The results of a 1.5-yr laboratory study and field investigation of three Virginia bridges are presented. Specimens with fly ash, slag cement, silica fume, silica fume with a corrosion inhibitor, and two specimens (controls) with Virginia Department of Transportation specification concrete (A-4) were built to study diffusion characteristics of these concretes and to estimate corresponding corrosion initiation times. The methodology used to estimate the corrosion initiation times is based on Fick's Second Law of Diffusion. It uses laboratory concrete diffusion characteristics and cumulative distribution functions of the field surface concentration and diffusion coefficient values. The calculations are performed for various cover depths, and a set of curves is provided for each concrete type and for low, mean, and high values of surface concentration (exposure severity) and diffusion coefficient (concrete quality). The analysis results demonstrate the benefits of using mineral admixtures, especially when combined with a corrosion inhibitor.