Effect of Calcium Fluoride on Slag Cementitious Activity and Volume Stability

The cementitious activity and the volume stability of reconstruction steel slag were improved by adding different proportion of calcium fluoride（CaF₂）.The cementitious activity index of the reconstructed steel slag showed a rising trend with the increase of CaF₂ content.It wass 120% when the amount of CaF₂ was 5%.At the same time,it was found out that the content of free calcium oxide（f-CaO）and free magnesium oxide（f-MgO）decreased continuously by means of EDTA chemical titration,and there dropped to 0.09 % and 0.19 % eventually.XRD and SEM observations showed that with the increase of CaF₂ content,the diffraction peak of C₂S decreased gradually,and the diffraction peak of C₃S increased gradually.The diffraction peaks of C₄AF and C₃A were observed when the content of CaF₂ was 1%.The results indicated that the addition of mineralizer（CaF₂）can promote the formation of 3 C₃S-CaF₂ and 2 C₂S-CaF₂ in the intermediate phase,in favor of reducing melting point of molten slag,increasing the liquid amount of reaction,reducing the viscosity of reconstructed steel slag,and promoting the formation of C₃S and C₂S.At the same time,CaF₂ increased the reactivity of CaO,SiO₂ and MgO,and reduced the content of f-CaO and f-MgO in slag,and promoted the formation of C₃S and C₂S.