Comparative assessment of activation strategies for coal mine tailings as supplementary cementitious materials

Abstract

The use of supplementary cementitious materials (SCMs) is an effective strategy for reducing cement consumption and associated CO2 emissions. This study investigates the potential of coal mine tailings (CMT) obtained from a coal washing plant as an alternative SCM through selective activation methods. Three activation approaches were evaluated: mechanical activation, thermal activation at 600 and 800 °C, and pozzolan-assisted blending with fly ash and trass. Mortar specimens were prepared according to EN 196-1 with cement replacement levels of 5-20 wt.%, and compressive strength was determined after 28 and 90 days of curing. The results showed that mechanical activation reduced particle size but did not improve compressive strength. In contrast, thermal activation significantly enhanced the cementitious performance of CMT. Thermal treatment at 600 °C provided the most balanced overall strength development, producing strength increases of up to 50% at 28 days and 65% at 90 days compared with untreated CMT. Activation at 800 °C yielded the highest compressive strength at specific replacement levels. Pozzolan-assisted blending mainly improved long-term strength development. The binary blend containing 2.5% CMT and 2.5% trass achieved the highest 90-day strength among the pozzolan-assisted mixtures. Overall, the findings show that coal mine tailings can be transformed into effective SCMs through appropriate activation, particularly thermal treatment, providing a sustainable pathway to convert coal-processing wastes into value-added construction materials and support circular economy objectives.