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Accueil du site > Productions scientifiques > Séminaires à PHENIX > 2012 > Séminaire 06.03.2012 - 15:00

Séminaire 06.03.2012 - 15:00

par Guillaume Mériguet - 2 mars 2012

Patrick BONNAUD, actuellement au département Materials Science and Engineering du Massachusetts Insitute of Technology, présentera un séminaire intitulé

Behavior of Confined Water in Porous C-S-H,

le mardi 6 mars à 15h à la bibliothèque du PECSA, Batiment F, 7e étage.

Résumé

In the multi-scale porosity inherent to cementitious materials, water may be present in the liquid, solid, and/or gas state depending on the thermodynamic conditions (temperature, pressure, presence of ions). It is thus appreciated that water may play an important role in cement paste damage processes. Here, computational simulations are particularly advantageous because water properties in nanoscale pores are challenging to access experimentally. We have considered how the nature of the water confined within and between C-S-H grains changes with a function of relative humidity at ambient temperature (T = 300K) using semi-Grand Canonical Monte Carlo techniques. To relate the relative humidity (%RH) of the environment with the water content in the cement paste, we calculated adsorption isotherms. When an overall hydrophilic behavior was observed, the intergranular isotherms exhibited discontinuities during the pore filling that can be attributed to surface roughness effects and capillary condensation. Furthermore, to understand the mechanical effects induced by the presence of water in C-S-H pores, we computed virial pressures normal to the pore surface for various %RH and various pore widths. We found that calcium ions are responsible for the overall cohesion in these materials (giving rise to a negative pressure). However, the role of water in reducing or reinforcing this intergranular and intragranular cohesion depended on separation distance between C-S-H grains. The reduced cohesion at separation distances < 5 Å and increased intergranular cohesion at intermediate distances of 5-10 Å were both amplified with increasing %RH. These findings give for the first time an atomistic picture of the confined fluid and its induced pressure effects on the solid structure in the lowest porosities of cement at ambient temperature and 100% RH. It is a first step to understand cement paste damage processes in more extreme conditions as high/low temperatures, high pressures, and/or various ionic concentrations.