Coal mining waste as a future eco-efficient supplementary cementing material: Scientific aspects

Abstract

The stockpiling of tailings around coal mines poses a major environmental problem. Nonetheless, this clay mineral (kaolinite)-based waste can be reused as a supplementary cementitious material (recycled metakaolinite) in the manufacture of future eco-efficient cements. This paper explores the most significant scientific questions posed in connection with the conversion of this waste into pozzolans, such as the variation in product mineralogy depending on the sintering temperature and its effect on reaction kinetics in the pozzolan/Ca(OH)2 system over a period of 365 days. The findings show that the optimal sintering temperature is 600°C, such that the cementitious properties of the activated product are determined solely by the conversion of kaolinite into metakaolinite and are unaffected by the other clay minerals (micas). The presence of 20% activated coal waste favors the formation of larger amounts of aluminous phases such as C4 AH13 and C4 AcH12 than in the reference paste and enhances C–S–H gel polymerization.