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Modeling Diffusive Ionic Transport in Concentrated Alkaline Cementitious Pore Solutions at 25 C: Comparison to Published Binary Salt Data

Published

Author(s)

Kenneth A. Snyder, Joseph B. Hubbard, J Marchand

Abstract

The applicability of a Nernst-Planck equation to characterizing diffusive transport in concentrated electrolytes typically found in cementitious systems is investigated using published experimental data for the collective diffusion coefficient of binary salts.The proposed transport equation requires estimates for bulk electrolyte properties(density and viscosity) and ionic species properties (self-diffusion, mobility, and activity coefficient). The resulting Nernst-Planck equation is then used to calculate the total flux of a binary salt in aqueous solution,from which the effective Fickian diffusion coefficient is calculated and compared to the published diffusion coefficient as a function ofconcentration. These calculations provide a rigorous test for the proposed transport equationbecause the bulk electrolyte properties are determined independently, and there are no adjustable transport parameters. Resultsindicate that corrections for density, mobility, and activity coefficient yield estimated collective diffusion coefficients accurateup to (0.2 to 0.5) mol/L for 1:1 binary salts. A correction to the self-diffusion coefficient using the bulk viscosity extends the accuracy of the diffusion equation to 1.0 mol/L in bulk electrolytes. Calculations of chloride andsulfate diffusive transport in simulatedpore solution indicate that the viscosity correction could be significant for cementitious systems. Similar calculations of the macroscopicdiffusion potential across the sample indicate that, for electrical measurements, accuracy depends on the model for ionic mobility.
Citation
Journal of Colloid and Interface Science

Keywords

cement, concrete, diffusion, electrolyte, mobility, transport, viscosity

Citation

Snyder, K. , Hubbard, J. and Marchand, J. (2017), Modeling Diffusive Ionic Transport in Concentrated Alkaline Cementitious Pore Solutions at 25 C: Comparison to Published Binary Salt Data, Journal of Colloid and Interface Science (Accessed February 6, 2023)
Created February 19, 2017