Electrochemical Properties of Oxide Scale on Steel Exposed in Saturated Calcium Hydroxide Solutions with or without Chlorides

Johan Ahlström,Luping Tang,Bror Sederholm,Johan Tidblad,Simon Leijonmarck

doi:10.1155/2018/5623504

Abstract

The electrochemical properties of various iron oxide scales on steel exposed in saturated calcium hydroxide solutions were investigated. The iron oxide scales were manufactured by different heat treatments and grinding processes and characterized using X-ray diffraction and scanning electron microscope. The electrochemical properties of the scales were assessed by measuring the corrosion potential and using electrochemical impedance spectroscopy and potentiodynamic polarization curves. It was found that wustite and magnetite are less noble compared to hematite but are more effective as cathodic surfaces. The results show that the electrochemical properties of the mill scale can be an important contributing factor in the corrosion of steel in concrete.

Highlights

Chloride induced corrosion of steel in concrete is an important deterioration mechanism for concrete structures
One explanation of the wide range is that studies have been conducted with steel samples in an as-received condition where the mill scale from production is intact or with modified surfaces obtained by, e.g., grinding, pickling, where the steel surface is without a mill scale
The manufactured oxide scales were analyzed with X-ray diffraction (XRD) and SEM/EBSD (SEM in combination with electron backscatter diffraction)

Summary

Introduction

Chloride induced corrosion of steel in concrete is an important deterioration mechanism for concrete structures. One explanation of the wide range is that studies have been conducted with steel samples in an as-received condition where the mill scale from production is intact or with modified surfaces obtained by, e.g., grinding, pickling, where the steel surface is without a mill scale. One effect is that a remaining mill scale decreases the electrical resistance and inhibits the formation of a passive film on the steel surface in concrete [8, 9]. Another effect is that the cathodic current is higher on a surface with a mill scale compared to a surface without mill scale [10] which affects the overall corrosion properties

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