## 5 Discussion  
Comparative Analysis of Test Results for Two Different Structures with Reference to the Applied Diagnostics Method  
As expected the values of corrosion \(T\) and relative humidity \(RH\) affecting corrosion in the surrounding of the tested structures and determined from the historical weather data resulted in the variation of shapes of obtained polarization curves (Figures 6 and 10). For the curves obtained for cores drilled from the tanks shown in Figure 6, there was a clear shift of all the curves towards positive values of potential at temperature \(T\) = 30 \({}^{\circ}\)C and relative humidity \(RH\) = 99%, which was related to monitoring the corrosion process through the reaction of oxygen depolarization. Total immersion in water limited oxygen and consequently reduced the rate of cathodic reaction. Hence, corrosion potentials approximated to potential of the iron electrode. However, no clear shift of the curves towards any (greater or smaller) corrosion current densities was observed at changed conditions in the chamber. But in the cores drilled from the tank T2--the tests in water--the curves tend to shift towards greater densities of corrosion current, while those drilled from the tank T1 were usually maintained in the same zone. Densities of corrosion current \(i_{corr}\) were determined for each polarization curve shown in Figure 6. Generally, two methods can be employed for this purpose. The first method consisted in extrapolating straight anodic and cathodic sections, and then determining the searched density of corrosion current at the intersection (cf. Figure 1a). The second method of linear polarization resistance (LPR) to determine densities of corrosion current is discussed in this paper [55]. This method included the occurrence--on the arithmetic scale of current densities--of the proportional ratio between corrosion rate and the slope of the polarization curve (cf. Figure 1b). This relationship (8) is referred to as polarization resistance \(R_{p}\)  
\[R_{p}=\left.\frac{dE}{di}\right|_{i\to 0,\ E\rightarrow\mathcal{E}_{corr}}, \tag{8}\]  
which is reversely proportional to corrosion density \(i_{corr}\)  
\[i_{corr}=\frac{b_{a}b_{c}}{2.303\ R_{p}(b_{a}+b_{c})}. \tag{9}\]  
Parameters \(b_{a}\) and \(b_{c}\) in the Equation (9) are constants of anodic and cathodic reactions, respectively (cf. Figure 1a). The detailed results from the analysis with the calculated densities for corrosion current are shown in Tables 12 and 13 of the Appendix A. It should be emphasized that the value \(i_{corr}\) of polarized area of the reinforcement \(A_{p}\) taken in the equations, each time was precisely determined after crushing core concrete in the testing machine and removing fragments of the tested rebars. For an easier comparative evaluation of the obtained test results, corrosion current densities \(i_{corr}\), based on values from Tables 12 and 13, are presented in Figure 12 in the form of horizontal bar graphs. Distribution of the values \(i_{corr}\) was divided into two parts characteristic for each of the two tested tanks. Moreover, the values \(i_{corr}\) obtained at the temperature \(T\) = 30 \({}^{\circ}\)C and maximum relative humidity \(RH\) = 99% are in green, while the values obtained for concrete cores in contact with water at the temperature of 7 \({}^{\circ}\)C are in blue. The analysis of these results does not give a clear answer as to which of these two sets of extreme temperature and relative humidity intensify the corrosion process of steel in concrete. In the tank T1, the reinforcement covered with concrete that is contact with water having a temperature of 7 \({}^{\circ}\)C can be regarded as the most prone to corrosion, while in tank T2, strongly damp hot air (\(T\) = 30 \({}^{\circ}\)C, \(RH\) = 99%) was the source of intensified corrosion processes of the reinforcement.