Civil Engineering Reference
In-Depth Information
Overall, in reviewing the literature and the experience of others in the
field, it is apparent that migrating corrosion inhibitors have only limited
usefulness in repair while flood coating, brushing or spraying methods are
used. They may be successful to some extent in permeable concrete with
low cover (say up to 15 mm) which does not contain excessive levels of
chloride (and certainly not more than 1% by mass of cement). For other
concretes which are less permeable or where the steel is at deeper cover,
they are unlikely to penetrate to a sufficient depth to be useful. Indeed, it has
been suggested that if they only partially reached the steel reinforcement,
they might exacerbate the problem by causing an electrochemical cell to be
set up between the area reached by the inhibitor and surrounding anodic
areas.
Broomfield (2007), in his book on corrosion of steel in concrete, made
the following conclusions regarding penetrating corrosion inhibitors:
•
There is very little field data on corrosion inhibitors.
•
The available field data is often poor, with no clear evidence of the
amount of inhibitor applied, whether it reached the rebar and if it is
reducing corrosion rates and extending time to cracking.
•
Many claims have been made about the transport of inhibitors through
hardened concrete; these need to be independently assessed.
•
We will need definitive evidence of the dosage vs. chloride level to
achieve a given (low) corrosion rate.
•
For application to hardened concrete, we need quantitative data on its
penetration vs. concrete cover and concrete permeability.
•
We need more information on the performance of inhibitors, particularly
well-controlled field trials and long-term corrosion monitoring.
There is little that this author would add to these conclusions. There are
better methods for dealing with repair of, especially, chloride-contaminated
structures, such as chloride removal, the use of galvanic anodes or a full,
impressed current, cathodic protection system and the reader should
consider their use in the first instance.
However, the ultrasonic pump idea for introducing inhibitor deeper
into a concrete or grout, trialled by Cailleux and co-workers definitely had
promise and deserves further investigation.
Acknowledgements
The author would like to acknowledge the help of Dr John Broomfield in
preparing this chapter.
