| The process of crude steel smelting discharges large amounts of carbon dioxide and steel slag(accounting for 10-15 wt.%of crude steel).Carbonation curing of steel slag to prepare building materials products was proposed in this paper.It can not only realize the carbon capture,but also realize the efficient utilization of steel slag,and at the same time,building materials with excellent performance can be produced.The following research about carbonation curing of steel slag were carried on and the main achievements are as follows:(1)Carbonation curing of steel slag can improve its volume stability effectively.Steel slags contain large amounts of free calcium oxide(f-CaO)and free magnesium oxide(f-MgO),which will cause poor volumetic stability and limits its application in the field of building materials.The results showed that the carbonation rate of f-CaO and f-MgO were rapid,and the contents of f-CaO and f-MgO decreased from 4.21%and 1.12%to 0.60%and 0.36%,respectively,after 2 h of carbonation.After steaming experiment,the steel slag without carbonation curing collapsed.However,the volume stability of steel slag was improved obviously after carbonated for only 10 minutes.The expansion degree gradually decreased from 0.62 ‰ to-0.2 ‰ with increasing carbonation curing time.(2)?-C2S showed greatest contribution to the compressive strength development in the carbonation progress.?-C2S can absorb more CO2 but make less contribution to compressive strength development.Steel slag with varing chemical compositions and mineral compositions showed significant differences in carbon capture ability and compressive strength development.The compositions of steel slags were calculated quantitatively and carbon capture ability of steel slag was evaluated by its mineral compositions.The main minerals in steel slag were synthesized in laboratory conditions and their carbon capture ability,carbonation products and compressive strength were preliminarily explored and the specific strengths of different minerals were defined in this paper.The results indicated that the main minerals in the steel slag are ?-C2S/?-C2S,bredigite,merwinite,akermanite,mayenite,cuspidine and srebrodolskite.The results showed that calcium carbonate and gels produced in carbonation progress of different minerals are all different.And the differences of carbonation products lead to a greater difference in strength.(3)The performances and structures evolution of carbonation products showed important effects on compressive strength development.The products of carbonation of ?-C2S are mainly calcite,amorphous C-S-H gel and silica gel.The calcium/silicon ratio of C-S-H decreases and its chain length increases in carbonation process.The carbonation products of ?-C2S are mainly calcite,vaterite and amorphous silica gel.Calcite and C-S-H gel impart ?-C2S higher compressive strength in carbonation progress.?-C2S and ?-C2S are dominant minerals in steel slag and are also important sources of strength development and carbon sequestration.The carbonation performance of ?-C2S/?-C2S are important for carbonation of steel slag and other C2S based new low-calcium cement.(4)Steel slags contain C-S-H gels with different C/S ratio,and it also produces C-S-H gels with different C/S ratio in carbonation curing progress.So the carbonation performance of C-S-H gels were analyzed in this paper.The effects of C/S ratio on carbonation degree and microstructures of C-S-H were analyzed.The results indicated C-S-H with higher C/S ratio showed higher carbonation rate and can absorb more CO2.Calcium carbonate formed in accelerated carbonation progress showed wider decomposition temperature range.Vaterite and aragonite decomposed in the range of 400?620 ?,and calcite decomposed in the range of 650?800 ?.The average gel pore size and specific surface area decreased in the carbonation process.Ca2+ in C-S-H gel gradually reacts with CO2 to form calcium carbonate,and silicon tetrahedron formed Q3 and Q4 structure with a higher polymerization degree,which also resulting in volume shrinkage.So C-S-H produced lower compressive strength due to shrinkage cracks,although it can absorb more CO2. |
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