While the utility of permeability reducing and corrosion inhibiting admixtures in concrete for forestalling the onset of corrosion initiation is generally recognized, there remains a general non-availability of long-term data upon which quantitative performance projections can be made. Of particular concern is that, while the rate of chloride ingress may be less for high performance concretes with pozzolanic admixtures compared to ordinary Portland cement concretes, the threshold chloride concentration for passive film breakdown and onset of active corrosion has been projected to be lower for the former material compared to the latter. This follows from the fact that pore water pH for these admixed concretes is relatively low and that the threshold concentration may be defined by a critical value for the ratio of chloride-to-hydroxide ions. The research reported herein was performed for the purpose of determining threshold chloride concentrations for high performance concretes under exposure conditions relevant to coastal bridge substructures in Florida. The experiments were based upon a series of reinforced and non-reinforced concrete specimens that contained 1) 20, 35, and 50 percent cement replacement by fly ash, 2) 3, 8, and 15 percent cement replacement by silica fume, and 3) control specimens (no pozzolanic
admixture). In addition, the utility of calcium nitrite as a corrosion inhibitor was evaluated based upon slabs that contained 1) 35 percent cement replacement with fly ash and...