The construction of projects on remote islands and reefs faces severe challenges, including insufficient corrosion resistance of traditional building materials and high costs for long distance marine transportation. The use of localized materials and composite materials represents a feasible solution, though the bonding performance between GFRP-steel composite bars and coral seawater sea-sand concrete (CSSC) remains unclear. To address this issue, this study designed five groups comprising a total of 15 central pull-out specimens to analyze the effects of CSSC strength, GFRP-steel composite bar diameter, and bond length on bonding performance. Bond strength and basic anchorage length calculation formulas for GFRP-steel composite bars and coral seawater sea-sand concrete were proposed. The results indicate that the ultimate bond strength of test specimen is primarily positively correlated with the cube compressive strength of CSSC and the bond length of GFRP-steel composite bars, while the initial bond stiffness shows a positive correlation with the cube compressive strength of CSSC. The experimental data can provide support for the application of localized materials in the construction of remote island and reef projects.

The early-stage service performance evolution of glass fiber reinforced polymer (GFRP) bars in tropical marine environments remains insufficiently understood. To address this, a comparative study was conducted using in-situ exposure tests (atmospheric, tidal, and seawater immersion) alongside accelerated aging tests (ultraviolet radiation, salt spray exposure, UV+salt spray coupling, and UV+condensation cycling). Macroscopic mechanical testing combined with microstructural characterization was employed to reveal the degradation behavior and deterioration mechanisms of the fiber-resin interfacial bonding under various environmental conditions. The results indicate that in environments involving UV radiation, the interlaminar shear strength (ILSS) of GFRP bars initially increase and then decrease. The UV+salt spray coupled environment has the most pronounced effect on ILSS, leading to an 18.19% reduction after 40 days of exposure. Fourier Transform Infrared Spectroscopy (FTIR) and Scanning Electron Microscope (SEM) analyses verify that, due to the synergistic effects of post-curing, hydrolysis, and molecular chain scission of the resin matrix, the fiber-resin interface gradually transitions from a dense state to a rough structure accompanied by debonding.