Study On Basic Properties And Application Of Recycled Fine Powder From Construction Waste

Along with the rapid development of urbanization and the upgrading of industrial innovation,the types and quantity of urban waste have also increased rapidly.As the inevitable product of urban renewal,construction waste is the largest part of urban waste,accounting for more than 50%.The recycling of construction waste has become a huge need for sustainable urban development.Recycled fine powder is a kind of powder with particle size less than 0.075mm in construction waste.Its popularization and application is an important way to increase the proportion of construction waste resources.This paper combines the development of the industry standard for"Recycled fine powder used in concrete and mortar"to explore the feasibility of using recycled fine powder as a mineral admixture.In this paper,the basic properties of recycled fine powder,including water content,specific surface area,water demand ratio,MB value,chemical composition,mineral composition and particle appearance of recycled fine powder are studied.This paper also explained the effect of the dosage,proportion and fineness of recycled fine powder on workability and strength of cement mortar;the effect of recycled fine powder on the loss of cement fluidity over time and the compatibility with water reducer;the effect of recycled fine powder on the strength and durability of concrete.The hydration products of recycled fine powder-cement system were analyzed by XRD and SEM.The results show that the recycled fine powder particles are disorderly in shape and have many edges and corners.The recycled fine powder has internal porous and large specific surface area.It also has high water demand,strong adsorption and high SiO2 and CaO content in the chemical composition.When the amount of recycled fine powder increases,the fluidity of cement mortar gradually decreases,but the fluidity decreases by less than 5%when the content is less than 15%.As the fineness of the recycled fine powder increases,the time-dependent loss of the fluidity of the cement slurry decreases,the recycled fine powder satisfying Andreasen equation can improve the cement particle size distribution,and the filling effect of micro-aggregate is obvious;the adaptability of the recycled waste brick fine powder to the polycarboxylate superplasticizer is worse than that of the the ordinary Portland cement,and the compatibility between them is similar to the naphthalene water reducer.With the addition of recycled fine powder,the flexural strength and compressive strength of cement mortar at different ages are reduced.When the content of recycled fine powder is less than 20%,the 28d strength activity index of cement mortar can reach 75%.The active oxide in the recycled waste brick powder reacts with Ca?OH?₂ in the cement hydration product and the hydrated calcium silicate gel has been formed,which densifies the entire structure and enhances the strength of cement motar and concrete.The incorporation of recycled fine powder reduces the overall compressive strength of concrete,and when the content exceeds 20%,the strength will decrease obviously.When the amount of recycled fine powder is less than 30%,it has little effect on the chloride ion permeability of concrete.