Microstructure of magnesium silicate hydrate pastes influenced by carbonate and mixing method

This study investigates the microstructure of magnesium silicate hydrate (M-S-H) pastes prepared with MgO and silica fume from different sources but of comparable properties, with varying sodium carbonate (NC) contents, using two mixing methods: conventional Hobart-style paddle mixing and low-speed ball-mill mixing. The latter method significantly improved silica fume dispersion and particle packing, resulting in a denser microstructure and substantially higher compressive strength compared to conventional mixing. A NC content of 2.5 wt.% was identified as optimal for enhancing microstructure and reducing porosity in conventionally mixed samples, while no clear effect of NC content observed in ball-milled ones. Brucite was detected in NC-containing samples by thermogravimetric analysis, but not by X-ray diffraction, indicating its poor crystallinity. Compressive strength increased with M-S-H formation and decreasing brucite content. These findings highlight the importance of optimising particle packing for improving the microstructure and mechanical properties of magnesium silicate binders. Supplementary Information: The online version contains supplementary material available at 10.1617/s11527-025-02837-0.