Reactivity activation of waste coal gangue and its impact on the properties of cement-based materials – A review

•Thermal temperature and fineness are critical in activation of coal gangue (CG).•Compound activation is most effective way in enhancing the reactivity of CG.•Activated CG as cement replacement should be controlled within 10–20 wt%.•Utilizing CG in concrete is a sustainable and green approach.•More research should be pain on durability or long-term performance aspects. Coal gangue is the main industrial solid waste that is physically separated from bulk coal during coal preparation. In China, the deposition amount of coal gangue is over 500 million tons with an annual production of more than 70 million tons. Extensive studies have been carried out to find a feasible way to reuse coal gangue in cement-based material in order to reduce its environmental burden and negative impact. High content of clay mineral in coal gangue is found to be a potential source of pozzolan. However, proper activation is needed to improve the pozzolanic reactivity of coal gangue due to its relatively stable (crystalline) chemical structure. The effects of four main activation methods including thermal, mechanical, microwave and compound activations are comprehensively reviewed with a focus on their interaction mechanisms with coal gangue. It is found that particle size and the degree of dehydroxylation of clay minerals dominates the pozzolanic activity. The pozzolanic reactivity, cement hydration, mechanical and durability-related properties of cement-based materials blended with activated coal gangue are further discussed. The information presented in the paper provides valuable ideas and guidance to allow better understanding of coal gangue valorization, in particular for reuse in cement-based construction materials.