Specifiers of bridge concrete repair works should be aware that the standard specification for galvanic anodes in patch repairs has been updated. The new specification CC484 section 9 replaces series 5700 clause 5712 within the latest Manual of Contract Documents for Highway Works.
To comply with the specification, the galvanic anode layout must be designed to provide a protective zone of influence around the patch repair of at least 300mm for the specified service life, typically 10 years. Protection is required due to the incipient anode effect, whereby corrosion accelerates around the repair boundary in chloride contaminated concrete. Galvanic anodes protect the steel by sacrificially corroding.
The use of half-cell potential testing to check anode installation and initial performance is retained and refined within CC484. Instead of testing every patch, the contractor is now required to test 20% of repairs, or 10% of all anodes (whichever is higher), on each structural element. Readings are to be taken 250mm from the repair boundary and at 250mm centres (previously 500mm centres). Measurements should be taken before anode attachment and after 14 days of steel polarisation, at the same locations. Readings should demonstrate a shift in steel potential around the patch. This demonstrates that the anodes have been installed correctly and that initial protective current is being delivered to the reinforcement.
The contractor must submit evidence that the proposed anode has been successfully used on similar projects for a minimum of 5 years, evidenced by an absence of cracking around the patches.
Whilst half-cell potential testing is mandated within CC484, CPT recommend that the methodology be more widely adopted for galvanic anode installations outside of the highways sector. A limiting factor is often lack of expertise in taking, and interpreting, half-cell potential readings. This is where CPT’s highly skilled team of Corrosion Technicians can assist.
If your organisation would like to learn more about the installation and monitoring of galvanic anodes on highway structures, or, indeed, any reinforced concrete structures, please contact CPT to arrange a lunchtime, in house CPD seminar from the experts.
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