Research On Carbonization Of Waste Concrete Powder And Its Application In Brick Makin

Currently,the treatment methods for recycled concrete are extensive,resulting in low value of the products.Additionally,one of the strengthening techniques for waste concrete is carbonation technology,which mainly involves carbonation treatment of recycled aggregates,generating calcium carbonate on the surface to fill pores,and then using them as a substitute for natural aggregates in concrete production.However,the recycled aggregates produced by this method have low activity,making it difficult to achieve efficient utilization.Therefore,in this paper,the recycled concrete was crushed into powder and activated by carbonation,and then the physical and chemical properties of carbonated concrete powder were studied from the micro-nano scale,and the carbonation mechanism was discussed in depth.Finally,the carbonized recycled powder was applied to the preparation of recycled bricks,and the strength formation mechanism of recycled bricks was explored to realize the high value-added utilization of recycled concrete.In this paper,the physical and chemical properties of recycled powder（RP）before and after carbonization were studied by X-ray diffraction（XRD）,thermogravimetric analysis（TGA）,Fourier transform infrared spectroscopy（FT-IR）and nuclear magnetic resonance（MNR）.The simulated solution was prepared according to the ionic characteristics of the cement paste pore solution.The adsorption properties of recycled powder（RP）and carbonized recycled powder（CRP）for related ions in simulated solution were measured by Zeta potential to characterize their surface chemical properties.The surface products of RP and CRP were analyzed by transmission electron microscopy（TEM）,and the effect of recycled powder on cement hydration was explored by scanning electron microscopy（SEM）to determine the activity of recycled powder.Then,the CRP powder and the slag or the calcium hydroxide are used to prepare the recycled brick by pressing and molding.This study examines the strength variation of carbonized CRP and RP-based recycled bricks under different mixing ratios and preparation parameters（steam curing temperature,time,forming pressure,and holding time）.Finally,XRD,TGA,FTIR,SEM and mercury method（MIP）were used to investigate the phase formation,fracture surface and pore structure of recycled bricks,and the formation mechanism of their strength was discussed.The results show that:（1）Ca（OH）₂in RP is completely carbonized within 6h,and Ca CO₃is formed.With the increase of carbonization time,C-S-H,C₃S and C₂S in RP were also carbonized to form silica gel and Ca CO₃.（2）The results of Zeta potential,TEM and SEM show that there is more Ca（OH）₂and C-S-H on the surface of RP.The surface of CRP particles carbonized for 6h is mainly Ca CO₃.The surface of CRP carbonized for 7d was covered with a layer of nano-silica gel,which had high activity and coated the carbonized Ca CO₃.（3）By exploring the mix proportion of recycled brick,it is found that the replacement rate of slag（SL）or Ca（OH）₂is 15%,which is cost-effective.In addition,there is an optimal water-solid ratio.When the water-solid ratio is low,the contact of raw materials in recycled brick in the pressing process is not dense enough.However,with too high water-solid ratio the raw materials will overflow the mold,which is not conducive to the formation of recycled brick.（4）Steam-curing temperature,steam-curing time,molding pressure and holding time also have a greater impact on the strength of recycled bricks.The strength of CRP-based recycled bricks is considerably higher than that of RP-based bricks under different conditions,indicating a significant enhancement in the activity of carbonized recycled concrete powder.Optimal regeneration conditions comprise a 60℃steam-curing temperature,15-hour curing time,and a molding pressure of 20 MPa,with the holding time exhibiting a negligible effect on brick strength.（5）The recycled brick was analyzed using XRD,FTIR,and TGA.The results indicated a significant reaction between CRP and either slag（SL）or Ca（OH）₂.The primary products of this reaction were C-（A）-S-H and C-S-H,which effectively refined the pores in the recycled brick,improved particle bonding,and ultimately led to increased strength development.