Volume 2, Issue 8 (September 2005)
A Comparative Evaluation of Three Commercial Instruments for Field Measurements of Reinforcing Steel Corrosion Rates
In this study, a comparative evaluation was made of three instruments, designed for field monitoring of reinforcing steel corrosion rates. The electrochemical operating principles of each instrument were determined by monitoring the potential and current of each electrode during operation.
Corrosion current densities (icorr) of reinforcing steel bar (rebar) in concrete determined with the three different instruments varied by as much as 50 times. The average of the ratios of corrosion rates between any two of the instruments varied between four and 14 times. The size of the polarized area of a section of reinforcing steel is assumed by the configuration of each instrument's counter electrode and guard ring electrode. It was observed that the guard ring electrodes affected the polarization of the reinforcing steel and this effect, together with the different electrode materials, is considered the principal cause of the variations in measured corrosion rate.
Corrosion rates of embedded corrosion monitoring probes were also measured. The variation in icorr for measurements on probes was smaller than those on the reinforcing bar and, on average, corrosion rates varied between two and six times. The observation that corrosion monitoring of probes is more consistent than measurements on reinforcing bar suggests that the use of such embedded probes may provide more reliable values for service-life predictions. This consistency was attributed mainly to the known size of the polarized area.