ABSTRACT

The formation of the corrosion products of iron (i.e. rust) involves a substantial volume increase, i.e. the volume of the corrosion products, assuming they are mainly Fe(OH)3, is some four times greater than that of the corroding iron. In reinforced concrete, such an expansion is subjected to volume restraint and, therefore, when rust is formed, pressure is exerted on the surrounding concrete. At some stage, this pressure may cause the cracking of the concrete cover over the reinforcement, and the corrosion is then aggravated due to the readily available oxygen and moisture, which are conditional for the corrosion process to proceed. At a more advanced stage, spalling of the concrete cover occurs, and the unprotected reinforcement is exposed to environmental factors. The continued corrosion of the reinforcement gradually reduces the cross-sectional area of the reinforcing bars (i.e. rebars) and thereby, also, the bearing capacity of the structural element involved. Hence, if no remedial means are employed, and depending on the severity of the exposure conditions, complete deterioration and failure may follow, and the end of the structure, the so-called ‘service-life’, is reached.