Experimental Study On Enhancement Of Mechanical Properties Of Recycled Coarse Aggregate Of Waste Concrete

Under the background of the rapid development of urbanization in China,the disposal of construction waste generated in the process of urban reconstruction has become a hot issue.Waste concrete accounts for the largest proportion of construction waste generated.Adhering to the concept of "limited resources,infinite cycle",the reuse of waste concrete can not only reduce the excessive mining and waste of natural resources,but also avoid the pollution caused by waste concrete to the living environment of human beings.Real sense to achieve the purpose of saving resources and reducing the emission of environmental harmful substances,to achieve sustainable development strategy.First of all,this paper designed a set of physical strengthening equipment of recycled coarse aggregate,the main role is to remove the surface adhesion mortar of recycled coarse aggregate,to get a higher quality of recycled coarse aggregate.The physical properties such as apparent density,bulk density,water absorption rate and crushing value of the original reclaimed coarse aggregate and the physical strengthened reclaimed coarse aggregate were preliminarily tested,and the basic physical properties of the reclaimed coarse aggregate before and after physical strengthened were analyzed.Results show that the physical strengthen basic physical properties of recycled coarse aggregate after good improvement,including water absorption and crushing index to improve the effect is more outstanding,physical strengthened after the water absorption of recycled coarse aggregate was reduced by 32.9%,crushing index was reduced by 23.9%,which showed that adhered on the surface of the recycled coarse aggregate mortar have bigger influence on the basic physical properties of recycled coarse aggregate.Secondly,nano-SiO2 solution with the concentration of 1%,2%and 3%was prepared to soak the recycled coarse aggregate for 24h and 48h,and chemical strengthening was carried out on the basis of physical strengthening to explore the influence of nano-SiO2 solution on the basic physical properties of the recycled coarse aggregate.In this paper,a comparative analysis was made on the recycled coarse aggregate after physical and chemical strengthening.The results showed that the water absorption rate of the recycled coarse aggregate after chemical strengthening was reduced by 57%at most,and the crushing index was reduced by 42.3%at most.The optimum soaking concentration was 2%,and the optimum soaking time was 48h.Then,to strengthen mixing way,selecting the vibration in the preparation of recycled coarse concrete mixing process,explore the physical way of strengthening methods,chemical strengthening method and mixing strengthening effect on recycled coarse bone mechanical strength of concrete,the results show that the old cement mortar adhered on the surface of the recycled coarse aggregate is the mechanical strength of recycled coarse aggregate concrete by one of the main factors.The compressive strength,splitting tensile strength and flexural strength of recycled coarse aggregate concrete strengthened by nano-SiO2 solution are all improved to varying degrees at different ages,but the improvement effect of nano-SiO2 on the early strength of recycled coarse aggregate concrete is significantly higher than that of the late strength,and when the concentration of nano-SiO2 solution exceeds 2%,It will even lead to the strength decrease of recycled coarse aggregate concrete.Compared with ordinary mixing,the mechanical properties of all types of recycled coarse aggregate concrete prepared by vibration mixing are improved,and the average increase of 28d compressive strength is more than 5%.Vibratory mixing technology can improve the uniformity of concrete,enhance the strength of the interface transition zone in concrete,and improve the low efficiency zone in the mixing process.By longitudinal comparison between the reference group and the control group,the flexural strength and splitting tensile strength of C30 recycled coarse aggregate concrete can be significantly improved by vibration mixing process.Finally,this paper used scanning electron microscopy to analyze the microstructure of recycled coarse aggregate concrete under different strengthening modes,and the results showed that:Under the same water-binder ratio,the number of cracks and pores on the section of the recycled coarse aggregate concrete after physical strengthening is reduced,and the structure is relatively compact,which fully shows that the basic mechanical properties of the recycled coarse aggregate concrete are greatly affected by the mortar attached to the surface of the recycled aggregate.The essence of chemically reinforced recycled coarse aggregate concrete is to improve the pore structure of recycled coarse aggregate,promote the hydration of cement and react with hydration products to generate C-S-H gel,so as to refine the interface structure of recycled coarse aggregate and make the transition zone of old and new interface more integrated.The pore cracks in the interface transition zone of recycled coarse aggregate concrete prepared by vibration mixing are dispersed and the hydration reaction is uniform,which provides a strong generating environment for C-S-H gel and improves the microstructure and strength of recycled coarse aggregate concrete.