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UFR 926

Séminaire de Roland PELLENQ à l’Institut de Chimie "THE BOTTOM-UP MODELLING APPROACH TO CEMENT PASTE" le 1er juin 2016

Abstract: Strength and other mechanical properties of cement paste and concrete rely upon the formation of calcium-silicate-hydrates (C-S-H) during cement hydration. Despite the potential for technological transformation, controlling the structure and properties of C-S-H phase is still a challenge, due to the complexity of this hydration product and of the mechanisms that drive its precipitation from ionic solution upon dissolution of cement grains in water. Departing from traditional models that are mostly focused on length-scales above the micrometer, molecular models have recently addressed the nanometer-scale structure and properties of C-S-H. However, small angle neutron scattering, electron-microscopy imaging, and mechanical nano-indentation experiments, all suggest that an even more important role is played by the mesoscale organization of the C-S-H structure that extends over hundreds of nanometers. New quantitative models are needed to address this unexplored meso-scale, elucidate the experimental observations, and complete the understanding of the multi-scale structure of cement paste. Here we present a novel description of the C-S-H meso-structure that offers an opportunity to translate results from the fundamental scales to the macro-scale of engineering properties. We use simulations that combine information of the nano-scale building units of C-S-H and on their effective interactions, obtained from atomistic simulations and experiments, into a statistical physics framework for aggregating nanoparticles. We compute small angle scattering intensities, pore size distributions and nano-indentation modulus and hardness, providing a new quantitative understanding of the relevant features observed experimentally. Our results suggest that specific heterogeneities developed during the early stages of hydration persist in the structure of C-S-H, impacting the rheological and mechanical performance of the hardened cement paste.







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