Experimental Study On The Resource Reutilization Of Recycled Fine Powder

With the accelerating process of urbanization in China,the massive demolition of old buildings and the massive construction of new buildings have led to a sharp increase in the total amount of construction waste in China.As an inevitable product of urban construction and development,it has become the main part of urban garbage,accounting for more than 40%.Therefore,the reutilization of construction waste has become an important part of sustainable urban development.The recycled fine powder?RFP?,whose particle size is less than 75 ?m,is generated or directly processed during the preparation of recycled aggregate by construction waste mainly composed of concrete,mortar,stone,brick,and tile.Its promotion and application is an significant way to improve the reuse of construction waste and the utilization rate of construction waste.This paper,which is supported by the major research foundation project of Shandong Natural Science Foundation?ZR2017ZC0737?combines the preparation of the industry standard for "Recycled Fine Powder for Concrete and Mortar" to explore the feasibility of using RFP as an admixture.The main research work and conclusions are as follows:The microstructure,chemical and mineral composition of RFP were observed by advanced testing methods such as SEM and TGA-DSC.The loss on ignition,water content,specific surface area and methylene blue MB value of RFP were determined by reference to relevant standards.The results showed that RFP particles were irregular in shape and polygonal,especially the surface of recycled concrete powder?RCP?was rough and porous.The chemical components of RCP and recycled brick powder?RBP?were mainly Si O₂.Carbonation led to the absence of common hydration products such as Ca?OH?₂ and ettringite in RCP,but the content of calcite was high.RCP had a much higher loss on ignition,water content,specific surface area,and methylene blue MB value than RBP;Different types,fineness?6±2%,21±2%,and 35±2%?of RFPs were prepared by planetary ball mill,and the changes of particle morphology and particle size distributionof RFP were observed too.Besides,the water requirement ratio?WRR?and strength activity index?SAI?of RFP were determined.Studies showed that as the fineness decreases,the RFP particles gradually was refined and the morphology of RFP particle gradually was improved,and the particle gradation of RFP was gradually optimized.The WRR of RCP and RBP decreased gradually,from 106% to 112% and 102% to107%,respectively.The SAI of RCP and RBP increased gradually,from 68% to 73%and 71% to 77%,respectively.Due to the good interfacial structure between RBP and cement paste,RBP had a positive effect on the growth of flexural strength of the mortar containing RBP;Based on the types of RFPs,interval time and amount of Superplasticizer?SP?,the effects of various types of RFP on the loss of fluidity as time?LFT?of mortar and the compatibility with SP?CS?were studied.The results showed that the order of 1h and 2h LFT of mortars mixed with RFPs was the mortar mixed with RCP > the mortar mixed with RBP > pure cement mortar.With the decrease of fineness,the 1h LFT of mortars mixed with RCP and RBP decreased gradually,but the 2h LFT gradually increased.The compatibility of RCP and RBP with polycarboxylate and naphthalene SP was lower than that of ordinary Portland cement,which was reflected in the higher saturation point of SP and the larger 1h and 2h the loss rate of fluidity as time,but the CS of RBP was close to cement,and the compatibility of RCP and RBP with naphthalene type SP was better than that of polycarboxylate SP;The stimulating feasibility of RFPs was investigated by triethanolamine?TEA?-ball milling,composite activator-ball milling,petroleum coke desulfurization slag?PCDS?-ball milling and heat treatment,respectively.The results showed that TEA could significantly improve the RFP efficiency of ball milling.When the particle size of RFP was less than 45?m,the continuous grinding of RCP and RBP would not significantly increase the SAI.The 28 d SAI of RCP and RBP could reach 75% and 78%,respectively.RBP exhibited a good 90 d SAI which could reach 90%,and the SAI of RCP only was 79%.The composite activator-ball mill could better stimulate the activity of RCP and RBP.Their 28 d and 90 d SAI were 80%,81% and 85%,94%,respectively.After ball milling and dispersion,the 28 d and 90 d SAIs of the composite RFP?the mixratio of RCP and PCDS was 1:3?could reach 79% and 83%,respectively.When the thermal excitation temperature was 600 °C,the activity of RCP could be well excited.The 28 d and 90 d SAIs of RCP could reach 80% and 86%.