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TECHNICAL PAPER

CORROSION MEASUREMENTS

IN CONCRETE STRUCTURES AND

INTERPRETATION OF DATA CARMEN ANDRADE*

Abstract if corrosion rate is high, the deleterious consequences will be
detrimental in short time after depassivation. Therefore, the
The measurement of the corrosion demands certain knowledge of the corrosion rate after depassivation is of critical
specialization as the best techniques are of electrochemical interest for predicting service life in new and, particularly, in
nature. The most common techniques used for the corrosion existing structures. In spite of this interest, the measurement of
assessment are based on corrosion potential, resistivity, and the corrosion rate has attracted very seldom interest and limited
polarisation resistance. The use of the galvanic current is not data is available in literature [2-10] Other aspects, however, related
approached because, it does not give better information than to corrosion (corrosion potential and resistivity) have been more
the polarization resistance technique in most cases. Corrosion measured due to their simplicity, although not of quantitative
potential provides information about the corrosion risk, and nature regarding the corrosion. They have limited application
resistivity is directly related to the moisture content/humidity when applied alone, although they are very important
level in concrete. Among these, the polarisation resistance is complement when measured together with the resistance of
the only technique that can quantify the loss of metal. In present polarization, which is the basic measurement technique able to
paper, their fundamentals are briefly described, together with quantify the corrosion process.
some general guidance on the meaning of their values and
where those ranges can be found. The methods that enable the The present paper briefly presents the basis of the main
correct measurement of the corrosion rate in large structures are three techniques associated in the polarization resistance and
also described. These measurements can be made using probes possibility to be introduced in sensors embedded in concrete.
that are embedded in or attached onto existing structures. Further is commented on their interpretation. A few guidelines
Finally, a model of prediction of the corrosion propagation is on interpretation of data are also summarized in the Rilem
discussed. Recommendations and in the ASTM-G-59/2014, ASTM G-876-15
and ASTM-C-1876-19 [6-8] .
Keywords: Electrochemical techniques, corrosion potential,
polarization resistance, corrosion rate, propagation. 2. TECHNIQUES FOR CORROSION
MEASUREMENT
1. INTRODUCTION
The only technique that quantitatively measures the corrosion
Among the deterioration risks of reinforced concrete, rate is the so named Polarization Resistance (R p ) or Linear
reinforcement corrosion is the most frequent one. In spite, Polarization Resistance (LPR). To measure R p , it is necessary to
there are several preventive techniques as they are: cathodic simultaneously measure the corrosion potential (E corr ) and the
protection, inhibitors, stainless steel reinforcement, their initial concrete resistivity (ρ or Ro). The three are summarized next.
higher cost make their use exceptional and in consequence They are generally applied to all systems metal-electrolyte
the steel protection is depending solely of the concrete although either the resistivity as the polarization resistance need
cover permeability to aggressive substance entering from the “geometrical standardization”, that is they need to be referred
environment. to a volume or steel area.

The steel is passivated by the high alkalinity of the hydrated 2.1 Corrosion Potential, E
cement phases. Reinforcement corrodes on arrival of chloride corr
[1]
or carbonation front to the rebar level . When steel corrodes, The measurement consists in making contact to the
several kind of oxides forms and diffuse out through the pore reinforcement as indicated in Figure 1 [2,7] . The difference
network or they accumulate at the steel-concrete interface. In between electrical potential of the rebar and the reference
addition to the conditions enabling the active corrosion, other electrode is measured using a voltmeter. The “reference
key aspects in rate of corrosion. If the rate is low, the corrosion electrode” are used because it has a fixed potential. The
may be not dangerous from a structural point of view. However, values measured are always those of the rebar with respect to

THE INDIAN CONCRETE JOURNAL | NOVEMBER 2020 7
*Corresponding author : Carmen Andrade, Email: candrade@cimne.upc.edu