Mechanisms underlying pozzolanicity formation in acid-activated serpentine: parallel effects of dissolution and polymerization

Serpentine is widely used for CO 2 sequestration, where Mg ions released during its dissolution react with CO 2 to form stable MgCO 3 . The resulting silica-rich residue is a promising low-carbon supplementary cementitious material because of its amorphous structure and high silica content. However, the mechanisms controlling the pozzolanicity of acid-activated serpentine (AAS) remain insufficiently understood. This research evaluates the pozzolanicity of AAS and elucidates the mechanisms that govern its reactivity. AAS samples were prepared through controlled acid-leaching under different temperatures, reaction durations, acid concentrations, and solid-to-liquid ratios. Crystalline and amorphous phases were characterized through X-ray diffraction and Raman spectroscopy, while pozzolanicity was accessed via the Frattini test. The results reveal that AAS pozzolanicity is governed by two concurrent processes: dissolution and polymerization of silicate species. Dissolution enhances reactivity by collapsing Q 3 structures into smaller silica oligomers and exposing additional reactive silanol groups, while polymerization consumes these reactive groups and suppresses pozzolanicity. Based on the evolution of silicate species, we proposed an index for quick assessment of pozzolanicity, which not only aligns well with results of traditional method but also has higher efficiency and clear chemical meaning.