Effect Of Different Erosion Conditions On Interface Performance Of Recycled Concrete Mixed With Fly Ash

Recycled concrete as a complex multiphase material,which contains three kinds of interface structure: Old aggregate-new slurry interface(LG-XJ interface),old slurry-new slurry interface(LJ-XJ interface)and old aggregate-old slurry interface(LG-LJ interface).These complex microscopic interfacial structures are important for the study of the durability of recycled concrete as the weakest link in recycled concrete.In this paper,the change of structural performance of different interfaces of recycled concrete with different strength grades under different effects of sulphate corrosion,chloride corrosion and carbonization are discussed by using the reconstructed model of recycle concrete.At the same time,the effect of external admixture on the performance of weak interface of recycled concrete was studied by adding fly ash.The problem of durability damage of recycled concrete is revealed through the study of microscopic mechanics and microstructure characteristics of interface transition zone,which for the performance of recycled concrete and large-scale promotion and application has a profound significance.(1)The micro-hardness values of different interfaces at different grades after 5% Na2SO4 solution eroded were measured by micro-hardness tester to determine the transition zone width of the fly ash recycled concrete interface.The influence of sulfate on the microstructures of different interfaces of fly ash recycled concrete at different ages was studied and the micro-morphology of recycled concrete was observed by scanning electron microscopy(SEM).Comprehensive utilization of multiple interface structure of the micro-mechanics and micro-morphology of the two changes in the law,the mechanism of performance degradation of recycled concrete with fly ash by sulfate was revealed from the micro-level.The results show that the interfacial transition zone width of LG-XJ interface and LJ-XJ interface and LG-LJ interface of the fly ash-regenerated concrete decreases first and then increases,and the micro-hardness values increase first and then decrease with the growth of sulfate salt age.And the performance of anti-sulfate attack of recycled concrete with fly ash is improved.(2)The change of the microhardness value of the interface with different strength grade fly ash recycled concrete after 3.5% NaCl solution erosion was carried out to determine the transition zone width of the interface of the fly ash mixed concrete.The influence of chloride salt on the microstructure of regenerated concrete with different fly ash at different ages was studied.And combined with the SEM micro-morphology of the multiple interface of recycled concrete,the mechanism of deterioration of recycled concrete mixed with fly ash was revealed from the micro-level.The results show that the interfacial transition zone width of LG-XJ interface and LJ-XJ interface and LG-LJ interface of the fly ash-regenerated concrete is gradually increasing the law of variation,micro-hardness values are gradually decreased trend with the growth of chloride salt age.And the chloride ion resistance of recycled concrete with fly ash is improved.(3)The microhardness values of the different interfaces of the fly ash regenerated concrete with different strength grades were measured by microhardness tester,and the width of the transition zone was obtained.The influence of microstructure on the interface of recycled concrete with fly ash before and after carbonization was studied.The microstructure of the recycled concrete was observed by scanning electron microscopy(SEM).Comprehensive utilization of multiple interface structure of the micro-mechanics and micro-morphology of the two changes in the law,The mechanism of performance degradation of recycled concrete with carbonized fly ash is revealed from the microscopic level.The results show that the interfacial transition zone width of LG-XJ interface and LJ-XJ interface and LG-LJ interface of the fly ash-regenerated concrete is gradually increasing the law of variation,micro-hardness values are gradually decreased trend after carbonization.And the anti-carbonization performance of recycled concrete with fly ash is reduced.