The di- and tricalcium silicate dissolutions

Advances in dissolution understanding and their implications for cement hydration

“…In particular, the system proceeds from far from-to near-equilibrium conditions within seconds, so that ΔG crit <ΔG at nearly all reaction times, and dissolution is expected to proceed through step retreat only. Indeed, etch pits are still observed under near-equilibrium conditions at early stages [32] (Figure 2a), as well after hours of hydration [30] (Figure 2b). This observation indicates evidences that, in the case of alite, etch pits continuously open up and grow in all ranges of under-saturation, provided that the deviation from equilibrium is locally high-enough.…”

“…Despite the above described state of the art in geochemistry, the dissolution of C 3 S was only recently replaced in the general framework of crystal dissolution [2]: like natural minerals, C 3 S exhibits a high reactivity at far from equilibrium conditions, while its dissolution rate decreases drastically in near-equilibrium conditions. The dependency of reactivity on the saturation state of the surrounding solution has been documented [30], indicating for several C 3 S polymorphs a trend similar to most natural minerals. This finding has been replicated [31] and corroborated by topological analyses [32].…”

“…However, as described above, the solution approach [30,31,33], i.e. continuous monitoring of the evolution of the released ions by inductively coupled plasma atomic emission spectroscopy (ICP-AES) of C 3 S powders stirred in an 'infinite' volume of solution to avoid any hydrate precipitation, is unspecific (i.e.…”

“…This was a key source of error in many subsequent works, which invoked the putative formation of a metastable hydrate membrane [36,37,38], instead of the partial hydroxylation of the C 3 S surface [34], to justify the discrepancy between the calculated solubility and the low hydration rates observed. Alternatively, Nicoleau et al [30] tried determining an experimental solubility product using a kinetic approach, showing by the way that the surface stability was pH dependent. This highlighted the importance of surface hydroxylation, recently supported by NMR [35].…”

“…Prior to thorough study [30], alite solubility was considered to be very high, whereas the discrepancy between putative solubility and measured ionic concentrations in the pore solution pointed to a central inconsistency. This observation supported the hypothesis of the formation of a protective hydrated layer, whose role was to retard the rate of alite dissolution [49].…”