Effect of CaO Sourced from CaCO3 or CaSO4 on Phase Formation and Mineral Composition of Iron-Rich Calcium Sulfoaluminate Clinker

Abstract

The performance of iron-rich calcium sulfoaluminate (IR-CSA) cement is greatly affected by mineral composition and mineral activity in the clinker. This study aims to identify the effect of CaO sources, either CaCO3 or CaSO4, on the phase formation and mineral composition of the IR-CSA clinker. Targeted samples were prepared with different proportions of CaCO3 and CaSO4 as CaO sources at 1300 °C for 45 min. Multiple methods were used to identify the mineralogical conditions. The results indicate that the mineral composition and performance of the IR-CSA clinker could be optimized by adjusting the CaO source. Both Al2O3 and Fe2O3 tend to incorporate into C4A3−xFxS¯ with an increase in CaSO4 as a CaO source, which leads to an increased content of C4A3−xFxS¯ but a decreased ferrite phase. In addition, clinkers prepared with CaSO4 as a CaO source showed much higher x value in C4A3−xFxS¯ and higher compressive strength than clinker prepared with CaCO3 as the sole CaO source. The crystal types of both C4A3−xFxS¯ and C2S were also affected, but showed different trends with the transition of the CaO source. The findings provide a possible method to produce IR-CSA cement at a low cost through cooperative utilization of waste gypsum and iron-bearing industrial solid wastes.