Study On Crack Resistance Of Rubber Concrete By Wedge Splitting Method

Concrete is the most widely used material in civil engineering.However,the existence of cracks have seriously consequences on the bearing capacity and service life of reinforced concrete structures.And the high brittleness of concrete materials can't avoid the occurrence and development of cracks.The incorporation of rubber aggregates can improve the toughness and ductility of concrete materials to inhibit the occurrence and expansion of cracks.Moreover,the rubber aggregates can dissipate more energy through good deformation ability to avoid brittle failure of the material.Therefore,the comprehensive and scientific study of the fracture performance of rubber concrete has great significance for the application of this material in civil engineering.The wedge splitting test is one of the main methods for measuring the crack resistance of concrete.Wedge splitting test is used to study the cracking resistance of rubber concrete.The important indexes of crack resistance of rubber concrete with different particle size(30 mesh,50 mesh),different content(0%,5%,10%,15%,20%)and different ratio of seam height(0.3,0.4)were measured and analyzed.And the process of the experiment was observed and recorded in detail.The effects of particle size,rubber content and crack height ratio on critical crack opening displacement,critical effective crack length,crack toughness,unstable fracture toughness and fracture energy were summarized.During the loading process of the specimens,the process of crack stable expansion of rubber concrete is longer than that of reference concrete after cracking.However,the bearing capacity and cracking toughness of rubber concrete specimens are lower than that of reference concrete specimens.The rubber content has a great influence on the fracture performance of rubber concrete.The critical crack opening displacement of each content of rubber concrete is greater than that of the reference concrete and the disparity increases with the increase of the content.The critical effective crack length of the rubber concrete specimens with different content is similar,but larger than that of the reference concrete.The fracture toughness and fracture energy of 5-15% rubber concrete are higher than that of reference concrete.The bearing capacity of 50 mesh rubber concrete is slightly lower than 30 mesh.However,the effective length of critical cracks,unstable fracture toughness and fracture energy are slightly greater than 30 mesh rubber concrete.Comprehensive comparison shows that rubber concrete is more difficult to enter the stage of instability failure than the reference concrete after cracking.Moreover,rubber concrete is more ductile and more difficult to crack,and it can consume more energy of material fracture.The fracture parameters of rubber concrete specimens with different aspect ratio are compared.It is found that when crack height ratio of specimens is 0.3,the parameters of crack load,unstable fracture load,critical effective crack length and fracture energy are all greater than the parameters of 0.4 crack height ratio specimens.This indicates that the above parameters of fracture properties have obvious size effect.However,the other fracture parameters are independent of the ratio of fracture height.Based on the test results,the curve and function expression of the rubber concrete fracture performance parameters with the change of the rubber content are fitted.Based on the simplified equation of Xu and Reinhart concrete softening curve,the softening curve of rubber concrete can be obtained by using the measured cohesive toughness.It can be seen from the softening curve that the axial tensile strength of the rubber concrete and the bite stress of the softening inflection point decrease with the increase of the content.However,the opening degree of the corresponding position of the virtual crack in the whole process of the material is increased.There is also a size effect on the softening curve of rubber concrete.