20120140506015

International Journal of Advanced Research in Engineering and Technology (IJARET), ISSN 0976 –
6480(Print), ISSN 0976 – 6499(Online) Volume 5, Issue 6, June (2014), pp. 99-107 © IAEME
99
AMOXICILLIN AS GREEN CORROSION INHIBITOR FOR CONCRETE
REINFORCED STEEL IN SIMULATED CONCRETE PORE SOLUTION
CONTAINING CHLORIDE
Abdulrasoul Salih Mahdi1*
1
Electrochemical Eng. Department, College of Engineering, Babylon University,
P.O. Box 4 Hilla, Iraq
ABSTRACT
Recently research works have been done on the use of antibacterial drugs as corrosion
inhibitor for mild steel. Amoxicillin which is an antibacterial drug has been proved as a good steel
corrosion inhibitor in acidic media. This paper presents an experimental study on the inhibition effect
of amoxicillin on corrosion of concrete reinforced steel samples immersed in alkaline solution
consisting of 2% KOH and 3% NaCl which is a simulation to the chloride contaminated concrete
Pore (SCP) solution using potentiodynamic polarization technique. Various concentrations (0.6 g/ l,
1.25 g/ l, 2.5 g/ l) of amoxicillin in SCP solutions were examined in these
Experiments Potentiodynamic polarization measurements after zero hr. showed a shifting in
corrosion potential (Ecor) toward positive direction and a decrease in corrosion current density
(Icor), and the corrosion rate (CR) with increasing inhibitor concentration compared with the control
sample which is an indication of formation of passive film on the steel surface.
Measurements after one day and 7 days of immersion of steel samples in the test solutions
also showed a decrease in the corrosion current density and corrosion rate with increasing the
inhibitor concentration which indicated that amoxicillin maintained stable passivity even in the
presence of the chloride ions. Tafel curves showed that amoxicillin act as mixed type inhibitor. The
results explained that the inhibition efficiency of amoxicillin increased with the increasing the
concentration and maximum efficiency of 95.03 % was achieved at amoxicillin concentration of
2.5g/l after 7 days of immersion in the test solutions. The formation of protective film was confirmed
by the optical microscope image that was taken after 2 days of immersion in the test solutions. The
experimental results of this paper showed that amoxicillin drug worked as an effective green
inhibitor, gave good corrosion inhibition for concrete reinforced steel immersed in SCP solutions
during the period of this research.
INTERNATIONAL JOURNAL OF ADVANCED RESEARCH
IN ENGINEERING AND TECHNOLOGY (IJARET)
ISSN 0976 - 6480 (Print)
ISSN 0976 - 6499 (Online)
Volume 5, Issue 6, June (2014), pp. 99-107
© IAEME: http://www.iaeme.com/IJARET.asp
Journal Impact Factor (2014): 7.8273 (Calculated by GISI)
www.jifactor.com
IJARET
© I A E M E

100
Keywords: Amoxicillin Drug, Reinforced Steel, Organic Corrosion Inhibitor, Corrosion Inhibition
Simulated Pore Solution.
1. INTRODUCTION
Organic inhibitors are commonly used to inhibit the corrosion of reinforced steel in concrete
[1-12]. The most effective inhibitors are the organic compound that contain aromatic rings,
π-electrons and hetro atoms such as sulphur, nitrogen, oxygen and phosphorus in their structures
which allow the adsorption of compound on the steel surface. This compound interact with the
anodic and or chathodic reaction, blocking the active sites by removing water molecule and forming
protective barrier over the steel surface resulting a decrease in the corrosion rate[13].
Most of organic inhibitors are expensive, toxic and have negative effect on the environment,
this properties restrict its use to inhibit the metal corrosion. Thus it is important and necessary to
develop low cost and environmentally safe corrosion inhibitors [14, 15]. Drugs are nontoxic, cheap,
negligible negative effects on environment, so it suggested to replace the traditional toxic corrosion
inhibitors. GokhanGece (2011) review from literatures the use of many types of drugs as corrosion
inhibitors of various metals [16]. Research efforts have been done recently on the use of antibacterial
drugs as corrosion inhibitors for carbon steel and aluminum in acidic and alkaline media [17, 18, 19].
Amoxicillin have been proved as a good steel corrosion inhibitor in acidic media but no
research work in alkaline media have been performed. Kumeret al (2013) investigated the effect of
amoxicillin on the corrosion of mild steel in HCL and H2SO4 solution and they was shown that
amoxicillin act as a mixed type inhibitor [20, 21]. However no reports are available for the corrosion
inhibition of concrete reinforced steel employing amoxicillin as corrosion inhibitor. Amoxicillin is
an N-S heterocyclic compound containing five oxygen atoms, three nitrogen atoms and one sulphur
atom as shown in figure 1 [21], this properties enable it to be an effective inhibitor.
Figure 1: Amoxicillin structure
Concrete pore solution is an alkaline solution pH = 13.5 [22]. In this paper experimental
study was done to examine the inhibition effect of amoxicillin on the corrosion of reinforced steel in
simulated chloride contaminated concrete pore solution (SCP) consisting of 2% KOH solution
containing 3% NaCl ( PH= 13.4) using potentiodynamic polarization technique.
2. EXPERIMENTAL WORK
2.1 Reinforced steel samples Preparation
The steel rebar was purchased from local supplier which is currently used as concrete
reinforcement. For potentiodynamic polarization tests, steel discs of 10 mm diameter were cut from
steel bar and then braded with abrasive grinder machine.
2.2 Inhibitor
Amoxicillin drug was purchased from medicine shop as a trade name Acamoxil500 capsule
made in Iraq and was used directly without any additional purification.

101
2.3 Solutions preparation
Potassium hydroxide KOH, Sodium chloride NaCl (analytical grade) was purchased from
local supplier, in order to use in this work. KOH solution was prepared by stirring appropriate
amount of solid KOH substance in de-ionized water to obtain 2% KOH solution to simulate the
alkalinity of concrete pore solution. 3% NaCl was added to this solution to form chloride
contaminated SCP solution (control solution PH = 13.46). 0.6 gm, 1.25 gm and 2.5 gm amoxicillin
were added to each liter of control solution to form three amoxicillin inhibitor solutions. In this study
four different solutions were prepared, the first one SCP solution (control solution) and the other
three solutions were the amoxicillin inhibitor solutions.
2.4 Polarization measurements
Experiments were carried out in SCP solution .Fixed concentrations of amoxicillin inhibitor
and corroding sodium chloride were used in these experiments. Corrosion rates and inhibition
efficiency were estimated using potentiodynamic polarization technique. Polarization measurements
were carried out with Wenking M Lab PotentiostatGalvanostat instrument (GERMAN origin) under
potentiodynamic conditions. This instrument itself is having programs to evaluate corrosion
parameters such as corrosion current (Icorr), corrosion potential (Ecorr), anodic Tafel slope (ba) and
cathodicTafel slope (bc). Three electrode cell consist of a specimens as a working electrode,
Platinum wire as a counter electrode and Ag/AgCl electrode as a reference electrode was used in this
experiment. The working electrode was rebar steel disk axially embedded in a Teflon holder to offer
a flat disc shaped exposed surface area of 0.785 cm2
. The steel discs were mechanically braded with
different grades of emery papers, degreased with acetone then rinsed with distilled water and dried
before each test. Control specimen was immersed in SCP solution and the other specimens immersed
in SCP solution containing amoxicillin at concentrations of 0.6 g/l, 1.25 g/l,2.5 g/l respectively. The
initial tests were performed at zero hour and one day of immersion. The final tests were performed
after 7 days of immersion to verify the stability of passive film in presence of corrosive chloride ions.
By changing the electrode potential automatically ± 200 mV around the open circuit potential
at a scan rate of 1 mV/s potentiodynamic polarization curves were conducted. From Tafel plot
corrosion parameters such as Ecorr, Icorr, ba and bc were recorded. Corrosion rate (mmpy),
corrosion inhibition efficiency (IE %) was calculated and reported using the following equations
[23].
Corrosion rate (mmpy) = 3.2 x Icor x equivalent weight / density
IE % = (Io - I) / Io× 100
Where:
Equivalent weight of steel = 27.93 gm,
Steel density = 7.8 gm/ cm3
,
Icor = current density mA/ cm2
IE = inhibition efficiency
Io and I are the corrosion current density without and with the inhibitor respectively.
2.5 Optical microscope image
5 mm diameter disc were cut from steel bar, braded with abrasive grinder machine and then
polished by polishing machine till mirror surface. The samples were immediately rinse in acetone
and air dried. Digital optical microscope was used to examine the specimens surface after two days
immersion in both inhibited and uninhibited solutions.

102
3. RESULTS AND DISCUSSION
3.1 Potentiodynamic polarization
Polarization curves of reinforced steel samples in chloride contaminated SCP solution
containing various concentration of amoxicillin inhibitor after zero hr. immersion are shown in
figures 2. Corrosion current (Icor), corrosion potential (Ecor), anodic Tafel slope (ba) and
cathodicTafel slope (bc) were measured from Tafel plots. Corrosion parameters such as corrosion
rate (CR), inhibition efficiency (IE %) calculated using potentiodynamic polarization are
summarized in table 1.
The table shows that the Icor and CR values of reinforced steel samples immersed in
amoxicillin inhibitor decreased with increasing amoxicillin concentration compared with control
sample. The results explain that Icor of steel sample immersed in control solution is 13.08 µA/cm2
and it decreased to 1.89 µA/cm2
for sample immersed in 2.5 g/l amoxicillin solution. Corrosion rate
of steel sample in control solution is 0.153 mmpy and it decreased in the presence of amoxicillin till
it reach 0.022 mmpy for sample immersed in solution containing 2.5 g/l amoxicillin These results
explain that the adsorption of inhibitor on reinforced steel increases with increase in inhibitor
concentration .
Furthermore it is clear from the table that the reinforced steel corrosion potential immersed in
SCP solution (control solution) was (- 452.2 mV Ag- AgCl) and it shifted toward the more positive
direction and a decrease in Icor in presence of amoxicillin in SCP solution, which is an indication on
the formation of protective film on the steel surface [24] . The table shows that the increasing in
inhibitor concentration decreased values of Icor and values of Tafel slopes ba and bc in indefinite
form Indicating that the amoxicillin acted under mixed type control [25]. Inhibition efficiency (IF)
increased with increasing antibiotic concentration. The maximum inhibition efficiency of 85.47%
was achieved at 2.5 g/l concentration.
Figure 2: Tafel polarization curves of the reinforced steel after zero hour immersion in the SCP
solutions without and with various concentrations of amoxicillin inhibitor

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Table 1: Corrosion parameters obtained from polarization curve of concrete reinforced steel after
zero hr. immersion in the SCP solution without and with different concentrations of amoxicillin
inhibitor
System Ecor
mV
Icor
µA/ cm2
ba
mV/dec
-bc
mV/dec
CR
mmpy
IE
%
Control -452.2 13.08 203.1 308.6 0.153
Control + 0.6 g/l amoxicillin - 439.4 6.33 234 210.9 0.074 51.6
Control + 1.25 g/l amoxicillin - 363 5.86 211.8 208 0.069 55.19
Control + 2.5 g/l amoxicillin - 378.5 1.89 202 207.4 0.022 85.47
For one day immersion the corrosion parameters also decreased with increasing the inhibitor
concentration Compared with control sample as shown in figures 3 and tables 2. The results show
that Icor and CR values for samples immersed in SCP solution containing amoxicillin decreased
higher than that after zero hour immersion, the lower values of Icor (1.72 µA /cm2
) and
CR (0.02 mmpy) was achieved at 2.5 g/l concentration with efficiency of 89.39%. Also there is more
shifting in corrosion potential toward the positive direction. This indicates that amoxicillin build up
more protective film on the steel surface.
Figure 3: Tafel polarization curves of the reinforced steel after one day immersion in the SCP
Table 2: Corrosion parameters obtained from polarization curve of concrete reinforced steel after
one day immersion in the SCP solution without and with different concentrations of amoxicillin
inhibitor
System Ecor
mV
Icor
µA/ cm2
ba
mV/dec
-bc
mV/dec
CR
Mmpy
IE
%
Control -408 16.2 333.7 221.6 0.189
Control + 0.6 g/l amoxicillin - 195.1 5.34 215 231.1 0.063 67
Control + 1.25 g/l amoxicillin - 328 5.02 165.6 154.5 0.059 69
Control + 2.5 g/l amoxicillin - 241 1.72 141.7 142.5 0.02 89.38

104
After 7 days of immersion of reinforced steel in SCP solution containing various amount of
amoxicillin inhibitor, the corrosion parameters values were decreased higher than the values of one
day immersion as shown in figure 4 and table 3. Table 3 informations explain that the Icor was
decreased to 0.83 µA/ cm2
and CR was decreased to 0.0096 mmpy and inhibition efficiency to
95.03 % in addition to Ecor also decreased toward more positive direction. This is an indication that
amoxicillin maintained stable protective film on the steel surface even in the presence of chloride
ions. According to table 4, this results reveal that amoxicillin has ability to be a good green corrosion
inhibitor for reinforced steel in concrete.
Figure 4: Tafel polarization curves of the reinforced steel after 7 days immersion in the SCP
Table 3 :Corrosion parameters obtained from polarization curve of concrete reinforced steel after 7
days immersion in the SCP solution without and with different concentrations of amoxicillin
inhibitor
System Ecor
mV
Icor
µA/ cm2
ba
mV/dec
- bc
mV/dec
CR
mmpy
IE
%
Control - 446.2 16.7 346.8 289.9 0.195
Control + 0.6 g/l amoxicillin -383 2.94 167.9 140.2 0.0343 82.4
Control + 1.25 g/l amoxicillin - 362 1.24 161.5 110..2 0.0146 92.6
Control + 2.5 g/l amoxicillin - 325 0.83 125.6 66.1 0.0096 95.03
3.2 Optical microscope image
Figure 5 shows the optical micrograph of reinforced steel discs surface immersed in control
solution and in control solution containing various concentration of amoxicillin. Observations of
micrograph (a) showed that the surface of steel sample immersed in control solution was rough and
damaged due to the direct chloride attack. Micrograph (b) and (c) showed that the surface roughness
was decreased due to the formation of a thin layer of inhibitor molecules that decreased the
dissolution of reinforced steel, micrograph (d) showed that the film formed cover large surface area
of steel and become thicker due to the increase in the inhibitor concentration ( 2.5 g/l ) [26].

105
(a) (b)
(c) (d)
Figure 5: Optical micrographs of reinforced steel surface after two days of immersion in
(a) Control sample, (b) 0.6 g/l amoxicillin sample, (c) 1.25 g/l amoxicillin sample,
(d) 2.5 g/l amoxicillin
4. CONCLUSION
The following conclusions can be drawn from this work:
a) Amoxicillin acts as a good green inhibitor for the corrosion of concrete reinforced steel.
b) The inhibition efficiency of amoxicillin increases with increasing inhibitor concentration.
c) After 7 days of immersion in test solutions the inhibitor showed maximum inhibition
efficiency of 95.03% at 2.5 g/l concentration.
d) Lower corrosion rate of 0.0096 mmpy at 2.5 g/l concentration.
e) Potentiodynamic polarization reveal that amoxicillin is a mixed type inhibitor.
f) Optical microscope images of reinforced steel samples enhanced the formation of protective
film on steel surface and the film formed at the surface of steel rebar immersed in 2.5 g/l
amoxicillin was thicker than that formed on steel surface immersed in the others solutions.
g) Studies with actual concrete specimens are needed to know the effect of amoxicillin on the
compression strength of the concrete.
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