Using pre-stressed carbon fibre reinforced polymer/plastic (CFRP) to strengthen bridge structures is currently considered a promising technology and the durability of the structure is closely related to the material property. CFRP have good corrosion resistance, but they also experience different degrees of swelling, corrosion and hydrolysis in water immersion environments. Stress accelerates this effect and leads to deterioration of the mechanical properties of the materials. This work aims to investigate the durability of CFRP grids under water, wet-dry cycles of seawater, seawater immersion and 0% fu (fu is the ultimate tensile strength of the tested CFRP grids and it is constant stress in this paper), 30%fu, 60% fu coupled environments.Test aging time at room temperature (25°C) of 30, 60, 120, 180, 270, 360 days. The results indicate that the surface of epoxy resin is smooth at the initial moment by comparing of scanning electron microscope (SEM) image. With the increase of deterioration degree with aging time, the cavities and cracks appeared in the matrix. The epoxy resin content between the fibers decreased, and the adhesion force decreased. When the aging time is short, the tensile damage section of CFRP grid is flaky and the matrix is tightly bonded with the fiber. The later damage is mainly blow-up damage, which the fracture section is typical filiform. After CFRP grids aged for 360 days, the tensile strength decreased by 6.2%, 10.2%, 10.9% in the water, seawater solution and seawater wet-dry cycle environments. The tensile strength decreased by 10.2%, 12.3% and 20.2% under the coupling of seawater and different stress levels. A semi-empirical model of durability is proposed to provide a good reference value for the durability prediction of FRP materials.
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