| The steel reinforced recycled concrete is a kind of composite structure with embedding section steel into recycled concrete and configuring stressed steel bars to resist external loads,which has the characteristics of saving resources and protecting the environment while ensuring the structural strength.Similar to the steel reinforced concrete structure,the bond-slip performance of the interface between section steel and recycled concrete is the foundation of their collaboration.However,the essential difference between recycled concrete and nature concrete is that the incorporation of recycled coarse aggregate changes the structure of new mortar of recycled concrete,which in turn affects the bond-slip performance of the interface between steel and recycled concrete.The current research on the bond-slip performance of steel reinforced recycled concrete is mostly based on the put-out test and the pulling test and the influence of recycled coarse aggregate characteristics on bond-slip is not considered.Therefore,from the perspective of material properties,this paper considers the influence of coarse aggregate pore structure to carry on the beam-type experimental and theoretical study on interfacial bond-slip behavior of steel reinforced recycled concrete.The main research contents are as follows:(1)The pore structure characteristics of recycled coarse aggregate and its influence mechanism on the interface structure change of recycled concrete were analyzed.The microstructure of recycled concrete and ordinary concrete aggregates,mortar,and interfacial transition zone were observed under scanning electron microscope.The results show that the old mortar attached to the surface of recycled coarse aggregate is the essential reason of the difference in pore structure between recycled coarse aggregate and natural coarse aggregate.The hydration degree of new mortar in recycled concrete is less than that of old mortar,which has a larger porosity and exists a few unhydrated cement particles.The surface of the old mortar is rough and has initial cracks generated during the original service and crushing process.The incorporation of recycled coarse aggregate leads to a variety of interfacial transition zones in recycled concrete,and the structure of each interfacial transition zones is different.(2)The pore structure characteristics of recycled concrete with different replacement of recycled coarse aggregate were analyzed by mercury intrusion porosimetry test.The results show that with the replacement of recycled coarse aggregate,the number of gel pores and transition pores of new mortar in recycled concrete decreases,and the number of capillary pores and macropores increases,which results in a corresponding increase in porosity,specific surface area,total pore volume and average pore size.The pore surface tends to tough and the pore structure distribution tends to be complex and irregular.The porosity and average pore size of the new mortar are lager than those of the old mortar,and the pore structure distribution is more complex and inhomogeneous.(3)Based on the parameter of replacement rate of recycled coarse aggregate,a two-stage beam-type experiment was designed and carried out to study the bond-slip behavior between steel and recycled concrete.The development process of cracks and the failure mode of beam-type specimens under bending and shearing action were obtained through the experiment.The slip of the loading end and the free end of the specimens was measured by the displacement meter.(4)The interfacial structure model between steel and recycled concrete was established,and the influence of recycled coarse aggregate pore structure on the interfacial formation mechanism and structural characteristics between steel and recycled concrete was analyzed.The interfacial bond-slip mechanism and bonding failure process considering the pore structure of recycled coarse aggregate were analyzed by the change rule of interfacial bonding force and the stress state of recycled concrete around steel during the experiment.(5)Based on the analysis of the experimental data,a modified calculation method for the strain of the steel section was proposed.According to the statistical regression,the strain distribution of the steel flange and web considering the coarse aggregate pore structure was established,and the distribution of the interfacial bond stress along the anchorage of the steel was calculated.(6)The characteristic bond strength of the interface between steel and recycled aggregate concrete in beam-type experiment was calculated.The results show that the characteristic bond strength of bottom flange increases first and then decreases with the increase of replacement rate.The influence mechanism of pore structure of coarse aggregate on characteristic bond strength was analyzed,and the regression formula of characteristic bond strength considering the influence parameters of pore structure of recycled coarse aggregate was proposed. |
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