Determining the locations for reference electrode installation in cathodic protection systems
The location of the reference electrodes is one of the most critical components related to cathodic protection (CP) system monitoring and adjustment.
In accordance to AS 2832.5-2008, the determination of the extent and location of permanently installed performance evaluation systems shall, for each zone, take into account areas of the concrete structure that have the following characteristics:
(a) Particular sensitivity to under-protection.
(b) Particular sensitivity to excessive protection.
(c) High corrosion risk or activity.
(d) Low corrosion risk or activity.
In order to select the optimum locations for reference electrode installation, external potential mapping of the concrete element to be protected must be performed prior to installation. The reference electrodes must be placed in both high and low corrosion risk areas in order to eliminate the possibility of over-protection and under-protection of the embedded reinforcement. Additionally, the location of a reference electrode must be made with consideration of the location of the anode (positive) connection, as this may impact on the sensitivity of test readings related to over and under-protection.
It is a requirement for a reference electrode to have a dedicated steel connection. The DC negative power return should not be used for potential measurements as the voltage flow within the CP circuit will impact on the readings recorded from the reference electrodes. Each reference electrode should be installed in a location with no direct contact between the mortar surrounding the reference electrode and the rebar.
For the protected concrete element, the size of the potential mapping area must be large enough to identify all areas of low and high corrosion activity with the cathodic protection zone. The number of embedded reference electrodes must be sufficient so that readings are taken in high and low corrosion activity locations, and in areas with vulnerability to under protection and excessive over-protection.
Left - Potential mapping to identify suitable location for reference electrode
Right - Structure with installed reference electrodes