Civil Engineering Reference
In-Depth Information
instant-off treatment was a useful approach, not least because the respective
areas were above a high traffic bearing road and would have led to severe
delays during a conventional repair.
The initial chloride profiles were varying in concentration and ingress
depth; in some areas the entire cross-section of the floor slab showed chloride
values > 2%, related to the cement mass. In a reference application on a 60
m² concrete surface, the effect of ECE has been investigated (see
Figure 8.7),
and despite more than 7 kg being removed, the chloride profiles down to 8
cm of concrete depth still contained chloride of more than 1.5% in places.
A repeated potential survey 4 months after finishing the first treatment still
showed corrosion active areas, so it was decided to run a second treatment,
which was successful and eliminated all signs of corrosion activity.
Consequently, for the remaining five chloride containing corrosion active
areas such a two-stage treatment was chosen from the beginning: 6 weeks
ECE, 6 weeks pause and again 6 weeks ECE. In total, 25 kg of chloride was
removed from ca. 200 m² concrete. The remaining chloride varied from
0.72% to 0.04% in the rebar vicinity (compared to more than 4% initially),
but with an impressed charge of about 1,000 Ah/m² an appropriate alkalinity
was developed to render even 0.72% as uncritical. (Corrosion depends on
the ratio of chloride to hydroxyl ions, not just on chloride content.)
floor slab.
