Corrosion Surveys and Half-Cell Potential Mapping

Frequently asked questions

What is half-cell potential mapping?

Half-cell potential mapping measures the electrochemical potential of steel reinforcement through the concrete surface using a reference electrode (half-cell). The readings indicate the probability of active corrosion at each measurement point. The results are plotted as a contour map showing zones of high, medium and low corrosion risk across the survey area.

What causes reinforcement corrosion in concrete?

The two main causes are carbonation and chloride ingress. Carbonation is a natural process where CO₂ from the atmosphere reacts with the cement paste, reducing its alkalinity and removing the passive protection of the reinforcement. Chlorides — from de-icing salts, marine spray or contaminated materials — accelerate corrosion once they reach the steel. Both processes are progressive and worsen over time without intervention.

Which structures most commonly need corrosion surveys?

Multi-storey car parks are the most common subject — they are exposed to de-icing salts from vehicles and often show early signs of corrosion within 20–30 years. Bridges, coastal structures, marine infrastructure and any reinforced concrete structure over 30 years old in an aggressive environment are also common candidates. We also carry out surveys on residential and commercial buildings where spalling or staining suggests active corrosion.