This recommendation covers the description of non-destructive electrochemical test methods for the estimation in large size concrete structures of the instantaneous corrosion current densiti, , expressed in , by means of the so called Polarization Resistance technique, , in order to asses the condition of embedded steel reinforcement related to its corrosion. The values of , can be used to assess the rate of degradation of concrete structures affected by reinforcement corrosión. However, the cannot give information on the actual loss in steel cross section which, at present, only can be assessed by means of direct visual observation. Values of the free corrosión potential or half-cell potential, [V], of the embedded reinforcing Steel and of the electrical concrete resistance, , are obtained as preliminary steps of the measurements. Values of the concrete resistivity, , can be calculated from values providing the geometrical arrangement of the electrodes enables this calculation. Both parameters, and (or ) may be used to complement the reliability of the measurements.