Durability of Bonded Basalt Fiber–Reinforced Polymer Rods in Prestressed Concrete Exposed to Seawater

In the context of concrete structures with prestressed reinforcement operating in marine environments, this study focused on the combined effect of prestressing and exposure to seawater on the durability of basalt fiber–reinforced polymer (BFRP) rods embedded in grout. Scanning electron microscopy (SEM) was used to explore the degradation mechanism of the specimens. In addition, a modified model was proposed to estimate strength degradation based on Fick’s law. The results indicate that resin hydrolysis and fiber–resin interface debonding caused the degradation of BFRP rods. The strength retention of prestressed specimens without conditioning in seawater exceeded 94% after 720 days of exposure. However, the tensile strength of the BFRP rods conditioned in seawater decreased significantly as the conditioning duration increased. The strength retention of nonprestressed rods decreased to 74% after 720 days of exposure, whereas strength retention decreased more severely in prestressed specimens. Thus, it is advisable to control alkalinity in concrete structures prestressed with bonded BFRP rods in practical applications. Finally, the long-term strength of BFRP rods may be effectively estimated through the proposed model.