Bond properties between carbon fibre-reinforced polymer plate and fire-damaged concrete

In this research, a single-shear test was conducted to investigate the bond properties between carbon fibre-reinforced polymer (CFRP) plates and fire-damaged concrete prisms. The investigation focused on the effects of fire exposure condition and the presence of internal steel reinforcements on the effective bond length, failure mode, bond strength (maximum joint load) and interfacial fracture energy. After being air-cooled, the concrete prisms were adhesively bonded with CFRP strips of different lengths, and then quasi-static tested at the ambient condition. The pull-off test results showed that the tensile strength of concrete substrate decreased after being exposed to elevated temperatures. Such deterioration of concrete substrate caused an increase in the effective bond length. It also decreased the bond strength and interfacial fracture energy. The steel reinforcements in concrete structures are beneficial as they minimize the effect of fire exposure on bond strength and effective bond length. An application of the fracture mechanics-based model for strength prediction of bond between fire-damaged concrete and the CFRP plate is proposed. A linear relationship between interfacial fracture energy and pull-off tensile strength of concrete could be assumed for the unreinforced concrete.