One key parameter influencing the service life of a concrete structure is the diffusivity of the concrete . In many cases, the rate of ingress of some deleterious species such as chloride or sulfate ions regulates the initiation of deterioration. In the 1990's, much research and development has been conducted to produce more durable (so-called high performance) concretes. It has been recognized that strength and durability are different properties of a concrete, and that the transport properties of the "covercrete" (the top exposed layer of the concrete) are particularly vital in determining its durability and service life.
In the 1970's, the Nordic countries initiated the incorporation of condensed silica fume (CSF) into concrete to produce higher strengths . Silica fume also offers many potential durability benefits (although its tendency to increase autogenous deformation , adiabatic temperature rise , and early-age cracking must be carefully controlled). Measurements of the diffusivity of concrete with and without silica fume [5, 6,7] based on the rapid chloride permeability test  or on more direct measurements of chloride ingress have all indicated a substantial reduction in diffusivity for the concretes containing silica fume. In this paper, a set of multi-scale computer models is used to develop an equation for predicting the diffusivity of a concrete containing silica fume based on four inputs: the water-to-cement ratio (w/c), the silica fume addition, the volume fraction of aggregates, and the degree of hydration of the cement. Previously, these techniques have been applied to ordinary concrete and mortar with no mineral admixtures [9,10], and here are extended to concretes with silica fume, based on recent experimental and computer modeling results on the influence of silica fume on the diffusivity of cement pastes .