Permeability of C-S-H

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Modélisation Multi-Échelle Multi-Physique MultiTechnique pour la corrélation composition-(micro)structure-propriétés des matériaux cimentaires

The central paradigm of materials science and materials engineering involves establishing processing- (micro)structure-property-performance correlations for materials. These correlations, in particular structure-property relationships, are fundamental in the study of cement-based materials, being a critical strategy for coping with the rise in the complexity of the mineralogical and chemical compositions of cement systems. Modeling and simulation approaches arise as important tools in establishing these correlations, especially when they are based on fundamental scientific principles. In this work, I present modeling and simulation techniques used in a multiscale and multi-physics framework with the goal of establishing composition-property correlations in cement systems. This manuscript follows a scale-wise organization, with the first chapter devoted to information from the molecular scale, followed by a chapter on how to upscale nanoscale information up to the scale of Civil Engineering applications. First, it is shown how molecular simulations can be used to calculate the elastic constants, thermal properties, mass transport properties, electromagnetic properties, and coupling properties of phases relevant to cement systems. It is also shown how molecular simulations help unveil the physical processes associated with sorption and hygro-thermo-mechanical couplings bottom-up. Then, a discussion on the mesoscale(s) of interest in the passage atomistic-to-continuum and in the realm of continuum mechanics up to the macroscopic scale (of industrial applications) of cement-based materials is presented. It is shown how Micromechanics theory provides estimates of effective properties in a multi-physics context but also information about local fields. Ongoing research and perspectives extending the multiscale multi-physics and multi-technique strategy to new phenomena and applications are finally presented

Einstein Explains Water Transport in C-S-H

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Quantifying the Processes at the Origin of the Dielectric Response of Cement-Based Materials with Molecular Dynamics Simulations

International audienceThe pore phase determines the dielectric and electrical responses of cement-based materials. Porosity is hierarchical in these materials with pore classes including macro, capillary, and nanopores. This work shows how molecular dynamics simulations provide quantitative information about the complex dielectric and electrical response for free water and ions, surface water and physically bound ions species, water and ions confined in nanopores, and also OH groups in the pore wall

Thermal conductivity, heat capacity and thermal expansion of ettringite and metaettringite: Effects of the relative humidity and temperature

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Mécanique des matériaux nanogranulaires

International audienceLes matériaux cimentaires (ainsi que d'autres matériaux nanoporeux comme les argiles et l'os) présentent une échelle mésoscopique qui peut bien être représentée par des grains interagissant via des forces colloïdales. Dans ce papier, je discute comment des phénomènes comme l'asymétrie tension/compression, l'expansion thermique et l'hystérésis associée à des chargements thermomécaniques émergent des systèmes qui interagissent par le bias des potentiels de force moyenne anharmoniques. Dans ce papier, je me concentre sur l'étude des silicates de calcium hydratés (C-S-H), qui sont le principal produit issu des processus d'hydratation des ciments Portland. L'objectif est d'identifier l'origine physique des phénomènes mentionnés ci-dessus afin de mieux comprendre le comportement des C-S-H

Modelagem micromecânica aplicada ao estudo de argamassas de revestimento

International audienceHomogenization techniques are used to estimate elastic and thermal effective properties of rendering mortars from their composition. The estimates are obtained as a function of time in order to describe the early age evolution of properties. A simplified approach is used to model the effects of cure and/or drying as microstructure (or property) gradient inducers. These results go towards a better understanding of the multiphysics behavior of rendering mortars as well as the effects of property gradients in the performance of cement-based materials.RESUMO Técnicas de homogeneização são utilizadas para modelar as propriedades elásticas e térmicas de argamassas de revestimento a partir de suas composições. As estimativas são obtidas em função do tempo a fim de descrever a evolução dessas propriedades desde as primeiras idades. Uma abordagem simplificada é empregada para modelar o efeito da cura e/ou secagem como inibidores/geradores de um gradiente de microestrutura ou de propriedade no revestimento. Esses resultados representam um avanço na compreensão do comportamento multifísico de revestimentos de argamassa assim como dos efeitos de gradientes de propriedades na performance de materiais à base de cimento

The processes associated with the hydrodynamics in calcium silicate hydrates nanopores are crucial to durability and confinement performance of concrete. We report Non Equilibrium Molecular Dynamics (NEMD) simulations of forced flows in crystalline calcium silicate hydrates nanopores. For slit pores larger than 4 nm, Poiseuille flow is observed for an imposed force parallel to both orthogonal directions of the basal plane. This result shows that Navier-Stokes, which is a priori restricted to the realm of continuum mechanics, can provide, even for nanopores, a reasonable description of the flow provided the adequate boundary conditions are employed. This observation go towards a better comprehension of water and aqueous solution transport phenomena in cement-based materials.

International audienceThe processes associated with the hydrodynamics in calcium silicate hydrates nanopores are crucial to durability and confinement performance of concrete. We report Non Equilibrium Molecular Dynamics (NEMD) simulations of forced flows in crystalline calcium silicate hydrates nanopores. For slit pores larger than 4 nm, Poiseuille flow is observed for an imposed force parallel to both orthogonal directions of the basal plane. This result shows that Navier-Stokes, which is a priori restricted to the realm of continuum mechanics, can provide, even for nanopores, a reasonable description of the flow provided the adequate boundary conditions are employed. This observation go towards a better comprehension of water and aqueous solution transport phenomena in cement-based materials

Triclinic tricalcium silicate: Structure and thermoelastic properties from molecular simulations

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