Hygrothermal aging effects on the diffusion-degradation process of GFRP composite: Experimental study and numerical simulation

•Water diffusivity of GFRP was obtained from a FE model with consideration of defects.•The penetrated water in GFRP resulted in fiber degradation at the local position.•The retained GFRP strength was derived from integration of fibers at each location.•A diffusion-degradation framework was developed and validated with experimental data.•The framework can rapidly predict long-term GFRP strength under a moist condition. The durability performance of glass fiber reinforced polymer (GFRP) has attracted wide attention, but conventional experimental methods for durability prediction are time-consuming, labor-intensive and not applicable to members with different sizes or geometries. To address this issue, a new modeling approach is developed in this study to simulate the diffusion-degradation process of GFRP composite in a moist environment. Taking a GFRP rebar as an example, the water diffusivity of composite is firstly obtained from a finite element model with the assumption of hexagonal fiber arrangement. With test results on the degradation of single coated fibers in the wet environment, and the simulated water front from the diffusion analysis, the strength retention at each location over the rebar section can be derived. The time-dependent degradation of tensile strength can hence be obtained from integration. To account for the defects (including matrix cracking, fiber erosion and fiber/matrix debonding) which can affect the water diffusivity, a refined diffusion model was also performed with increased water diffusivity (from 4.0 × 10-6 mm2/s to 4.5 × 10-6 mm2/s) and presence of interfacial crevices in the corroded region. While the refined model can lead to faster water diffusion and tensile strength degradation, the difference with the original model is within 10%. More importantly, both models are able to correctly predict the GFRP tensile strength degradation measured in the laboratory over a 12-month period. As the diffusion-degradation framework proposed in this study is applicable to any member size and geometry, it supplies engineers with an evaluation method to quickly predict the long-term tensile performance of GFRP structures.