Calcination_of_bauxite_residue_with_kaolinite_to_enhance_its_performance_as_supplementary_cementitious_material

The cement industry is one of the world’s largest users of mineral waste streams and is continuously searching for alternative resources to reduce its environmental impact. With a global cement production of around 4 Gt/year and global bauxite residue (BR) generation of approximately 160 Mt/year, the cement industry is an often-targeted market for BR valorization. The use of industrial residues as supplementary cementitious material (SCM) – a material partially replacing the CO₂ intensive clinker in Portland cement – is one of the key solutions to decrease the CO₂ emissions of the cement industry on the short term. The use of BR as SCM can thus be a solution for both the alumina industry and cement industry. Unfortunately, the performance of BR as SCM is poor without additional treatments. Calcination (i.e. thermal treatment at 600 – 900 °C) has been shown to enhance the reactivity of BR and the contribution of BR to compressive strength of cement mortars to some extent. The results of this work show that co-calcination of a blend of BR and kaolinite drastically boosts the reactivity and performance as SCM of the calcined BR-containing product. The calcination of a mixture of 70 wt% BR and 30 wt% kaolinite produces a reactive SCM. When this SCM is blended with Portland cement (30 wt% SCM) in mortar samples, the strength after 7 and 28 days is 85-90% of that of the reference sample, outperforming conventional SCMs such as coal combustion fly ashes.