Review of the use of floating electrode for detection of corrosion of reinforcing steel

7/28/2019 Review of the use of floating electrode for detection of corrosion of reinforcing steel

1/13

M. Keddam a, X.R. Nvoa b, V. Vivier

Corrosion Science 2009

Presented by Dianne Seepersad


2/13

Terminology Background Introduction Experimental Set-up

Objectives Findings Numerical Modelling Discussion Authors Conclusions

Critical Review Strengths of the Paper Weaknesses Potential for Further Work


3/13

Corrosion is the degradation of amaterial due to reactions with itsenvironment. A current is inducedon the surface of rebar whencorrosion is actively taking place.

Electrochemical Impedance Spectroscopy (EIS) Impedance is the ability to resist the flow of current, like resistance, but

is more applicable when alternating current (a.c.) is used.

Thepolarization resistance, Rp, is the low frequency limit of theimpedance; this provides information about corrosion.

An electrically f loating electrode (EFE) is one that is not directlyconnected to the object under study (the reinforcing steel in this case)


4/13


5/13

The feasibility of using an EFE is explored to examinethe electrochemical behavior of an electronicallyconducting body immersed in an electrolytic mediumthrough impedance (EIS) measurements.

Reinforced concrete is the subject of this paper,however, the EFE is applicable to a variety of othersystems and can be used to investigate: Corrosion behavior metallic particles in zinc-rich paints

Conductability of metallic particles in suspension

The ability of micro electrodes to probe within aprotective coating


6/13

EIS was performed

using two different

methods

Three electrodecell used in

literature

Four electrodecell being

Investigated


7/13

To investigate the effect of cover thickness on theimpedance spectra of a 4-electrode system

To estimate the potential of the bar-cement interfaceindirectly based on its contribution to the current andpotential distributions between the measuring electrodes

by comparing data collected to numerical simulations.

Note that the analysis was done by comparing the comparingexperimental impedance data to numerical simulationsbased on the frequency dependent distribution of potential

and current computed by a 3-D finite element method(FEM) software. Moreover, a comparison was done withprevious results simulated with a 2-D model


8/13

Nyquist Plot where

the imaginary part

of the impedance is

plotted against thereal part for different

frequencies. The Rp

is the diameter of

each plot.


9/13

3-D model


10/13

The distance between the two reference electrodes is agood approximation of the rebar length sensed.

At high frequencies the injected current flowspreferentially within the steel bar.

The apparent Rp of the reinforcing bar, measured bythe 4-electrode technique, can be related to theeffective Rp by considering the concrete resistivity.


11/13

Within realistic ranges of concrete resistivity and polarisationresistance values, the technique can be used for extracting meaningfulimpedance characteristics of the reinforcement bar

Why is this important?

Cross-section of Reinforcing Bar

(no corrosion)

Charge, e-

from applied, a.c.current

Longitudinal Section of Reinforcing Bar

(with corrosion)

Applied a.c. current is interrupted, at pitand d.c. current now generated by

corrosion

A.C. CurrentD.C. Current


12/13

Strengths of paper Interesting and relevant research topic Thorough and clear description of 4-electrode experiment (which

was my primary interest here)

Weaknesses of paper

Traditional 3-electrode EIS was done as part of the experimenthowever, no mention of it was made in the presentation of results oranalysis.

Lack of background information on the numerical analysisconducted, the presentation of which was heavy with electrical

jargon and difficult to follow.

Potential for further work As stated in the paper, the contact-less technique can be extendedto the detection and characterisation of corrosion on the surfaces ofembedded reinforcing steel bars


13/13

THANK YOU!

Documents

Review of the use of floating electrode for detection of corrosion of reinforcing steel