Use of galvanostatic pulse measurements on active reinforcing steel in concrete to assess corrosion rate

This paper reports the results of galvanostatic pulse transient response experiments to determine the corrosion parameters associated with actively corroding reinforcing steel in concrete. Galvanostatic pulse measurements have been conducted on a number of short 100 mm sections of steel reinforcing bar embedded in chloride contaminated concrete. The duration of the applied galvanostatic pulse was 90 s and the lateral distance of the point of measurement from the bar varied from zero to 400 mm. All of the bars monitored were conditioned so that they were actively corroding at different rates. Analysis of the galvanostatic pulse transient response has enabled the separate components that make up the measured transients to be isolated and evaluated. These components display a range of resistivities and capacitances, dependent on the corrosion condition of the reinforcing steel, which may be attributed to the corrosion process, to effects within the concrete cover, or to film effects on the surface of the concrete. Other investigators using this technique have evaluated the corrosion rate by summation of the separate corrosion components, i.e. simply summing all of the resistance values to obtain an aggregated corrosion resistance. However, it is possible that not all resistances identified are associated with the loss of steel from the surface of the reinforcement. Significant variations in corrosion rates have been observed dependent on the assignment of the separate components to either corrosion or to other processes. The data indicate that it is not feasible to assign the component based solely on the capacitance. An inappropriate selection of measurement time or equilibrium time may result in part of the resistance associated with the corrosion process being left out or an additional resistance not controlling the rate of corrosion being include