Fracture properties of CFRP–concrete bond subjected to three environmental conditions

This paper presents results of a series of single shear tests of carbon fiber–reinforced polymer (CFRP) bonded concrete prisms exposed to three environmental conditions, namely, temperature cycles, wet-dry cycles, and outdoor environment, in terms of shear stress-slip relationships and fracture energies. Temperature cycles and wet-dry cycles were chosen in a manner to study the sole effects of temperature cycles and wet-dry cycles. The maximum temperature of the temperature cycles was intentionally kept below the glass transition temperature of epoxy resin. In the wet-dry cycles, specimens were exposed to varying humidity while temperatures close to ambient were maintained. Also, outdoor environmental exposure was applied to address the lack of test data on natural aging of FRP-concrete bond system. All the environmental conditions were applied for extended durations (the maximum duration of 18 months). Single shear tests (pullout test) were conducted to investigate maximum normal stress developed in CFRP (pullout strengths), strain distribution along the bond line and failure modes of control (unexposed) and exposed specimens. Local shear stresses and slips at the debonding tip were obtained from the strain profiles and CFRP stiffness values for both unexposed (control) and exposed conditions. Subsequently, local shear stresses at the debonding tips were fitted to corresponding slips and fracture energies were determined from the numerical integration of the shear stress-slip curves. Fracture properties, namely, peak shear stresses and fracture energies, of exposed specimens were compared with the control specimens. In addition, the change of material properties of concrete and CFRP were investigated and the effect of the changing material properties on the fracture properties of bond are presented in this paper. Based on the results, the most significant degradation of fracture energy was observed for wet-dry cycles, whereas the outdoor environment caused only initial deterioration. The temperature cycles, however, did not cause any negative effect on the fracture energy during the one year exposure.