Earlier on-site investigations and laboratory studies have shown that varying corrosion rates are obtained when different commercially available instruments are used. The different confinement techniques, rather than the different electrochemical techniques used in the instruments, are considered to be the main reason for the discrepancies. This paper presents a method for the quantitative assessment of confinement techniques. The assessment is based on monitoring the operation of the corrosion rate instrument and following the current distribution between the electrode assembly on the concrete surface and a segmented reinforcement bar embedded in the concrete. The applicability of the method was demonstrated for two commercially available corrosion rate instruments based on different confinement techniques. The method provided an explanation of the differences in performance of the two instruments. Correlated measurements of linear polarisation resistance and macro-cell currents allowed the determination of calibration factors. Both instruments overestimated the corrosion rate of passive reinforcement, but underestimated the corrosion rate of reinforcement with intense localised corrosion.
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