Experimental Study On Freeze-Thaw Damage Of Steel Polypropylene Hybrid Fiber Reinforced Concrete

In the severe cold area of northern China,many concrete structures are prone to freeze-thaw damage due to the alternation of positive and negative environmental temperature,which leads to the reduction of structural durability,and has a considerable economic loss to the society,but also endangers the safety of users.This paper studies the freeze-thaw damage mechanism of concrete and improves the freeze-thaw resistance of concrete,so as to apply higher performance concrete materials to practice It is of great practical significance in international engineering.Previous studies have shown that adding appropriate amount of steel fiber and polypropylene fiber can effectively improve the mechanical properties of concrete,but the research on the frost resistance durability of steel polypropylene hybrid fiber concrete is relatively less.Therefore,in this paper,steel fiber(volume ratio 1.2%)and polypropylene fiber(volume ratio 0.11%)are separately and mixed into concrete,and their mechanical properties and frost resistance durability are tested(1)Research on rapid freeze-thaw test of fiber reinforced concrete: four groups of concrete specimens were tested by rapid freeze-thaw cycle,and the effects of steel fiber and polypropylene fiber on the mass loss rate and the change rate of relative dynamic elastic modulus of concrete specimens were studied.The test results show that the addition of fiber can effectively improve the frost resistance of concrete,and the steel polypropylene hybrid fiber concrete has the best frost resistance.(2)Experimental study on mechanical properties: the cube compressive strength,splitting tensile strength and flexural strength of four groups of concrete were tested,and the effects of steel fiber and polypropylene fiber on the mechanical properties of concrete were studied.The results show that the mechanical strength of concrete can be improved by adding fiber,and the mechanical property of steel polypropylene hybrid fiber concrete is the best.(3)Based on the freeze-thaw damage mechanism of fiber reinforced concrete,the concept of damage variable based on the calculation of relative dynamic elastic modulus is proposed,and the freeze-thaw damage model of hybrid fiber reinforced concrete is established.The fitting accuracy of four groups of experimental data and the model is above 0.98,which indicates that the model can better predict the freeze-thaw damage degree of different kinds of fiber reinforced concrete.(4)The existing freeze-thaw damage models of concrete are analyzed and summarized,and the freeze-thaw damage evolution equation of hybrid fiber concrete is established based on the probability function of Weibull two parameter distribution.The regression analysis of four groups of test data and the equation shows that the fitting determination coefficient is above 0.97,which indicates that the damage evolution equation can better reflect the freeze-thaw damage evolution law of fiber concrete It has strong applicability in practice.