## 5 Discussion
Because it was not possible to unambiguously determine two critical sets of parameters \((T-RH)\) for the tanks, this issue can be the reason for further searching for more combinations of these parameters in future. In this case, as the determined values of corrosion current density were similar, usually in the\"low corrosion\" range, searching for the combination of \((T-RH)\) parameters would not affect the conclusions concerning the corrosion state of the tanks. However, the analysis of polarization tests conducted on the reinforcement of cores drilled from the silos S1 and S2 give other observations concerning the impact of determined critical parameters of relative humidity and air temperature at the structure. In the determined thermal and humidity conditions favourable for the development of reinforcement corrosion (\(RH\) = 95% i \(T\) = 30 \({}^{\circ}\)C), the obtained polarization curves (Figure 10b,d) were noticeably shifted towards lower potentials and higher values of corrosion current density compared to the curves obtained at lower temperature and relative humidity (Figure 10a,c). The specified direction of curve shift was related to the control over corrosion activation where higher temperature and higher concrete conductivity, which was caused by greater humidity, had a significant impact on the increased rate of reactions (2) and (3) in accordance with the relationships (5) and (6). Following the same process as for the analysis of polarization results obtained for the reinforcement in cores drilled from the tanks, the results for cores from the silos obtained from the method of linear polarization resistance of the corrosion current density \(i_{corr}\) are presented in Tables A3 and A4 of the Appendix A. The obtained values \(i_{corr}\) are compared on bar graphs in Figure 13. The analysis of graphical presentation of distributed densities of corrosion current for both tested silos quite clearly confirmed predictions about the critical parameters of humidity and temperature which could maximize or minimize corrosion rate. High relative humidity and air temperature (blue bars) caused the expected increase in corrosion current density even to the level of 1.42 \(\mu\)A/cm\({}^{2}\). On the other hand, low relative humidity and air temperature resulted in significant reduction of corrosion current density, which in only one case (0.38 \(\mu\)A/cm\({}^{2}\)) resulted in exceeding range of values characteristic for passivation. Figure 12: Distribution of corrosion current densities \(i_{corr}\) presented as horizontal bar graphs, obtained for reinforcement of cylindrical concrete cores drilled from reinforced concrete tanks for fresh water: (**a**) results for the tank T1; and (**b**) results for the tank T2; blue bars represent the tests in water with a temperature \(T\) = 7 \({}^{\circ}\)C; green bars represent the tests at the air temperature \(T\) = 30 \({}^{\circ}\)C and relative humidity \(RH\) = 99%; information in orange above the graphs show corrosion risk for reinforcement in concrete of the tested cores. According to the proposed testing methodology (Section 2.3), evaluation of causes of corrosion was a complementary and important part to testing corrosion rate for reinforcement in the cores drilled from the structure. Distributions of the main factors specifying conditions favourable for corrosion development were determined along the cover thickness in both analysed types of structures -- the tanks and the silos (Figures 7 and 11). For the cores drilled from the tanks T1 and T2, the obtained pH values noticeably exceed 12, except for the external ones near a 10-mm cover (Figure 7a,b). On the other hand, for the silos S1 and S2 (Figure 11a,b) the pH profile significantly varied depending on the place of drilling the core. Moreover, considerable drops in pH values, often below the range of 11.0-11.5, were observed. They were found to initiate decomposition of passive layer of reinforcing steel in concrete.