Effects of a red mud mineralogical composition versus calcination on its pozzolanicity

Past research indicates that red mud (RM) has negligible pozzolanicity unless calcined. An iron-rich and silicate-poor RM was calcinated at 600, 800 and 1000 °C to investigate this issue. Tests were performed on mortars made with Portland cement (control) and with 85 wt% cement and 15 wt% RM. At 91 days, the mortar containing non-calcined RM reached 94% of the compressive strength of the control mortar, but the ones containing calcined RM attained much lower strength. Mineralogical, microstructural, and thermodynamic analyses are performed to find the mechanisms undergirding this behavior. The crucial influences of Al/Si ratio and crystalline transformations are highlighted.