Dissolution kinetics of cementitious magnesium silicate hydrate in air-equilibrated water

Magnesium silicate hydrate (M-S-H) represents a promising alternative to traditional cement, particularly for low-pH construction applications such as nuclear waste encapsulation and carbon dioxide injection. The durability of construction materials, a critical aspect of their suitability for various purposes, is primarily governed by the kinetics of dissolution of the binder phase under service conditions. In this study, we employed in situ atomic force microscopy to assess the dissolution rates of M-S-H in water equilibrated with air. Quantitative analysis based on changes in volume and height revealed dissolution rates ranging from 0.18 to 3.09 × 10⁻¹² mol/cm²/s depending on the precipitate Mg/Si ratio and morphology. This rate surpasses its crystalline analogs, talc (Mg₃Si₄O₁₀(OH)₂) and serpentine (Mg₃(Si₂O₅)(OH)₄), by about three to five orders of magnitude. Interestingly, oriented M-S-H dissolved faster than non-oriented M-S-H. Spatially resolved assessments of dissolution rates facilitated a direct correlation between rates and morphology, showing that edges and smaller crystallites dissolve at a faster pace compared to facets and larger crystallites. The outcomes of this study provide insights into the mechanisms governing the dissolution of M-S-H and the factors dictating its durability. These findings hold implications for the strategic design and optimization of M-S-H for various applications.