Experimental Study On Bond-slip Behavior Of Steel-fiber High-strength Recycled Concrete

With the rapid development of urbanization in China,the replacement of old and new concrete structures is also accelerating.In this process,not only more steel and concrete are needed,but also a lot of waste concrete is produced.If these waste concrete cannot be reused,it will cause serious environment pollution.The application of recycled concrete can reduce the consumption and waste of natural resources.At present,the research staff’s research on the role of rebar and other recycled engineering concrete bonding is relatively mature,but the research on the bonding of high-strength recycled concrete and rebar of steel fiber is still lacking.The basic properties of recycled concrete can be effectively improved by adding steel fiber with better tensile properties.Adding steel fiber may directly change the bonding mechanism of the original concrete interface and affect the performance of concrete,so it is necessary to conduct systematic analysis through tests.The recycled concrete used in this experiment is C60 highstrength recycled concrete,through the non-hamstring-bound monotonous loading center pull test piece pull test,study the regeneration of coarse aggregate replacement rate(0%,30%,50%,75%,100%)and steel fiber addition rate(0%,0.35%,0.8%,1.5%)of the two parameters on the steel fiber high-strength recycled concrete stick performance effect,analysis of the difference of bonding performance.1.Based on the results of the experiment and the theoretical analysis,the ultimate bond strength of concrete increases with the increase of steel fiber addition rate under the condition of the same replacement rate of coarse aggregate.With the increase of the addition rate(0%,0.35%,0.8%)of steel fiber,the ultimate bond stress of concrete specimens increases obviously.With the increase of the addition rate of steel fiber from 0.8% to 1.5%,the influence on the increase of ultimate bond stress of concrete specimens begins to weaken;Under the same addition rate of steel fiber,when the replacement rate of recycled coarse aggregate is in the range of 0%,30% and 50%,with the increase of the replacement rate of recycled coarse aggregate,its ultimate bond stress starts to decrease slightly.When the replacement rate of recycled coarse aggregate is in the range of 50%,75% and 100%,with the increase of the replacement ratio of recycled coarse aggregate,the decrease rate of ultimate bond stress begins to increase.2.Based on the results of the experiment and the theoretical analysis,under the condition of keeping the replacement rate of recycled coarse aggregate unchanged,the specimens without adding steel fiber mainly suffered from splitting failure,the bonding force instantly drops to 0,and the bond-slip curve has no descending section.When the addition rate of steel fiber is 0.35% and 0.8%,splitting pull-out failure occurs and the bond-slip curve is complete.When the addition rate of steel fiber is 1.5% of the specimen,pull-out failure occurs and the bond-slip curve is complete;The increase of the replacement rate of recycled coarse aggregate has little effect on the failure mode of the specimen,which mainly depends on the addition rate of steel fiber.3.Based on the results of the experiment and the theoretical analysis,when the addition rate of steel fiber remains unchanged,the replacement rate of recycled coarse aggregate increases,and the slippage of steel bar decreases;Keeping the replacement rate of recycled coarse aggregate unchanged,when the addition rate of steel fiber increases,the slippage of steel bars also increases.When the addition rate of steel fiber is 0.8%,the slippage of steel bar reaches the maximum value.4.Through the analysis and calculation of the experimental data obtained from the cube compressive test,it is found that the conversion coefficient of the compressive strength of steel fiber high-strength recycled concrete specimens is mainly in the range of 0.89,0.90 and 0.91,so it is feasible for the cube compressive strength conversion coefficient to be in the range of 0.89-0.91.5.By analyzing the test results of 20 groups of recycled concrete specimens,the strength failure criterion formula of the ultimate bond strength of concrete under the influence of the addition rate of steel fiber and the replacement rate of recycled coarse aggregate is obtained,and the bond-slip constitutive relation model of steel fiber highstrength recycled concrete is given.