Experimental Study On Bond Slip Behavior Of Reinforced Recycled Concrete Under Different Loading Rates

As China's urbanization develops faster and faster,various infrastructures and civil buildings are increasing,and the demand for concrete is increasing,so a large amount of natural resources are needed.In addition,because all kinds of engineering buildings have longevity,especially in China,the life of buildings is much less than other developed countries,which will generate a lot of construction waste.If it is not reasonable to place and use these Construction waste can cause a lot of pollution to the environment.Recycling of construction waste can effectively alleviate the problem of resource consumption pressure and increasing construction waste.However,during the actual work,the reinforced concrete structure will not only be affected by static load,but also by other dynamic loads.Therefore,it is urgent to study the influence of loading rate on the performance of recycled concrete.In the early part of this paper,we studied various domestic and foreign literatures,including various mechanical properties and bond-slip properties of ordinary concrete and recycled concrete,determined the test plan,carried out the central pull-out test,and then combined the test data for theoretical analysis.Completed the following work;1.In this test,the effects of three parameters on the bond-slip performance of recycled concrete were studied by a central pull-out test without stirrups,namely:the strength grade of recycled concrete,the replacement rate of recycled coarse aggregate and the test loading rate.A total of 20 sets of five test pieces with a strength grade of C20,a substitution rate of 30%,50%,and 70%,and a strength grade of C40 and a substitution rate of 30%and 50%,respectively,were produced.The test pieces correspond to four loading rates of 0.1KN/s,1KN/s,2KN/s and 5KN/s,and 20 kinds of bond slip curves are obtained,which are similar in shape to ordinary concrete.2.The test pieces with a strength grade of C20 recycled coarse aggregate at a loading rate of 0.1KN/s,1KN/s,2KN/s,and 5KN/s are 30%,and the strength grade is C20 recycled coarse aggregate.For the test pieces with the substitution rate of 50%and 70%,the test piece with the strength grade of C40 recycled coarse aggregate replacement rate of 30%and the strength grade of C40 recycled coarse aggregate replacement rate of 50 were also obtained.The test pieces of%are compared.The test results show that the bond strength of recycled concrete can be improved by increasing the replacement rate of recycled coarse aggregate when other conditions are the same.3.The test grades with a strength grade of C20 and a coarse aggregate replacement rate of 30%at a loading rate of 0.1KN/s,1KN/s,2KN/s,and 5KN/s,respectively,and a strength grade of C40 recycled coarse aggregate For the test piece with a substitution rate of 30%,the test piece with the strength grade of C20 recycled coarse aggregate replacement rate of 50%and the strength grade of C40 recycled coarse aggregate replacement rate of 50%were also tested.For comparison,the test results show that increasing the strength grade of recycled concrete can effectively improve the bond strength between steel and recycled concrete.4.By comparing the bond slip curves of each test piece under the loading of 0.1KN/s,1KN/s,2KN/s and 5KN/s,it can be concluded that when the strength grade is the same,the recycled aggregate When the substitution rate is the same,the higher the loading rate,the greater the bond strength of the recycled concrete.5.The initial bond stiffness k0 and the ultimate bond stiffness ku are defined.The geometric meaning of the bond stiffness is the slope of the ascending segment of the concrete bond slip curve.The actual meaning is the required pull corresponding to the relative slip of the steel bar and the concrete.Pulling force,the larger the value of ku,the greater the external pulling force required for the specimen to slip the same distance during the failure process,indicating that the bonding performance of the specimen is better,and it is concluded that with the concrete strength grade The increase in the replacement rate of the aggregate and the increase in the aggregate rate and the decrease in the loading rate increase the value of k0/ku.6.The bond slip curves of C20Q30,C20Q50 and C20Q70 specimens at four loading rates were compared to obtain the relationship between the ultimate bond strength and the strength criterion of the recycled coarse aggregate replacement rate and loading rate.7.The bond-slip constitutive model of steel recycled concrete under the influence of three grades of recycled concrete strength grade,recycled coarse aggregate replacement rate and loading rate is given,and the values of various parameters in the model are obtained according to the experimental data.