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The transport properties of porous media are of interest in connection with a variety of environmental, infrastructural, and technological problems. Among the systems of interest are heterogeneous catalysts, reservoir rocks, and cement-based materials like mortar and concrete. Concrete is a generic term describing a mixture of porous cement paste (formed by the hydration of cement powder) and inert aggregate particles usually comprised of sand grains and rock fragments. In a mortar, the aggregate particles are limited to sand grains whose diameter typically does not exceed a few millimeters.
The D.C. electrical conductivity of mortar and concrete is important both as a means of probing the structure of these materials and as a measure of ionic diffusivity [1], via the Nernst-Einstein relation [2]. Diffusivity is of interest in connection with a range of issues related to durability; examples are sulfate attack and chloride ion-induced corrosion of steel reinforcing bars [3]. These materials conduct electricity via the electrolytic pore fluid [4,5,6] in the cement paste matrix. The conductivity of the paste depends on the original water-cement mixing ratio; for a given ratio, the matrix will be comprised of calcium silicate gel and unhydrated cement powder. Much recent work has been done on understanding how the complex microstructure of cement paste determines its electrical conductivity [4,5,6,7]. However, relatively little work has been done on how the conductivity of concrete depends on quantities like the density and size distribution of aggregate particles and on the geometry and properties of the cement paste-aggregate interfacial zone [6].