EC-Lab – Application Note #22
2010
Corrosion of reinforced concrete
I – INTRODUCTION
During its lifetime, the metallic structure of a H 2 O + e − → HO − + 1 H 2 (1)
building is attacked by the environment, 2
especially by CO2. Indeed, the iron is stable in
basic media inside the concrete (pH = 12-14),
but carbonates, dissolved in water, migrate
through the concrete to the metallic sub-
structure. This phenomenon implies a
decrease of the pH localized around the
metallic structure. This pH shift is represented
by an arrow in the Pourbaix diagram [1] in
Figure 1. Consequently, at this acidic pH, the
iron is no longer passivebut is actively
corroding. This means that the strength of the
building is affected. For instance, the “Tour
Perret” in Grenoble (Figure 2), which is the
first building to be made of reinforced
concrete in Europe in 1924, is currently falling
apart because of this process.
Figure 2: The first building to be made of reinforced
concrete: the “Tour Perret” in Grenoble.
Figure 1: Pourbaix diagram of iron [1].
In this context, an electrochemical process
was developed to keep the vicinity of the
metallic rods used in reinforced concrete in
basic conditions [2-7]. In order to achieve this,
the metal to preserve, which in this
experiment is a cathode, is immersed into a Figure 3: Scheme of realkalisation method.
basic electrolytic paste (K2CO3 or Na2CO3) with
an electrode inserted into it (Figure 3). The In this note, the corrosion process of the
reduction of the water carried out through metallic rod in a concrete block is
electrolysis at the electrode in the basic media investigated. Realkalisation (electrolysis in
produces OH--. Hydroxide ions migrate to the basic media) is performed, and the benefits of
reinforced concrete, creating a basic the treatment are checked by Cyclic
environment around the metallic rod.(Eq. 1). Potentiodynamic Polarization (CPP).
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EC-Lab – Application Note #22
2010
II – EXPERIMENTAL CONDITIONS
Investigations are carried out with the VMP3
instrument driven by EC-Lab® software in NaCl
(3%) or NaOH solution (0.4 mol.L-1). The
concrete block is immersed for two days into
the solution before the measurements take
place.
A three-electrode set-up is used:
- steel rod inside the concrete block as a
working electrode with a surface area:
A = 10 cm2 (Figure 4),
- Ag/AgCl electrode as reference electrode,
- alloy wire as the counter electrode.
Figure 5: “Parameters Settings” window of
Figure 4: Scheme of concrete reinforced block. potentiostatic electrochemical impedance
spectroscopy measurements (PEIS) performed in NaCl
(3%).
III – RESULTS
III - 1 CALCULATION OF POLARIZATION
PEIS_concrete_in_NaCl.m pr
-Im(Z) vs. Re(Z)
RESISTANCE
6
First of all, we have to check if the ohmic drop
(RΩ) is negligible compared to the polarization
4
resistance (Rp) of the system such that Tafel
-Im(Z)/kOhm
relatioships can be applied [8,9]. These two
characteristics can be determined by 2
Rp > 12.8 kOhm
electrochemical impedance spectroscopy Fq = 1 mHz
Z = 202 Ohm
(EIS) measurement (Figure 5). RΩ = 202 Ω is 0 Fq = 0.3 MHz
negligible versus Rp > 12,800 Ω (Fig. 6).
Consequently, the conditions of « Tafel Fit » -2
are respected.
0 5 10
Re(Z)/kOhm
Rp determination is also possible using
Figure 6: Nyquist diagram of concrete block.
voltamperometric measurements under a
steady-state condition (very slow scan rate,
i.e. 2.5 mV.min-1) and in a narrow potential
range (± 10 mV around the Open Circuit
Voltage, i.e. -547 mV vs. Ag/AgCl). The
voltamperogramm and the « Rp Fit » are
displayed in Figure 7 and give Rp = 11,744 Ω.
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EC-Lab – Application Note #22
2010
CP_realkalisation_NaOH.m pr
Ew e vs. time dQ vs. time #
-1.5 -0.5
Ewe/V vs. Ag/AgCl
-1
dQ/kC
-2
-1.5
-2.5
-2
0 20 40 60
time/h
Figure 9: Plot of potential (blue curve) and charge (red
curve) during the electrolysis.
Figure 7: Voltamperogramm and “Rp Fit”of the block
in NaCl (3%). III - 3 CHARACTERIZATIONS OF THE METALLIC
ROD.
III - 2 REALKALISATION In order to check the efficiency of the
Realkalisation treatment is performed with realkalisation, CPP experiments are carried
the chronopotentiometric (CP) techniques in out before and after the treatment. The
NaOH (0.4 mol.L-1; pH = 13) for 66 h (Figure 8) parameters of these experiments are given in
at Is = -10 mA. Potential and charge during the Figure 10.
electrolysis are plotted in Figure 9. At the end
of the electrolysis, a stable potential of -2.4 V
vs. Ag/AgCl is reached.
Figure 8: “Parameters Settings” Window of
chronopotentiometry (CP).
Figure 10: “Parameters Settings” Window of CPP
experiments.
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EC-Lab – Application Note #22
2010
A comparison between CPP before and after Table I: Data from CPP investigations.
realkalisation (Figure 11) displays a cathodic Before After
shift due to steel rod reduction. “Tafel Fit” Ecorr/mV vs. Ag/AgCl -616 -1097
Icorr/µA 404 272
analysis is performed for both curves and
βc/mV vs. Ag/AgCl 646 240
gives Ecorr = -616 and -1077 mV vs. Ag/AgCl for βa/mV vs. Ag/AgCl 670 325
the CPP measurement performed before and Corrosion rate/mmpy* 0.315 0.213
after treatment, respectively. *mmpy: mm per year
Other parameters (Icorr, βc, βa, and corrosion
rate) are computed (Figure 11 and Table ). The IV – CONCLUSION
corrosion rate is given by Eq. 2: This note demonstrates that electrochemical
EW techniques are able to recondition (electro-
CR = I corr K (2)
( d ⋅ A) lysis) and characterize (CPP, impe-dance, and
in which K is a constant, EW is the equivalent their corresponding analysis) the metallic
weight, d is the density, and A is the surface structure of buildings.
area of the electrode. In the case of steel, EW It is a good example of the contribution of
and d are 18.616 g/eq. and 7.8, respectively. electrochemistry to the field of civil engi-
These fits show that corrosion rate is 50% neering.
higher before than after realkalisation. This
decrease of the corrosion rate demonstrates Data files can be found in :
the efficiency of the realkalisation process. C:\Users\xxx\Documents\EC-
Lab\Data\Samples\Corrosion\
PEIS_concrete_in_NaCl,
1
MP_concrete_in_NaCl,
0
CP_Realkalisation_NaOH,
CPP_Before_Realkalisation and
log ( <I>/mA )
-1
CPP_After_Realkalisation
-2
-3 REFERENCES
1) M. Pourbaix, in : Gauthier-Villars (Ed.) Atlas
-4
-1 0 1 d'équilibre électrochimiques, Paris (1963).
Ewe/V
2) E. Cailleux, E. Marie-Victoire, in : L'actualité
Before After chimique, n°312-313 (2007) 22.
3) http://www.novbeton.com/html/index5.htm
l
4) N. Davison, G. Glass, A. Roberts,
Transportation Research Board, 87th Annual
Meeting (2008).
5) D. A. Koleva, K. van Breugel, J. H. W. de Wit,
E. van Westing, N. Boshkov, A. L. A. Fraaij, J.
Electrochem. Soc., 154 (2007) E45.
6) D. A. Koleva, J. H. W. de Wit, K. van Breugel,
Z. F. Lodhi, E. van Westing, J. Electrochem.
Figure 11: Evans diagram of the reinforced concrete
before (in red) and after (in blue) realkalisation (top) Soc., 154 (2007) P52.
and “Tafel Fit” results (bottom). 7) D. A. Koleva, J. H. W. de Wit, K. van Breugel,
Z. F. Lodhi, G. Ye, J. Electrochem. Soc., 154
(2007), C261.
Bio-Logic Science Instruments, 4 Rue de Vaucanson, 38170 Seyssinet-Pariset, FRANCE
Tel: +33 476 98 68 31 – Fax: +33 476 98 69 09 www.bio-logic.net
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EC-Lab – Application Note #22
2010
8) M. Stern, A. L. Geary, J. Electrochem. Soc.,
104 (1957) 56.
9) D. Landolt, Traité des Matériaux, Vol. 12,
Presses Polytechniques et Universitaires
Romandes, Lausanne (2003).
Revised in 08/2019
Bio-Logic Science Instruments, 4 Rue de Vaucanson, 38170 Seyssinet-Pariset, FRANCE
Tel: +33 476 98 68 31 – Fax: +33 476 98 69 09 www.bio-logic.net
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