Durability and long-term life prediction of hybrid FRP bars embedded in SSC under seawater environment

This paper investigates the degradation patterns and mechanisms of carbon/basalt hybrid fiber reinforced polymer (HFRP) bars in seawater sea-sand concrete (SSC). The degradation of HFRP bars was investigated using aging tests, tensile tests, interlaminar shear tests, transverse shear tests, scanning electron microscopy and X-ray computed tomography (X-CT). The degradation patterns of HFRP bars were compared with those of BFRP and CFRP bars. The results showed that after immersion in seawater at 55 °C for 120 days, the tensile strength (TS), interlaminar shear strength (ILSS), and transverse shear strength (TSS) of HFRP bars decreased by 13.84 %, 43.76 %, and 38 %, respectively. The resin content decreased by 9.02 %, while porosity increased by 13.17 %. This is mainly due to the hydrolysis of the resin and the degradation of the fiber-resin interface. Moreover, HFRP bars demonstrate better TS retention compared to BFRP and CFRP bars after immersion. This is due to the fact that the TS of the degraded HFRP bars is mainly determined by CFRP, while the external basalt fiber layer withstands the external erosion and retards the environmental erosion of CFRP. According to microscopic analysis, the degradation in HFRP bars is primarily due to resin matrix hydrolysis, fiber-resin interface degradation, fiber corrosion and CFRP-BFRP interface delamination. Finally, the Arrhenius equation is used to predict the strength retention, the results showed that the TS retention of HFRP bars embedded in SSC will decrease to 70 % within 1.6-2.2 years, while the ILSS retention will decline to 70 % within 0.62-1.1 years.