Experimental Study On Bond-Slip Performance Of Steel Reinforced Rrecycled Concrete Based On Pushout Test

The recycled concrete referred to in this paper is the concrete prepared by replacing natural coarse aggregate with recycled coarse aggregate after crushing and grading of waste concrete.Due to the large amount of waste concrete accumulation,serious environmental pollution and low utilization rate,the recycling of waste concrete has become a hot issue in the field of civil engineering research.With the high quality of China’s economic construction,sustainable development requirements,for environmental protection needs to make natural sand and gravel mining is limited,but also caused by a shortage of resources;and recycled coarse aggregate sources,large amounts,according to the structural strength requirements can be fully or partially replaced by natural coarse aggregate used in concrete,construction of recycled concrete structures.It can not only realize the bulk consumption and waste utilization of waste concrete,but also reduce the consumption of natural aggregate resources,which can help to realize the sustainable development of construction industry.In this paper,eight groups of 14 specimens were fabricated with 10%,60% and 100%coarse aggregate replacement rates as the basic parameters to carry out the bond-slip rollout test of recycled concrete with steel sections.Based on the test results,the changes of chemical bond force,frictional bond force and mechanical bite stress at different loading stages were analyzed;the influence mechanism of recycled coarse aggregate on the bondslip behavior of steel-recycled concrete was analyzed,and the distribution law of the bond surface of recycled concrete was determined by its bond-slip stress-strain curve;the mechanical model of the interfacial bond failure of steel-recycled concrete was established and the mechanical mechanism of the interfacial bond failure of steel-recycled concrete was investigated from the stress perspective.The mechanical model of the interfacial bond failure of steel recycled concrete is established and the mechanical mechanism of interfacial bond failure is analyzed from the stress point of view,the bond strength calculation formula is proposed,and the bond-slip damage criterion is established.The main research contents of this paper are as follows:(1)Under different replacement rate of recycled aggregate concrete,considering the strength grade of recycled aggregate concrete,the thickness of flange protective layer of section steel,the thickness of protective layer of web of section steel,anchorage length,volumetric hoop ratio and longitudinal reinforcement ratio,theoretical modelling and experimental analysis were carried out using the full displacement curve of recycled concrete with steel reinforcement.A simplified model of the load-displacement curve of reinforced concrete reinforced with recycled materials is proposed,and the change rule of strain in the process of pushing out is summarized.(2)By means of ANSYS finite element analysis software,the numerical simulation of the position function of the profile recycled concrete launch specimens can prove the accuracy of the finite element model after comparative analysis,and the characteristic bond stress and slip distribution laws are obtained by processing and analyzing the results of the simulation results and the characteristic slip values derived from the tests,and the new average bond-slip intrinsic structure relationship is established and corrected,and its correctness and applicability are verified.(3)After the test analysis,the crack growth pattern and damage morphology were recorded and analysed,and the effect of the test on the strength level and replacement rate of the recycled concrete,the thickness of the transverse flange protection layer and the thickness of the transverse web protection layer were investigated,the anchoring length,the hoop distribution rate and the reinforcement rate of the longitudinal reinforcement on the bond strength was found and introduced,and one formula for expressing bond strength was also summarised.(4)Through the study data of the section steel recycled concrete structure,Formulas for calculating the critical thickness of the protective layer and the minimum volume fraction of the recycled reinforced concrete ring structure were developed,a reliability analysis of the anchorage length of recycled reinforced concrete was performed,and a formula for calculating the critical anchorage length was proposed.Based on the study of the steel section recycled concrete structure,we proposed a new damage criterion,i.e.,bond-slip damage criterion.