Physical Properties And Microstructure Of Aerated Steel Slag Block Prepared By Accelerated Carbonation

Carbonation of steel slag is a combination of resource utilization of steel slag and carbon dioxide emission reduction.In order to further improve the carbon sequestration efficiency of steel slag products,the following aspects were studied in this paper:?1?The present paper discusses investigated the foaming behaviors and microstructure of three aerated steel slag block?ASSB?samples prepared with three different foaming agents?namely animal protein,hydrogen peroxide,aluminum powder?and by accelerated carbonation.It is an advisable method for foamed steel slag products to use the aluminum powder and accelerated carbonation technology.The aluminum powder favored a good foaming behavior for steel slag owing to?i?a high porosity and low dry density,?ii?a high hydration degree of minerals in steel slag,including brownmillerite,larnite,and lime,which confirmed by the analysis of mineral compositions using Rietveld method,and?iii?the interlaced lamellas of monocarboaluminate and calcium silicate hydrate?C-S-H?gel strengthen the bubbles wall,which confirmed by morphology analysis using FE-SEM.After accelerated carbonation,the monocarboaluminate shifted to aragonite,vaterite,calcite and amorphous aluminum hydroxide?Al?OH?₃?,which confirmed by XRD,TGA and FT-IR.The network skeleton formed by aragonite crystals improved the compressive strength of ASSB prepared by aluminum powder.?2?Monocarboaluminate?AFmc?is the main hydration product of steel slag when it foams through aluminum powder,accounting for nearly 30%.After accelerated carbonation,AFmc are carbonated to produce calcium carbonate and amorphous aluminum hydroxide,which is the strength source of the ASSB carbonated.Therefore,this paper is of great significance for the synthesis and carbonation of AFmc.The results show that AFmc is a hexagonal plate with particle size over 4 microns,which is converted into three crystal forms of calcium carbonate?calcite,aragonite,spheroidal aragonite?and microcrystalline aluminum hydroxide after carbonation.In addition,the reactions of the formation and carbonation of monocarboaluminate phase were proved to be thermodynamically possible in this work.?3?The influence of different water-cement ratio and cement content on the performance of steel slag fresh slurry and ASSB was studied,and the changes of compressive strength,porosity,dry density and water absorption rate of ASSB were explained through the connection between fresh slurry and ASSB.With the increase of water-cement ratio,the bonding strength and shear stress of the fresh slurry decrease,and the thickening speed slows down,the porosity and water absorption of ASSB increase,the dry density and compressive strength decrease.With the increase of cement content,the early strength of the fresh slurry increases gradually,the setting time decreases gradually,the thickening speed increases rapidly,the porosity of the ASSB decreases gradually,the compressive strength increases,and the dry density increases.