Bond Behavior Between Recycled Coarse Aggregate Concrete And Rebar After Salt-frost Cycles

A large amount of construction waste is generated during the demolition of old buildings,as a result of this production,the problems of the environmental pollution and the depletion of landfill space are becoming serious nowadays.Recycling construction waste through the development and application of recycled coarse aggregate concrete(RAC)is one way to solve these problems.The technology of RAC is beneficial from the perspective of environmental preservation and effective utilization of resources.In addition,a good state of bond behavior is the basic for co-ordinated working of reinforced concrete.However,in zones of middle and high latitudes,the reinforced concrete(RC)structures in marine environments are damaged due to salt-frost cycles.Therefore,it is necessary to investigate the bond behavior between RAC and rebar after salt-frost cycles.In addition,many RC structures,e.g.roads,bridge structures and industrial constructions,are also subjected to repeated loading.The bond behavior between RAC and rebar decreases severely under salt-frost and repeated loading.Therefore,it is necessary to investigate the bond behavior between RAC and rebar under salt-frost and repeated loading.In this paper,the basic properties of RAC after salt-frost cycles are investigated by fast freeze-thaw cycle test,which mainly includes the appearance,the mass,the cubic compressive strength and the relative dynamic elastic modulus of RAC.The results show that the frost resistance of RAC in salt solution is lower than that in water,and the frost resistance of RAC is lower than that of natural coarse aggregate concrete(NAC).According to the existing theory of salt-frost damage,the salt-frost damage mechanism of concrete is analyzed,and the reason for the poor salt-frost resistance of RAC is explained.The bond behavior between RAC and rebar after salt-frost cycles is investigated by pull-out test,which mainly includes the bond failure mode,initial slip bond strength,the ultimate bond strength,the relative bond strength,the residual bond strength,the peak slip and the bond-slip curve.The results show that the degradation degree of bond behavior of RAC specimens in salt solution is higher than that in water after the same salt-frost cycles,and the degradation degree of bond behavior of RAC specimens is higher than that of NAC specimens.The stirrups inhibit the degradation of bond behavior of RAC specimens after salt-frost cycles.A prediction model of the bond-slip between RAC and rebar after salt-frost cycles is established,and the influence of salt-frost cycles on the bond-slip distribution along with the rebar is investigated.The deterioration mechanism of bond behavior between concrete and rebar after salt-frost cycles is analyzed,and the reason for the serious deterioration of bond behavior between RAC and rebar after salt-frost cycles is explained.The reason is that the development speed of the cracks caused by salt-freeze cycles and the cracks caused by extrusion of the rebar ribs in RAC specimens are faster than that in NAC specimens,and the two types of cracks in RAC specimens are more likely to converge.The bond behavior between RAC and rebar under salt-frost and repeated loading is investigated by pull-out test,and compare with that under salt-frost and monotonic loading.The results show that the ultimate bond strength of the specimens under repeated loading is lower than that under monotonic loading after the same salt-frost cycles,while the peak slip of the specimens under repeated loading is higher than that under monotonic loading.The repeated loading resistance coefficient of RAC specimens after salt-frost cycles(in salt solution)is lower than that after normal freeze-thaw cycles(in water);the repeated loading resistance coefficient of RAC specimens is lower that of NAC specimens.A prediction model of the bond-slip between the RAC and rebar under salt-frost and repeated loading is established,and the influence of repeated loading on the bond stress distribution along with the rebar is investigated.The deterioration mechanism of bond behavior between RAC and rebar under salt-frost and repeated loading is analyzed,and the reason for change in bond stress distribution caused by repeated loading is explained.The bond behavior between RAC and rebar after salt-frost cycles is analyzed by the ABAQUS finite element software.The finite element model is verified by experimental results,and the influence of different parameters on the bond behavior between RAC and rebar is investigated.