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.

The online version contains supplementary material available at 10.1617/s11527-025-02837-0.