Research On Damage Of Hybrid Fiber Reinforced Concrete In Freeze-thaw Cycles

Internal damage different degrees of concrete engineering in cold regions, especially in the freezing and thawing environment, has greatly influenced the life of concrete structure and its safety. Therefore concrete structure loses its effectiveness in advance and is not able to achieve the expected design life. All of these cause the economic and property damage that cannot be estimated. Therefore, the analysis and research on the freezing and thawing resistance of concrete structure is of great economic and practical significance. At present, domestic and international researchers focus on the study of the freeze-thaw resistance of concrete freeze-thaw cycles and the prediction of the life span of the structure. However, there are few studies on the laws and models of hybrid fiber reinforced concrete with freeze-thaw damage.In this paper, the following research work has been carried out on the rapid freezing and thawing cycles of single steel fiber, polypropylene fiber and steel polypropylene hybrid fiber in concrete:(1)The frost resistance and durability of steel polypropylene hybrid fiber reinforced concrete are analyzed in this paper. Analysis and calculation show that: From the mass loss rate, relative dynamic elastic modulus of two freeze-thaw performance evaluation index, the four groups of concrete antifreeze properties are sorted as follows: the frost resistance of steel fiber reinforced concrete is better than that of ordinary concrete. polypropylene fiber concrete is better than steel fiber, and the frost resistance of hybrid fiber concrete is best in the four groups.(2)The compressive strength and flexural strength of fiber reinforced concrete after freeze-thaw cycles are analyzed. At the same time, the intensity attenuation model of fiber reinforced concrete under freeze-thaw cycles is established. Study analysis shows that: After 200 times of freezing and thawing cycles, the loss rate of compressive strength and flexural tensile strength of concrete with fiber reinforced concrete were significantly lower than that of ordinary concrete. The addition of fiber, in particular, improves the flexural performance of concrete. It is known that the strength loss rate of concrete after freezing and thawing cycles is decreased. The attenuation model of concrete compressive strength and the bending strength attenuation model of each group are more than 0.97. It is showed that the model of strength attenuation and the fitting of test data are good, which can predict the strength attenuation of different kinds of fiber reinforced concrete after freeze-thaw cycles.(3)Through the relationship between the probability distribution function of Weibull and the degree of damage and probability theory and the theory of concrete freeze-thaw damage, In this paper, the damage evolution equation of hybrid fiber reinforced concrete is established. Analysis and calculation show that: The coefficient of determination of the freezing thawing damage evolution equations of the four groups were 0.988, 0.985, 0.992, 0.984, respectively. Each concrete freeze-thaw damage model accuracy is above 0.98. It shows that the damage evolution equation and the experimental data fit well.(4)The relative dynamic elastic modulus is used to characterize the degree of freeze-thaw damage of concrete specimens. According to the test data obtained through the freeze-thaw cycle test, the freeze-thaw damage model of different fiber concrete is obtained. The analysis and calculation results show the fitting accuracy of the two degree polynomial model is higher than that of the exponential function. And the accuracy of the two degree polynomial model is more than 0.994, which indicates that the damage model can predict the degree of freeze-thaw damage of different kinds of fiber reinforced concrete.