Bond durability of steel-FRP composite bars embedded in seawater sea-sand concrete under constant bending and shearing stress

The combination of the new steel-FRP composite bar (SFCB) and natural seawater and sea-sand concrete (SWSSC) has good prospects to be applied in development along the ocean coast and offshore islands. However, at present, there is still a lack of clear understanding on the durability of this new combination under actual marine service conditions. Therefore, in this paper, the interfacial bond durability, which is critical to the overall durability of SFCB reinforced SWSSC structures, was evaluated by accelerated aging tests. A new type of eccentric pullout test was designed to take into account the bending and shearing stress states of the concrete. The experimental results showed that the bond strength of SFCBs decreased by 5% after 9 months of aging in a 40 °C seawater wet-dry cycling environment and decreased by 26.2% after 9 months of aging in a 50 °C seawater immersion environment. Due to the surface degradation of the basalt fiber reinforced polymer (BFRP) after exposure, the sheared failure layer gradually transferred from the interface to the inner layer. Based on Fib Bulletin 40, the predicted bond strength retentions of SFCBs with SWSSC were 84% to 96% after 50 years of service.