Presentation: Comparative Evaluation Of Epoxy Treated Reinforcement And Enamel Treated Reinforcement

COMPARATIVE EVALUATION OF
CORROSION RESISTANCE OF EPOXY
TREATED REINFORCEMENT AND
ENAMEL TREATED REINFORCEMENT
By
Prof.(Dr) Pravat Kumar Parhi
Professor, Civil Engg Deptt, College
of Engineering & Technology,
Bhubaneswar
Mr. Soumya Ranjan Mohanty
M Tech Scholar, Civil Engg. Deptt,
College of Engg. & Technology,
Bhubaneswar

Comparative Evaluation of
Epoxy Treated Reinforcement
and Enamel Treated
Reinforcement

What is corrosion of steel ?
 Corrosion is the chemical or electrochemical
reaction between a material, usually a metal, and
its environment that produces a deterioration of
the material and its properties.
 For steel embedded in concrete, corrosion results
in the formation of rust which has two to four
times the volume of the original steel.
 Corrosion also produces pits or holes in the
surface of reinforcing steel, reducing strength
capacity as a result of the reduced cross-sectional
area.

Can corrosion be avoided ?
Yes if:
 Concrete is always dry, then there is no H2O to form rust. Also
aggressive agents cannot easily diffuse into dry concrete.
 Concrete is always wet, then there is no oxygen to form rust.
 Cathodic protection is used to convert all the reinforcement into
a cathode using a battery. This is not easy to implement
because anodic mesh is expensive, and this technology is not
easy to install and maintain.
 A polymeric coating is applied to the concrete to keep out
aggressive agents. These are expensive and not easy to apply
and maintain.
 A polymeric coating is applied to the reinforcing bars to protect
them from moisture and aggressive agents. This is expensive

How we can prevent corrosion?
 Watertight concrete and proper cover
 Non-chloride accelerators
 Cathodic protection
 Sealers
 Polymer concrete overlays
 Silica-fume concrete overlays
 Epoxy-coated rebar
 Stainless steel rebar
 Galvanized steel reinforcement
 Glass-fiber-reinforced-plastic rebar
 Corrosion-inhibiting admixture

Alternative to epoxy coating
ENAMEL COATING

Three different types of enamel
coatings
1.Reactive enamel
2.Pure enamel
3. Double enamel
The reactive enamel was obtained by
combining pure enamel with calcium silicate
(cement) at a 1-to-1 ratio by weight.
The double enamel was composed of an inner
layer of pure enamel and an outer layer of
reactive enamel.

OBJECTIVES
The main objective of this study is to characterize the relative
corrosion resistance of three enamel coatings that have been
applied to deformed steel reinforcing bars through a non-
electrostatic dipping process.
 (1) evaluate the relative corrosion performance of the newly developed
reactive enamel coating when embedded within a highly alkaline
environment through designing, constructing, and monitoring of several
reinforced concrete ponding specimens;
 (2) evaluate the relative corrosion performance of the three enamel
coatings when placed within a humid, sodium chloride (NaCl)
contaminated environment with an elevated air temperature;
 (3) quantify each coating’s overall ability to postpone the onset of
corrosion when placed within a corrosion cell;
 (4) conduct a forensic investigation upon the reinforced concrete
ponding specimens;

RESEARCH PLAN
PART-1:
 Ponding Test specimens were constructed to evaluate the
corrosion resistance of the enamel coating within a cementitious
environment. As a baseline for comparison, both uncoated, enamel
coated and epoxy-coated steel reinforcement were also tested.
The test consisted of subjecting a total of 25 ponding specimens to
a continuous two week wet / one week dry cycle, for a period of
54 weeks. Concrete resistivity and half-cell potential readings were
carried out every 6 weeks over the course of the testing period.
Upon completion of the test, each reinforced specimen was then
forensically evaluated.
 Using both the AASHTO T259 and ASTM C1543 standard as
guidelines, ponding specimens were constructed to evaluate the
corrosion resistance of the 50/50 enamel coating within a
cementitious environment. As a baseline for comparison, both
uncoated and epoxy-coated steel rebar were also tested.

The typical reinforced ponding
specimen and formwork.

Ponding specimen during either
the wet or dry phase of testing

Ponding test procedure
 The specimens were subjected to a series of consecutive
wet/dry cycles.
 The wet phase of a wet/dry cycle lasted for a total of two
weeks and consisted of placing 2 litres of saltwater within a
specimen’s reservoir. The saltwater remained within a
specimen’s reservoir during the entire two weeks and consisted
of distilled water with 5 percent sodium chloride (NaCl) by
weight.
 The dry phase of a wet/dry cycle began when the saltwater
contained within the specimen’s reservoir was removed and the
specimen was then permitted to air dry for a period of one
week.
 The wet/dry cycling of the specimens began directly after
collecting the baseline resistivity and corrosion potential
measurements for each specimen. Baseline readings were
conducted within the first week after a group of specimens had
reached an age of 28 days.

Two types of Measurements
 Concrete Resistivity Measurements.
The resistivity of each specimen was measured every two weeks with
the use of a Multi-meter, an analyzing instrument which had a fixed electrode
spacing of 2 in. (5.1 cm) and a nominal alternating current AC output of 180
μA at a frequency of 50 Hz. The equipment had an impedance of 10 MΩ and
an operating range of 0 to 99 kΩcm with a 1 kΩcm resolution. The
equipment was portable and required two AA batteries. Resistivity
measurements began immediately after a wet phase of testing had been
completed.
 Corrosion Potential Measurements.
The corrosion potential of the rebar embedded within a specimen was
measured immediately after the specimen’s resistivity readings were
recorded. Using the Multi-metre equipment, which had an operating range of
±999 mV, the corrosion potential at three locations along the length of each
embedded bar was measured. These locations were spaced 6 in. (15 cm) on
centre and were offset a distance 3 in. (7.6 cm) from a specimen’s side.

The overall average resistance of each
specimen type throughout the testing period.

An average representation of the final
corrosion potential of each specimen group at
week 54

Findings of Ponding Test
 Concrete Resistivity Measurements. The significance of these values is a relative
indication of the corrosion resistance of the concrete/rebar system for each coating
type. With the reinforced specimens having been constructed with the same concrete
and steel reinforcement, the discrepancy within the resistivity readings is most likely
attributed to the coating applied to the embedded reinforcement. This result would
indicate that the epoxy coating provided the greatest resistance to the applied
electrical current, while the uncoated bar provided the least resistance. The 50/50
enamel-coated bars provided a degree of resistance between that of the epoxy and
uncoated bars.
 Corrosion Potential Measurements. Taking into account these results, it was found
that the corrosion protection provided by the epoxy coating was jeopardized when
damaged, while the corrosion protection provided by the 50/50 enamel was unaltered
when damaged. Although the corrosion protection of the 50/50 enamel coating was
unaffected by the areas of damage, the coating consistently provided a lower level of
protection when compared to that of the intentionally damaged epoxy-coated bars.
The final set of corrosion potential measurements indicated a “high > 90% ”
probability that the reinforcement contained within each specimen group was actively
corroding. With a severe chance that the reinforcement contained within the two

PART-2:
 A salt spray test was used to rapidly assess the relative
corrosion performance of the three enamel coatings
along with a standard epoxy coating. The test consisted
of subjecting a total of 64 specimens to a series of
wet/dry cycles for a period of 12 weeks. After testing, the
uniformity of each coating, as well as the steel-coating
bond along both the deformed and smooth bars, was
evaluated through visual and microscopic cross-
sectional examination.
 A modified ASTM B117 salt spray test was used to
assess the corrosion resistance of three enamel coating
configurations along with a standard epoxy coating.

Salt Spray test
 A standard salt spray test method specifically designed to evaluate the relative
corrosion resistance of various metals and/or coatings. Today, salt spray chambers
are designed according to the ASTMB117 standard and are automated to maintain a
specified environment within the chamber.
 A salty fog is injected into the enclosed chamber through a nozzle or atomizer
centrally located along the chamber’s floor.
 The distribution of the salt fog throughout the chamber shall have a fallout rate such
that 2.0 to 4.0 ml of solution. 1.0 to 2.0 ml per second is collected upon a horizontal
surface measuring 80 cm2.
 Specimens within the chamber shall be oriented at an angle of 15° to 30° from the
vertical and positioned in such a manner that prevents the specimens from
contacting one another.
 A specimen’s exposure to the salt fog shall be unobstructed. Solution that
accumulates inside the chamber may be disposed of through a drain positioned
within the chamber’s floor. Prior to opening the chamber, a ventilating system may be
used to expel any salt fog lingering within the chamber; however, opening of the
chamber shall be held to a minimum.
 The validity of the test may also be established by examining standard test

Representation of a salt spray
chamber

The specimen layout within the
salt spray chamber

Testing & procedure
 During the twelve weeks of testing, the set of 64 specimens
was broken up into two groups of 32 specimens. Group 1
contained all of the deformed bars, and Group 2 contained all
of the smooth bars.
 The two groups of specimens were transferred from one
condition to the other on Monday, Wednesday, and Friday of
each week. The total duration of the salt spray test was 2000
hours with each of the two groups spending half of the time in
a dry environment and the remaining 1000 hours in a salty
fog (wet) environment.
 After a group had spent 72 hours within the wet environment,
the group would spend the following 72 hour phase in the dry
environment. This cycling was maintained throughout the
2000 hours of testing and resulted in each group spending an
equal amount of time in both the wet and dry environments.

The condition of a typical deformed 50/50 enamel-
coated specimen after the fifth and twelfth week of
testing.
(a) Fifth week. (b) Twelfth week.

The areas along a deformed double enamel-coated
specimen showing various amounts of corrosion.
a “Minor.” b
“Moderate.

The areas along a deformed pure enamel-coated specimen
showing various amounts of corrosion.
a “Minor.” b “Significant.”

The deformed epoxy-coated salt
spray specimens after testing.

Conclusions
1. The 50/50 enamel coating is more susceptible to impact
damage than that of the epoxy coating.
2. When embedded in concrete, the 50/50 enamel coating can
reduce the electrical conductivity of a steel bar. However, the
insulating properties of the coating are lower than that of an
epoxy coated steel bar.
3. An area of damage, measuring approximately 0.2 in.2 (1.3
cm2) in size, will have no influence upon a 50/50 enamel-
coated bar’s performance during a ponding test.
4. Of the three enamel coatings, the 50/50 enamel coating
provides the least amount of protection to the underlying
steel, while the double enamel provides the highest
amount of protection, and the pure enamel provides a
degree of protection between the double and 50/50
enamel coatings.

5. The overall performance of the three enamel coatings depended
significantly on the minimum thickness of each coating.
6. The excellent bond created between the steel reinforcement and both pure
and double enamel coatings actively prevents corroding areas from travelling
along the steel-coating interface (i.e., no undercutting); whereas, the epoxy
coating is unable to do so.
7. When undamaged and properly applied, both pure and double enamel
coatings can protect steel reinforcement from chloride induced corrosion;
whereas, the 50/50 enamel coating cannot.

Reference
 ASTM A 775 (2007). Standard Specification for Epoxy-Coated Steel Reinforcing
Bars. American Society of Testing and Materials, West Conshohocken, PA.
 ASTM B 117 (2009). Standard Practice for Operating Salt Spray (Fog) Apparatus.
American Society of Testing and Materials, West Conshohocken, PA.
 ASTM C 876 (2009). Standard Test Method for Corrosion Potentials of Uncoated
Reinforcing Steel in Concrete. American Society of Testing and Matierals, West
Conshohocken, PA.
 ASTM A 934 (2007). Standard Specification for Epoxy-Coated Prefabricated Steel
Bars. American Society of Testing and Materials, West Conshohocken, PA.
 ASTM C 1543 (2009). Standard Test Method for Determining the Penetration of
Chloride Ion into Concrete by Ponding. American Society of Testing and Materials,
West Conshohocken, PA.
 Doppke, T. and Bryant, A. (1983). "The Salt Spray Test: Past, Present, and
Future."Proc. of the 2nd Automotive Corrosion Prevention Conference, 57-72.

Presentation: Comparative Evaluation Of Epoxy Treated Reinforcement And Enamel Treated Reinforcement

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Presentation: Comparative Evaluation Of Epoxy Treated Reinforcement And Enamel Treated Reinforcement