The selection of an equivalent circuit that faithfully models the steel - concrete interface response to the application of electrical signals is a fundamental aspect of the electrochemical determination of reinforcement corrosion rate. Experimental evidence is provided in favour of using a modified Randles circuit in which the corroding interface is characterised by a parallel combination of a constant phase element and a charge transfer resistance in series with a Warburg element. An advantage of having an appropriate model of the steel -concrete system is the possibility of carrying out studies of quality of the information that is extracted from the experimental data. A sensitivity-algorithm is applied with the object of identification of the conditions in which the system's response is dominated by certain parameters or combinations of them.