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Electrochemical
Chloride Extraction (ECE) is also know as electrochemical
chloride removal or desalination. The technique uses
a temporary anode and passes a high current (about 1A/m2
of steel or concrete surface area) to pull the chlorides
away from the steel. A proportion (usually around 50
to 90%) of the chloride can be completely removed from
the concrete with very significant removal immediately
around the steel and a high level of repassivation of
the steel is obtained.
ECE
can be used in many of the situations where cathodic
protection can be applied. It is at its best where the
steel is reasonably closely spaced, the chlorides have
not penetrated too much beyond the first layer of reinforcing
steel and future chlorides can be excluded. It has been
applied to highway structures, car parks and other structures
in Europe and North America.
The
treatment typically takes six to eight weeks. On completion
the anode is removed and there are no ongoing monitoring
requirements. If sufficient chloride is removed and
further chlorides excluded, then it is a "one off" treatment.
Field and laboratory research showed an improvement
in concrete properties such as freeze thaw, chloride
and carbonation resistance, and water uptake resistance
for one set of experiments. The treatment time can be
too long for some applications, e.g. bridge decks that
cannot be closed for six to eight weeks. The problems
with isolated steel, prestressing and ASR mentioned
for impressed current cathodic protection are exacerbated
for ECE due to the high voltages and current densities.
Some concerns with reduction in bond strength have been
identified, but these only apply to structures containing
smooth reinforcement where the mechanical interlock
of ribbed steel is not available. A lithium based electrolyte
has been used in trials to mitigate the ASR risk, but
results are not yet conclusive on its effectiveness |
