Optimizing Co-Calcined Red Mud As A Sustainable Binder For Geopolymer Concrete – A Materials Based Approach To Cement Replacement

Zaid Alnessir

The construction industry is under increasing pressure to reduce its environmental footprint, particularly by minimizing reliance on energy-intensive Portland cement. This research explores the development of sustainable geopolymer concrete using co-calcined red mud and kaolinite as aluminosilicate precursors, combined with recycled construction aggregates. The study addresses the potential of utilizing bauxite residue (red mud), an industrial by-product with low inherent reactivity, by thermally enhancing its structure through co-calcination with kaolinite. Recycled aggregates were incorporated to further reduce resource consumption and align with circular economy principles. Kaolinite was calcined at various temperatures and durations to identify optimal conditions for metakaolin formation, with 750 °C for 90 minutes producing the most amorphous and reactive phase. Co-calcination of kaolinite with red mud was then conducted across six blend ratios (0–100% RM) using both untreated and pretreated red mud. Fourier-transform infrared spectroscopy (FTIR) confirmed phase transformations, while small-scale binder samples were tested for 7-day compressive strength to evaluate performance. Pre-treatment of red mud by drying and milling significantly improved consistency and strength outcomes. A binary alkaline activator composed of 8 M sodium hydroxide and sodium silicate (SS:SH ratio of 2.3:1) was used to produce binder pastes and full-scale concrete samples with recycled aggregates. Aggregates were characterized for particle size and moisture content, and mix designs were adjusted to SSD conditions. The 50:50 and 70:30 kaolinite-to-red mud blends exhibited optimal early-age strength, validating the role of co-calcined precursors in producing effective geopolymer binders. The resulting geopolymer concrete achieved 7-day compressive strength suitable for structural applications, demonstrating that co-calcined red mud and kaolinite, when combined with recycled aggregates, offer a promising alternative to Portland cement. Future research should explore long-term strength development, durability, and alternative activator systems to further enhance performance and sustainability.

Optimizing Co-Calcined Red Mud As A Sustainable Binder For Geopolymer Concrete – A Materials Based Approach To Cement Replacement

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