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Cement Polymer Composite Coating System
for Corrosion Protection of Reinforcing and Prestressing Steels
Approach adopted in new technology to
evade technological gap in the exiting one
State of Art Technologies – International
Scenario
In USA corrosion of concrete bridges is
a very serious problem During 1982, the annual cost of corrosion
damage to bridge deck and support structures was estimated
to be in the range of $165 to $500 million. The annual cost
of repair of parking garage dueo to corrosion was estimated
at $300 to $400 million. Out of 500,000 bridges in USA, 200,000
were reporte to be under severe distress. Remaining 300, 00
also needed repair and rehabilitation measures of cost replacement
of 300,000 bridges was worked out to be around $112 billion.
Currently, the bridge deck maintenance
in USA is considered as a trillion-dollar proble. Many repair
techniques such as overlay, fusion bonded epoxy coating, cathodic
protection etc. had been tried on an experimental basis in
few selected bridges. Among these, fusion bonded coating has
been widely used. Epoxy coating can no longer be considered
a viable primary protective system, as it suffers from the
following disadvantages.
Being a barrier type of coating, it facilitates
localized pitting corrosion through pinholes. This was very
much evident in the Florida Bridge by undercutting of the
fusion-bonded epoxy coated reinforcing bars.
- It affects the bond strength
between steel and concrete.
- It undergoes degradation on long term
exposure to sunlight and hence necessitates storing of the
coated reinforcement under sheltered condition.
- It shows generally poor alkali resistance.
- It needs additional electrical interaction
of the rebars to facilitate cathodic protection and other
electrochemical process that may needed for then and there
maintenance of the structures.
Above all, the application of fusion bonded
epoxy coating needs carefully prepared surfaces. This poses
difficulties in field preparation and the long-term performance
is not satisfactory. Realizing these difficulties, CECRI has
developed a cement polymer composite coating system which
may be a suitable substitute for fusion bonded epoxy coating
system but with a better-cost benefit ratio. The findings
will create new solution to the existing to the existing corrosion
problem.
Advantages:
- It is a factory process amendable
for field repair and rehabilitation.
Coating has high flexibility
- As per BIS2770 part it has sufficient
bond strength
- Coating can withstand high tensile
stresses and hence applicable to prestressing steels
- As per ASTM & Indian standards,
it has good corrosion resistance and chemical resistance
- It has good weathering resistance (UV
resistance)
- As per ASTM & Indian standards,
it has good abrasion resistance
Brief description
The base metal used as rebar, namely iron,
contains electrons which gets readily released in any corrosive
environment (e.g. atmospheric oxygen) leading to oxidation
with the formation of Fe2O3 (the rust), a principal deterrent.
To prevent this oxidation, a surface coating capable of interacting
/ nullifying the released electrons should be provided. Further,
prestressing and reinforcing steels during service are exposed
to an alkaline medium and this necessitates additional measure
by way of a topcoat, which should be compatible to primer
and and alkaline environment. To meet these two requirements,
a primer and a compatible topcoat as mentioned above are proposed.
CECRI has developed CEMENT POLYMER COMPOSITE
COATING (CPCC) system for corrosion protection of reinforcing
steel. The coating system consists of a primer and a sealing
coat. The process covers the following patents.
- An improved
formulation for a rapid setting primer useful for corrosion
protection of reinforcing and prestressing steels.
- Indian Patent No.481/DEL/93 dated 13.05.93
- An improved coating composition for
corrosion protection of reinforcing steel and prestressing
steel.
Indian Patent No.259/DEL/92 dated
25.03.92
The polyblend of polyacrylics and polyquinones
is p electrons rich and hence can readily chemisorb via ¶
electrons with unfilled "d" orbital of iron surface
to prevent corrosion in prestressing and reinforcing steel.
So the products proposed to be evaluated involve solution
blending process for preparation of polyblends based on acrylic
copolymers and quinine copolymers which offer a flexible and
water resistance layer on steel for corrosion protection.
The flexibility of acrylate copolymer, its film forming capability
and water repellency characteristics of quinine based polymers
are carefully tailored through the formation of a single phase
in the polyblend which offers the necessary mechanical and
physical properties. Besides, this precursor has the possibility
of accepting rust as a filler in the polyblend film which
facilitate the application of surface coating derived from
this polymer precursor or rusted steel surface thus making
surface preparation non critical one. Further, the cement
polymer composites based on these polymers is expected to
serve as precursor for the formulation of a topcoat which
will tae care of the alkaline environment that is anticipated
in the concrete structure. Additional feature of this system
is that the curing time of the coating can be manipulated
to suit the specific process requirement (minutes to hours).
Advantages: A Novel Coating System for
Rebar Protection
CECRI has been carrying out R&D activities
in this vital area over four decades and more recently it
has come out with a novel coating system is actually a composite
coating system designed and tailor made utilizing the desirable
attributes of Portland cement and a polymer.
Uniqueness of the System
Primer :
Chemical bondage with rebar surface leads to better adhesion.
Primer with Rapid setting Properties:
Amendments for Mechanism
Cement Polymer Seal Coat :
Good compatibility with base primer and surrounding concrete.
Assured bond Strength
Rapid setting Properties :
Amendable for Mechanism
Special Features
Flexibility
: Coated rods can be bent and fabricated as per the
requirements of building codes.
Bondability : Bonding strength
equivalent to that of uncoated rebar as per standard Pull
out Test
Weatherability- : The system
designed to have better UV resistance CPCC coated prestressing
strands under tension and exposed to aggressive open environment
– coating was intact even after 3 years.
Durability : A durability
factor of more than 10 is obtainable under most aggressive
environmental conditions
Applicability : By brushing,
dipping or any other suitable method
Feasibility : Automation;
Site application and Insitu repair
Applications:
Protection of steel reinforcement inconcrete from corrosion.
Detailed Description
Cement polymer composite coating (CPCC)
technology has developed for the protection of steel einforcement
rods against corrosion in aggressive marine atmosphere after
analyzing the merits and demerits of various protective coatings
systems currently in operation including FBEC and our own
earlier technology of cement – slurry anticorrosive system.
The CPCC technology has been evolved & custom designed
from the consorted inputs originating from polymer science
and electrochemistry (corrosion is an electrochemical reaction)
to meet the structural engineering requirements of steel reinforcement
rod.
The data are confidentially documented
after a careful R&D practice and also by following the
internationally prescribed standards (ASTM). Based on these
R&D strength, CECRI has evolved a code of practice for
standard tests to be followed in maintaining the highest quality
of CPCC by the manufacturers and applicators of this coating
to give better performance. Incidentally, the code of practice
prescribed for CPCC imparted rods has a better ease in handling
and transportation than the set of conditions prescribed in
your own addition letter appended to the main construction.
Chemical Features of CPCC System
The basic resin matrix based in which
coating formulation arrived at our custom designed specifically
to counter the corrosion reactions of concrete structures
in marine environment susceptible to severe corrosion. They
possess required chemical feature to provide spontaneous adhesion
and corrosion resistant and the over all coating process adaptable
both in the field and shop floor
Technology
Transfer Assistance Offered: Know-how, Training
Extent of Commercialisation:
Seeking to license or sell this innovation
Contact for
more information:
Director
Central Electrochemical Research Institute (CECRI),
Karaikudi -630 006,
Tamil Nadu, India
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