Interfacial Bonding Properties Of FRP-Strengthened Concrete After Exposed To Elevated Temperature

Recently,fiber reinforced polymer(FRP)bonding system has been widely used in repairing and retrofitting the concrete structures.However,the concerns and unknowns surrounding the uncertainty in mechanical and bond properties under varying temperature,moisture and other environmental factors have therefore hindered the attempts to apply FRP bonded system in concrete structure.Thus,enormous amount of research effort has gone into the field in durability of FRP bonded concrete system.However,the effect of the interfacial properties of such structure still has not been well understood.This research aims to illuminate the effect of elevated temperature on the interfacial bonding properties of FRP strengthened concrete system after exposed to elevated temperatures.Tensile,peel and shear tests were performed to measure and evaluate the mechanical properties and bond behavior of FRP coupon sheets and FRP strengthened concrete specimens after heating at 80,200 and 300℃,respectively.The elastic modulus of FRP unchanged at elevated temperature but the ultimate strength and the ultimate strain of FRP decrease with the temperature increases.A significant reduction of mechanical properties including the interfacial fracture energy,peak load and bond stress can be obtained after exposing at the temperature above 200℃ and the degradation can be up to 60%for the specimens of FRP-strengthened concrete conditioned for 300℃ exposure.The failure mode of FRP-strengthened concrete shows a trend from concrete delamination at lower temperature to interface at epoxy/concrete at higher temperature.It also showed that the thickness of concrete peeled by the FRP sheet decreased with the increased of temperature.Additionally,the elevated temperature performances of two different types of FRP materials(AFRP and CFRP)has been discussed in this research.It shows that CFRP material is the better choice to use in the FRP bonded concrete system even AFRP strengthened concrete has much better performance than CFRP bonded system in peel tests.But AFRP shows a poor capacity in tensile strength,leading the AFRP sheet could be failure earlier than concrete substrate that cannot provide and enhance the concrete beam.