Predicting Times to Corrosion from Field and Laboratory Chloride Data

Abstract

Corrosion of steel in concrete is one of the major causes of the premature failure of steel reinforced concrete. In marine and deicing salt environments the ingress of chloride is the primary cause for the breakdown of passivity and the onset of severe corrosion. In this paper, we show how to develop effective diffusion coefficients for chloride ingress based on chloride profiles from several marine structures. Predictions of the times to reach chloride levels associated with initiation of severe corrosion are made. Chloride profiles using effective diffusion coefficients determined in other studies are given for bridge decks and parking structures. There are significant benefits of increased concrete cover and the use of corrosion inhibitors in increasing the time to corrosion. Finally, comparisons of Standard Test Method for Electrical Indication of Concrete's Ability to Resist Chloride Ion Penetration (ASTM C 1202) coulomb values with effective diffusion coefficients, determined from field and laboratory studies, indicate that effective diffusion coefficients for low permeability concretes can be estimated using simple modifications of this test method. Thus, we demonstrate that knowledge of the chloride profile is useful to assess the future performance of existing structures that are not undergoing active corrosion, and in predicting the time to corrosion initiation of new structures.