TY - JOUR T1 - Atomistic and mesoscale simulation of sodium and potassium adsorption in cement paste JF - The Journal of Chemical Physics Y1 - 2018 A1 - Dufresne, Alice A1 - Arayro, Jack A1 - Zhou, Tingtao A1 - Katerina Ioannidou A1 - Franz-Josef Ulm A1 - Roland Jean-Marc Pellenq A1 - BĂ©land, Laurent Karim AB -

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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VL - 14963 UR - https://aip.scitation.org/doi/10.1063/1.5042755 IS - 7 JO - The Journal of Chemical Physics ER -