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Corrosion query

LETTERS

I read your article on the new Fosroc sacrificial anode system for reinforced concrete with a little amount of scepticism (NCE 27 May).

As a civil engineer with some experience of installing cathodic protection systems, I think that the system falls down on several key aims of CP, such as integrity of installation, steel continuity, controllability and durability.

Continuity as an example seems to be 'overcome' by removing a patch of concrete and installing an anode on every rebar. These anodes will in turn corrode - by definition of being sacrificial - and, I assume, protect the entire rebar to which it is physically connected. This should therefore form a void in the new 'repair' in time as the zinc is used up, corrosion protection to the rebar will also diminish.

Even assuming that the entire rebar is protected there seems to be a durability issue, which does not exist with impressed current CP systems.

I would be interested to see comment on the passage of sacrificial current to the neighbouring corrosion processes outwith the location of the zinc anodes.

Since it is known that conventional patch repair can cause macrocell corrosion leading to failure of the repair, it surely follows that the new repair coupled to the new anode without CP in neighbouring areas may also induce such a local corrosion effect. Once again, I believe this does not exist with a distributed impressed system.

The system highlighted in the article, in my opinion, asks more questions than it answers but maybe the corrosion specialists at Aston University and Fosroc can put my fears to rest.

Paul Filkin (S), 32 Warwick Road, Broughton Astley, Leicestershire LE9 6SB

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