Residual compressive strength of seawater sea sand concrete filled hybrid carbon-glass fibre reinforced polymer tubes under seawater: effects of fibre type and orientation

Despite the superior mechanical and durability properties, the higher cost of carbon, compared to other fibre options, remains a major concern in the widespread use of carbon fibre-reinforced polymer (CFRP) composites in construction applications. The hybrid formation of carbon fibres with other fibres could help reduce the cost while remaining appropriate structural properties. The present study examines the durability performance of Seawater Sea Sand Concrete (SWSSC) filled hybrid carbon-glass fibre-reinforced polymer (HFRP) tubes after exposure to seawater. Ninety-six samples filled with an alkaline solution simulating SWSSC were exposed to seawater for different durations and at different temperatures. The compressive mechanical properties of the conditioned samples were compared to the unconditioned reference samples to determine the level of mechanical degradation of the tubes. Based on Arrhenius's theory, long-term performance was predicted using the collected experimental data from short-term performance. Fibre type (i.e. carbon, glass, and hybrid carbon-glass) and fibre orientation (cross-ply and hoop) were considered as the material-based variables. When exposed to the most severe condition of 5 months at 60 °C, CFRP showed the highest average strength retention of 86.01%. The hybrid cross-ply tubes exhibited better strength retention than GFRP with strength retention of 64.84% for HFRP compared to 57.23% for GFRP. However, over the long term, the difference in performance between the two types of FRP tubes decreased and became more comparable. The onset of damage in GFRP tubes started sooner than that in HFRP. However, the long-term ultimate strength reduction of HFRP tubes was found similar to the weaker fibre type (i.e. GFRP tubes).