Utilization of kaolinite-containing bauxite tailings in limestone calcined clay cement: Hydration, microstructure, and foundational insights for future performance optimization

To mitigate the high cost and uneven availability of high-quality clay in Limestone Calcined Clay Cement (LC3), this study investigates an LC3 formulation incorporating calcined bauxite tailings (LC3-BT), which contain 30.6% kaolinite, and systematically compares its mechanical properties, hydration behavior, and microstructural evolution with Ordinary Portland Cement (OPC) and LC3 made with metakaolin (LC3-MK). LC3-BT exhibits 15.7%–34.3% lower 28-day compressive strength than LC3-MK, primarily due to the limited pozzolanic reactivity of BT, which restricts C-(A)-S-H gel formation. Nonetheless, BT enhances clinker hydration, reflecting a dual functional effect. Microstructural analysis reveals the presence of a particle-rim transition zone (PRTZ) around unhydrated particles, which may influence structural integrity. Contrary to conventional assumptions, inert particles, due to a less pronounced PRTZ, may not benefit from dense packing and could potentially affect performance. In contrast, reactive particles may help densify the matrix through hydration. These findings provide critical guidance for optimizing the performance of LC3 systems incorporating industrial residues and offer additional insights into the behavior of low-grade clay-based solid wastes in such systems.