Mechanically activated wet carbonation of steel slag powder: Microstructure and cement hydration

Traditional wet carbonation of steel slag powder faces issues such as low reaction rates and difficulty in transforming deep calcium phases. Although a wet grinding carbonation method has achieved breakthroughs, the specific influencing factors and the relationship between carbonation products and their morphological states still require further exploration. This paper uses wet grinding carbonation technology to systematically investigate the factors affecting the energy-material transformation of steel slag powder carbonation products and their optimal conditions, as well as the impact of wet-ground carbonated steel slag powder on hydration and overall performance in cement-based materials. Steel slag was processed via wet grinding carbonation at varying rotation speeds (300–500 rpm) and durations (10–150 min). CaO and lawsonite contents decreased while CaCO 3 formed progressively. The exponential decay model of gehlenite underscored the dominant role of mechanical energy in activating deep calcium phases. pH dropped sharply from 12.5 to 10.5 within 20 min and stabilized thereafter. CaCO 3 transformed from aragonite to calcite, reflecting a two-stage shift from reaction-to diffusion-controlled carbonation, with grinding continuously disrupting the product layer. When 50% cement was replaced by carbonated slag, compressive strength approached that of pure cement after 7 days. The slag advanced the hydration peak by 1.5–7 h via heterogeneous nucleation and reduced early heat release. Its refined surface structure promoted interface densification, pore refinement, and micropore formation, indicating enhanced later-age performance. This work quantifies the energy–material transformation in wet grinding carbonation, offering a practical route for deep CO 2 sequestration and high-value use of slag in cement-based materials.