24 May Corrosion Analysis – Factors Affecting the Half-Cell Potential Measurement Principle
Corrosion analysis in seemingly healthy concrete reduces unwanted risk to structural safety of buildings. The reinforcement condition is evaluated by measuring cover depth, rebar thickness and by using the half-cell potential method.
Provided that the corrosion conditions are equal (chloride content or carbonation of the concrete at the steel surface) the main influences upon the half-cell potentials for corrosion analysis are:
- Moisture: Moisture has a large effect on the measured potential leading to more negative values
- Temperature: In order to measure the potential there must be a contact between the probe and the electrolytes in the pore system of the concrete. Therefore corrosion analysis with the half-cell potential below the freezing point is not recommended and can lead to incorrect readings.
- Concrete Cover Thickness: The potential that can be measured at the surface becomes more positive with increasing concrete cover. Variations in the concrete cover can cause deviations in the measurements. Very low concrete cover can lead to more negative potentials which would seem to indicate high levels of corrosion. Therefore it is advisable to make concrete cover measurements along with the corrosion analysis.
- Oxygen content of the reinforcement: With decreasing oxygen concentration and increasing pH-value at the steel surface its potential becomes more negative. In certain cases of concrete components with a high degree of water saturation, low porosity and/or very high concrete cover and thus low oxygen supply, the potential at the steel surface may be very negative even though no active corrosion is taking place. Without checking the actual corrosion state this may lead to misinterpretation of the potential data.