IstoPore Seminar – by Bilal Mahmoud Hawchar

Abstract

The in-pore crystallization of salts is considered one of the major sources of degradation of construction materials, geo-materials, and built heritage. When crystallizing, salts may exert mechanical pressure against the surface of the pore, which can damage materials. Crystallization within the porous network remains one of the most misunderstood phenomenon in porous media mechanics. We propose an investigation combining molecular simulations and theoretical development to quantify and clarify the origin of the crystallization pressure at the finest scale. This study should allow the identification of the parameters controlling the phenomenon and thus pave the way to mitigate or prevent salt damage.
At thermodynamic equilibrium, crystallization pressure results from the change of solubility of a crystal as it is compressed. Direct molecular dynamics simulations to compute the solubility of salts are challenging because the time scale of dissolution and precipitation, microseconds or more, is at the limit or beyond computing capabilities. For this reason, we use a thermodynamic integration approach to overcome this issue. With this approach, we can quantify the effect of stress on NaCl solubility, and more specifically the effect of stress anisotropy which has been disregarded so far. We use these results to revisit the existing theory describing crystallization pressure and extend it to account for stress anisotropy. A limitation of the study of bulk solubility is that it disregards the role of the wetting film at the interfaces between the salt crystal and the pore wall. Because of confinement, the thermodynamics of this film are expected to differ from that of the bulk solution. Ongoing work focuses on the application of the thermodynamic integration method to this film in order to determine how the solubility is affected by the confinement of the film.