Analytical Evaluation of Time-to-Corrosion for Chloride-Exposed Reinforced Concrete with an Admixed Corrosion Inhibitor: Part 1-No Inhibitor Egress

A first-principles-based equation from the literature was modified such that the cumulative distribution function (CDF) of Cl- concentration ([Cl-]) in concrete at the reinforcement depth after a given exposure time was calculated by numerical integration. The approach accommodates the fact that surface Cl- concentration (C-s), the effective diffusion coefficient (D), and reinforcement cover (x) each conform to a distribution, rather than being discreet. Calculations were performed for a range of mean D, Cs, and x values. The previously reported limiting [Cl-] for which various dosages of the corrosion inhibitor calcium nitrite (CN) are effective in maintaining reinforcing steel passivity was superimposed upon the CDF. From probability distributions of, first, [Cl-] and, second, Cl- threshold to initiate active corrosion, as enhanced by a particular CN addition, the percentage of reinforced concrete elements for which active corrosion initiates after specific times and, hence, inhibitor effectiveness, were determined using a load-resistance factor design-type approach. Inhibitor effectiveness in reducing total corrosion, once initiated, is discussed, as are scenarios and implications thereof for chlorides and CN being solely in the cement phase as opposed to being uniformly distributed throughout the concrete.