Mechanical Performance of the Wet-Bond Interface between FRP Plates and Cast-in-Place Concrete

The mechanical performance of the bond between fiber-reinforced polymer (FRP) plates and cast-in-place concrete (referred to as the wet-bond interface) is investigated. The wet-bond interface is named with respect to the dry-bond interface. The dry-bond interface is a chemical bond that is developed to adhere FRP sheets or plates to cured concrete, whereas the wet-bond interface is a chemical-bond interface that is developed to connect stay-in-place FRP formwork and cast-in-place concrete. The double-lap shear test method is adopted to evaluate the effect of the bond. The mechanical properties of the wet-bond interface are compared with that of the conventional dry-bond interface using the same epoxy adhesive, including the load-slip curves, strain distributions, load capacity, and interfacial fracture energy. The results show that the failure modes of the wet-bond and dry-bond interfaces are different. In the dry-bond specimen, debonding occurs in the thin concrete layer and is accompanied by an inclined crack near the loading end; however, in the wet-bond specimen, debonding occurs in the shallow mortar layer adjacent to the concrete-adhesive interface, and no inclined crack appears. The shear stress and slip between the FRP and concrete are obtained by differential and integration operations on the measured strain values. A bond-slip constitutive model for the wet-bond interface is proposed by a regression analysis of the test data. Numerical simulations are performed using the ANSYS finite-element software, incorporating a spring unit to simulate the overall mechanical performance of the wet-bond interface. The results show that the average wet-bond strength value is approximately 0.54–0.68 times that of the dry-bond strength value. Finally, the fracture energy and the load capacity value of the wet-bond are compared. The results show that the proposed constitutive model in this paper sufficiently simulates the overall mechanical performance of the wet-bond interface.