EFFECT OF MgO ON THE COMPOSITION AND PROPERTIES OF BELITE-BARIUM CALCIUM SULPHOALUMINATE CEMENT IN THE PRESENCE OF Na₂O AND K₂O

摘要

The purpose of this study is to explore the effect of MgO (1 - 9 wt. %) on the composition and properties of belite-barium calcium sulphoaluminate cement with additions of Na_(2)O and K_(2)O. The results show that 1 - 5 wt. % content of MgO can stabilize crystal types of M_(3)-C_(3)S, R-C_(3)S and β-C_(2)S. Moreover, MgO can promote the formation of C_(3)S and C4AF, but has little effect on the formation of C_(2.75)B_(1.25)A_(3)$ and C_(3)A. The C_(3)A/C_(4)AF ratio is reduced by 22 % at 5 wt. % MgO, which indicates that appropriate MgO can decrease the liquid viscosity. In the presence of Na_(2)O and K_(2)O, the highest limit of incorporated amount of MgO is about 3 wt. %, which is higher than that in Portland cement clinker of 2 wt. %. Besides, MgO favors the formation of small C_(3)S crystals in size of 4 - 20 μm. MgO enhances the hydration rate and mechanical property of cement at an optimal dosage (1 - 5 wt. %), beyond which an adverse effect could be resulted. At a MgO dosage of 5 wt. %, the compressive strengths of the cement at 1, 3, 7 and 28 days are 15.8, 39.3, 68.6 and 97.3 MPa, which increases by 116 %, 17 %, 10 % and 6 % respectively compared to the cement without MgO dopant. This study could lead to the effective use of magnesia-rich limestone in industrial production of belite-barium calcium sulphoaluminate cement.