Study on the durability of GFRP bars and carbon/glass hybrid fiber reinforced polymer (HFRP) bars aged in alkaline solution

Using glass fiber reinforced polymer (GFRP) bars as the reinforcement of concrete structures is becoming more and more popular. Carbon/glass hybrid-fiber reinforced polymer bars (HFRP bars), formed by wrapping a thin layer of carbon fiber reinforced polymer (CFRP) on GFRP bars, is expected to have better durability than GFRP bars. In order to evaluate the effects of CFRP layer on the durability of GFRP bars, the water absorption behaviors of both GFRP and HFRP bars were characterized, and the interlaminar shear strength degradation of GFRP and HFRP bars aged in alkaline solution was investigated with short beam shear test. The results indicate that after being aged in alkaline solution, the remaining interlaminar shear strengths of HFRP bars were larger than that of GFRP bars. And, the deterioration of HFRP bars aged in alkaline solution was found occurring at the CFRP/CFRP interface. The long-term interlaminar shear strength of GFRP and HFRP bars aged in alkaline solution was predicted using the Arrhenius theory. The present study shows that the CFRP layer enhances the durability of GFRP bars in alkaline environment, due to the delayed water and OH– diffusion in CFRP and the better alkaline resistance of CFRP.