## 3 Chemical Tests  
### Need for Chemical Tests  
An analysis of numerous technical studies concerning repairs of RC structures after many years of operation shows that the most frequently recommended works are those consisting in the removal of visible damage to concrete and reinforcement. Therefore, the recommendations come down to a number of activities which, assuming a certain simplification, can be described as follows: Hacking off damaged or weakened concrete, cleaning the surface of concrete and the uncovered reinforcement, supplementation of significant reinforcement losses, application of a bonding layer (in some systems preceded by application of corrosion inhibitors on rebars), filling of deep losses, filling of shallow losses (patching), and (not always) application of protective layers. Typical polymer cement concrete (PCC) repair systems are usually recommended here.  
The range and scope of necessary repairs with the relevant requirements have been described in detail in a group of Polish standards PN-EN 1504--Products and systems for the protection and repair of concrete structures (part 1 to 10) [26].  
Such an approach leads to the restoration of the original geometry of the element (and restoration of reinforcement, if necessary). However, the success may be ostensible if the original concrete in structure is strongly carbonated or contaminated with harmful ions retained in the deeper layers. In such a case, the original concrete and the reinforcement are exposed to corrosion which starts virtually right after repair completion. The application of appropriate corrosion inhibitors does slowdown that process, but it progresses much faster than in new concrete anyway.  
One must also remember that supplementing the corroded reinforcement so that the original amount is restored, which is often done in practice, may prove insufficient. First, the deformations of the original and new reinforcement are not compatible. Second, the yield strength of corroded rebars is lowered [27]. The latter aspect is also related to chemical contamination of concrete and the possibility of a durable repair of the structure.  
Meanwhile, there is a simple and cheap method of determining the potential effectiveness of RC repairs throughout a longer period. In each case, one should conduct at least random examinations of the basic chemical features of the original concrete, including pH and the content of chloride and sulfate ions. Depending on the obtained results, the structure may:  
* Be repaired without additional treatment;
* Undergo additional treatment (e.g., re-alkalization or electrochemical chloride extraction ECE) if the results point to a corrosion threat, but the condition of concrete can be improved;
* Not be qualified for repair due to a significant threat to durability.  
Unfortunately, the last option is rarely applied in practice. Examples of the effects of such conduct shall be shown in the next chapter.  
The authors argue that in the case of every RC structure used for a long period or in conditions threatening it with concrete penetration by chlorine or sulfur compounds, the decision to repair the corrosive damage should be determined by conducting basic chemical examinations of concrete. Those examinations are relatively cheap and do not take much time. Their results, if interpreted correctly, allow one to make an informed decision about repairing the RC structure with its durability in mind.