Comparative Evaluation of Corrosion-Inhibiting Chemical Admixtures for Reinforced concrete

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Title: Comparative Evaluation of Corrosion-Inhibiting Chemical Admixtures for Reinforced concrete

Author(s): C. K. Nmai and P. D. Krauss

Publication: Special Publication

Volume: 145

Issue:

Appears on pages(s): 245-262

Keywords: admixtures; chlorides; corrosion; corrosion tests; cracking (fracturing); reinforced concrete; reinforcing steels; Materials Research

Date: 5/1/1994

Abstract:
There are currently several commercially available corrosion-inhibiting chemical admixtures for reinforced concrete. The two most commonly used are a calcium nitrite-based admixture that inhibits corrosion by reacting to ferrous ions to form a protective ferric oxide film; and a water-based organic admixture, consisting primarily of amines and esters, which functions by reducing chloride ion ingress into concrete and by forming a coating on the surface of the embedded steel. Because of the different mechanisms by which these two inhibitors function, comparative accelerated time-to-corrosion evaluations were performed to obtain a measure of their effectiveness relative to one another in both uncracked and cracked reinforced concrete specimens. Concrete of moderate to low quality was used. The calcium nitrite inhibitor was evaluated at dosages of 10, 20, and 30 L/m 3 and the water-based organic inhibitor was evaluated at a dosage of 5 L/m 3. Companion untreated concrete specimens, which served as controls, were also evaluated. The duration of the cracked concrete time-to-corrosion evaluation was 23 weeks and was 48 weeks for the uncracked concrete. The time-to-corrosion evaluations indicate that both inhibitors were effective. The water-based organic inhibitor was particularly effective in the cracked concrete time-to-corrosion evaluation relative to the calcium nitrite inhibitor. The degree of effectiveness of the calcium nitrite increased with increasing dosage.