer (FRP) repairs and the concrete substrate can significantly deteriorate under hygrothermal conditions. The present study evaluated the epoxy adhesive toughening with core-shell rubber (CSR) nanoparticles and concrete surface functionalization with an epoxy-functional silane coupling agent as a means of improving the bond durability under hygrothermal exposure. To determine the effect of environmental degradation, beam bond test specimens were subjected to control conditions (standard laboratory conditions: 23 +/- 2 degrees C and RH 50 +/- 10%) and a hygrothermal accelerated conditioning protocol (ACP) (water immersion at 45 +/- 1 degrees C) for 8 weeks. Bond test results indicate that CSR toughening and silane coupling agent can improve FRP-concrete adhesive bond strength retention following accelerated conditioning by up to 15% over that of neat epoxy. Following accelerated conditioning, CFRP coupons prepared with CSR-modified epoxy retain their mechanical properties, while the CFRP prepared with the neat epoxy exhibited a significant reduction in strength (40%) and elongation (54%). CSR nanoparticles demonstrated good compatibility with the base epoxy resin, as evidenced by differential scanning calorimetry (DSC) glass transition temperature measurements. (C) 2019 Elsevier Ltd. All rights reserved.