Abstract
Techniques for inspection/ monitoring of the corrosion of reinforcing steel in concrete structures are at present limited to either mechanical inspection, chemical analysis and/or iso-potential ('half cell') mapping. In all cases these techniques can only provide information on the likelihood, or otherwise, of the presence of corrosion. But in particular they do not provide information on the rate or type of corrosion occurring.
New electrochemical techniques have been applied which allow both corrosion rate and corrosion type (i.e. general corrosion, pitting, etc.) to be estimated.
A 'Guard Ring' method, where a central auxiliary electrode polarises the reinforcement locally whilst the outer ring simultaneously supplies polarisation to the surrounding mat, is described and has been successfully used for linear polarisation and electrochemical impedance determinations. It should be noted that absolute polarisation resistance cannot normally be obtained on steel in concrete but that apparent polarisation resistance is able to assess the comparative corrosion rates.
Electrochemical noise measurements, the self generated fluctuations of potential and current, were also used to estimate the corrosion rate and assess the degree of localised corrosion. In particular a polarisable platinum probe electrode may be used to advantage for field applications of the noise determinations.
