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[inchak at tatasteel.com]

Dear Mr Ashu Patel
There, indeed, had been a lot of argument on the subject of effectiveness
of Fusion Bonded Epoxy Coated Bars to prevent corrosion of steel
reinforcement embedded in concrete. I quite agree that this can confuse
someone who is not very deeply involved in this subject. I, therefore,
avail myself of this opportunity to put down a few INCONTROVERTIBLE points
on this subject which can be easily appreciated by all concerned.




1. Epoxy coating functions purely as a PASSIVE barrier coating with no
ability to provide sacrificial anodic protection. Integrity of the coating
is, therefore, an absolute precondition for its ability to prevent
corrosion. In real life, however, there are always small gaps in the
coating which are commonly called holidays. It has been found that
corrosion progresses in a highly localized manner around these holidays.
The ruling specification, ASTM A-775 suggests special care during loading,
unloading, cutting, bending, straightening in the field, laying etc. which
can rupture the coating and therefore, introduce opportunities of local
corrosion. However, it is extremely difficult to ensure that adequate
precaution is actually taken all through the handling including during
pouring and ramming of concrete. Therefore integrity of coating is always a
suspect.

2. Epoxy coating is also known to peel off or DISBOND from the base steel
during service, making room for severe under-the-film corrosion. To quote
from the conclusions of the report to Florida DOT, "

In his report entitled "CORROSION OF EPOXY COATED REBAR IN FLORIDA BRIDGES"
(Final Report to Florida D.O.T., WPI No. 0510603, State Job No.
99700-7556-010) Mr Alberio A. Sagues, P.I., Department of Civil I
Engineering and Mechanics College of Engineering, University of South
Florida observes:

"The present field and laboratory investigation has identified two factors
that appear to be critical to the development of severe corrosion in ECR.
The first factor is the presence of breaks in the coating that expose some
of the metal surface to direct contact with the surrounding electrolyte.
Coating breaks relevant to corrosion initiation can range from holidays
invisible to the naked eye, produced at the time of manufacturing, to
narrow cracks in the coating produced during fabrication bending of tl1e
rebar, to macroscopic abrasion, gashes and cuts caused during
transportation, field handling and vibration while concreting. The second
factor is the development of extensive loss of adhesion between the coating
and the base metal after relatively short service times in concrete, even
in the absence of chloride ion contamination..........(p-40)..
"The most important finding of ECR deterioration in this study was the
observation of coating-metal disbondment at almost all of the structures
examined. As indicated in the previous section, coating disbondment is
considered to be a key step in the corrosion development. The ECR in all
these structures appears therefore to be already susceptible to the
development of severe crevice corrosion if the chloride concentration
reaches the value for corrosion initiation.......(p-4"
这135页的详尽的的全文,高度revealing and impartial
research report is available in the following URL:

http://www.cobrae.org/htmlfolder/papers/epoxyrebartestsflorida.pdf

3. Bare steel bars participate in chemical reaction with cement concrete
and therefore, there is a formation of a composite layer, which ensures
good bond with the concrete. Epoxy coating, being itself nearly neutral to
the environment within concrete, precludes formation of any such composite
layer. As a result, there is a perceptible drop in the bond strength of
epoxy coated bars when compared with uncoated deformed bars.

There are a few more finer points given below which are also worth noting:

a. Study has also shown that chloride irons are able to permeate even the
undamaged coating and, therefore, corrosion can progress underneath the
epoxy coating, while the coating itself remains unaffected.

b. Prolonged exposure to sunlight can be a cause of unacceptable
degradation of the epoxy coating due to the ultra violet radiation from the
sunlight. Such a problem is only likely to be more acute in a tropical
country like India.

In view of the above it can be concluded that the real root of all
controversy is that under some PERFECT conditions it may be possible to
demonstrate some outstanding performance for Fusion Bonded Epoxy Coated
Bars. However, under realistic situations Fusion Bonded Epoxy Coated Bars
are not only suspect but also have known to lead to serious premature
恶化的关键结构。

I hope this will help in putting some of your doubts to rest.





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