Experimental Study On Shrinkage And Cracking Behavior Of Concrete Under Restraint Of Steel Bars

With the large-scale application of high-strength concrete in China's engineering practice,the cracking problem has also attracted more and more attention.A large number of engineering practices have shown that the restraint of concrete by concrete will cause shrinkage and cracking of concrete,and thus reduce the service life of the building structure.Therefore,it is necessary to study the shrinkage and cracking behavior of concrete under the constraint of steel bars.More than 80% of the reinforced concrete cracking is caused by the shrinkage of concrete.The steel bars placed inside the concrete will restrain the free shrinkage of the concrete,and the restraining tensile stress will be generated by the restraining action.When the restraining tensile stress exceeds the tensile strength of the concrete,it will Causes concrete to shrink and crack.In this paper,the engineering status of concrete under the constraint of steel bars is easy to crack.Through theoretical research,reinforced concrete shrinkage behavior test and reinforced concrete CT scanning test,the shrinkage and cracking behavior of concrete under the constraint of steel bars is studied.The main research contents and results are as follows:(1)By deriving the shrinkage model of concrete under the constraint of steel bar,the results show that the confined shrinkage strain of concrete increases with the increase of free shrinkage deformation of plain concrete,with the ratio of the elastic modulus of steel to concrete and the reinforcement ratio of concrete.The increase is reduced,and the distance between the steel and the confined concrete affects the ability of the steel to restrain the concrete.(2)Based on the reinforcement ratio,reinforcement method and concrete strength as the research variables,under the sealing condition,the confined shrinkage test and research of concrete under the constraint of 6 sets of steel bars showed that under the restraint of steel bars,when the concrete strength and distribution When the ribs are the same,the higher the reinforcement ratio,the stronger the restraining ability of the steel bars on the concrete,and the greater the risk of concrete cracking;when the reinforcement ratio and the reinforcement method are the same,the higher the concrete strength,the smaller the shrinkage strain.When the concrete strength and the reinforcement ratio are the same,the distributed reinforcement method can make the distribution of the restraining effect of the steel on the concrete more uniform and reduce the risk of cracking.(3)Based on the reinforcement ratio,reinforcement method and concrete strength as the research variables,under the sealing conditions,the CT scan test and research of concrete under the constraint of 9 sets of steel bars were used to verify the restrained shrinkage model of steel bars for concrete,and the following conclusions were drawn.When the concrete is cracked under the restraint of the steel bar,the cracking time is mainly concentrated in 1-3 days after the initial setting of the concrete.The origin of the crack is the edge of the steel bar.The spacing between the cracks has no obvious regularity,and the crack width is basically the same.The crack develops along the direction of the cement matrix and develops toward the diagonal of the concrete farther from the origin of the crack.The pores and defects inside the concrete further induce the crack.