Study On Multi-interface Microstructure Of Recycled Concrete

With the environmental problems,economic problems and social problems caused by construction waste are increasingly prominent,the Chinese government has paid more and more attention to the recycling of construction waste resources.If we can be prepared using waste recycled aggregate concrete,not only can save a lot of natural aggregate resources,but also reduce environmental pollution,which is of great significance to the sustainable development of the construction industry and the improvement of the environment.But due to the complexity of the source and the strength grade fluctuation of waste concrete,the recycled aggregate with surface often accompanied by a large number of hardening cement mortar is angular and surface roughness.Therefore,the use of recycled aggregate prepared recycled concrete is a more complex multi-phase composite material.In order to improve the performance of recycled aggregates and to find out the deterioration mechanism of recycled concrete,this paper attempts to study the microstructure of recycled concrete from the microscopic point of view,based on the interface structure strength and interface morphology of the multiple interface structure model.Supported by the National Natural Science Foundation of China(51578297,51378270),the following research work is carried out:1.Compared with ordinary concrete,recycled concrete has multiple interface structure.In this paper,the method of reconstructing the multiple interface structure of recycled concrete is proposed for the first time.This method can be used to establish the reconstruction model of three interface structures in recycled concrete: Old aggregate-old slurry interface(LG-LJ),old aggregate – new slurry interface(LG-XJ),Old slurry – new slurry interface(LJ-XJ).The method can be applied to the study of microstructure,interface mechanics and lifting technology of recycled concrete.2.On the basis of constructing the multiple interface model of regenerated concrete,the existing models were sliced and polished,and then the Vickers hardness of the recycled concrete interface structure was tested by using microhardness tester to characterize the transition zone of recycled concrete interface.The results show: the microhardness of mortar matrix and interfacial transition zone increases with the increase of strength grade of recycled concrete and the extension of curing age.Waste concrete processed into the recycled coarse aggregate,the preparation of low strength or the same strength recycled concrete,the weak interface for the LG-XJ interface,adhesive mortar on the surface of the recycled aggregate does not need to be removed in the absence of erosive destruction of the waste concrete.While the weak interface of high strength recycled concrete is LG-LJ interface and LJ-XJ interface,and the adhesive mortar on the surface of recycled coarse aggregate should be removed.3.Based on the multiple interface structural model of the recycled concrete,the micro-morphology observation and the hydration product analysis of the regenerated concrete interfacial transition zone were carried out by scanning electron microscopy(SEM)and energy dispersive spectrometer(EDS).The results show: the interface will have a fine cracks and holes exist.The fractures in the LG-XJ interface and LJ-XJ interface are dominated by primary fractures,and LG-LJ interfaces are mostly secondary fractures.The fracture extends from the interface to the mortar matrix through the interface transition zone.The hydration products in the interface transition zone mainly consist of network-like C-S-H gel and C-S-H gel in lamellar form,which is the main source of interfacial transition zone strength.Ca(OH)2 mainly exists in the form of interfacial linker and crack filler,which can repair the internal defect of interface transition zone and form enrichment in certain area.At the same time,the surface of C-S-H gel surface a small amount of ettringite attached.