Hydration of belite–ye’elimite–ferrite cement with addition of red mud and waste concrete

The hydration kinetics, phase assemblage, microstructure and mechanical properties of belite–ye’elimite–ferrite (BYF) cement containing different secondary raw materials (red mud and waste concrete) and cured at 5, 20 or 60°C were examined. Different secondary raw materials were found to lead to changes in cement hydration. The influence of these materials on the hydration processes of belite and ferrite became more noticeable at a curing temperature of 5°C, but diminished with an increase in curing temperature. The BYF cement made with red mud exhibited accelerated hydration, particularly at 5°C, due to higher contents of mayenite and alkali sulfate compared with cement with natural materials and waste concrete. Red mud inhibited early ettringite formation due to the presence of aphthitalite but promoted monosulfate through accelerated ye’elimite hydration. Ferrite hydration was delayed by red mud, as alkali sulfates promote belite reactivity and calcium silicate hydrate (C-S-H) formation over strätlingite. Periclase increased siliceous hydrogarnet formation at higher temperatures, supporting delayed yet stable strength development. The curing temperature impacted the morphology of the C-S-H (transitioning from a fine fibrillar-like structure to a foil-like structure) and affected the chemical composition of hydrates, resulting in a lower incorporation of iron in hydrogarnet and C-S-H at higher temperatures. Increased curing temperatures promoted aluminium uptake in calcium aluminium silicate hydrate.