Preparation of geopolymer concrete with Bayer red mud and its reaction mechanism

[Display omitted] •In cement-based materials, Bayer red mud (BRM) has very low activity and presents 'fake activity index'. It's difficult to use BRM as supplementary cementitious material.•A creative solution by integrating BRM into geopolymer concrete was devised. By leveraging the natural alkaline properties of red mud, the number of alkaline activators needed was decreased.•The mechanical properties and hydration products of BRM based geopolymer were investigated. A reliable, affordable, and efficient way to use BRM on a large scale was developed. Red mud (RM) is a hazardous waste product resulting from alumina production in the aluminum industry. In China, the alumina industry generates a significant amount of solid waste RM annually. The accumulation of RM not only occupies a large area of land but also leads to environmental pollution. Currently, Bayer red mud (BRM) constitutes the majority of the piled-up RM in China. Due to its high alkalinity and low activity, BRM cannot be directly used in the cement industry, and its comprehensive utilization is severely limited. Thus, finding a bulk, safe, and cost-effective utilization method is crucial in tackling the massive accumulation of BRM. This study primarily focuses on the reactivity and reaction mechanisms of BRM in cement-based and geopolymer material. Firstly, it was demonstrated through compressive strength, chemical bound water content, SEM microstructures, and flowability that BRM exhibits relatively low reactivity in cement-based material. Experimental investigations were conducted to study the impact of the BRM addition and curing methods on the mechanical properties of BRM based geopolymer materials. The dosage range of BRM under different conditions was given. Through SEM-EDS analysis, the influence of BRM with its high-temperature activation on the early hydration products in geopolymer material was investigated. The reaction mechanism of BRM in geopolymers was analyzed, and a reliable, affordable, and efficient way to use BRM on a large scale was developed.