Mechanical properties and durability of all-solid-waste concrete with calcined 0–1 mm coal gangue

This study pioneers the development of eco-friendly concrete utilising 100% solid waste as cementitious materials and fine coal gangue (CG) aggregates (0–1 mm). The research methodology encompassed three phases: (a) a comprehensive evaluation of mechanical properties, (b) systematic durability assessment including chloride ion permeability, sulfate wet–dry cycling, freeze–thaw (FT) resistance, and (c) nuclear magnetic resonance (NMR) analysis and scanning electron microscopy (SEM) to identify the microstructural characterisation. A key finding was that thermal activation of 0–1 mm CG particles (800°C) significantly enhanced concrete performance. Concrete composites made with calcined CG achieved 20.9 MPa compressive strength at a water/binder (w/b) ratio of 0.3 (7 days), exceeding the strength of raw CG concretes (19.8 MPa), while all-solid-waste concrete with natural aggregates (NAs) attained a strength greater than 38 MPa at 28 days. Regarding durability, calcined CG improved the sulfate resistance (32% lower strength loss compared with raw CG after 60 wet–dry cycles) and a reduction in chloride diffusion coefficient by 32% (0.49 × 10−12 m2/s for a w/b ratio of 0.3). The specimens made with NAs endured 100 FT cycles with progressive strength loss. Microstructurally, NMR/SEM analyses confirmed refined pore structures with the calcined CG, inhibiting crack propagation under erosive environments. This work validates a sustainable strategy for dual-waste valorisation (binding matrix and aggregates), delivering cement-comparable strength (25 MPa at 56 days for systems with a w/b ratio of 0.5) while enhancing durability, with significant implications for resource-efficient infrastructure development.