Macrocell and microcell corrosion of steel in ordinary Portland cement and high performance concretes

Microcell corrosion is the term given to the situation where active corrosion and the corresponding cathodic half-cell reaction take place at adjacent parts of the same metal. Macrocell corrosion can occur when the actively corroding bar is coupled to another bar which is passive, either because of its different composition or because of different environment. The present study was undertaken to determine the influence of concrete type and properties on the relative microcell and macrocell corrosion rates. The samples were monitored for more than 3 years and the results confirm that microcell corrosion is the major mechanism in corrosion of steel reinforcing bars in concrete. Furthermore, results show that, for high performance concrete, the difference between microcell and macrocell corrosion is far more significant than for ordinary Portland cement concrete because of its high resistance to ionic flow.