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 C4AH13 and C4AcH12 than in the reference paste and enhances C–S–H gel polymerization.
Highlights
Today’s society is undergoing a change from a linear to a recycling-based circular economic model that pursues two ends: the generation of less waste and its reuse as raw materials in industrial processes
Cement manufacturing is a benchmark in this regard, in light of its use decades-old use of industrial by-products and waste in different stages of production: as alternative fuels, raw materials or supplementary cementitious materials (SCMs) to produce eco-efficient cements [2,3,4]
Prior research conducted by Frías et al [22,23], García et al [24] and Vegas et al [25] has shown that this inert waste can be converted by thermal activation into a high added value pozzolan apt for use in the manufacture of innovative eco-efficient cements
Summary
Today’s society is undergoing a change from a linear (produce-use-discard) to a recycling-based circular economic model that pursues two ends: the generation of less waste and its reuse as raw materials in industrial processes. This sustainable approach is one of the mainstays of Europe’s 2020 strategy [1]. Metakaolinite, a material well known for its high pozzolanicity that can be obtained by thermally activating natural kaolinite, is one of the standardized SCMs [5,6,7,8,9,10,11]. The findings are compared to the results for a reference Ordinary Portland Cement (OPC) paste to determine the effect of the pozzolanic reaction between the ACW and the portlandite in the blended cement system
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