EFFECT OF IMPRESSED CURRENT ON CORROSION OF
REINFORCING BAR IN REINFORCED CONCRETE
1
NABEEL SHAIKH, 2SHEETAL SAHARE
1
PG student 2Assistant Professor,
Vishwakarma Institute of Information Technology, Pune, Maharashtra, India
Email: 1sknabeel12@gmail.com, 2sheetal4488@gmail.com
Abstract— Corrosion of steel reinforcing bar is one of the major causes of premature deterioration reducing service life of
reinforced concrete (RC) structures. This increases maintenance and repair cost of the RC structures. In RC structures,
corrosion of steel in natural condition is very slow process. Hence generally accelerated corrosion techniques are used in the
laboratory to simulate natural corrosion process. An experimental work was carried out to study effect of impressed current
on corrosion of steel reinforcing bar in concrete. In this experiment, three different voltages 4V, 6V and 10V were used and
was impressed on reinforced bar in concrete. Cylindrical specimen of 100mm diameter and 200mm height reinforced with
bar diameter 16mm and 20mm concentrically were used and studied for the effect of different voltages applied.
Keywords— Reinforced Concrete, Corrosion mechanism, Accelerated corrosion, Impressed Current.
of corroding RC structures at dangerous levels of
steel corrosion or when load-bearing capacities of
structures are still adequate. For the safety of
occupants of corroding RC structures, as well as to
minimize costs from unnecessary repairs, there is
need to understand well how to apply (if at all
applicable) results from accelerated laboratory tests to
in-service structures. The focus of the paper is to
study the effect on steel corrosion caused by chloride
attack due to application of different voltages.
I. INTRODUCTION
Corrosion of steel reinforcing bar provokes premature
deterioration of RC structures [1]. Corrosion results
in loss of cross sectional area of bar, development of
cracks in the surrounding concrete due to volumetric
expansion of corrosion product and reduction in bond
strength [2].Corrosion of steel leads to the reduction
of bond strength [3]-[6], flexural strength [7],
ductility [8] and load carrying capacity [9] of RC
element reducing service life span of the structure.
This leads to the increase in repair and maintenance
cost of the structures. Thus corrosion of steel is a
serious phenomenon and it needs to be addressed and
researched extensively.
Corrosion of steel is aggressive in marine
environment and causes most damage to the RC
structures in service condition. In natural condition
the steel corrosion is a very slow process; needs
number of years to cause reasonable structural
damage. Francois & Arliguie (1998)[10], Castel et al
(2003)[11], Vidal et al (2007)[12] and Zhang et al
(2009a,b; 2010)[13]-[15] allowed RC specimens to
corrode naturally in the laboratory. Four years were
required to start corrosion and additional two years
for appearance of first visible crack on the concrete
surface. Reasonable structural damage was obtained
after 20 years of corrosion. Such a long duration
cannot be afforded for research in the laboratory tests.
Hence researchers have to use various techniques to
accelerate steel corrosion to shorten the testing time.
In doing so they anticipate that structural damage
under accelerated corrosion test is proportional to the
damage caused by steel corrosion. Generally results
obtained by the researchers from laboratory tests for
the specimens subjected to accelerated corrosion are
often passed on to engineers and asset managers to
apply them to real life RC structures.
If they are not applicable to those structures then
there is likelihood for engineers to authorize repairs
1.1 Corrosion Mechanism Of Reinforced Concrete
Corrosion of steel embedded in concrete is an
electrochemical process. The surface of the corroding
steel functions as a mixed electrode that is a
composite of anodes and cathodes electrically
connected through the body of steel itself, upon
which coupled anodic and cathodic reactions take
place. Concrete pore water functions as an aqueous
medium i.e. a complex electrolyte. Therefore, a
reinforcement corrosion cell is formed as shown in
Fig.1 [16].
Fig. 1: Schematic illustration of the corrosion of steel
reinforcement in Concrete [16].
Anodic and Cathodic Reactions:
The chemical half-cell reactions occurring at the
anodic and cathodic areas are as follows [17]:
At the anode: Fe → Fe2+ + 2e-
Proceedings of 45th IRF International Conference, 13th December 2015, Pune, India, ISBN: 978-93-85832-70-3
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Effect of Impressed Current on Corrosion of Reinforcing Bar in Reinforced Concrete
-
At the cathode: 2e + H2O + (1/2)O2→2(OH)-
II. METHODOLOGYAND EXPERIMENTAL
DETAILS
The hydroxyl ions, OH- arriving at the anodic area
electrically neutralize the Fe2+ ions dissolved in pore
water and from a solution of ferrous hydroxide at the
anode:
Fe2+ + 2(OH)- → Fe(OH)2.
2.1 Concrete, Steel
Ordinary Portland cement of nominal strength 53
MPa, fine aggregate (natural sand) and crushed stone
coarse aggregate with maximum size of 20 mm were
used in concrete. The ratio of cement: sand: coarse
aggregate was 1:1.66:2.63 (As per Revised IS 10262:
2009). The water–cement ratio was 0.45. The average
resulting strength of concrete was 30 MPa. The
material properties of concrete mixture are shown in
Table 1. Steel of bar diameters 16mm and 20mm
were used. The grade of steel used was Fe500
This compound Fe(OH)2 reacts further with
additional hydroxide and available oxygen, to form
the water insoluble red rust: Red rust is not the only
product of corrosion of steel in concrete. Compounds
such as black rust Fe3O4, green rust, FeCl2 and other
ferric and ferrous oxides, hydroxides, chlorides
hydrates are also formed.
It is possible, with varying degrees of
accuracy, to measure the amount of steel dissolving
and forming oxides i.e. rust by faradays law i.e.
Table 1: Material Properties of Concrete
m = MIt/zF
Where,
m =mass of steel consumed in g
M=atomic weight of metal (56 g for Fe)
I=Average current (amperes)
t=time (seconds)
z=ionic charge (2) and
F=Faraday’s constant 96,500 amperes/seconds.
2.2 Preparation of Specimen
Cylindrical concrete specimens of 100mm diameter
and 200mm height were cast using 16mm and 20mm
bar diameter of length 750mm plus 8 times diameter
embedded concentrically in concrete cylinder. The
embedment length was 8 times diameter of
reinforcing bar. Before placing the bar in concrete,
the bar was cleaned of the dust particles and was
coated with epoxy sealant leaving 200mm at the top
for passing of electrical current and 8 times diameter
at the bottom. The epoxy served as sealant to avoid
the corrosion of protruded part of bar. The geometry
of specimen is shown in fig 3.The specimens were
casted and demoulded after 24 hour holding. And
then the specimens were cured in tap water at room
temperature for 28 days.
Three groups each containing two specimen of each
diameter (16mm and 20mm) diameter were formed.
Each group was impressed with constant voltage of
4V, 6V and 10V and was studied for corrosion.
1.2 Accelerated Corrosion Technique (Impressed
Current Method)
In this method a constant positive potential (4V, 6V
and 10V) was applied to the steel bar embedded in
concrete and current from the reinforcing steel to
counter electrode was measured periodically. A sharp
rise in current is indicative of the onset of corrosion
[18]. The anode is the specimen to be tested and
cathode is a steel bar, the current impressed into steel
bar was obtained from DC power supply at constant
voltage (4V, 6V or 10V). This volt was sufficient for
a significant change in current value. The degree of
corrosion intensity was estimated using faradays law.
Fig. 2 shows a general view of the specimens while
exposed to accelerated corrosion.
Fig. 3: Geometry of specimen (all dimension in mm)
Fig. 2: Schematic view of accelerated corrosion technique.
Proceedings of 45th IRF International Conference, 13th December 2015, Pune, India, ISBN: 978-93-85832-70-3
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Effect of Impressed Current on Corrosion of Reinforcing Bar in Reinforced Concrete
cracking, in which one surface crack at the side of the
specimen parallel to the corroded reinforcing bar was
observed. In type 2 cracking, two surface cracks were
observed, one of them at the side surface of the
specimen parallel to one of the corroded reinforcing
bar and the other at the top surface directly above the
reinforcing bar. However there was no association
between the type of cracks and the level of voltage
applied, it appears that the voltage level had no effect
on the final crack pattern. Both the bars of different
diameters (16, 20)mm showed similar crack patterns
for different voltages (4V, 6V, 10V).
2.3 Corrosion Acceleration
After curing, the specimen was immersed in 3.5%
NaCl solution for 24 hours before testing for
accelerated corrosion. The concrete specimens were
immersed in a tank such that water was 20mm below
the top of concrete. After 24 hours specimens was
introduced to accelerated corrosion process in the
same tank by applying constant voltage (4V, 6V and
10V) till the development of first visible crack on the
surface of specimen. The current was induced by DC
power supply at a constant voltage (4V, 6V and 10V)
with a built-in ammeter to monitor the current. The
water solution in the tank was changed after every 3
days. The direction of the current adjusted so that the
reinforcing steel became an anode and a stainless
steel plate placed on the tank in sodium chloride
solution served as a cathode.
Fig. 6: Crack pattern
3.2 Time vs. Crack
The time required for the development of first crack
on the surface of specimen was different for different
diameter as well as for different voltages. Time vs.
crack can be related with cover to diameter ratios
i.e. C/D ratio (Table 2).
Fig. 4: Accelerated corrosion technique setup
2.4 Measurement and Quantification of Corrosion
After the visibility of first surface crack on
specimens, the steel reinforcing bars were retrieved,
cleaned of rust using stiff metal brush and then
weighed to determine the actual mass loss of the steel
reinforcing bars. The stage of the steel retrieving is
illustrated in fig 5.
Table 2: Time Required For First Visible Surface
Crack for C/D Ratio (Average of Two Specimens)
Fig. 5: Retrieving steel after corrosion.
Time required for the development of first visible
crack on concrete surface increases with the increase
in C/D ratio for same voltage applied (Table 2). This
is because, due to increase in concrete cover, the path
required for the chloride ions to penetrate upto the
reinforcing bar increases, also the surface area for the
chloride ions to attack is reduced in smaller bar
diameter. This implies that the concrete cylinders
with increasing C/D ratio undergo slow corrosion.
However the time required for development of first
III. RESULTS AND DISCUSSIONS:
3.1 Crack pattern
The crack pattern due to expansion of corrosion
products was monitored for each specimen applied
for different voltages. Two types of crack patterns
were observed in most of the specimen. Fig.6 shows a
schematic of the different crack patterns observed in
this study. Most of the specimens had type 1
Proceedings of 45th IRF International Conference, 13th December 2015, Pune, India, ISBN: 978-93-85832-70-3
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Effect of Impressed Current on Corrosion of Reinforcing Bar in Reinforced Concrete
visible crack on concrete surface decreases with
increase in voltage for same C/D ratio. This is
because due to increase in voltage the steel liberates
more electrons hence chloride ions are consumed
faster and corrosion process is enhanced.
Table 4: Mass Loss For Different Applied
Voltages (Mass Loss Is Average Of Two
Specimens)
3.3 Mass loss
The mass loss according to faradays law is
proportional to the average current applied. Greater
the average current greater is the mass loss. The
following table 3 gives the range of current and
current density induced due to different applied
voltage by accelerated corrosion technique from
initial current upto the development of first visible
surface crack on concrete specimen.
Current density due to natural steel corrosion is often
between 0.1 and 10µA/cm2 but occasionally reaches
100µA/cm2 [19]. However that current density is
increased in the accelerated corrosion technique. The
lower the voltage the more accuracy towards natural
corrosion can be achieved but time required to
achieve the required corrosion also increases. Hence
lab experiment must consider all parameters and
condition before applying the accelerated corrosion
test.
By the result obtained in the table mass loss increases
as the voltage decreases upto the first visible surface
crack. And mass loss increases as the bar diameter
increases for every voltage applied.
CONCLUSION
The influence of varying the impressed current level
to accelerate steel reinforcing corrosion in concrete
structures was experimentally investigated. The study
evaluated the concrete crack pattern, time vs. crack,
and the mass loss due to accelerated corrosion upto
development of first visible surface crack on concrete
specimen. The main conclusions are as follows:
Table 3: Current Range And Current Density
Range For Different Voltages
1.
2.
3.
4.
5.
6.
The level of voltage applied had no effect on
the final crack pattern. For all test
specimens, the cracks due to corrosion of
reinforcement were parallel to the steel
reinforcing bars regardless of the level of
voltage applied to induce the corrosion of
reinforcement.
Time required for the development of first
visible crack on the surface of concrete
increases with the increase in C/D ratio for
same voltage applied (4V, 6V, 10V).
The time required for development of first
visible crack on concrete surface decreases
with increase in voltage (4V, 6V, 10V) for
same C/D ratio.
Mass loss decreases with increase in C/D
ratio for same voltage applied upto
development of first visible surface crack on
concrete specimen.
Mass loss decreases with increase in voltage
for same C/D ratio upto the development of
first visible surface crack on concrete
specimen
More research work is required to
investigate the ability of corrosion of
reinforced concrete at higher voltage and at
higher degrees of corrosion.
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The theoretical mass loss calculated by faradays law
and the actual mass loss for different voltages applied
are shown in the following table 4.
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Effect of Impressed Current on Corrosion of Reinforcing Bar in Reinforced Concrete
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