Civil Engineering Reference
In-Depth Information
bridge in Northamptonshire. A similar system can be used for realkalisation, though
transparent plastic tanks are preferred to observe the anode condition and state of
filling of the cassette tank.
Electrolytes
As stated above, sodium carbonate solution is the preferred electrolyte to
give long-lasting protection against further CO
2
ingress, although potassium
carbonate has been found to be less prone to leaching after treatment.
However, introducing sodium or potassium ions can accelerate alkali-silica
reaction (ASR) so in some cases just water is used, although this can evolve
chlorine if any chloride is present in the concrete. Also, some problems have
been found with adhesion of coatings when sodium carbonate is used, so the
tendency is now to use a very low dose of sodium carbonate, or just to use
water.
The UK Building Research Establishment comments:
Following the removal of the anode and thorough cleaning of the
concrete, a protective (anti carbonation) coating is often applied. This
will help to keep the concrete in a dry condition and to improve the
aesthetics. A meticulous cleaning process must be followed to prevent
crystallisation of electrolyte compounds behind coatings since this
