| The emergence of recycled aggregate concrete solves the problem of waste landfilling of concrete materials and realizes the reuse of materials,and also improves the impact of construction waste on the environment.However,recycled aggregate concrete has disadvantages in physical and mechanical properties compared to concrete,therefore,research on the modification of recycled aggregate concrete came into being.Steel fiber recycled aggregate concrete is a new type of multi-phase composite material formed by mixing randomly distributed steel fibers in the recycled aggregate concrete.Steel fibers have a significant strengthening and toughening effect on recycled aggregate concrete and can play a better crack resistance.The steel reinforced concrete structure has the advantages of large bearing capacity,good seismic performance,small cross-section,and good overall efficiency,so is widely used in various construction engineering.The combination of steel fiber modified recycled aggregate concrete and steel is not only an environment-friendly structure,but also can give full play to the excellent properties of various materials and overall structures.The good bonding action between steel and concrete is an important basis for ensuring the collaboration work of the two interface,therefore,the study of bond-slip behavior is a basic research work.At present,there are many researches on the bond-slip behavior of steel and concrete or recycled aggregate concrete,however,there are few experimental studies on the bond-slip behavior of steel-steel fiber recycled aggregate concrete(referred to as S-SFRAC).Therefore,four test variables of steel fiber volume ratio,steel fiber aspect ratio,steel cover thickness and steel embedment length were set in this paper,the push-out test of 16 standard test specimens was carried out,and the preliminary study on the steel-steel fiber recycled aggregate concrete(S-SFRAC)was conducted.The main research work and main results obtained in this paper were as follows:(1)The crack types and failure characteristics of the test specimen were summarized: the failure cracks at the steel loading end of the test specimen mainly include bonding cracks and expansion cracks,and the lateral cracks of the test specimen mainly include vertical through cracks and diagonal cracks.All test specimens have longitudinal bond splitting failure,and some test specimens have local compression failure.(2)The measurement of the relative slip of the steel-steel fiber recycled aggregate concrete interface and the strain at the steel flange and web were completed,the relative slip and strain measurement curves both change in a negative exponential form during the ascending section of the load and change linearly during the descending section of the load.(3)The load-slip curve of each test specimen was analyzed,and it was divided into different slip phases.The characteristic bond strength was defined,and the influence of each test variable on the characteristic bond strength was taken into consideration,the formula for calculating the characteristic bond strength of steel-steel fiber recycled aggregate concrete was proposed.The principle and effect of steel fiber reinforcement were studied.The reinforcement effect of steel fiber is shown from the aspects of interface bond strength,interface bond stiffness and interface bond energy consumption.(4)The characteristic slip values were defined,and the average bond stress-load side slip constitutive relationship was established.The laws of equivalent bond stress and relative slip between the interfaces were analyzed and summarized,by introducing the position function H(x)considering relative slip and the position function G(x)considering bond stress,the bond-slip constitutive relationship reflecting the change of position was established.(5)ABAQUS software was used to establish a numerical simulation model for the bond-slip of the test specimen,the interface bonding element was created using the average bond stress-load side slip constitutive relationship,the software simulation calculation of the bond-slip of the test specimen was performed.The stress cloud diagram and load-slip curve obtained by simulation calculation of some test specimens were obtained,and the results are consistent with the test results,the feasibility of the average bond stress-load side slip constitutive relationship is indicated. |
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