An economical method for identifying areas of corrosion ASTM C-876.

A high impedance voltmeter is connected between the reinforcing steel and a Cu-CuSO4 reference electrode on the concrete surface where a measurement can be made for the half-cell potential.

This measurement of the probability of corrosion activity. By testing at a fixed distance apart, a grid of half-cell potentials can be developed and areas delineated.