Ceramics-Silikáty 69, (1) 138 - 145 (2025)

Red mud, a by-product of the alumina manufacturing process, has not been effectively utilised due to its various drawbacks. This study explores the calcination of red mud by combining calcium carbonate and iron oxide and the corresponding effect of the calcined red mud on the mechanical strength and sulfate resistance of Portland cement. The X-ray diffraction results show that the belite (C₂S) and ferrite phase minerals are successfully synthesised in red mud by the calcination at 1150 °. The addition of the calcined red mud used as mineral fillers decreases the compressive and flexural strength of the cement materials at early age of 3 d, but can exert limited impacts on reducing the strength at 28 d. Besides, the incorporation of the calcined red mud effectively enhanced the resistance of the cement materials to sulfate corrosion. The synthesised ferrite phase of 6CaO·Al₂O₃·2Fe₂O₃ (i.e., C₆AF₂) in the calcined red mud exhibits greater sulfate resistance for the cement than that of brownmillerite (4CaO·Al₂O₃·Fe₂O₃, C₄AF).