INTERFACIAL TRANSPORT IN POROUS-MEDIA - APPLICATION TO DC ELECTRICAL-CONDUCTIVITY OF MORTARS

A mortar is a composite of inert sand grains surrounded by a porous ce ment paste matrix. We investigate the electrical conductivity of model mortars that include enhanced electrical conduction in the matrix-san d grain interfacial region. The electrical conductivity is evaluated b y a combination of finite element, finite difference, and random walk methods for periodic and disordered models of mortar. Since the effect ive conductivity within the interfacial zone is often much higher than the bulk matrix conductivity, the qualitative features of transport i n these systems is often controlled by the connectivity of the interfa cial zone. Special attention is thus given to the geometrical percolat ion of this zone. A family of effective medium approximations give a g ood qualitative description of the disordered model's electrical prope rties. A simple four parameter Pade approximant is found to successful ly describe the electrical conductivity of the periodic model over the entire range of parameters studied. Finally, we show that our calcula tions can be used to obtain a reasonable estimate of the permeability to viscous fluid flow. (C) 1995 American Institute of Physics.