The combined effects of wet-dry cycles and sustained load on the bond behavior of FRP-concrete interface

Effective bonding between the adherents plays a key point when dealing with the retrofit of concrete structures by using fiber-reinforced polymers (FRPs). However, lack of adequate studies on the long-term performance of the bond behavior of FRP-concrete interface under harsh environments will inhibit their application in the repair of aged structures. Therefore in this study, 60 double-lap shear-bonded FRP-concrete composite specimens were designed and tested under wet-dry cycles and sustained loading. The effect of FRP type (GFRP and CFRP), wet-dry cycling times (0-360 days) and sustained loading level (0-60% of the ultimate load of the control specimen) on the failure modes, stress transfer, and local bond-slip curves of the composite specimens were investigated. The experimental results showed that wet-dry cycling exposure changed the failure mode of the composite specimens from the concrete substrate to the adhesive-concrete interface, further extended the local debonding area and decreased the ultimate strains of composite specimens from 12,000 to 8,000 mu e. The degree of the degradation will be further increased under the combined effect of sustained loading and wet-dry exposure. The effects of FRP type, wet-dry cycling times and sustained loading level on the fracture energy of the specimens were quantitatively analyzed. A regression model was then proposed that was able to predict the fracture energy after environment exposure with reasonable accuracy, which can provide a reference for the design of bond durability factors in relevant specifications, such as ACI 440R-08 POLYM. COMPOS., 40:1006-1017, 2019. (c) 2018 Society of Plastics Engineers