Corrosion potential mapping is used to identify rebar spots that are undergoing corrosion. It is a non-destructive technique carried out on concrete structures in order to determine corrosion status related to the identified corrosion potential value. The contours and measurements obtained by using plotting potential corrosion values are also significant in delineating corroding portions of structures from `healthy` non-corroding portions. The half-cell, open circuit potential test method is a more frequently used technique for potential corrosion mapping, although double-probing is also applicable. The half cell testing method is suitable for on-site (in-situ) evaluation as well as for research and development work. It applies to concrete members regardless of size or depth of covers over reinforcing steel. Half-cell circuit potential testing and measurement can also be used any time during the lifespan of a concrete member. It is an inexpensive test method that is simple and quick to perform and analyse, even when surveying an entire structure.