Modeling ion and fluid transport in unsaturated cement systems in isothermal conditions

A description of ionic transport in unsaturated porous materials due to gradients in the electro-chemical potential and the moisture content is developed by averaging the relevant microscopic transport equations over a representative volume element. The complete set of equations consists of time-dependent equations for both the concentration of ionic species within the pore solution and the moisture content within the pore space. The electrostatic interactions are assumed to occur instantaneously, and the resulting electrical potential satisfies Poisson's equation. Using the homogenization technique, moisture transport due to both the liquid and vapor phases is shown to obey Richards' equation, and a precise definition of the moisture content is found. The final transport equations contain transport coefficients that can be unambiguously related to experimental quantities. The approach has the advantage of making the distinction between microscopic and bulk quantities explicit.