Chloride-induced corrosion of steel reinforcement in alkali-activated slag/ metakaolin blended concretes

Chloride-induced corrosion of steel reinforcement in alkali-activated slag/ metakaolin blended concretes

GevaudanE, Juan Pablo (University of Leeds, United Kingdom)
Bernal, Susan A. (University of Leeds, United Kingdom)

2021-04-29

The aim of this study is to understand the corrosion mechanism of steel embedded in alkali-activated slag/metakaolin blended concretes via electrochemical testing after 407 days of exposure to a 3.5 wt.% NaCl solution, with an emphasis on characterising the material prior to the onset of corrosion. In order to accurately depict the material’s state, the importance of timedependent stability of the corrosion potential (Ecorr) is discussed in the context of both twoelectrode cell set-up on a carbon-steel exposed to basic solutions (0.8 M NaOH and 0.8 M NaOH + 1.2 M NaCl) and reinforced alkali-activated concretes. When carbon-steel is exposed to NaOH solutions, the Ecorr values did not attain a logarithmic equilibrium or passive condition prior to 72 hours of exposure. At the same NaOH concentration, and in the presence of chlorides, Ecorr values fluctuated as a consequence of localised corrosion activity at the metal surface. In order to circumvent the instability caused by chlorides, both direct-current (linear polarization resistance) and alternating-current (electrochemical impedance spectroscopy) techniques were utilized to determine and cross-validate the polarization resistance (Rp) in steel-reinforced alkali-activated concretes. With a 0.6% difference in Rp values, results demonstrate excellent agreement by utilizing both techniques. Thus, results demonstrate that these concretes do not initiate corrosion activity before 158 days of aggressive exposure to chloride. These results demonstrate some stability of the oxide films forming in alkali-activated concretes, and highlight the need for long duration testing of these materials to truly understand how corrosion might take place in reinforced concretes.

corrosion potential
alkali-activated cements
corrosion
electrochemistry

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