Comparative Analysis of Carbonation Strengthening Mechanisms in Full Solid Waste Materials: Steel Slag vs. Carbide Slag

Maximizing the use of solid wastes to replace energy-intensive cement while maintaining the comparable mechanical properties is a promising strategy for developing negative carbon building materials. In this paper, full steel slag/carbide slag blocks were prepared by pressing and subsequent carbonation to enhance mechanical properties and capture CO₂. The evolution of carbonation degree and compressive strength with varying liquid to solid ratios and carbonation durations were characterized, followed by a comparative analysis of carbonation strengthening mechanisms. The results show that carbonation significantly improves compressive strengths, exhibiting a linear relationship between carbonation degree and compressive strength. The maximum carbonation degrees and compressive strengths achieved were 24.56% and 79.68 MPa for full steel slag blocks, and 64.46%, 44.64 MPa for full carbide slag blocks, respectively. Although the maximum carbonation degree of full steel slag blocks is only about one-third of that of the full carbide slag blocks, their superior compressive strength can be attributed to denser microstructures, stronger bonding properties between steel slag particles and carbonated products, and a larger effective elastic modulus. This study provides a new insight into the carbonation strengthening mechanisms based on the inherent properties of different materials and introduces a novel concept for creating high-performance, eco-friendly building materials.