Degradation Mechanism and Predictive Model of <scp>GFRP</scp> Bar‐Concrete Interfacial Bonding Behavior Under Alkaline Conditions

ABSTRACT This study examined the degradation of GFRP bars and their bond behavior with concrete under alkaline conditions. Two specimen types were prepared: a damaged group preloaded to 25% of the ultimate bond load and an undamaged group. Both were exposed to alkaline environments via static immersion and wet‐dry cycling. Macroscopic mechanical properties and interfacial micro‐morphology were evaluated after 30, 90, 150 days of aging. Results show that after 150 days, compared to non‐immersed specimens, the tensile strength of GFRP bars decreased by 20.44%–25.76% in the undamaged group and by 28.17%–29.83% in the damaged group. Bond strength was most significantly influenced by immersion duration, decreasing by up to 62.67% and 44.3% for the damaged and undamaged groups, respectively, compared to non‐corroded specimens. Microscopic analysis revealed that prolonged immersion loosened the bar‐concrete interface, accelerating OH − penetration. This promoted resin matrix hydrolysis (N content decreased from 14.84% to 0%) and fiber damage (Si content increased from 1.81% to 21.10%), resulting in continuous bond deterioration. Based on the results, a bond strength prediction model was developed using a 16 mm bar diameter threshold; a time‐dependent bond strength model under natural exposure in an alkaline environment was developed using cumulative heat, and a single‐logarithmic model.