Assessment of glass fibre-reinforced polymer concrete bond strength after high-temperature exposure

External bonding with fibre-reinforced polymer (FRP) laminates is widely employed for strengthening and retrofitting concrete structures. However, exposure to high temperatures can degrade concrete and adversely affect the bond strength between FRP and the damaged material. This study investigates the bond behaviour of glass fibre-reinforced polymer (GFRP) laminates adhered to heat-damaged concrete using a double-shear test. Concrete specimens were subjected to temperatures of 200, 400, 600 and 800°C. Subsequently, the specimens were bonded to GFRP sheets with varying lengths (100, 150 and 200 mm) and a constant width of 80 mm. Results indicate a decrease in bond strength with increasing exposure temperature. Conversely, bond strength exhibited a significant increase with longer bond lengths. For specimens heated below 400°C, the thickness of the delaminated concrete layer beneath the GFRP composite was negligible. However, at 600°C and 800°C, delamination thicknesses ranged from 4 to 25 mm. In addition, bond length influenced the ultimate bond stress, with higher values observed for shorter bond lengths.