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*

1Electrochemical 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.



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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



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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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20120140506015

Technology

corrosion of reinforced

corrosion of mild steel

good steel corrosion

organic corrosion inhibitor

green corrosion inhibitor

corrosion rate13

metal corrosion

good corrosion inhibition