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9/2 Reinforcement corrosion
Figure 9.1 Expansive corrosion products on steel in chloride contaminated concrete.
Figure 9.2 Corrosion induced by carbonation of a concrete beam which has resulted in a crack in the
concrete cover following the line of the reinforcement.
9.2 The corrosion process
Corrosion may be defined as the deterioration of a metal by reaction with species in the
environment to form chemical compounds. At room temperatures it is an electrochemical
process; that is, the chemical reactions occur in conjunction with the flow of an electric
current. This is illustrated in Figure 9.3.
The metal dissolves at one site to form positive ions leaving free electrons in the metal.
A reaction that results in a more positive product is termed oxidation, and the location
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