## 5 Discussion
### Assessment of Benefits of the Modified Testing Methodology
Consequently, precise and sensitive instruments used for the analysed measuring systems on concrete cores produced instable results. The procedure of moving the reference electrode 4 closer to the rebar 3 through the performed opening 6 (Figure 14b) within a distance of only a few millimetres, proposed in this paper, resulted in significantly lower resistance of concrete, which was within a green frame (Figure 14d). As a result, we obtained the proper compensation of \(IR\) drop and stability of the results. Providing better electrical contact between all the electrodes of the measuring system was the final benefit. Apart from the working electrode 3 enclosed with concrete, the reference electrode 4 and the auxiliary electrode 1 are usually applied through the wet or damp spacer 7 (Figure 14a). Introduction of the additional source of humidity, particularly during the tests simulating dry environmental conditions, could considerably change the measurement results. In the paper [64] which described modelling of steel corrosion, moisture content of concrete was associated with the level of pore filling, and consequently with coverage of rebar surface with pore solution (Figure 14e). In the electrochemistry limiting the electrode surface is related to absorption of inert substances, where the degree  
Figure 14: Benefits obtained from using solid reference and auxiliary electrodes for polarization measurements of concrete cores drilled from the structure: (**a**) drilled concrete cores with electrodes conventionally applied on the bottom; (**b**) drilled concrete core with electrodes placed in an opening or applied on the surface; (**c**) polarization distribution for the working electrode at the auxiliary electrode on the bottom and side surface, cf. [32]; (**d**) compared resistance of concrete layer between the reference and working electrode, with reference to cases (**a,b**); and (**e**) an impact of increased humidity in the cylindrical specimen on steel covering with pore solution, 1—applied auxiliary electrode, 2—solid auxiliary electrode, 3—a rebar fragment used as the working electrode, 4—reference electrode, 5—measurement probe, 6—an opening in the core concrete for the reference electrode, 7—wet or damp spacer, \(R_{\Omega}\)—resistance of concrete layer between the reference and the working electrode, \(\theta\)—degree of steel covering with pore solution, \(P\)—potentiostat—description and notes in the text. of electrode covering is defined by the value \(\theta\). Following the same procedure, the rate of electrode reactions was assumed to decrease proportionally to the contact surface with pore solution. Assuming that the reduction of corrosion rate referred to the same degree to cathodic and anodic reactions, and that no other process connected with a change in moisture content of concrete occurred, then a change in the relations \(\eta\)-\(i\) expressed by the Equations (6) and (7) was related to a new term \(\frac{RT}{\alpha_{e}T}\ln\theta\). Taking into account that component in the Equations (6) and (7), the following relationships (14) were (15) obtained--cf. [34]  
\[\eta_{a}=-\frac{RT}{\alpha_{e}F}\ln i_{0,Pe/Fe^{2+}}+\frac{RT}{\alpha_{e}F}\ln i _{a}-\frac{RT}{\alpha_{e}F}\ln\theta \tag{14}\]  
\[\eta_{c}=\frac{RT}{\alpha_{e}F}\ln i_{0,O_{2}/OH^{-}}-\frac{RT}{\alpha_{e}F} \ln(-i_{c})+\frac{RT}{\alpha_{e}F}\ln\ \theta \tag{15}\]  
On the other hand, applying the counter electrode in the form of conductive coating using the painting technique and permanently fixing the reference electrode in the core using cement grout, the electric contact with concrete was provided without the damp spacer. The final filling of concrete pores after long exposure in the dry environment is shown in the upper part of Figure 14e. The potential impact of additional moisture content in the volume of concrete pores is presented in the bottom part of this Figure. In this case, additional moisture content of concrete resulted in an increased coverage of steel with pore solution (an increase in coefficient \(\theta\)).