Quarry waste clays as supplementary cementitious materials: Mineralogical evolution and pozzolanic performance after thermal activation

This study investigates the potential of thermally activated quarry waste as alternative supplementary cementitious materials (SCMs) for sustainable binder systems. Three clay-rich materials were collected from a sand quarry located on the European side of Istanbul: two natural overburden clays (Yellow Layer-YL and Blue Layer-BL) and one process-derived sludge waste (TA) generated during sand washing. All samples were sieved (<150 μm), dried, and calcined at 800 °C for 2 h. Mineralogical (XRD), chemical (XRF), and thermal (TG, FTIR) analyses were conducted to evaluate phase transformation and amorphous phase development. Pozzolanic reactivity was assessed by the R 3 test, including heat release and bound water measurements. Results showed that the TA sample exhibited the highest reactivity due to its kaolinite content and fine, homogeneous particle structure. In contrast, the BL sample demonstrated limited reactivity owing to the dominance of thermally stable phases such as muscovite and albite. Mortar specimens prepared with 20 % SCM replacement were tested for compressive strength at 7, 14, and 28 days using both CEM I and CEM II binders. The TA-C mixture achieved a compressive strength index (CSI) of 102.9 % with CEM I at 14 days, indicating strong early-age performance, while YL-C showed the highest 28-day strength with CEM II (CSI = 97.9 %). These findings confirm that sludge-based SCMs, when properly activated, can match or even exceed the performance of conventional systems, offering a viable strategy for resource-efficient and low-carbon cementitious materials. • Quarry-derived clays and sludge were calcined at 800 °C for SCM applications. • Kaolinite-rich sludge showed the highest pozzolanic reactivity after activation. • Muscovite- and albite-rich clays retained low reactivity due to thermal stability. • TA-C achieved a 14-day CSI of 102.9 % in CEM I mortar, outperforming the reference. • Reactivity was governed by the chemical quality of the amorphous phase rather than its total quantity.