Civil Engineering Reference
In-Depth Information
•
extent of corrosion activity (detection of hot spots)
•
state of corrosion on the reinforcement (may deviate from current
corrosion activity!)
•
extent of chloride ingress by size and depth
•
profiles of chloride and water content down to
≥
8 cm and behind the
upper reinforcement layer
•
concrete defects (spalls, cracks, delamination, patches).
It is obvious that all this information requires a sequence of different
measurements - not only a potential survey, and the comparison of all values
gives a very precise impression of the state and needs of a structure. This is
demonstrated by
Figure 8.5,
where measurement results from a box girder
floor slab can be seen. The rest potentials show some corrosion activity;
the related chloride contents were up to 3.5% in the reinforcement vicinity.
The surface distribution of the chlorides could be made visible by surface
resistivity readings, which show a much larger extent than the corrosion
activity. Chloride contents in locations with low surface resistivity (< 1,000
ohm.cm) and moderate potentials (ca. -150 mV vs. CSE) were about 0.5 to
1.5% in the vicinity of reinforcement. The concrete cover was quite high
in the area with rather positive potentials and low in the areas with very
negative potentials.
In conclusion, although the chloride content in the floor slab was generally
high, it has resulted only in high corrosion activity where the reinforcement
was getting closer to the surface. At the same time, corrosion active
reinforcement was protecting reinforcement in less chloride-containing
concrete. It was wrong to treat only the temporary corrosion active areas;
chloride had to be removed in a larger scale.
8.11 Termination of treatment
It is very difficult to define, predict or to calculate parameters on which an
ECE application can be terminated. As mentioned at the beginning, several
factors influence the treatment progress and its dynamics. For a practical
approach the following factors can be used:
•
Chloride content: the average content of the surveyed profile should not
exceed 0.4%, related to the cement mass; the maximum content in the
reinforcement vicinity should be max. 0.8%.
•
Impressed charge: depending on the extent of initial corrosion products
on the reinforcement, the total impressed charge should range between
1,000 and 2,000 Ah/m², related to the reinforcement surface.
It has to be considered that the chloride content cannot be reduced to
zero; often even an increase of chloride can be observed within the sampling
depth during the treatment as chloride has penetrated far behind the upper
