## 5 Discussion
### Assessment of Benefits of the Modified Testing Methodology  
The employed methodology described in point 2.3 delivers benefits in four aspects. First, which was the main topic of this paper, natural variability of corrosion rate over a long service life of the structure was simulated in the climate chamber on the cores drilled from the structure. Therefore, the extreme values of corrosion current density were obtained, which were similar to the effect produced during a continuous, long-term monitoring of the structure. The second benefit was the precise determination of the polarized (tested) surface area of the reinforcement. The range of current impact in the structure during the polarization measurements was not known because according to [44], this range was determined by the present corrosion rate and concrete conductivity. The equipment with a double counter electrode, where the outer electrode was used as the guard ring [60; 61; 62; 63] is usually employed to reduce the polarization range and precisely determine the tested surface area. As it was mentioned in the introduction part, unfortunately the application of the guard ring is not always effective, particularly when the crossing multi-layer reinforcement is present in the tested element or when local corrosion is observed. On the other hand, drilling of the cores with fragments of rebars caused that the counter electrode 1 (Figure 14) applied on the core base or the coated counter electrode 2 applied on the side surface of the core (Figure 14b) had considerably greater surface area than the working electrode 3 (a rebar fragment). The paper [32] described simulation with FEM, within which distributions of the polarizing potential were analysed after applying the electrode on the bottom of the cylindrical specimen. As illustrated in Figure 14c, distributions of potential were different, but each time the rebar was uniformly polarized on the whole contact area between concrete and steel. Moreover, the tested surface, including the surface of ribs, could be precisely measured after completing the tests because the reinforcing steel was not smooth. The third advantage was the minimized ohm drop of potential between the working electrode 3 and the reference electrode 4. The distance in the electrochemical cell, illustrated in Figure 2, between the working electrode 1 and the reference electrode 2, with Luggin capillary 6 was a few millimetres. This small layer of solution between the electrodes was characterized by some resistance \(R_{\text{\tiny{D}}}\), which in the theoretical description is expressed by introducing additional members \(i_{a}R_{\text{\tiny{$\Omega$}}}\) and \(i_{c}R_{\text{\tiny{$\Omega$}}}\), to the relationships \(\eta\)-\(i\) defined by the expressions (6) and (7), giving the following Formulas (12) and (13)--cf. [34]. \[\eta_{a}=-\frac{RT}{\alpha_{a}F}\ln i_{0,Fe/Fe^{2+}}+\frac{RT}{\alpha_{a}F}\ln i _{a}+i_{a}R_{\text{\tiny{$\Omega$}}} \tag{12}\]  
\[\eta_{c}=\frac{RT}{\alpha_{c}F}\ln i_{0,O_{2}/OH^{-}}-\frac{RT}{\alpha_{c}F}\ln (-i_{c})+(-i_{c})R_{\text{\tiny{$\Omega$}}} \tag{13}\]  
In the era of modern measuring devices, the effect of the unfavourable drop of \(IR\) on shapes of the polarization curve had some significance during the tests performed in the electrochemical cell. In front of each recorded measuring point modern potentiostats actively compensate the effect of potential drop across the resistor during formation of the polarization curve. However, the universal high response potentiostats are calibrated against small drops of \(IR\). On the other hand, in traditional measurements performed on concrete structures, the electrode is applied through the probe 5 (Figure 14a), in which the above mentioned counter electrode 1 and the reference electrode 4 were integrated [60, 61, 62, 63]. Resistance of concrete cover layer \(R_{\Omega}\), presented within a red frame in Figure 14a, was greater by a few orders than in the electrochemical cell, reaching even the value of a few k\(\Omega\).