Performance of corrosion inhibiting admixtures in a marine environment

Corrosion of reinforcing steel is a major contributor to early deterioration of concrete structures in a coastal environment. This paper presents the results of an eight year field study involving 25 reinforced concrete panels exposed to a marine tidal zone. Seven different corrosion inhibiting admixtures and two pozzolans were used to compare their effectiveness at preventing or delaying onset of corrosion. This study was funded by the Hawaii Dept. of Transportation, Harbors Division, in order to evaluate commercially available corrosion inhibiting admixtures when used in concretes made with basalt aggregates common to Hawaii and other Pacific Islands. The corrosion-inhibiting admixtures included in this project were Darex Corrosion Inhibitor (DCI), Rheocrete CNI, Rheocrete 222+, FerroGard 901, Xypex Admix C-2000, Latexmodifier, Kryton KIM, and the pozzolans were fly ash and silica fume. This paper presents an assessment of the amount of corrosion on the reinforcing steel in the field panels and compares the results with companion laboratory specimens with the same concrete mixtures. It was found that DCI, CNI, fly ash and silica fume all provided improved corrosion protection compared with the control specimens. Kryton KIM performed well in a field panel, but was not included in the laboratory study. As expected, the control mixture with lower water-cement ratio (0.35) performed better than a control mixture with higher water-cement ratio (0.40). Concrete mixtures using Rheocrete 222+, FerroGard 901, Xypex Admix C-2000 or Latex-modifier showed mixed results. Some mixtures exhibited improved performance compared with the control mixtures, while others did not. Based on the results of this study, these corrosion inhibiting admixtures cannot be recommended for concrete using Hawaiian aggregates in a marine environment.