Half Cell Potentio Meter (Corrosion Test)
Half Cell Potential (ASTM C876-9), Resistivity and RCPT (ASTM C1202) is used to know about extent and rate of ongoing corrosion activity. the method of half-cell potential measurements normally involves measuring the potential of an embedded reinforcing bar to a referance half-cell placed on the concrete surface. The half cell is usually a copper/copper sulphate or silver/silver chloride cell but other combinations are also used. The concrete functions as an electrolyte and the risk of corrosion of the reinforcement.
The method of half –cell potential measurements normally involves measuring the potential of an embedded reinforcing bar relative to a reference half-cell placed on the concrete surface. The half-cell is usually a copper/copper sulphate or silver/silver chloride cell but other combinations are used. The concrete functions as an electrolyte and the risk of corrosion of the reinforcement in the immediate region of the test location may be related empirically to the measured potential difference. In some circumstances, useful measurements can be obtained between two half –cellls on the concrete surface. ASTM C876-91 gives a Standard Test Method for Half –Cell Potentials of Uncoated Reinforcing Steel in concrete.
Risk of Corrosion against the Potential Difference Readings
Potential difference
Chance of re-bar being corroded
< -500
Visible evidence of corrosion
-350 to -500
95%
-200 to -350
50%
More than -200
5%
Factors Affecting Test Results
Moisture
Temperature
Concrete Cover Thickness