Effect of impurity components in titanium gypsum on the setting time and mechanical properties of gypsum-slag cementitious materials

The use of titanium gypsum instead of gypsum as a raw material for the preparation of gypsum-slag cementitious materials (GSCM) can reduce the cost and improve the utilization of solid waste. However, titanium gypsum contains impurities such as Fe₂O₃, MgO, and TiO₂, which make its effect on the performance of GSCM uncertain. To investigate this issue, GSCM doped with different ratios of Fe₂O₃, MgO, and TiO₂ were prepared in this study, the setting time and the strength of GSCM at 3, 7, and 28 days were tested. The effects of different oxides on the performance of GSCM were also investigated by scanning electron microscopy, energy spectrum analysis, X-ray diffraction analysis, and thermogravimetric analysis. The experimental results showed that Fe₂O₃, MgO, and TiO₂ all had a certain procoagulant effect on GSCM and a slight effect on the strength. Through micro-analysis, it was found that the main hydration products of GSCM were AFt phase and calcium–alumina–silicate–hydrate (C–(A)–S–H) gels. Fe-rich C–(A)–S–H gels were observed with the addition of Fe₂O₃, and Mg(OH)₂ and M–S–H gels were observed with the addition of MgO. The addition of TiO₂ did not result in new hydration products from GSCM.