Long-Term Behavior of FRP-Bar Reinforced Seawater Sea Sand Concrete Beams Under Load Sustaining and Environment Weathering

Concerns have been raised regarding the long-term durability of FRP-bar reinforced seawater sea sand concrete (SWSSC) members in coastal engineering structures. In this context, an experimental study was conducted to investigate the long-term flexural behavior of GFRP-bar reinforced SWSSC beams, which were subjected to sustaining loads and exposed to both natural and chamber-accelerated coastal environments. Following the exposure period, twelve beams were tested under four-point bending loads. The results indicate that both the natural outdoor and chamber accelerated environments exhibited higher load-carrying capacity and lower deflection than the natural indoor environment. The load-carrying capacity showed an improvement ranging from 10.3% to 34.8%, while deflection decreased by 6.5% to 19.9% when compared to the indoor environment. However, the presence of seawater and sea sands in SWSSC beams resulted in a reduced load-carrying capacity compared to normal concrete (NC) counterparts, with the reduction reaching up to 15.8%. Furthermore, an increase in the sustaining load led to decreased load-carrying capacity but increased deflection, with values of 26.0% and 11.0%, respectively. To evaluate the appropriateness of current modern design codes, the load-carrying capacity and ultimate deflection of both NC and SWSSC beams were calculated and compared with the test results. The analysis revealed that the American code ACI440.1R-15 and Chinese code GB50608-2020 exhibited a conservative approach in predicting bending moment capacity. Additionally, the American code ACI440.1R-15 and Canadian code CSA S806-12 underestimated the ultimate deflection, whereas the Chinese code GB50608-2020 overestimated it. These findings provide valuable insights for designing coastal structures using GFRP-bar reinforced SWSSC materials.