Theoretical analysis of the measurement of polarisation resistance in reinforced concrete

Polarisation resistance (R-p) technique based on Stern-Geary equation is one of the most widely used methods of measuring corrosion rate of reinforcement in the field. With the aid of a sensorised guard ring, this electrochemical technique is claimed to be able to determine corrosion rate (I-corr) within a given measuring area. However, there are three theoretical problems in the application of this technique: (1) the original Stern-Geary equation is applicable in a uniform corrosion system at its corrosion potential, whereas the reinforced concrete structure may be subjected to non-uniform corrosion or strong polarisation by macro-cell galvanic effects or imposed currents; (2) the value of the parameter B in the original Stern-Geary equation has been estimated to fall within the range 25-52 mV. This may not be suitable for all the corrosion cases of reinforced concrete structures; (3) The polarised surface area of steel may theoretically not always be fully confined by the sensorised guard ring when the cover concrete is too thick. This paper aims at discussing the theoretical problems. A general relationship between the dissolution rate of steel reinforcement and the measured polarisation resistance is deduced under general conditions. The range of B value is also analysed based on all the possible corrosion situations of reinforced concrete. Furthermore, unsatisfactory confinement by sensorised guard ring on a thick cover concrete is demonstrated. (C) 2000 Elsevier Science Ltd. All rights reserved.