Experimental Research On Hybrid Fiber Concrete Under The Salt Frozen Cycles

In the salt frozen environment,concrete materials will suffer the surface denudation,the internal crack propagation,the bearing capacity declining and the chloride ion erosion.Adding fiber into concrete can effectively improve the crack resistance ability of concrete,and perfect concrete frozen damage.At present,the domestic and the foreign scholars’ researches on the salt frozen resistance of the single fiber concrete and the mechanical properties of steel-polypropylene hybrid fiber concrete are concentrated.However,researching the damage law,the chloride ion erosion and the model of PVA-Polypropylene hybrid fiber concrete in the salt frozen environment is less.In this paper,the salt frozen cycling test,the mechanical properties test and the determination of free chlorine ion content test are carried out through the ordinary concrete,PVA fiber concrete,polypropylene fiber concrete and PVA-Polypropylene hybrid fiber concrete.The main research works and achievements are as follows:(1)Four kinds of concrete specimens’ appearance shape,mass loss rate,relative dynamic elastic modulus are carried out the research,and the salt frozen resistance’s damage mechanism of fiber concrete is discussed.The experimental results show that adding fiber into concrete can inhibit the concrete surface denudation,slow down the loss speed of quality and relative dynamic elastic modulus,and enhance the salt frozen resistance of concrete.The salt frozen resistance of polypropylene fiber concrete is better than PVA fiber concrete,and that of PVA-Polypropylene hybrid fiber concrete is best.(2)The influence of concrete specimens’ the compressive strength and the flexural strength for the salt frozen cycles and the fiber types is researched.At the same time,the strength attenuation models of fiber concretes under the salt frozen cycles are set up.The experimental results show that the attenuation amplitude of the fiber concrete compressive strength and flexural strength is lower than the ordinary concrete,and the fiber reinforced rate of PVA-Polypropylene hybrid fiber concrete is highest.Adding fiber into concrete can effectively reduce the strength loss rate after the salt frozen cycles,and mixed fiber can play a positive hybrid effect and stack effect.In addition,the fitting precisions of strength attenuation model and experimental data about four kinds of concrete are above 0.91 under the salt frozen cycles.(3)The determination of free chlorine ion content test is happened after the difference of salt frozen cycles.At the same time,the influences of chloride ion diffusion performance for the fiber types and the salt frozen cycles are researched.The experimental results show that with the times of salt frozen cycles increasing,free chlorine ion content gradually increases,and that of single fiber concrete is less than the ordinary concrete,and PVA-Polypropylene hybrid fiber concrete is the maximum.In addition,with the times of salt frozen cycles increasing,the chloride ion diffusion coefficient decreases.(4)The frozen damage degree within concrete specimen because of the salt frozen is described by the degree of damage.The salt frozen damage evolutions of different fiber concrete are got by the experimental data and regression fitting.Its precision is all above 0.92.At the same time,Based on Weibull distribution of the salt frozen damage model of hybrid fiber concrete is set up in this paper,the fitting precision of the model and the experimental data is above 0.94.In addition,the mathematical relationships of the damage degree and the chloride ion diffusion coefficient are deduced through the regression fitting of the chloride ion diffusion coefficient and the salt frozen cycles,and combining the salt frozen damage model.