Study On Mechanical Properties And Chloride Ion Diffusion Of Fiber-reinforced Concrete Under Wetting-drying Cycles

Chloride corrosion is an important factor leading to the durability failure of fiber reinforced concrete,resulting in huge economic losses.The wetting-drying cycles greatly accelerate the process of chloride corrosion of fiber reinforced concrete,so that the durability of fiber reinforced concrete structure under the wetting-drying cycles chloride corrosion environment has become the focus of the engineering community.Therefore,it is of great significance to study the macro-mechanical properties and chloride ion diffusion of fiber-reinforced concrete in an environment of alternating wet and dry chloride salts,and to comprehensively evaluate the resistance of fiberreinforced concrete to chloride penetration.Under the influence of 12-hour dry and wet cycle system and 10% chlorine salt,this article studies the effects of four factors on mechanical properties,which the ages of erosion(0d,30 d,60d,90 d,120d),fiber types(steel fiber,imitation steel fiber,hybrid fiber),fiber mixing method and fiber volume(single fiber is 0%,0.5%,1.0%,1.5%,steel-imitation steel mixing ratio is 0.5%:0.5%,0.5%:1.0%,1.0%:0.5)and matrix strength(C30,C45,C60).At the same time,the chloride concentration of each layer of concrete is tested.Based on Fick's second law,the chloride diffusion coefficient is fitted to measure the resistance of fiber coagulation to chloride penetration.The main conclusions are as follows:(1)Erosion of 120 d does not reduce the compressive strength and splitting tensile strength of concrete,and it is more sensitive to the effect of splitting tensile strength.However,the chloride diffusion coefficient of fiber-reinforced concrete decreases with the increase of erosion age.(2)The incorporation of fiber,especially the steel fiber and the mixed fiber with a high proportion of steel fiber,improves the compressive resistance and splitting tensile strength of concrete.Fiber can inhibit the permeability of chloride ion in concrete,the imitation steel fiber can reduce the chloride ion diffusion coefficient in the later period of erosion.(3)When the volume of steel fiber increases from 0% to 1.5%,the compressive strength increases first and then decreases,and reaches the maximum at the volume of 1.0%,while the splitting tensile strength increases all the time;For the hybrid concrete,at the test age of 120 d,the hybrid fiber concrete with steel-imitated-steel fiber mixing ratio of 0.5:1.0 and 0.5:0.5 presents relatively close the compressive strength and the splitting tensile strength,but lower than the hybrid fiber concrete with mixture ratio of 1.0:0.5.The incorporation of excessive fiber is not good for the chloride ion penetration resistance of concrete;Within the scope of this study,it is recommended that the volume of steel fiber a be 1.0% or that the proportion of steel fiber be appropriately increased in the hybrid fiber to further improve the resistance of concrete to chloride salt erosion.(4)For each age of erosion within 120 d,the compressive strength and splitting tensile strength of the three fiber series are positively correlated with the matrix strength,and the incorporation of fiber in the high strength concrete can give play to its resistance to chlorine salt degradation advantage,so to improve the concrete strength grade is an effective way to improve the concrete resistance to chloride ion corrosion.