Bond Performance Between Prestressed GFRP Bars and Seawater Sea-Sand Concrete

To address the shortage of river sand resources and the corrosion of steel reinforcement in coastal regions, this paper systematically investigates the bond performance between prestressed glass fiber-reinforced polymer (GFRP) bars and glass fiber-steel composite bars (GSFCB) and seawater sea-sand concrete (SWSSC) through central pull-out tests. A total of 24 sets of specimens were designed, focusing on the effects of prestressing level, bar diameter, anchorage length, bar type, and concrete type on bond strength, bond-slip curves, and failure modes. A bond stress-slip constitutive model applicable to prestressed GFRP bars was subsequently established. The results indicate that GFRP bar specimens predominantly exhibit pull-out failure, whereas GSFCB bar specimens tend to undergo brittle bar rupture or concrete splitting failure due to excessive interfacial bond strength. The prestressing level has a significant dual effect on bond performance: compared to non-prestressed specimens, a prestress level of 0.3 times the ultimate tensile strength reduces the bond strength by 42.1%~64.0%, while a prestress of 0.6 times increases it by 3.8%~17.4%. Bond strength decreases with increasing anchorage length and bar diameter; specimens with an anchorage length of 5 times the bar diameter exhibit an average bond strength 15%~25% higher than those with 7 times the diameter, and bars with an 8 mm diameter show an average bond strength 62.1%~107.4% higher than those with a 12 mm diameter. The use of seawater sea-sand instead of ordinary concrete significantly enhances bond strength. At 7 days of curing, SWSSC specimens exhibit bond strengths 28%~33% higher than those of ordinary concrete, and at 28 days, this advantage remains at 11%~14%. The bond strength of GSFCB is substantially higher than that of GFRP bars, exceeding by 122.3%, 87.7%, and 65.7% at anchorage lengths of 5, 7, and 9 times the bar diameter, respectively. The piecewise bond-slip constitutive model, based on experimental data, shows good agreement with the test curves, providing a theoretical basis for the nonlinear analysis and design of prestressed FRP bar-reinforced SWSSC structures.