Thermodynamic prediction of and synthesis of sulfoaluminate-phosphate cementitious material clinker using high magnesium solid waste

Abstract

The extended setting time and hysteresis expansion characteristics of high magnesium solid waste restrict the large-scale utilization in cement. The novel sulfoaluminate-phosphate cementitious material (SAC-MKPC) clinker including MgO, 2CaO·SiO₂ (C₂S) and 3CaO·3Al₂O₃·CaSO₄ (C₄A₃$), furthermore, MgO combined with KH₂PO₄ formed MgKPO₄·6H₂O in the hydration reaction, which eliminates the disadvantage of MgO in the cement system and significantly increases the use of high magnesium solid waste in cement production. The present work provides an prediction method based on thermodynamic calculations using FactSage software of thermodynamic data pertaining to the key phase C₄A₃$ and the interactions of representative oxides in the raw materials, and then, the accuracy of the prediction method was verified by experiment. Simulation results have shown that C₄A₃$ may be generated through four possible pathways, and the corrected standard formation enthalpy, standard Gibbs free energy, and standard entropy of C₄A₃$ are −8458.41 kJ mol⁻¹, -8338.97 kJ mol⁻¹, and 400.79 kJ mol⁻¹, respectively. The simulation results obtained with FactSage showed good consistency with those obtained experimentally, confirming the main phases (MgO-C₄A₃$-C₂S) can co-exist in the system CaO-SiO₂-Al₂O₃-CaSO₄-MgO at 1100–1300 °C. The results presented here not only provide theoretical support for the key thermodynamic data of C₄A₃$, but may also further the application of high magnesium solid waste in novel SAC-MKPC cement.