## 5 Discussion
The tests on chloride content in concrete cover, both in the tanks (Figure 7c,d) and the silos (Figure 11c,d) demonstrated no risk caused by high concentration of Cl\({}^{-}\) ions in the pore solution. According to the standard [56] 0.4% by weight of cement in concrete is considered as the limit value of chloride concentration in reinforced concrete units. Chloride content along the whole thickness of 40 m cover in the tanks T1 and T2 did not exceed 0.2%. The chloride concentration also did not increase near rebars in the silos S1 and S2; however, these values were slightly higher in the tanks and locally exceeded 0.3%. Some papers [57,58] reveal that the most reliable criterion for evaluating corrosion risk for reinforcement posed by chloride ions was the so-called Hausman criterion [59]  
\[\frac{\text{C}_{\text{Cl}^{-}}}{\text{C}_{\text{OH}^{-}}}=0.6 \tag{10}\]  
This criterion includes the total effect of concentration of chloride C\({}_{\text{Cl}^{-}}\) and hydroxide C\({}_{\text{OH}^{-}}\) ions on the surface of reinforcing steel, which is contact with pore solution. With an increasing concentration of OH\({}^{-}\) ions, Cl\({}^{-}\) ions are displaced form steel surface, which impeded decomposition of a passive layer by chlorides in the pore solution. Knowing both the distribution of pH values and concentrations of chlorides ions, obtained from the tests conducted on the tanks and the silos, this criterion (10) could be directly applied assuming that C\({}_{\text{OH}^{-}}\) was the function of pH in accordance with the following Formula (11)  
\[\text{C}_{\text{OH}^{-}}=10^{\text{pH}-14} \tag{11}\]  
Figure 13: Distribution of corrosion current densities \(i_{corr}\) presented as horizontal bar graphs, obtained for reinforcement of cylindrical concrete cores drilled from reinforced concrete silos for cement: (**a**) results for the silo S1; and (**b**) results for the silo S2; blue bars represent the tests at air temperature \(T=30\)\({}^{\circ}\)C and relative humidity \(RH=99\%\); green bars represent tests at 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. The calculated ratios of concentrations C\({}_{\text{CI}^{-}}\) and C\({}_{\text{OH}^{-}}\) for each thickness layer of concrete cover in the cores are presented as the distribution of curves in Figure 7e,f, and Figure 11e,f. By illustrating the coordinate of 0.6 in the form of a horizontal dashed line corresponding to the ultimate level, it is easy to visually assess whether the Hausman criterion (10) is met or exceeded. The analysis of results for concrete cores drilled from the tanks T1 and T2 (Figure 7e,f) clearly indicated no risk of chloride-induced corrosion of the reinforcement. The above confirmed the previously analysed very satisfactory high values of pH (Figure 7a,b) and desired low concentrations of chloride ions (Figure 7c,d). For the silos S1 and S2, the limit level based on the Hausman criterion was definitely exceed for the majority of concrete cores (Figure 11e,f). It means chloride-induced corrosion risk for the reinforcement even though the analysis of only chloride concentrations with reference to cement weight in concrete did not indicate that risk (Figure 11c,d). The obtained results were obviously affected by the increased concentration of hydroxide ions near reinforcing steel, which was caused by increased pH of pore solution (Figure 11a,b).