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Concrete – Corrosion – Application Note 22

Latest updated: May 6, 2020

Abstract

Reinforced concrete is the most widely used composite material for building construction. The service life of this material depends on the corrosion of the steel reinforcement in concrete mainly due to the chloride (Cl-) and dioxide species (CO2). One method to protect and reduce the corrosion rate of the reinforced concrete is called electrochemical realkalinisation.
In this note, the corrosion process of a metallic rod in a concrete block was investigated. The realkalinisation of the sample was performed in alkaline solution using chronopotentiometric technique. The effect of the realkalisation on the corrosion rate was estimated using Impedance, Linear polarization and cyclic potentiodynamic polarization

 

Introduction

During its lifetime, the metallic structure of a building is attacked by the environment, 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 part. 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. Then, at this acidic pH, the iron is no longer in its passive form but in its corrosive form. Consequently, the strength of the building is affected. For instance, the “Tour Perret” in Grenoble (Figure 2), which is the first edifice built in reinforced concrete in Europe in 1924, is currently falling apart because of this process.

 

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