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TRANSPORTATION RESEARCH DIGEST

ARIZONA TRANSPORTATION INSTITUTE

e-mail jsemmens@cox.net

NOVEMBER 2005

Evaluation of Two Corrosion Inhibitors Using Two Surface Application Methods for Reinforced Concrete Structures by Stephen R. Sharp, Virginia Transportation Research Council, 530 Edgemont Road, Charlottesville, VA 22903; (434) 293-1900 (Virginia Department of Transportation, 1401 E. Broad Street, Richmond, VA 23219; vdotinfo@virginiaDOT.org) (December 2004)

Highlights

The topical application of inhibitor for corrosion mitigation is ineffective.

The vacuum/pressure injection method shows promise, but the methodology requires refinement.

Macro-cell measurements indicate that if a sufficient quantity of inhibitor can be injected into the concrete, the charge passed can be reduced.

In the United States, the direct annual maintenance and capital costs associated with corrosion of concrete bridge decks is between $1.07 billion and $2.93 billion. The associated indirect costs are approximately 10 times higher. 1 Despite these substantial costs, an estimated savings of up to 46 percent of the annual corrosion cost can be recovered by improving maintenance practices. Therefore, technology that reduces corrosion in highway bridges financially benefits the bridge owner, especially if the corrosion mitigation technique has only a minor impact on traffic flow.

The application of corrosion inhibitors is one possible corrosion mitigation technique for reinforced concrete structures. This technique reduces the corrosion rate by hindering the anodic reaction, the cathodic reaction, or both. Although numerous studies have investigated the influence of corrosion-inhibiting concrete admixtures in new construction, corrosion mitigation techniques designed to rehabilitate the aging

infrastructures are also needed. Currently, inhibitors designed for application to the external surface of existing structures are being evaluated for their use in revitalizing corroding structures. Some researchers have indicated that inhibitors designed to penetrate concrete provide some protection, and others have found that post-treatment of a concrete structure was not effective at mitigating corrosion.

Although the idea of simply applying an inhibitor to the concrete surface is appealing, it is critical that the inhibitor not only penetrate the concrete but also reach the reinforcing steel in sufficient concentrations to inhibit corrosion. The use of a vacuum to remove residual moisture from within the concrete followed by the application of pressure to inject an inhibitor into the concrete has also been suggested by the manufacturer of one of the inhibitors evaluated in this study. The manufacturer proposed that this method of application will increase the dose applied to the structure and ensure a sufficient concentration of inhibitor reaches the steel surface. Although both techniques for applying corrosion inhibitors can be used with only a slight impact on traffic flow, the use of a vacuum/pressure injection system increases the complexity of the application process because of the need for additional equipment.

In addition, although the costs of these two methods of application are expected to be small since the material costs are relatively low, such corrosion mitigation techniques will be beneficial only if the corrosion rate is

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