Exploration of low-carbon and sustainable concrete products: Using activated clay as supplementary cementitious materials

Clay-based supplementary cementitious materials (SCMs) offer a practical and increasingly important pathway for reducing the carbon footprint of cement and concrete materials. Clays can partially replace Ordinary Portland cement (OPC) when properly activated, owing to their wide availability, tunable reactivity through activation, and potential to be derived from low-grade or secondary resources. This review highlights how key factors such as kaolinite content, Si/Al ratio, and overall mineralogical composition that govern clay reactivity, and summarizes recent advances in clay activation strategies. While thermal activation of kaolinitic clays remains the most established route, emerging approaches, including mechanical-thermal, thermal-chemical, and alkali-thermal fusion, have broadened the applicability of clays with low kaolinite and high inert-phase contents by lowering activation thresholds and enhancing reaction kinetics. When appropriately activated and proportioned in application, activated low-grade clays can improve strength development, refine pore structure, and reduce permeability, enhancing both mechanical performance and long-term durability. Although challenges remain with respect to process integration, feedstock variability, quality assurance/control, this review demonstrates that activated clay-based SCMs provide a technically robust and environmentally advantageous solution for low-carbon cement and concrete products.