## 4 Discussion Based on Practical Examples
### Technical Condition of the Structures--Correlation with Chemical Examination Results
It is worth noting that the power boilers supported by group B structures were supplied with imported coal with a very low content of sulfur compounds and hardly any contact with mine water. The test results for elements from structures A, C1, and C2 were much worse. The pH value was as low as 10 or even less (except the foundation in structures C). The chloride ion content was enormous--it exceeded the permissible values several times. The worst situation was in all elements from structure A. The same applies to sulfate ion content. The permissible values in the parts of structures C1 and C2 above the ground were drastically exceeded. The underground parts of structures C1 and C2 were an exception because their pH exceeded 11 and the content of chloride and sulfate ions fell within the permissible range. The above was caused by tight flooring which did not let harmful agents come into contact with the concrete surface. The technical condition of the facilities determined on the basis of a visual assessment of the structures (Table 4) perfectly corresponds to the abovementioned test results--all the elements above the ground showed extensive corrosive damage to concrete and rebars; corrosion reduced the original cross-section of some rebars by as much as 50% or more (Figure 3a,b and Figure 4a,b). Figure 2: Examples of corrosive damage: (**a,b**) corrosion of steel rebars in defected concrete cover. Simultaneously, the concrete in the underground parts of structures C1 and C2 retained its original structure and no reinforcement corrosion was found in the uncovered areas (the technical condition was found as satisfactory). The boilers on foundations A, C1, and C2 were supplied with Polish coal with a high content of sulfur compounds; in the case of A, the coal was supplied directly from the mine and was damp due to contact with water containing sodium chloride. In both cases, the RC structural elements were also very damp and had contact with solid products of combustion. The support structure of pipelines (D) showed relatively diversified results, but in all cases, the condition of structural elements was bad or very bad. In terms of pH value, a high threat of corrosion, especially concerning the columns was observed. The sulfate ion content was exceeded only in the columns, but the chloride ion content was drastically exceeded in all structural elements. The above was perfectly visible as enormous damage to concrete, reinforcing steel and additional steel elements (Figure 5a,b). Figure 4: Examples of corrosive damage in A facility: (**a**) concrete and steel corrosion, (**b**) traces of completely corroded stirrups. Figure 3: Examples of steel damage in one of the structure C: (**a**) corrosion of steel rebars with concrete damage, (**b**) locally interrupted reinforcement. In many cases, the concrete burst by swelling corrosion products (Figure 6a). The structure columns were embedded in concrete and confined in an external skeleton made of steel sections approximately 20 years ago. That concrete was strongly damaged (Figure 6b), which proves that the repairs had been conducted in conditions that had not ensured their effectiveness. Similarly, the repairing layers on the beams, made using one of the PCC systems, were destroyed. It must be mentioned that the sodium chloride source was processed water in the open channels under the support structure.