The potential for reinforcement corrosion will be assessed using the measurement of half-cell potential, as detailed within American Standards for Testing Materials (ASTM) C876, with the rate of reinforcement corrosion assessed by the measurement of resistivity in general accordance with the procedures described within BRE Digest 434 and Concrete Society Technical Report 60.
This procedure is covered by CRL Surveys UKAS Accreditation, UKAS Ref: 2728. For further details please visit www.ukas.com
Half-cell potential surveying will generally be carried out using either a copper/copper sulphate, or a silver/silver chloride half-cell, the latter with values recorded as equivalent copper/copper sulphate.Further information concerning these procedures can be found in BRE Digest 434, Transport and Road Research Laboratory (TRRL) Application Guide (AG) 9 and The Concrete Society’s Concrete Bridge Development Group, Technical Guide No.2.
The continuity of the reinforcement across the area to be surveyed will be checked and electrical resistance measured. Connections to the reinforcement, suitable for the areas of continuity will then be made.
Measurement node points, arranged in an orthogonal grid, to suit the subject, will be treated with an appropriate wetting agent and the potential values will then be recorded.
The potential values, where appropriate, will be tabulated and then used to plot colour coded, iso-potential, contour maps.
Resistivity surveying will be carried out using a Wenner type, four-electrode resistivity meter.
The electrodes will be placed on the concrete surface, using the same arrangement of node points as for the half-cell potential survey above, but only using the most ‘anodic’ and ‘cathodic’ nodes, and the resistivity values will be recorded.
In addition to the above and currently outside our UKAS Schedule of Accreditation, Linear Polarisation Resistance can be measured, using a BAC Corrosion Control Limited “Portable LPR” kit.
Measurements would be made on the concrete surfaces at the most ‘anodic’ and ‘cathodic’ nodes highlighted during the half-cell potential survey and the corrosion rate values would be recorded.
In addition to the above and currently outside our UKAS Schedule of Accreditation, Site-specific Validation can be undertaken, specifically to check and balance the instrumental data. The reinforcement within selected ‘hot’ or anodic and ‘cold’ or cathodic areas can be exposed and inspected for evidence of deterioration and corrosion. The reinforcement, at progressively greater depths of cover could be exposed and inspected in order to assess the likely depth at which the reinforcement is potentially at risk.
Reinforcement bar types could be identified using the classifications described within CIRIA, Special Publication 118.