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Introduction

As a construction material, concrete is used in a wide variety of applications. In order to reliably fulfill its intended function, the concrete must withstand attack by the environment to which it is exposed. Predicting the service life of concrete is thus a subject of considerable interest, as discussed in a recent review [1]. Empirical and physical models of degradation processes in concrete have been developed [2], but one complication in this approach is that the material parameters on which the models are based are actually changing as the degradation occurs. For example, relative ionic diffusivity, hereafter abbreviated as diffusivity, a key material parameter in a variety of degradation processes such as rebar corrosion and sulfate attack, will almost certainly change as the pore space of the concrete is modified by the degradation process. Relative ionic diffusivity is defined to be the ratio D/D_o, where D is the measured diffusivity of ions through a water-saturated porous material, and D_o is the diffusivity of the same ions in bulk water [3,4]. Understanding the influence of degradation on material properties is thus necessary to enable comprehensive service life models to be developed.

This paper explores one specific area of the effect of degradation processes on properties via microstructural changes: the effect of the leaching or dissolution of calcium hydroxide on the capillary pore space connectivity and the diffusivity of neat cement paste and silica-fume-modified cement paste. A microstructure model [5] is used to study the effects of water:solids (w/s) ratio and silica fume content on the extent of leaching. Diffusivities are directly computed using an electrical conductor network analogy [6] and a conjugate gradient relaxation algorithm [7].