Corrosion
of reinforcing bars (tor steel) in
RCC construction, particularly those
located in saline corrosion &
industrially polluted areas, is one
of the major problems encountered
by the structural engineers in our
country. In India, it is estimated
that corrosion of steel costs Rs.
20,000 Crores annually, which is about
4.2 percent of our Gross Domestic
Product (GDP). Half of the construction
budget in the country is spent on
repair and rehabilitation of structures
that have deteriorated prematurely.
To cite a few examples, the Thane
Creek bridge repairs for enhancing
its life by five years cost eight
times the cost of the original project.
In Delhi, repairs to a small section
of the Janak Setu flyover in 1999
cost Rs.32 Crores, compared to the
original cost of Rs.9 Crores for the
whole project.
Recent
years have seen a sharp rise in the
keen interest among engineers and
concrete specialist around India and
worldwide regarding the long-term
durability of concrete structures.
Ways and means are constantly being
sought to increase the durability
and simultaneously also decrease the
lifecycle costs associated with the
structure. Amongst the long-term measures,
one of the methods for protection
of concrete reinforcing bars against
corrosion is epoxy coating on these
bars by electrostatic spraying of
fusion-bonded epoxy powder. Keeping
in view the country’s need for
appropriate corrosion-resistant reinforcing
bars of accepted quality, is this
kind of an application by non-technical
personnel feasible on remote sites?
PRIMARY
CORROSION
Corrosion
during metal manufacturing process
is a phenomenon resulting out of primary
corrosion cells. This corrosion is
inevitable and is not always visible
to the naked eye.
Primary corrosion can be controlled
/ reduced / arrested at the time of
manufacturing the metal by Z300TM
process. This process reduces primary
corrosion percentage substantially,
and prevents its multiple, progressive
growth. Therefore, it is advisable
that the manufacturers take necessary
cognizance of such treatment on the
metal before it is dispatched to the
consumer for use. This will take care
of corrosion during transit, storage
and actual use.
CORROSION
DUE TO ENVIRONMENTAL FACTORS
Environmental
corrosion-free metal is far from fact
and can never be a possibility. Multiple
factors existing in the environment
attribute to corrosion at different
levels. Primary corrosion cells, if
present, could further propagate environmental
corrosion.
Presently, many expensive
methods of protecting metal
/ preventing corrosion such as epoxy
coating, zinc coating, stainless steel
coating etc. are adopted. However,
with use of such treatments, corrosion
in patches is still observed
on the metal. None of these treatments
offer a solution to overcome corrosion
patches. Z300TM
process provides
an ideal solution since it can also
be used to treat patchwork corrosion.
STRUCTURAL
STEEL & CORROSION
Out
of the total steel manufactured per
annum for construction purposes, 70%
of it is consumed by structural steel
and balance for other usage, including
reinforcing bars.
Structural steel gets corroded because-
·
It has sharp edges
– Vulnerable to static charge
concentration at point for corrosion.
· It needs to be cut by using
high temperature
– High temperature enhances
the rate of corrosion in the given
environment.
· Its connectivity is possible
either by welding or bolting
– Welding / bolting creates
bimetallic corrosion due to cavities
created between two metals. These
cavities lead to electrolytic process,
thereby causing heavy corrosion, which
is known as bimetallic corrosion.
There
is always a concentration of structural
forces at the nodes / junctions of
structural members. If the effect
of corrosion, as explained above,
is not taken care of at an appropriate
stage by adopting appropriate methods,
weakness remains in the structure.
Growth in weakness reduces the life
of structure.
Presently,
after welding, primer coat of paint
is applied to the surface to prevent
corrosion. Application of primer paint
on the welded surface only hides the
corrosion; it does not prevent. Cavities
in the joints where paint cannot reach,
bimetallic corrosion continues. Spot
treatment (at such locations) with
Z300TM
takes care of corrosion reduction,
it reaches in small cavities. Due
to wetting power and thin liquid it
works at one micron film level.
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