Thermal analysis, hydration kinetics, and rheological behaviour of non-kaolinitic waste clay materials for low-cost mixed cement

Increased material costs and stringent environmental regulations have driven the construction industry to research alternative supplementary cementitious materials (SCMs). While calcined kaolinite is well-understood, it is often economically unfeasible. This study investigates the potential to transform locally sourced, non-kaolinitic waste clay materials, originally a byproduct of limestone production, into viable SCMs. The study explores the possibility of using these materials for mixed cement. Samples were characterized using thermal analysis (TG-DTA-EGA and calorimetry), modified Chapelle test to quantify pozzolanic reactivity, and rotational rheometry to determine fresh paste behaviour. Finally, cement pastes were prepared to simulate behaviour under real-world conditions. Results indicate that all studied clay materials could reduce CO 2 emissions compared to Portland cement clinker, with evolved gas analysis confirming minimal carbonate decomposition for most samples. Samples exhibited remarkable activation potential through calcination, increasing their pozzolanic activity by more than tenfold in some cases. Rheological measurements revealed shear-thinning behaviour in all mixtures, with no evidence of shear-thickening even at high substitution levels and shear-rates. Compressive strength tests validated the results of previous analyses, demonstrating that properly processed non-kaolinitic waste clay materials increase the compressive strength of cement pastes up to 30% cement substitution. In some cases, compressive strength was improved even at higher cement substitution. These non-kaolinitic waste clay materials offer a widely available, high-performance, low-cost, low-carbon alternative to traditional binders.