Enhancing the Reactivity of Dicalcium Silicate Using Aluminum and Sulfur Ions Co‐Doping

ABSTRACT Belite‐rich cements are a lower‐energy and lower‐CO 2 alternative to Portland cements, but the low hydraulic activity of belite remains a major limitation. This study explores the impact of aluminum and sulfur co‐doping on the structure and hydration of synthetic dicalcium silicate (C 2 S). Al/S‐doped C 2 S powders were synthesized and characterized using X‐ray diffraction (XRD), Raman spectroscopy, and solid‐state nuclear magnetic resonance (NMR). XRD and Raman confirmed stabilization of a disordered form of β‐C 2 S. Specifically, Rietveld refinement showed unit cell expansion (from 344.966 to 346.084 Å 3 ), and NMR showed structural distortions in the doped C 2 S. Consequently, isothermal calorimetry and thermogravimetry demonstrated a significant reactivity enhancement, with the 3% Al/S‐doped C 2 S sample achieving ∼4× the cumulative heat @ 72 h versus control (∼82 J/g vs. ∼21 J/g) and ∼2.5× increase in Ca(OH) 2 formation (7.4% vs. 3.0%). These results introduce Al/S co‐doping as a potential pathway toward enhancing C 2 S reactivity in belite‐rich sustainable cements.