Mechanochemical activation of phyllosilicates: Residual hydroxyl groups and their impact on surface properties and pozzolanic reactivity

Abstract

Mechanochemically activated (MCA) phyllosilicates are promising supplementary cementitious materials (SCMs) due to their pozzolanic reactivity and CO ₂ reduction potential. MCA of 2:1 and 2:1:1 phyllosilicates can induce significantly higher reactivity than thermal activation (TA). Unlike TA, which removes hydroxyl groups, MCA partially retains these groups, with OH bonds weakened, broken, or restructured by induced structural disorder. The effects of MCA on the physical and surface properties of phyllosilicates remain insufficiently understood. This study investigated the availability and binding state of residual hydroxyls after MCA, the temperatures for their removal, and the impact of remaining water on reactivity. MCA samples were heated up to 600°C. Changes in morphology, specific surface area, and pozzolanic reactivity were analyzed. Spectroscopic methods revealed how surface properties related to the bonding of the hydroxyl groups, which could be an important aspect when considering water demand and workability in cementitious systems, providing insights into the usability of MCA materials.