Structure and properties of red mud-modified high-ferrite portland cement under different carbonation paths

High-ferrite Portland cement (HFPC) offers substantial low-carbon potential but suffers from sluggish early strength and belite stabilization challenges. Herein, Bayer red mud was valorized to synthesize reactive HFPC clinker at a reduced sintering temperature of 1320 °C. The mechanical and microstructural evolution was comparatively investigated under two distinct curing regimes: "hydration followed by carbonation" (Path I) and "carbonation followed by hydration" (Path II). Results indicate that red mud facilitates satisfactory clinker burnability (f-CaO < 1.0%) while promoting the retention of reactive β-C 2 S and the formation of C 4 AF. Under Path I, progressive late-age hydration constructs a densified and tortuous C-S-H network, effectively refining the capillary pore structure and physically impeding the inward gaseous diffusion of CO 2 . Under Path II, soluble alkalis derived from red mud promote early mineralization kinetics within the restricted moisture environment, achieving a high CO 2 uptake of 12.10% and superior early strength. A core-shell-like mechanism is proposed wherein rapid early carbonation establishes a rigid, porous CaCO 3 skeleton along particle boundaries, followed by continuous interior clinker hydration during water curing to densify residual pores in situ. This study provides valuable insights into industrial red mud valorization and early-strength carbonatable cements.