Effect of Mechanical Interlocking Damage on Bond Durability of Ribbed and Sand-Coated GFRP Bars Embedded in Concrete Under Chloride Dry–Wet Exposure

The substitution conventional steel reinforcement with glass fiber-reinforced polymer (GFRP) bars is a widely adopted strategy used to improve the durability of concrete structures in chloride environments, offering benefits such as enhanced corrosion resistance, reduced maintenance needs, and increased service life. This study investigates the bond behavior between glass fiber-reinforced polymer (GFRP) bars and concrete under long-term chloride dry-wet cycling exposure. Pull-out tests were conducted on various specimens subjected to exposure durations of 0, 3, 6, 9, and 12 months. The experimental results indicate that, after 12 months of chloride dry-wet cycling, the bond strength retention rates of threaded ribbed GFRP with a bond length of 5d, sand-coated GFRP with a bond length of 5d, and threaded ribbed GFRP with a bond length of 7d were 57.9%, 62.2%, and 63.8%, respectively. To predict the GFRP-concrete bond performance after chloride exposure, a novel bond strength model for GFRP bars embedded in concrete, considering the mechanical interlocking effect of ribs, was proposed and validated by the test results. The overall prediction errors for RG-5d, SG-5d, and RG-7d specimens were 0.98, 0.81, and 0.93, respectively. Additionally, a sensitivity analysis was conducted on the main parameters in the model. Finally, the long-term GFRP-concrete bond performance deterioration was estimated using the proposed model. These findings are expected to provide valuable insights into the long-term bond performance and service life prediction of GFRP-concrete members in chloride environments.