Tensile performance of fluorocarbon/polyurethane-coated GFRP bars exposed to southern marine environment

Traditional metal materials have serous corrosion problems when exposed to marine environment, while fiber reinforced Composite (FRP) bars have the advantages of light weight, high strength, fatigue resistance, and corrosion resistance, etc. The application of FRP bars to replace steel bars has become an effective choice to improve the durability of marine concrete structures. However, for the long-term exposure to high ultraviolet (UV), high salt, high humidity and other environments, the resin matrix of FRP is relatively fragile, and the chemical structure of materials is prone to be changed, resulting in the performance failure of FRP composite materials to cause the decline of the stiffness and durability. The application of coating protection can effectively improve the resistance to aging and corrosion of FRP materials. Based on this, considering high radiation, high salinity, and high humidity southern marine environmental factors, the degradation law for the tensile performance of glass fiber reinforced Composite (GFRP) bars protected by fluorocarbon and polyurethane coatings under the action of ultraviolet radiation and different corrosive media (deionized water and real seawater) was studied. And the effect of different exposure ages (0, 7, 14, 30, and 60 d) on the tensile performance of GFRP bars coated by two systems was analyzed. The microstructure and performance degradation law of the coatings before and after corrosion were characterized by scanning electron microscopy (SEM). The results showed that after 7-days UV aging, the residual crosslinking actions of coatings increased the tensile strength of GFRP bars by 3% to 5%. After then, the chemical structures of the coatings were destroyed and molecular chains were broken. After 60-days UV aging, the retention rate of GFRP tensile strength was 85% to 90%. After soaking in deionized water and seawater for the duration of 60 days, the retention rates of tensile strength ranged from 92% to 95% and 91% to 93%, respectively. Compared to polyurethane coatings, fluorocarbon coatings have relatively excellent durability and higher retention of tensile strength under the same degradation conditions. This is due to the superior F-C bonding structure of fluorocarbon coatings, where fluorine atoms are tightly arranged around the polymer carbon chain, providing the good protection and endowing fluoropolymers with excellent durability.