Page 22 - Concrete-Technology-Interacted_Book_Prof-MIK_Neat

Reinforcement
corrosion

9.1 Introduction

Corrosion of reinforcing steel in concrete is the most significant deterioration process
affecting reinforced concrete structures. It has, for example been estimated that the
remediation of concrete bridges in the USA undertaken as a direct result of corrosion of
the reinforcing steel cost the US state departments $5 billion in the year 2000 (Federal
Highway Administration, 1999). In addition to bridges, other highway structures, buildings
and marine facilities are affected. An estimate of the cost incurred in the UK in 1997 as
the result of all forms of corrosion damage to concrete was £750 million (BRE, 2001).

The two most important causes of corrosion of the reinforcing steel are carbonation
and chloride contamination of the concrete. Carbonation is a problem that mainly affects
buildings. Chloride contamination affects structures that are exposed to de-icing salts or
marine environments. Other less common causes of corrosion are acidic gases such as
sulphur dioxide, aggressive ions such as sulfates, fluorides and bromides and stray
electrical currents.

Corrosion is accompanied by a loss of rebar cross-section and a build-up of corrosion
products. The corrosion products occupy a larger volume than the original metal from
which they were derived (Figure 9.1). This generates the tensile stresses causing cracking
and spalling of the concrete cover. Very often the first indication of a problem is the
appearance of a crack following the line of reinforcement (Figure 9.2).

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