# Monitoring of Reinforced Concrete Corrosion: Active and Passive Bars Exposed to Climate
## 2 Methodology  
In the field of research on reinforced concrete corrosion, potentiodynamic polarization tests are frequently employed as a rapid method for determining corrosion rates. These tests typically yield parameters such as corrosion potential and corrosion current density. In the case of polarization activation alone, the potentiostat-measured current density can be related to the corrosion current density by means of the Butler-Volmer equation. A linear polarisation resistance (LPR) was estimated by applying a polarisation value of \(\pm 20\) mV relative to the open circuit potential (OCP) and a scanning rate of 0.166 mV/s. Figure 1: Service life of structures. The corrosion rate was then calculated using the slope of the electric potential-cell current curve, minus the resistance drop, which was taken as Rp. The Stern-Geary equation was employed to ascertain the corrosion rate, icorr. In electrochemical impedance spectroscopy (EIS), an electric potential of varying frequency is applied to an electrochemical cell, and the resulting current's complex field is measured. A Randles-type equivalent circuit was employed to simulate the system's electrochemical response with a time constant [26; 29; 32]. In order to obtain accurate in-situ measurements of corrosion, it is essential to have proper control over the area being measured [26; 33]. Additionally, it is necessary to estimate the ohmic drop during the measurements, as is done in laboratory measurements. The methodologies employed may be categorised into two distinct groups: those that necessitate direct contact with the reinforcement and those that do not. The method of modulated current confinement utilises a guard ring during measurement [34]. To ensure accurate measurements, it is necessary to implement a system that controls the current to remain confined between the central counter electrode and the guard ring. This system comprises two reference electrodes known as 'confinement controller electrodes'. Their potential difference is used to verify that the electrical field remains the same with and without current applied [33]. This verification must be monitored during the current application, which takes approximately 100 s to reach a steady-state condition. This operation is electronically complex. During this time, the two reference electrodes (confinement controllers) provide information to the galvanostat so that it can apply more or less current through the guard ring to confine the current applied beneath the counter electrode. This process is known as'modulated confinement' because it requires monitoring both counters and actively varying the current applied through the guard ring during the measurement. Non-contact methods are based on the Wenner method for resistivity measurement [31; 35]. These methods have the advantage that it is not necessary to make a connection to the reinforcement; however, it is not possible to obtain the corrosion potential of the reinforcement. In this method, the current is applied by the external electrodes and the change in potential is measured by means of the two internal reference electrodes [36]. The external electrodes were small pieces of reinforcing steel, and the two internal reference electrodes were Ag/AgCl. Currents of 10-500 uA were applied. The difference in potential is measured by means of the two internal reference electrodes. The developments achieved in these studies make it possible to establish a correlation between the ohmic drop and the \(R_{p}\) values [36]. An electrical model has also been obtained to explain the behaviour of the system with respect to an external electric field [37]. This work presents a new measurement method called MONITORIZA, which accurately measures corrosion potential, resistivity, and temperature. The sensors used in this method are based on previous developments with over 25 years of research [23]. Measurements are scheduled every 2 h and the results are automatically analysed. The procedure is verified both in the laboratory and through in-situ measurements.