Prediction of long-term durability of unidirectional/multidirectional basalt fiber- and hybrid fiber-reinforced polymer profiles under concrete environment

Recently, concrete composite structures based on a fiber-reinforced polymer (FRP) profile, which serves in the corresponding alkaline concrete environment have been widely used. Unlike FRP bars, the long-term durability of FRP profiles in concrete remains unclear, particularly for those with multidirectional (MD) or hybrid fibers, whose internal structure differs from that of FRP bars. This study focused on the tensile strength degradation of FRP profiles exposed to an artificial concrete environment solution at various ambient temperatures. Three types of FRP specimens were considered, including unidirectional (UD) basalt FRP (BFRP), MD BFRP and MD basaltcarbon hybrid FRP profiles. The results show that the alkaline environment of the concrete caused a decrease in the tensile strength of the FRP profiles, and the rate of degradation in strength significantly accelerated as the ambient temperature increased; however, the environment had no apparent effect on the elastic modulus. In addition, the strength degradation of MD FRP profiles was more significant than that of UD FRP profiles after corrosion due to insufficient impregnation of the fibers by the resin, which results in initial defects as well as increased intrusion of external moisture and corrosive media. Scanning electron microscopy (SEM) was employed to analyze the morphology and degradation mechanism of FRP profiles in a concrete environment. Moreover, a long-term prediction method for tensile strength retention of three types of FRP profile in arbitrary ambient temperatures is proposed based on the Arrhenius equation.