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(1) Presentation(s)

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Jeu. 07/02/2019 14:00 Amphi Jean Jacques Moreau, Bâtiment 2, RdC

Séminaire
IOANNIDOU Katerina (LMGC)
Mesoscale modeling of cement: texture, mechanics and durability

Sommaire:

Cement is a multiscale porous material, widely produced, more than any other synthetic material on Earth. In this talk, I will present a multiscale bottom-up approach for cement and specifically for calcium-silicate hydrate (C-S-H) that is the most abundant phase of cement. During cement hydration C-S-H nano-scale particles precipitate in the pore solution and form a cohesive gel that is the main binding agent in cement and concrete, crucial for the strength and the long-term evolution of the material. Even more than the molecular structure of C-S-H particles, the C–S–H mesoscale texture over hundreds of nanometers plays a crucial role for material properties. We use a statistical physics framework for aggregating nanoparticles and numerical simulations to obtain a first, to our knowledge, quantitative model for such a complex amorphous material. Our approach is based on precipitation of colloidal particles interacting with effective potentials associated to the chemical environment. The effective potential can be calculated from atomistic models of C-S-H and are corroborated by experiments. This multiscale informed modelling approach generates realistic micron scale textures in terms of pore size distributions and solid volume fractions and allows to calculate mechanical properties. The extensive comparison with experiments ranging from small-angle neutron scattering, EM imaging, adsorption/desorption of N2, and water to nano-indentation provides new fundamental insights into the microscopic origin of the cement properties measured. Our results provide a quantitative insight into how the heterogeneities developed during the early stages of hydration persist in the structure of C-S-H and impact the mechanical performance of the hardened cement paste. Moreover, this approach allowed to address durability issues on cement such as freeze-thaw and alkali-silica reaction damage leading to the formation of cracks and fractures.


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