Pore Solution Composition and Electrochemical Behavior of Steel Bars in Mortars with Nitrite Corrosion Inhibitors


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Title: Pore Solution Composition and Electrochemical Behavior of Steel Bars in Mortars with Nitrite Corrosion Inhibitors

Author(s): M. Kawamura, S. Tanikawa, R. N. Swamy and H. Koto

Publication: Special Publication

Volume: 173


Appears on pages(s): 35-54

Keywords: Corrosion; nitrites; porosity; sands; sodium chloride; strength

Date: 9/1/1997

The effectiveness of Ca(NO2 )2 and NaN02 as corrosion inhibitors has been confirmed. However, the behavior of NO2 - ion and its stability in the pore solution in concrete containing the inhibitors is a matter of concern for their effective use as a corrosion-inhibiting admixture. Furthermore, it may be important from the viewpoint of the corrosion of reinforcement in concretes contaminated with Cl- ion to examine the behavior of NO2 - ions in relation to Cl-ion concentration in the pore solution in concrete. In this study, the analyses of pore solutions expressed from NaCl containing-mortars with and without the inhibitors were carried out to elucidate effects of the inhibitors on the chloride binding capacity of mortars. Simultaneously, the corrosion rate of steel bars embedded in the mortars was monitored by measurements of the potential and polarization resistance. The N02 - ion concentrations in the pore solutions in NaCl-containing mortars treated with 1% Ca(N02 )2 by mass of cement were lower than those in the corresponding mortars with NaN02 . The addition of NaN02 raised the OH- ion concentration slightly, but the OH- ion concentration was somewhat reduced in the mortars with Ca(NO2 )2 . The combined addition of NaCl and NaNO2 on the other hand, greatly raised the OH- ion concentration. However, the Cl’ /NO2 - ratios in the pore solutions in mortars containing Ca(N02 )2 were slightly lower than in mortars containing NaNO2 because of the dissipation of greater amounts of Cl- ions from the pore solutions in the former than in the latter.