Determination of Polarization Resistance of Reinforcement with a Sensorized Guard Ring: Analysis of Errors Available to Purchase

Reinforcement corrosion is the main cause of damage to concrete structures. The main source of errors in measuring the corrosion rate of rebars on-site is the unknown and nonuniform current distribution between the small counter electrode on the concrete surface and the large rebar network in reinforced concrete construction. Guard ring electrodes are used in an attempt to confine the excitation current within a defined area, so that errors caused by the nonuniform current distribution along the length of a rebar can be eliminated. To better understand the functioning of sensorized guard electrode (GE), and to assess its effectiveness in eliminating errors due to spread of current signal from the small counter electrode (CE), measurements of the polarization resistance of reinforcement with the use of the sensorized GE device have been numerically simulated. The results indicate that the sensorized GE arrangement is not able to deliver accurate values of the polarization resistance of reinforcement within the whole range of corrosion activity when a constant extent of the CE current spread is used for the calculations. When corrosion is uniform, the current distribution under the sensorized GE is a superposition of both CE and GE currents and depends strongly on testing conditions. As a consequence, the sensorized GE is not able to confine the lateral spread of the CE current within a defined and constant distance from the border of CE (diameter of confinement area). An error of one order of magnitude may be expected when calculating the polarization resistance with an a priori defined and fixed diameter of confinement area for differing test conditions. At high corrosion activity, an “overconfinement” through the GE takes place, and may be a source of serious underestimation of the corrosion rate. When the reinforcement is passive, the corrosion rate is overestimated. When the corrosion is localized, the corrosion rate of the corroding part is seriously underestimated even for a relatively large size of the active spot. This may cause difficulty in differentiating between mild homogeneous corrosion and severe local corrosion.