The Onset of Chloride-Induced Corrosion in Reinforced Cement-Based Materials as Verified by Embeddable Chloride Sensors

Farhad Pargar, Dessi Koleva, H Kolev, Klaas van Breugel

Research output: Chapter in Book/Conference proceedings/Edited volumeChapterScientific

4 Citations (Scopus)

Abstract

The need for an accurate determination of the chloride threshold value for corrosion initiation in reinforced concrete has long been recognized. Numerous investigations and reports on this subject are available. However, the obtained chloride threshold values have always been, and still are, debatable. The main concern is linked to the methods for corrosion detection and chloride content determination in view of the critical chloride content itself. In order to measure the chloride content, relevant to the corrosion initiation on steel, destructive methods are used. These traditional methods are inaccurate, expensive, time consuming and noncontinuous. Therefore, the application of a cost-effective Ag/AgCl ion selective electrode (chloride sensor) to measure the chloride content directly and continuously is desirable. The advantage would be an in situ measurement, in depth of the concrete bulk, as well as at the steel/concrete interface.

The aim of this work was to evaluate the importance of the sensor’s properties for a reliable chloride content measurement. The main point of interest with this regard was the contribution of the AgCl layer and Ag/AgCl interface within the process of chloride content determination in cementitious materials. The electrochemical behavior of sensors and steel, both embedded in cement paste in a close proximity, hence in identical environment, were recorded and outcomes correlated towards clarifying the objectives of this work. The main point of interest was to simultaneously detect and correlate the time to corrosion initiation and the critical chloride content.

The electrochemical response of steel was monitored to determine the onset of corrosion activity, whereas the sensors’ electrochemical response accounted for the chloride content. For evaluating the electrochemical state of both sensors and steel, electrochemical impedance spectroscopy (EIS) and open circuit potential (OCP) measurements were employed. The results confirm that determination of the time to corrosion initiation is not always possible and straightforward through the application of OCP tests only. In contrast, EIS is a nondestructive and reliable method for determination of corrosion activity over time. The obtained results for corrosion current densities for the embedded steel, determined by EIS, were in a good agreement with the sensors’ half-cell potential readings. In other words, the sensors are able to accurately determine the chloride ions activity at the steel/cement paste interface, which in turn brings about detectable by EIS changes in the active/passive state of steel.

The electrochemical response was supported by studies on the morphology and surface chemistry of the sensors, derived from electron microscopy (ESEM) and X-ray photoelectron spectroscopy (XPS). It can be concluded that the accuracy of the sensors, within detection of the time to corrosion initiation and critical chloride content, is determined by the sensors’ properties in terms of thickness and morphology of the AgCl layer, being an integral part of the Ag/AgCl sensors.
Original languageEnglish
Title of host publicationConcrete Durability
Subtitle of host publicationCementitious Materials and Reinforced Concrete Properties, Behavior and Corrosion Resistance
EditorsL.E. Rendon Diaz Miron, D.A. Koleva
PublisherSpringer
Pages23-55
ISBN (Electronic)978-3-319-55463-1
ISBN (Print)978-3-319-55461-7
DOIs
Publication statusPublished - 2017

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