Civil Engineering Reference
In-Depth Information
8.12 Other criteria of success
The total amount of removed chloride is another useful parameter; it depends
on the total initial chloride content, so no values can be given for orientation.
But in conjunction with the remaining chloride and the development of the
chloride profiled during the application, the ECE progress and the necessary
extent can be evaluated much better than referring only to the chloride in
the concrete.
As stated above, the main task of ECE is to rehabilitate a concrete
structure/element from corrosion activity. Thus, a repeated potential
survey will show considerably different results: a generally more positive
level of measurement values and a reduced spread between the maximum
and minimum potentials. As macro elements are being dissolved by ECE,
formerly very negative potentials have to become much more positive, and
formerly positive potentials become more negative. Overall, the potential
spread should stay within 150 mV. The repeated potential survey is not
suitable to obtain the termination of treatment, because during ECE the
reinforcement has been shifted deeply into the cathodic range. It has to
recover from that polarisation back into a rest stage, and the high water
content in the concrete has to be reduced to a normal level (from ca. 7% to
3%), until useful potential values can be measured. This requires at least 3
to 4 months.
Because of the wet concrete directly after the ECE, other repair actions
especially the application of protective coatings, may have to be delayed.
8.13 Experiences from practical applications
Between 2001 to 2007, the author conducted ECE applications on 15
structures with treatment areas ranging between 10 and 280 m². Interest
in ECE then waned in the UK in favour of cathodic protection, but is still
used elsewhere, in Germany and the USA, for example. So far, more than
65 kg of chloride have been removed from over 1,200 m² of concrete, non-
destructively, which corresponds to an amount of ca. 100 kg NaCl that had
penetrated into the concrete. The elimination of corrosion activity could be
verified in all cases. At the time of writing, more than 600 m² of concrete are
under treatment. Based on the use of the CITec system, some typical projects
and their results and conclusions are discussed in detail below, but see also
(Schneck, 2006).
Box girder floor slab of a highway bridge
The bridge had corrosion problems resulting from leaks in the internal
drainage system and some high chloride concentrations in the box girder
floor slabs. A condition survey clearly determined the corrosion active areas,
and since no significant structural damage was found, a non-destructive
