Half Cell Potential Test
The half cell potential test is the only corrosion monitoring technique standardized by ASTM. It is used to determine the probability of corrosion within the rebar in reinforced concrete structures.
Process
Measurements are made in either a grid or random pattern. The spacing between measurements is generally chosen such that adjacent readings are less than 150mv with the minimum spacing so that there is atleast 100 mvbetween readings . A direct electrical connection is made to the reinforcing steel with a compression clamp or by brazing or welding a protruding rod . To get a low electrical resistance connection the rod shoukd be scraped before connecting it to the bar. It is necessary to drill into the concrete to expose a reinforcing bar. The bar is connected to the positive terminal of the voltmeter. One end of lead wire is connected to the half cell and the other end to the negative terminal of the voltmeter. Measurements can be presented either with maps which provides a graphical delineation of areas in the member where corrosion activity may be occurring.