AROPUB-IJMSI-13-33

International Journal of Material Science Innovations (IJMSI) 1 (2): 73-86, 2013 ISSN: 2289-4063 Academic Research Online Publisher

Research Article

Effect of anodic inhibitors on corrosion of carbon steel bar reinforced

concrete

Saeid Kakooeia, S. Valid Jaberi b, Kourosh Sharifi b, Mokhtar Che Ismaila, Abolghasem Dolatic

a Center For Corrosion Research, Mechanical Engineering Department, Universiti Teknologi PETRONAS, Bandar Seri Iskandar, 31750 Tronoh, Perak, Malaysia. b Corrosion Engineering Group, Engineering Faculty, Kish University, Kish Island, Iran. c Department of Materials Engineering, Sharif University of Technology, Tehran, Iran * Corresponding author. Tel.: 0060174958196; E-mail address: [email protected]

ARTICLE INFO Article history Received:1May2013 Accepted:10May2013

A b s t r a c t The effect of a mixture of anodic inhibitors used to mitigate the corrosion rate of steel embedded in concrete caused by chloride ion has presented. For this purpose, two different ratio combinations of Calcium Nitrite and Sodium Molybdate were employed to study their functions and synergistic effects. For corrosion accelerating of steel, different amounts of Sodium Chloride were added to the designed solution and samples were exposed to wet and dry cycles for one, two and six months. Three electrochemical methods including linear polarization, impedance spectroscopy and cyclic potentiodynamic polarization were used to evaluate inhibitor behavior on the corrosion rate of steel embedded in concrete. Inherent permeability, compression strength, four-pin electrical resistance, and pH measurement tests have been done to study the effect of inhibitors on the mechanical properties of concrete. It was observed that the mixture of Calcium Nitrite and Sodium Molybdate improved inhibition corrosion of steel embedded in concrete and improving concrete mechanical properties as well. Academic Research Online Publisher. All rights reserved.

Keywords: Inhibitor Steel reinforced concrete Marine environment Corrosion

1. Introduction

As a construction material, reinforced concrete offers various properties such as good

formability, low cost, high strength and durability which have good function in different

work conditions. Concrete coating on steel bars makes both physical and chemical obstacles

against corrosive agents. Concrete has naturally high alkalinity that forms a protective

passive layer on steel bars. The specific electrical resistivity of concrete could be up to 30

k.cm [1]. The above reasons cause reinforced concrete structures to be more corrosion

resistant than metallic ones. Some factors such as chloride ion diffusion in the concrete and

S. Kakooei et al. / International Journal of Material Science Innovations (IJMSI) 1 (2): 73-86, 2013

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pH drop due to carbonating destroy the passive layer and the corrosion of steel bars begins.

One of the most important factors in destruction of concrete structures is the corrosion of

steel bars [2-5].

The degradation of concrete structures due to the corrosion of steel bars starts with the

formation of corrosion production at the surface of the steel and continues with the reduction

of the cross section area of bars and consequently increasing in stress applied to concrete

structures [6, 7]. In addition, the integration of corrosion products at the surface of steel bars

causes volume expansion and concrete cracking. The mentioned factors cause the structure to

fail [8]. Corrosion inhibitors influence Cathodic/anodic reaction or both and since all these

reactions are in equilibrium together, reduction in either rate of them causes the corrosion rate

to decrease [9]. Calcium Nitrite and Sodium Molybdate as two anodic inhibitors were

investigated in this work.

2. Experimental procedures

Raw material and test matrix for preparing concrete specimen are listed in Table 1. Samples

prepared in three different molds, a couple was made without carbon steel bar for mechanical

testing and one with the steel bar in the middle of the mold for corrosion studies (Figure 1).

After cleaning with acid and rust removing from the carbon steel bar, a part of them were

painted as shown in figure 1 to prevent crevice corrosion which can make error in real

corrosion measuring. Table 2 shows the Portland cement component. Concrete specimens

pulled out from molds after 24 hours and located in fresh water for seven days, then

submerge into sea water. The immersion mode was done in wet and dry cycles (three days in

water and four days in a dry place). Corrosion cell includes Ag/AgCl reference electrode,

steel bar inside concrete as working electrode and 316L semicircle stainless steel plate with a

surface area of 1020 cm2 as counter electrode.


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Fig.1: SEM image of schematic of concrete sample

To study the corrosion of embedded carbon steel bars, linear polarization and

electrochemical impedance curves were employed according to ASTM G102 and G3

standards, respectively. Zahner potentiostat Model IM6 was used for polarization curves. To

measure potential and electrical resistivity measurement a digital potentiometer (CANIN

model) and RESI equipment from Switzerland were applied, respectively. Since the concrete

is not carbonated, pH is assumed to be fixed. Wet and dry cycles applied simulate to the real

sea tide. The number of samples for each mix design were calculated and named based on the

number of experiments (Table 3).

Table1. The raw materials used in the presented mixture design

Cement Type Portland type II

The amount of cement (kg/m P3P)

350

Water/cement ratio 0.45 Sand or aggregate 0-8

mm (kg/m P3P) 990

Aggregate 8-16 mm (kg/m P3P)

750

[NOR2RP- P/Cl P- P] 1 [Molybdate-

Nitrite/Chloride] 1

[NOR2RP- P/MoOR2RP- P] 2


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Table 2. Hormozgan cement composition type II KR2RO SOR3 MgO CaO FeR2R OR3 AlR2ROR

3 SiOR2

0.86 2.38 2.01 62.7 3.68 5.2 21.1 CR4RAF+2CR3RA CR4RAF CR3RA CR2RS CR3RS L.O.I NaR2RO

26.75 11.2 7.55 28.72 42.13 0.8 0.22

Table 3. Introducing the samples containing inhibitors and chloride ion [index x shows the time (month)].

Sample [ClP- P/0H P- P] Inhibitor 0.6 1 15 Ca(N0R2R)R2 [N0R2R- /MoOP4- P] 2 1

AR2x

X

X

---

X

---

---

BR2x

---

X

---

X

---

---

CR2x

---

---

X

X

---

---

AR3x

X

---

---

X

X

---

BR3x

---

X

---

X

X

---

CR3x

---

---

X

X

X

X

AR4x

X

---

---

X

---

X

BR4x

---

X

---

X

---

X

CR4x

---

---

X

---

---

---

3. Results and discussion

Figure 2 shows the cyclic polarization of steel bars without inhibitor and chloride ions. No

significant change in polarization curves is observed on the wet and dry cycles of reinforced

concrete by time. Nevertheless, the repassivation potential of sample A11 decreases from 800

mV to 300 mV for A13 after six months. The corrosion densities increased with time even in

the absence of chloride ion. It shows the electrical resistance of passive layer, formed on the

surface of steel bar, decreases even in the absence of chloride ion only by applying wet and

dry cycles.


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Fig. 2. Cyclic polarization diagram of steel bars embedded in concrete without chloride ion and

inhibitor in different times.

Figure 3 and Figure 4 demonstrate the corrosion behavior of steel bars in concrete

containing chloride ion with [Cl-/OH-]=1 and [Cl-/OH-]=15, respectively. It is seen that the

pitting potential (Epit) for samples including chloride ion, increases by time, so that anodic

potential is transected before approaching to Epit. Because it is not reaching the transpassive

area and polarization keeps going in reverse direction.

Figures.5, 6 and 7 show the Nyquist curves for steel bars embedded in the concrete without

inhibitor and chloride ion. It demonstrates an increase in the number of wet and dry cycles

makes the impedance curves smaller and reduces the resistance Rp, while raises the corrosion

rate. Its obvious that impedance and Rp for samples without chloride ion are considerably

more than samples with chloride ion which remarks less corrosion rate for them.

Table 4 represents the extracted values of Cdl, Rct and Rs via extra-polarization curve (Z

Z). According to Rct data, the maximum values belong to samples without chloride ion

and by the time its going to reduce that mark more corrosion. It could be deduced that Rct

values decreased due to increasing of chloride ion in samples including chloride ion with the

ratio of [Cl-/OH-]=1 and 15.


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Fig.3. Cyclic polarization diagram of steel bars embedded in concrete in the presence of chloride ion

with the value of [Cl-/OH-]=1 without inhibitor.

Fig.4. Cyclic polarization diagram of steel bars embedded in concrete in the presence of chloride ion

with the value of [Cl-/OH-]=15 without inhibitor.

Table 4. The parameter values of Rct, Rs, and Cdl extracted by extrapolation diagrams (ZZ).


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Cdl(f/cm2)x (10-

6) Rct(ohm.cm2) Rs(ohm) Name

76.5 365740 6100 A11 94.5 142330 5250 A12 145 84610 5900 A13

1260 14980 5830 B11 610 11400 6850 B12

3000 3730 6980 B13 580 10730 4220 C11

3000 2300 4830 C12 5690 1940 5200 C13

Typically the effect of increasing of chloride ion concentration on the impedance spectrum

of carbon steel appears as a reduction of the second arc that is created due to the destruction

of the passive layer. Several researchers stated when passive layer is not being damaged,

chloride ion is not consumed and the consequently corrosion rate would not decrease by time

[8].

The function of nitrite ion as anodic inhibitor in the forming/mending of passive layer on

the metal surface in solutions with pH higher than 4.5 is as below[8, 10]:

9Fe(OH)2+NO2-3Fe3O4+ NH4+ + 2OH- + 6H2O (1) In addition another iron oxide with higher purity might form following reaction:

9Fe(OH)2 +NO2- 3(Fe2O3)+NH4++2OH- +3H2O

(2)

As shown in Table 3, index number shows what inhibitors are used for samples. Samples

with index 2 just include Calcium Nitrite whereas samples with index 3 and 4 contain both

Nitrite and Molybdate with 1:2 and 1:1 ratio, respectively. In this study cyclic

potentiodynamic polarization, linear polarization and impedance spectrometry were hired to

evaluate the inhibitors electrochemical function.


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Fig.5.Nyquist diagrams and circuits of the steel bars inside the concrete without chloride ion.

Figure 8 shows the cyclic polarization of concrete samples containing various levels of

chloride ion and Nitrite Calcium inhibitor. It is observed that the noticeable variation in these

diagrams happens in the repassivation potential and passive current densities. Moreover,

diagrams of samples with chloride ion and without inhibitor have transferred to the low

values of current densities after the presence of Nitrite ion. It shows the constructive effect of

Nitrite ion in the reduction of passive current density. Figures 9 and 10 are cyclic polarization

diagrams of samples include Nitrite and Molybdate together. The main contrast is in their

current densities. Overall, the third group samples (index 3) were inhibited better than others

with passive current density. More positive ERcorrR values have shown better prohibition.

Research done about the role of Nitrite in the corrosion behavior of steel in aqueous

environment has shown protection by oxidizing FeP2+ P (created from the corrosion process) to

Fe+3 and forming an insoluble ferric oxide on the metal surface while in pH


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Figure 6- Nyquist diagrams and circuits of the steel bars embedded in the concrete with chloride ion

[Cl-/OH-] =1.

Figure 7- Nyquist diagrams and circuits of the steel bars embedded in the concrete with chloride ion

[Cl-/OH-] =15.

According to Figure 8, a noticeable difference in the repassivation potential and passive

current densities was detected. Specimens with chloride ion and without inhibitor have shown

a shift to the low values of current densities. Presence of Nitrite ion clearly shows the

constructive effect of Nitrite ion in the reduction of passive current density.

Figure 8- The cyclic polarization of concrete samples containing chloride ion in the present of

Calcium Nitrite.


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Figure 9- The cyclic polarization of concrete samples containing chloride ion in the presence of

Calcium Nitrite and Molybdate with a ratio of [NO2-]/[MoO4-]=2.

Figure 10- The cyclic polarization of concrete samples containing chloride ion in the presence of

Calcium Nitrite and Molybdate with a ratio of [NO2-]/[MoO4-]=1.

Table 5. The obtained values of Rp from linear polarization of steel bars embedded in the concrete. Sample Rp :Polarization Resistance

(k.ohm.cm2)

X=1 X=2 X=3 First Week 8th

Week 25thWeek

A1 56.6 90 56.8 B1 14.4 21.8 14.2 C1 15 7.1 8.6 A2 27.1 51.8 24.6 B2 42 57.2 28 C2 12.9 51.4 24 A3 44.8 91.2 149.6 B3 48 85.1 121.1 C3 70.7 111 154.6 A4 21 111.5 92.5 B4 47.4 94.2 116.4 C4 92 84 112.2


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Table 6. The obtained values of inhibitor efficiency from linear polarization of steel bars embedded in the concrete.

Sample Rp1 Rp2 Rp3 IE1% IE2% A2 37.1 51.8 34.6 61 57 B2 43 57.3 28 66 61 C2 12.9 51.4 24 12 57 A3 44.8 91.3 149.6 67 76 B3 48 85.1 131.1 70 74 C3 70.7 111 154.6 79 80 A4 31 111.5 92.5 53 80 B4 47.4 94.2 116.4 69 76 C4 92 84 113.3 84 74

Table 7. Evaluation of mechanical properties evaluation of concrete samples containing various

inhibitor components. Compression

strength of concrete (kg/cm3)

Inherent permeability X

10-8 (m2)

Electrical resistance

(kohm.cm2)

Density of concrete (kg.cm3)

pH

non inhibitor 260 8.5 4.8 2151.3 12.8 With [NO2-] 257 8.4 4.1 2186.7 12.75 With [NO2- /MoO4-]=2

268 7.4 4.6 2221.3 12.81

With [NO2- /MoO4-]=l

263 7.6 4.4 2208.4 12.71

Table 8. Concretes classification based on the permeability [12] Quality of Cover concrete

Index kT(10-16m2)

Very bad 5 10 Bad 4 1.0-10 Normal 3 0.1-1.0 Good 2 0.01- 0.1 Very good 1 0.01

Form figures 9 and 10, it can be understood the third group samples (index 3) were

inhibited better than the others in terms of passive current density and more positive Ecorr

values.

Polarization resistance (Rp) values related to E-Logi curves of steel bars embedded in the

concrete after 1 week and 2 and 6 months are presented in Table.4. It is seen that generally

linear polarization resistance of samples containing Nitrite-Molybdate increases by time

whereas it decreases in the samples containing Calcium Nitrite. Also Rp for Nitrite-

Molybdate with a ratio of [NO2-]/[MnO4-]=2 after 6 months exposing to wet and dry cycles

showed the highest value. Based on whatever mentioned above, it is found out Molybdate


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particularly with the ratio of [NO2-]/[MnO4-]=2 applies a synergistic effect on Nitrite to

reduce the corrosion rate. The efficiency of various components of consuming inhibitors is

calculated by following equation[13], and presented in Table.6.

IE(Inhibitor Efficiency) = RP RPRP

100 (3) Where RP and RP are the polarization resistance of concrete samples with and without inhibitors, respectively.

Three concrete samples were prepared for the compression strength test. Table 7 shows the

triple average strength. All samples were chloride ion free, and according to the Table 7 were

compared with respect to the reference sample which was free of additives. Concrete

permeability will be highlighted when there are some aggressive factors such as chloride ion

and oxygen attack. The inherent permeability depends on the type of material and fluid (is

inversely proportional to the fluid viscosity) and its unit is square meter. A cubic sample with

the size of 101015 cm3 after 28 days curing and drying in the ambient environment was

chosen for permeability measurements (Fig. 11) that is taken from different components.

According to Table 7 the obtained values are more than 10-19. In comparison with presenting

data in Table 8 they are considered moderate from the inherent permeability viewpoint. As it

can be understood from Table 7, concrete inhibitor does not show significant changes in

concrete strength. Although, a mix combination of Calcium Nitrite and Sodium Molybdate

slightly increased concrete strength.

4. Conclusions

The following conclusions can be drawn from this research:

1. Corrosion current density of steel rebar has increased in the present of chloride ion in

concrete. It means in samples containing chloride ion with a little more than critical limit,

passive layer probably has destroyed and the existence of chloride ion will not let passive

layer reform. Then corrosion rate was enhanced.

2. The lower arc of Nyquest diagram of steel bars embedded in the concrete appears in

frequencies less than 1 KHz that might belong to the interface reactions that have been

formed from passive film formation and transfer reaction processes.


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3. The result shows that Calcium Nitrite has less inhibition in comparison to Molybdate-

Nitrite and the efficiency decreases by the time. Among the two combinations of Nitrite-

Molybdate the inhibition of ratio equal to 2:1 is the highest and the efficiency increases

by time.

4. Adding Molybdate to the concrete component does not have a significant effect on the

mechanical properties of the concrete.

Acknowledgments

Facilities and funding for this study were provided by Kish University, Iran. Also authors

would like to thank Universiti Teknologi PETRONAS for supporting the research work.

References

[1] Sundberg, N.B.D.F.S.a.K.M.s, Comparison of the polarization resistance technique to macro-cell

corrosion technique. Corrosion rate of steel in concrete: American society for testing and materials.

[2] Ghods, P., M. Chini, R. Alizadeh, M. Hoseini, M. Shekarchi, and A. Ramezanianpour.

Proceedings of the 3rd International Conference on Construction Materials: Performance, Innovations

and Structural Implications. 2005.

[3] Ann, K., J. Ahn, and J. Ryou, The importance of chloride content at the concrete surface in

assessing the time to corrosion of steel in concrete structures, Construction and Building Materials.

2009, 23(1): 239-245.

[4] Ismail, M., A. Toumi, R. Franois, and R. Gagn, Effect of crack opening on the local diffusion of

chloride in cracked mortar samples, Cement and Concrete Research. 2008, 38(8): 1106-1111.

[5] Miyazato, S. and N. Otsuki, Steel Corrosion Induced by Chloride or Carbonation in Mortar with

Bending Cracks or Joints, Journal of Advanced Concrete Technology. 2010, 8(2): 135-144.

[6] Kakooei, S., H.M. Akil, M. Jamshidi, and J. Rouhi, The effects of polypropylene fibers on the

properties of reinforced concrete structures, Construction and Building Materials. 2012, 27(1): 73-77.

[7] Kakooei, S., H.M. Akil, A. Dolati, and J. Rouhi, The corrosion investigation of rebar embedded in

the fibers reinforced concrete, Construction and Building Materials. 2012, 35: 564-570.


86 | P a g e

[8] Bentur, A., S. Diamond, and N.S. Berkes, Steel corrosion in concrete: fundamentals and civil

engineering practice: Taylor & Francis. 1998

[9] Monticelli, C., A. Frignani, and G. Trabanelli, A study on corrosion inhibitors for concrete

application, Cement and Concrete Research. 2000, 30(4): 635-642.

[10] Islamdulal, C.M.M.S.M.S.A., Corrosion behavior of mild steel in moderately alkaline to acidic

simulated cooling water containing molybdate and nitrite, British corrosion Journal. 1997, 32(2): 133-

137.

[11] Gaidis, J.M., Chemistry of corrosion inhibitors, Cement and Concrete Composites. 2004, 26(3):

181-189.

[12] Pack, S.W., M.S. Jung, H.W. Song, S.H. Kim, and K.Y. Ann, Prediction of time dependent

chloride transport in concrete structures exposed to a marine environment, Cement and Concrete

Research. 2010, 40(2): 302-312.

[13] Alagbe, M., L. Umoru, A. Afonja, and O. Olorunniwo, Effects of Different Amino-acid

Derivatives on the Inhibition of NST-44 Mild Steel Corrosion in Lime Fluid, Journal of Applied

Sciences. 2006, 6(5): 1142-1147.

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