Half Cell Potential Testing

The Half Cell Potential Test is another non-destructive test for re-inforced steel corrosion. Steel embedded in good quality concrete is protected by the high alkalinity pore water which, in the presence of oxygen, passivates the steel.

The loss of alkalinity due to carbonation of the concrete or the penetration of chloride ions (arising from either sea or rock salt) can destroy the passive protective film.

In the presence of oxygen and humidity in the concrete, corrosion of the steel bars starts. A symptom of the corrosion of steel in concrete is the development of macrocells, which is the co-existence of passive and corroding areas on the same reinforcement bar. The current flow in the steel is accompanied by an electrical field which is measured at the concrete surface, identifying the location of the most corroded areas at the most negative values.

This is the basis of the half cell potential testing applied to the routine inspection of reinforced steel concrete structures. When surface measurements are taken, they are obviously measured away from the reinforcement due to the concrete cover. The potentials measured are therefore affected by the potential ohmic drop in the concrete. Several factors have a significant effect on the potentials measured

  • Concrete Cover Depth
  • Concrete Resistivity
  • High Resistive Surface Layers
  • Polarisation Effects

How do we do Half Cell Potential Testing

To measure half cell potentials, an electrical connection is made to the steel reinforcement in the concrete member to assess. This is connected to a high impedance digital multimeter, backed up with a datalogging device. The other connection to the millivoltmeter is taken to a copper half cell, which has a porous connection at one end which can be touched to the concrete surface.

This will then register the corrosion potential of the steel reinforcement nearest to the point of contact.

We measure the results on a regular grid and by plotting results as a contour map, areas of corroding steel may readily be seen. In any case, we never use this technique in isolation, but as part of a combined measurement of the chloride content of the concrete and its variation with depth and also the cover to the steel and the depth of carbonation.

Call us on 0800 433 4788 or email info@globeropeaccess.co.uk
if you’d like us to quote for a half cell potential test