Effects of hygrothermal aging on glass-fibre reinforced polymer laminates and adhesive of FRP composite bridge: Moisture diffusion characteristics

Moisture absorption and hygrothermal aging in glass-fibre-reinforced polymer laminates and a structural adhesive of FRP composite bridge are studied. By gravimetric experiments, the moisture diffusion in GFRP laminates and adhesive is characterised in four environmental aging conditions (20 °C–50% RH (relative humidity), 20 °C–water, 40 °C–96% RH and 40 °C–water). Based on the analytical models from 1D and 3D moisture diffusion theories, the moisture diffusion coefficients are determined by the best least-square curve fitting to experimental data. Finite Element models are further developed, which subsequently validate the analytically obtained moisture diffusion coefficients. The FE analysis indicates that, for identification of 3D moisture diffusion coefficients of anisotropic FRP materials, the equivalent diffusion coefficient method is unreliable, and the 3D moisture diffusion theory is essential. Furthermore, mass loss is found for the Square and Rectangular specimens under 40 °C–water condition. Polymer relaxation is observed for structural adhesive.