Experimental and theoretical study on compressive strength of FRP rebars under different stress levels in alkali and salt solution

To study the influence of temperature, stress level and other factors on the compressive strength of FRP (Reinforced Plastic Fiber) rebars in alkali and salt solution, FRP rebars were placed in 60℃ and 25℃ of alkali and salt solution, respectively. The compressive stress levels of FRP rebars at 60℃ were 0%, 20% and 40%, exposed for 10 d, 21 d and 42 d, and the stress levels of FRP rebars at 25℃ were 0%, exposed for 36 d, 64 d and 100 d. By observing the surface topography, the surface erosion degree of FRP rebars increases with time. Under the same conditions, the surface erosion degree of FRP rebars in alkali solution is greater than that in salt solution. Compressive strength tests of FRP rebars after erosion show that the increase of temperature and stress accelerate the degradation of FRP rebars. After 42 d of exposure of alkali solution, compressive strength of glass fiber reinforced polymer(GFRP), basalt fiber reinforced polymer(BFRP) and carbon fiber reinforced polymer(CFRP) rebars at 0% stress are decreased by 31.8%, 43.6% and 51.5%, while the compressive strength at 40% stress level are decreased by 44.2%, 54.8% and 57.1%. After 42 d of exposure of salt solution, compressive strength of GFRP, BFRP and CFRP at 0% stress are decreased by 22.2%, 31.8% and 18.1%, while the compressive strength at 40% stress level are decreased by 29.0%, 37.2% and 23.5%. Based on Fick's law, a compressive strength prediction model of FRP rebars was proposed, which considers stress level, temperature and time and can be used to predict the degradation of FRP rebars under actual conditions.