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Atomistic and mesoscale simulation of sodium and potassium adsorption in cement paste

TitleAtomistic and mesoscale simulation of sodium and potassium adsorption in cement paste
Publication TypeJournal Article
Year of Publication2018
AuthorsDufresne A, Arayro J, Zhou T, Ioannidou K, Ulm F-J, Pellenq RJean-Marc, Béland LKarim
JournalThe Journal of Chemical Physics
Volume14963
Issue7
Pagination074705
Date PublishedAug-21-2018
ISSN0021-9606
Abstract

An atomistic and mesoscopic assessment of the effect of alkali uptake in cement paste is performed. Semi-grand canonical Monte Carlo simulations indicate that Na and K not only adsorb at the pore surface of calcium silicate hydrates (C-S-H) but also adsorb in the C-S-H hydrated interlayer up to concentrations of the order of 0.05 and 0.1 mol/kg, respectively. Sorption of alkali is favored as the Ca/Si ratio of C-S-H is reduced. Long timescale simulations using the Activation Relaxation Technique indicate that characteristic diffusion times of Na and K in the C-S-H interlayer are of the order of a few hours. At the level of individual grains, Na and K adsorption leads to a reduction of roughly 5% of the elastic moduli and to volume expansion of about 0.25%. Simulations using the so-called primitive model indicate that adsorption of alkali ions at the pore surface can reduce the binding between C-S-H grains by up to 6%. Using a mesoscopic model of cement paste, the combination of individual grain swelling and changes in inter-granular cohesion was estimated to lead to overall expansive pressures of up to 4 MPa—and typically of less than 1 MPa—for typical alkali concentrations observed at the proximity of gel veins caused by the alkali-silica reaction.

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URLhttps://aip.scitation.org/doi/10.1063/1.5042755
DOI10.1063/1.5042755
Short TitleThe Journal of Chemical Physics
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