Effects of marine environment and fatigue pre-damage on the residual tensile properties of SFCBs

Steel-fiber reinforced polymer (FRP) composite bars (SFCBs) present a promising solution to corrosion issues associated with conventional reinforcement in marine environments, offering a viable alternative. While the performance of SFCBs under marine environments or fatigue loading is well understood, their behavior under combined conditions remains unreported. This study conducted tension-tension fatigue tests on seawater-immersed SFCBs to assess the effects of fatigue loading (at a stress level of 0.36), various aging temperatures (23°C, 40°C, and 60°C), and durations (30, 180, and 360 days) on their residual properties. Microscopic analysis was used to investigate the degradation mechanisms due to environmental aging. The results indicate that environmental aging deteriorates the GFRP matrix in the outer layer of SFCBs, with fatigue loading further causing matrix cracking and reducing the quasi-static tensile strength. The residual tensile strength of SFCBs decreases with increasing aging times or temperatures, while aging shows no significant effect on their fatigue life. Additionally, a model predicting the residual tensile strength of SFCBs based on damage accumulation was proposed. According to the model, tensile strength initially rapidly decreases with aging time and eventually stabilizes. These findings offer practical insights for the application of SFCBs in concrete structures.