Molecular dynamics and multiscale homogenization analysis of seepage/diffusion problem in bentonite clay

Abstract

SUMMARYA scheme combining a molecular behaviour and macro-continuum phenomenon is presented for bentonite clay, which is a key component of a barrier system for disposal and containment of hazardous wastes. On designing a disposal facility we use a macro-phenomenological model. However the existing model is not su ciently e ective. Bentonite is a microinhomogeneous material. Properties of the saturated bentonite are characterized by montmorillonite and water, called montmorillonite hydrate.Since the crystalline structure of montmorillonite determines the fundamental properties of the montmorillonite hydrate, we analyse its molecular behaviour by applying a molecular dynamics simulation to enquire into the physicochemical properties of the montmorillonite hydrate such as di usivity of chemical species. For extending the microscopic characteristics of constituent materials to a macroscopic di usion behaviour of the microinhomogeneous material we apply a multiscale homogenization analysis, especially in order to treat micro-level of adsorption behaviour.

Investigation of nanoscale electrohydrodynamic transport phenomena in charged porous materials

“…It should be noted that material parameters chosen for the nanoscale numerical simulations are very sensitive with respect to the size of the problem. According to References [13,14] the viscosity of water strongly increases in the vicinity of charged surfaces of the material (e.g. surfaces of clay-mineral particles).…”

Self-Consistent Channel Approach for Upscaling Chloride Diffusivity in Cement Pastes

“…4 yields a pore-scale chloride diffusivity separated from the chloride diffusivity in bulk solution by factor 10.91, the homogenization schemes of Dormieux and Lemarchand (2001) and Hashin (1968), respectively, yield pore-scale chloride diffusivities separated from the chloride diffusivity in bulk solution by factors 13.16 and 24.16, respectively. Considering that the molecular dynamics studies of Ichikawa et al (2000Ichikawa et al ( , 2002 suggest that this factor amounts to 7, we conclude that our model yields significantly more accurate results than previous models. All these homogenization approaches may be qualified as "Fickian diffusion," delivering diffusivity quantities which relate concentration gradients to molar fluxes.…”

“…Thus, we would qualify our approach as a typical "micromechanics strategy." Concerning the "structural," "layered," or "glassy" water phase, it has been shown by the landmark molecular dynamics studies of Ichikawa et al (2000Ichikawa et al ( , 2002 that the changes in physics due to the "structuring" or "layering" of water molecules express themselves simply in a different, namely reduced, pore diffusivity, which, however, may still enter the upscaling strategy related to further above. From a more general viewpoint, we wish to remark that it is well known that the structure of water changes in the immediate vicinity of charged surfaces (such as the surfaces of hydrates), resulting in some kind of layering effect (Pollack 2001(Pollack , 2013.…”

“…Layered water exhibits physical properties that vary significantly from the properties of bulk water. For example, as shown by molecular dynamics studies, water layering leads to increased viscosity and reduced diffusivity (Ichikawa et al 2000(Ichikawa et al , 2002. The thickness of layered water can amount up to a few millimeters (Zheng et al 2006(Zheng et al , 2009bPollack 2013;Florea et al 2014).…”

“…The aforementioned molecular dynamics studies (Ichikawa et al 2000(Ichikawa et al , 2002 are particularly insightful, as they reveal that for a geomaterial which is somewhat similar to cement paste, i.e., clay, the diffusivity decreases from bulk to pore solution by a factor of 7; from d bulk = 1.61 × 10 −9 m 2 /s to d Ichikawa pore = 2.3 × 10 −10 m 2 /s. Our new prediction for the pore solution diffusivity,d pore = 1.476 × 10 −10 m 2 /s (being separated from the bulk solution diffusivity by factor 10.91) is considerably closer to molecular dynamics-derived pore solution diffusivity than the one reported in Sect.…”