Bond Durability of GFRP Bars and Seawater Sea-Sand Concrete in Hygrothermal Marine Environment

To investigate the bond durability of glass fiber-reinforced plastics (GFRP) reinforcing bars in seawater-sea-sand concrete (SSSC) under a hot and humid marine environment, a 6-month durability test was conducted with environmental temperature (20 °C, 40 °C, 60 °C) , exposure conditions (humidification and immersion), and concrete cover thickness (25 mm, 35 mm) as variables. The bond strength and failure modes of the specimens were determined through pull-out tests, and the microstructural evolution of the GFRP reinforcement was observed using a scanning electron microscope (SEM). The results indicate that all specimens failed due to pull-out, and the GFRP helical stirrups effectively suppressed splitting failure; high temperature was the dominant factor in the degradation of bond performance, with the most severe decline in bond strength observed at 60 °C; the microstructural mechanisms included hydrolysis of the resin matrix, chemical corrosion of the glass fibers, and interfacial delamination caused by thermal expansion mismatch; under the same temperature and 100% relative humidity, after 6 months of exposure, the macroscopic degradation effects on bond performance were similar between the immersion and humidification environments, indicating that the impact of differences in humidity forms diminishes under long-term exposure; Increasing the protective layer thickness can lengthen the corrosion medium transmission path, enhance the confining effect, and improve the long-term retention rate of bond strength. These research findings provide a scientific basis for the durability design of GFRP-reinforced SSSC structures in humid and hot marine environments.