Multi-scale mechanisms behind the particle-size effect of basalt powder in concrete performance

This study examines the particle size-dependent effects of basalt powder as a supplementary cementitious material and develops a predictive model linking fineness to concrete strength. Four basalt powders (400, 800, 1600, and 2400 mesh) replaced slag at a constant dosage and water-binder ratio. Compressive strength was measured at 3, 7, 28, and 90 days, and XRD, TG-DTG, MIP, and SEM were used to investigate hydration, Ca(OH) ₂ consumption, pore structure, and microstructure. The results show that finer basalt powder enhances both early and long-term strength. Coarse basalt powder mainly contributes through micro-filler effects, while ultrafine basalt promotes additional C-(A)-S-H formation through both micro-filling and pozzolanic reactions, significantly reducing porosity. A strong inverse linear relationship between D90 and compressive strength at 28 and 90 days is established, offering a reliable tool for performance prediction. This work provides insights into the structure–property relationship of basalt powder fineness and introduces a particle-size-based design framework for high-performance, low-carbon concrete.