United States Department of Transportation
i
Corrosion Inhibitors in Concrete Interim Report
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2002-03-01
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[PDF-5.43 MB]
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Abstract:The overall objective of this work in progress is to assess the effectiveness of corrosion inhibitors for steel in concrete. Three commercially available inhibitors, DCI-S (calcium nitrite-based), and FerroGard 901 and Rheocrete 222+ (Both based on organic compounds), were selected for detailed examination. To determine the amount of inhibitor remaining in concrete, an accurate method to analyze for calcium nitrite was developed, and analyses for the other two inhibitors are being explored. The ability of calcium nitrite to stay in place was examined by laboratory experiments of inhibitor diffusion in concrete and by examination of available concrete samples exposed for long times to the outdoors environment. Results indicated a nitrite ion diffusivity comparable to that of chloride ions in concrete. Tentative tests with FerroGard 901 suggest similar behavior. Examination of long-term outdoor specimens indicated that a high level of corrosion protection was achieved when the mass of nitrite ion per volume of concrete equaled or exceeded that of chloride ions. Tests with DCI-S also disclosed that typically only a fraction of the inhibitor resides in the pore water of the concrete, but in simulated pore water experiments that fraction was enough to provide substantial protection to chloride-induced corrosion. Although nitrite in the pore water slightly reduced pH, this potentially detrimental effect was amply counteracted by the overall beneficial action of the nitrite ion. During the early phase of tests in progress with laboratory concrete specimens DCI-S was the most effective of the three inhibitors in mitigating corrosion. Under those test conditions the organic inhibitors showed modest or little evidence of effective corrosion protection. In early testing none of the inhibitors evaluated substantially affected the penetration of chloride ions in concrete, or its strength and sulfate resistance. The presence of DCI-S did reduce the resistivity of the concretes tested by about 1/3.
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