Civil Engineering Reference
In-Depth Information
reinforcement layer (see
Figure 8.6).
Then, a multi-stage application is
required. The ratio/efficiency of chloride removal is less important than a
generally low chloride content at the end.
Figure 8.6
shows how first the chloride within the concrete cover
is mobilised, and as it is removed, more chloride arrives from deeper
concrete zones. This may result in an increase of chloride content within
the sampling profile and the (wrong) conclusion that the ECE might not
have worked. If the amount of removed chloride can be analysed, this
is very useful additional information to trace the ECE dynamics. Within
a pause of about 6 weeks which is recommended to allow the concrete
drying, more chloride is moved towards the concrete surface by capillary
suction/evaporation. Furthermore, bound chloride can be released, but
these are normally not large quantities. In a second treatment stage the
chloride which has now accumulated in the concrete cover zone can be
reduced to an uncritical level.
The impressed charge is the second parameter for the termination
of the ECE; the above suggested range may be not achieved in case the
reinforcement is still in good condition and the chloride content of the
respective treatment area is rather low. Then, ca. 400 Ah/m² shall be a
sufficient value, also because no or not much oxide has to be reduced
on the rebar surface and hence almost all charge will be put into oxygen
reduction.
concrete surface
upper reinforcment
second reinforcment
weeks (typically)
0
6
12
18
initial chloride
profile
chloride profile after
six weeks of chloride
(first treatment)
chloride profile after
six weeks pause
chloride profile after
six weeks of continued
chloride extraction
(second treatment)
high chloride ingress depths and with more than one reinforcement layer.
