Hydration Activity And Expansibility Of MgO-FeO-MnO-CaO Phase In Steel Slag

The silicate phase contained in steel slag has cementitious activity,which makes it potentially valuable for applications in the field of building materials.However,the presence of over-burned f-CaO and f-MgO causes problems with the volume stability of the steel slag.And the solid solution phase formed by divalent metal oxides within the steel slag（RO phase）.It mainly consists of MgO and FeO,and solid solution of trace amounts of MnO and CaO,with a content of about 30%.There is no uniform conclusion has been reached as to whether the RO phase affects the hydration activity and swelling properties of steel slag,thus limiting its application in cement concrete.In this paper,the solid solution of MgO-x FeO-0.2MnO-0.1CaO system with different ratios was simulated and synthesized according to the chemical elemental composition of the RO phase in the steel slag.Then the hydration activity of the synthesized four-component RO phase was studied under ambient,boiling and autoclaving,respectively.Carbonization experiments were conducted on the RO phase to analyze the effect of carbonization on the RO phase.It is clear that the RO phase after carbonation treatment will improve the volume stability of the cementitious material.The RO phase composition in steel slag is variable and widely distributed.The hydration experiments of the quaternary MgO-FeO-MnO-CaO phase yielded that the components that undergo hydration are MgO and CaO.Under the condition of autoclave,the hydration rates of the quaternary MgO-FeO-MnO-CaO phase with the best hydration performance was 18.80%for MgO and 50.45%for CaO,respectively.The four-component RO phase exhibits low hydration activity,and delayed hydration causes poor volume stability of the steel slag.For the carbonization experiments of the quaternary MgO-FeO-MnO-CaO phase.The results show that the four-component RO phase can be carbonized for the lower FeO content.The components that undergo carbonation are mainly MgO and CaO.And by extending the carbonation time,the amount of CO₂fixed and sequestered by the RO phase increases.After 10h of carbonization treatment,52.51%of MgO was carbonized to Mg CO₃and55.75%of CaO was carbonized to Ca CO₃in the four-component RO phase with the highest carbonization activity.To some extent,the carbonation reaction depletes the content of magnesium and calcium oxides in the RO phase.By comparing the expansion rate of the four component RO phase before and after carbonization.It is concluded that the carbonization of four-component RO phase can improve the poor volume stability to a certain extent.