Research On Failure Mechanism Of Recycled Aggregate Concrete Modified By Nano Materials

Recycled aggregate concrete(RAC)is a kind of cement based composite material which is partly recycled from waste concrete and has the characteristics of green,environmental protection and so on.Although the application prospect of RAC is broad,so far,RAC has a certain disadvantage in mechanical performance compared with ordinary concrete.Therefore,many researchers have been exploring the change of this situation.In this paper,the failure mechanism of RAC and the performance improvement of Nano material on RAC were studied on how to improve the failure properties of RAC.Through high speed real-time camera shooting the development and evolution process in RAC failure process of crack,by comparing the different replacement ratio of recycled aggregate,water cement ratio of the initial position and development process of crack development,this paper made a qualitative analysis of RAC failure mechanism,to further define the interface transition zone(ITZ)is RAC weak area,which lays foundation for the use of Nano silicon sol(NS),Nano CaCO3(NL)to improve the research on the mechanical properties of RAC.Therefore,based on the existing research results of RAC,this paper focuses on RAC damage mechanism,ITZ and Nano silica sol,Nano calcium carbonate to the RAC strength.the main conclusions are as follows:(1)From the failure process of RAC,the failure process of RAC and ordinary concrete is basically similar:presenting two of the top of the pyramid shaped failure surface.But the difference is that in the destruction of RAC,the failure surface mostly presents the fracture of old mortar and the destruction of ITZ.(2)Initial cracks tend to be concentrated in the RAC recycled aggregate ITZ in the crack process of RAC,and where the crack is depending on the strength of interface in the new mortar and old mortar around ITZ.It usually develops from the weak area.Then,with the increase of the load,the crack further extends to the four sides,and finally forms a failure mode,which is mainly composed of a longitudinal crack and a plurality of transverse oblique cracks.(3)From the study of the strength of RAC modified by Nano materials,Nano silica sol can significantly improve the strength of RAC,the early compressive strength is increased by 21%-24%,and the later compressive strength is increased by 14%-21%.Nano CaCO3 is not obvious to improve the performance of RAC,and it is not helpful to improve its strength.(4)Whether the scanning electron microscopy(SEM)observation of recycled aggregate concrete ITZ morphology,or the mercury testing technology(MIP)analysis of pore structure parameters of recycled aggregate concrete ITZ shows that NS can effectively compact hole structure of the transition zone in RAC interface,enhancing the mechanical properties of RAC.(5)Comprehensive research on micro level and macro level shows that NS of good dispersion has good volcano activity,which promotes the hydration reaction of RAC,and to a certain extent the combination of hydration products and materials’ characteristics can fill RAC pore structure,strengthen its own performance.But for the agglomeration effect of NL,it is difficult to play out the Nano characteristics,so its effect on RAC is not obvious,intend,the mechanical properties can be damaged to some extent.