Concrete Preservation Technologies Ltd statement on anode ageing pattern

One anode manufacturer has claimed that all galvanic anodes used to control corrosion in reinforced concrete structures exhibit an ageing pattern which follows an exponential decrease in current output similar to a ‘half-life’ principle where current is halved at constant periods of time¹. They claim that published CPT anode data from the first nine years of anode life at Whiteadder Bridge in the north-east of England² supports this hypothesis and, furthermore, that this data is predictive of a short anode life. This is incorrect.  

Whiteadder Bridge has now been monitored for over 17 years and the long-term data demonstrates that anode current has stabilised and does not show any exponential decrease with time. Troughs and peaks in current output reflect changes in the environment, particularly wetting and drying. The initial period of higher current is a desirable design feature of the anode system. A graph showing Whiteadder Bridge anode current and steel potentials up to 15.5 years was featured in The Concrete Society’s Concrete Journal in June 2023³ and a graph showing log current from years 7 through 16 featured in the ICorr journal, Corrosion Management, in January 2024⁴. A graph of data updated to 17 years of anode performance at Whiteadder Bridge is shown below.

All indications are that the protected steel remains in a passive condition and there has been no need for further intervention within the first 17 years of the life of the corrosion protection system.

In conclusion, CPT anodes do not exhibit an ageing pattern consistent with a half-life principle and after 17 years the anode system at Whiteadder Bridge is performing as was intended in the design.

References

1. Whitmore, D., Sergi, G. ‘Long-term monitoring provides data required to predict performance and perform intelligent design of galvanic corrosion control systems for reinforced concrete structures’. Submitted AMPP Corrosion virtual conference and expo 2021, paper 16712.

2. Bewley, D. ‘High power, low maintenance hybrid corrosion protection’, Concrete, Oct 2016, pp. 25 – 27.

3. Bewley, D., Stone, C. ‘Long-term monitoring of innovative corrosion control system yield fascinating results’. Concrete June 2023, pp. 43 – 45.

4. Stone, C., Glass, G., Bewley, D. ‘The Performance and assessment of galvanic anodes in concrete structures’. ICorr Corrosion Management January/February 2024, pp. 25 – 29