A Review of Preparation of Low-Carbon Cementitious Materials from Chemically Activated Red Mud: Synergy, Hydration Mechanism, Rheological Properties and Applications.

Red mud, a byproduct of the alumina refining process, is generated at a rate of 1-2.5 tonnes per tonne of alumina produced. In 2022, China's alumina production totaled 77.475 million tonnes, contributing over 4 billion tonnes of accumulated red mud, which is the third-largest industrial solid waste in the country. Red mud's high alkalinity and presence of toxic elements pose environmental challenges, particularly in terms of disposal. This review provides a comprehensive examination of red mud-based cementitious materials, focusing on their preparation, properties, and environmental impact. By combining red mud with high-calcium and silica-aluminum solid wastes and enhancing its reactivity through mechanical grinding or thermal activation, red mud's cementitious activity can be significantly improved. Optimized compositions, with a Ca/Si ratio of 2.05 and Al/S ratio of 0.70, have achieved compressive strengths of up to 63.9 MPa at 28 day. Durability studies highlight the material's resistance to chloride ion penetration and sulfate attack, with reduced permeability enhancing long-term performance. Additionally, environmental assessments confirm that stabilization and solidification techniques effectively mitigate heavy metal leaching, ensuring compliance with EPA standards. Despite these advancements, challenges remain in optimizing red mud activation processes, improving rheological properties, and reducing production costs. Future research should focus on refining activation methods, enhancing hydration mechanisms, and developing scalable industrial applications. By addressing these gaps, red mud-based cementitious materials can become a sustainable solution for eco-friendly construction, supporting global efforts to repurpose industrial byproducts into low-carbon, durable building materials.