Measuring Metallic Corrosion with Half Cell Potential Test

When reinforcing steel corrodes inside concrete, an electro-chemical process occurs and its characteristics can be identified with a half-cell potential (HCP) measurement, also known as a ‘half cell potential test’. HCP measures metallic corrosion to determine the regions of potential corrosion and the risk it can impose on the structure. Date interpretation is nuanced and specific to particular sites, but generally a more negative potential means a risk of corrosion occurring in unsaturated marine exposed concrete. To conduct the test, an electrode is used to form one part of the bimetal cell, while the reinforcing steel within the concrete serves as the other half. Silver/silver chloride in a potassium chloride solution or a simple Copper/Copper Sulphate cell is the ideal reference electrode for use on-site. An electrode that is made of copper/copper sulphate is widely used, too.


An advanced half cell potential meter is a great instrument to have for a more reliable way to locate corrosion in embedded reinforcing steel. The best meters are versatile and can work with either a silver/silver chloride or copper/copper sulphate half-cell.

Cover concrete is locally removed over an appropriate bar, and the electrical connection is established to the steel. During the test, you need to ensure electrically continuous steel by determining the resistance between the two points which are widely separated. The reinforcing bar is linked to a half-cell through a meter’s internal digital voltmeter and readings of the half-cell potential are identified about regular grid points to create a prospective map of the area. Advanced machines may offer a wheel electrode for quick data collection.

Operators may plot contour lines between the points of equal potential while measuring metallic corrosion with a half cell potential meter. That way they can indicate that those areas possess the highest risk of corrosion. It is recommended that you expose and inspect reinforcing steel in places where low and high risks of corrosion exist as a final point of data to confirm an inspection method. That way, you can estimate the rate of corrosion and evaluate the need for repair or further investigation.

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