Degradation mechanism of tensile properties and life prediction of hybrid carbon/basalt fiber reinforced polymer bars in seawater sea-sand concrete

To investigate the degradation pattern of tensile properties of epoxy resin-based hybrid carbon-basalt fiber reinforcing bars (CF-BF/Epoxy) in seawater sea-sand concrete (SSC) under seawater immersion, the CF-BF/Epoxy in SSC were soaked in seawater at different temperatures (25℃, 40℃, and 55℃) for durations of 60, 90 and 120 days. The tensile performance of the CF-BF/Epoxy in SSC was examined through tensile tests, and the changes in their microstructure were analyzed by SEM and FTIR. The results indicate that ambient temperature significantly affects the tensile properties of CF-BF/Epoxy. After 120 days of immersion at 55℃, the tensile strength decreases by 13.84%, the elastic modulus experiences a slight fluctuation within a 3% range, and pseudo-ductility is observed in the CF-BF/Epoxy. Additionally, blending of basalt fibers and carbon fibers delay the further intrusion of OH− from SSC into CF-BF/Epoxy, while the hydrolysis of the resin in the outer basalt fiber region and the degradation of the resin-fiber interface are identified as the primary causes of the decline in the tensile properties of CF-BF/Epoxy. Lastly, based on the Arrhenius equation, it is predicted that the tensile strength retention rate of CF-BF/Epoxy embedded in SSC will drop to 70% between 584 and 803 days. © 2024 Beijing University of Aeronautics and Astronautics (BUAA). All rights reserved.