Study on the mechanical and durability properties of geopolymer concrete mixed with coal gangue coarse aggregate

Coal gangue (CG) is a solid waste generated during coal mining and washing processes, which has long been regarded as an environmental burden. This study aims to partially or completely replace natural aggregates with CG in concrete preparation in order to alleviate the supply pressure of natural aggregates and effectively conserve natural resources such as sand and gravel. Both raw and calcined CG as coarse aggregates (CAs) were used to replace crushed stone at different substitution rates to prepare CG-geopolymer concrete (CGGC). The effects of CG content on compressive strength, chloride ion permeability resistance, and frost resistance of CGGC were analyzed. The correlations among concrete performance indicators, the appropriate substitution rate of CG, and the necessity of its calcination were comprehensively investigated. In addition, the internal mechanisms were further explored using scanning electron microscopy. The results indicate that the compressive strength, impermeability, and frost resistance of CGGC all weaken to varying degrees with the increasing content of CG. The influence of frost resistance performance was the most significant. Compared to the geopolymer concrete mixed with raw CG (RCG), the geopolymer concrete mixed with calcined CG (CCG) exhibited a significant advantage in compressive strength. The resistance to chloride ion penetration of CCG was inferior to that of the RCG, and the difference in frost resistance between RCG and CCG was very small.