Utilization and Modification of Large-Size Coal Gangue Aggregate with Alkali-Activated Materials for Sustainable Concrete

This study investigated the collaborative utilization of large-sized coal gangue aggregate (CGA), specifically within the size range of 5–20 mm, in conjunction with alkali-activated material (AAM). The aim was to minimize the environmental footprint of this prevalent industrial waste. Initially, the research focused on analyzing how CGA’s inherent properties and the proportions of fly ash (FA) and slag in the binding materials influenced the workability, strength, and durability of concrete. The study found that a slight change in CGA’s water absorption (2.7%) had a significant impact on concrete’s slump (20.6%) and drying shrinkage (6.3%). Apparent density, crushing index, and needle-shaped particle content of CGA linearly correlated with concrete strength. The increased FA content mitigated the potency of inferior CGA performance on concrete slump and strength, regardless of adjustments made to the binding material ratios. Notably, increasing the FA content mitigated the adverse effects of suboptimal CGA performance on both concrete performance. Subsequently, five coating modifications applied to CGA were tested to improve the performance of aggregate and the resulting concrete. Among these, slurry modifications (cement or AAM coating) were found to be more effective in enhancing CGA’s crushing resistance and density than were hybrid modifications (slurry after silicone resin treatment). However, despite being thicker, the AAM coating had cracks, reducing its crushing resistance compared with that of cement-based modifications. Regarding the concrete performance, the cement modification showed the most efficient improvement to concrete’s slump, compressive strength and splitting tensile strength, which increased 15.2%, 20.4%, and 25.6%, respectively. The study also found that slurry modifications had a decreasing effect on concrete’s shrinkage resistance over time, and silicone resin–treated specimens had the lowest shrinkage after 60 days. This research expands the possibilities for large-size CGA utilization, providing a new approach for the sustainable development of building materials.