Abstract:In order to study the damage degree of both hybrid fiber and fly ash reinforced concrete under freeze-thaw cycle, the compressive strength test and ultrasonic testing test of normal concrete, hybrid fiber concrete as well as hybrid fiber fly ash concrete were carried out under freeze-thaw cycle conditions, the compressive strength and relative dynamic elastic modulus of concrete after freeze-thaw damage are obtained, the compressive strength damage, relative dynamic elastic modulus damage and internal structure failure mechanism are analyzed, and the strength attenuation equation based on relative dynamic elastic modulus is established. The test results show that the compressive strength and relative dynamic elastic modulus of normal concrete, hybrid fiber concrete and hybrid fiber fly ash concrete decrease with the increase of freeze-thaw cycles; after 60 freeze-thaw cycles, its compressive strength and relative dynamic elastic modulus decreased to varying degrees; the damage of compressive strength and dynamic elastic modulus of hybrid fiber fly ash concrete is smaller than that of reference concrete when the fly ash content is less than 10%, but larger than that of reference concrete when the fly ash content is 20% and 30%; by fitting the relationship between relative compressive strength and relative dynamic elastic modulus of concrete under freeze-thaw cycle, the exponential function expression of relative compressive strength and relative dynamic elastic modulus with good correlation coefficient is obtained; the freeze-thaw damage of concrete and the freeze-thaw resistance mechanism of fiber and fly ash reinforced concrete are analyzed. The research shows that fiber and proper amount of fly ash can enhance the freeze-thaw damage resistance of concrete.