Field measurements of corrosion rate of steel in reinforced concrete

The corrosion of steel reinforcing bars is one of the biggest problems facing owners of reinforced concrete structures today. Corrosion is initiated by cast-in or ingressing contamination and propagates out of sight until the damage level causes cracking or spalling. Many structure assessment strategies rely on a visual inspection to highlight problem areas. Remediation at this stage is much more costly than earlier preventative action. A more sophisticated strategy can make use of half cell potential mapping to locate regions of corrosion initiation. but this technique gives no evaluation of the severity of the problem. The linear polarisation resistance (LPR) method is a pcrturbativc electrochemical method which can give an evaluation of the instantaneous rate of active corrosion and which is gaining in popularity in Europe, USA and Australia. llowever corrosion is a dynamic process which may fluctuate with changes in the ambient environmental conditions. A corrosion rate measurement on one occasion may not give a representative evaluation of the severity of corrosion problem over an extended period. This paper reports on a continuous study of the linear polarisation resistance method on externally exposed reinforced concrete in the UK to evaluate the etTects of the environment on corrosion rate measurements. The results show how the etTects of temperature and rainfall can influence the measurements and guidelines arc suggested for using LPR to assess corrosion over an extended period.