The methodology for diagnosing concrete pathologies involves the combination of visual assessment of the structure with appropriate instrumental methods of diagnosis damage and analysis techniques to establish sufficient evidence of the condition of the structure. Choosing correctly the location and selection of samples to be examined is important for drawing correct conclusions concerning the whole structure. A sufficient number of inspections should be conducted in order to select the correct intervention strategy and prevent misjudging the overall part of the structure that needs to be repaired.
Following international practices, structures inventories and hierarchical valuations should be conducted in three successive phases:
- Primary inspection: Quick visual inspection
- Secondary screening
- Tertiary screening
An experienced crew must conduct the inspections under a specialised engineer’s guidance, ensuring the following:
• The implementation of appropriate diagnosis methods, including the use of necessary equipment.
• The selection of the appropriate inspection and investigation methods and the location of the elements and parts of the structure to inspect and investigate according to the type of inspection and the type of failure to investigate.
• The elaboration of an accurate and detailed description of the investigation’s results, and an interpretation of them.
Ideally, an on-site diagnosis always starts with a visual inspection to get an overall picture of the structure and the damage it has incurred.
Visual observations must be recorded on rough plans of floor plans and elevations. The drawings shall identify all the elements inspected, including their location and orientation. Specifically, the visual inspection of the condition of a structure to determine whether it has defects or damages will include the following issues to be examined and recorded on technical drawings:
• Detachments of coatings.
• Excess of rising or falling moisture in the wall structures and wooden supports.
• Existence of cracks.
• Existence of vertical cracks parallel to the reinforcement, indicating the presence of corroded reinforcement.
• Disaggregation of the structural mortar.
• Chromatic deterioration of materials, particularly after fire.
• Presence of biological damage on the structure.
However, it should be noted that there are some limitations to visual inspection, such as diminished reliability and subjectivity of interpretation, and their results are only qualitatively useful for assessing the condition of a structure. In contrast, the results of instrumental tests are considered reliable.
When the visual inspection is completed, a “working hypothesis” must be made about the cause of the damage. Based on this hypothesis, diagnostic methods can be selected. If the initial visual inspection reveals problems further investigations should be conducted. The structure should be tested for structural integrity, the geometry of critical load-bearing elements verified, and the approximate seismic loads calculated, among others.
After all planned inspections have been completed, visual observations and the results of further investigations should be combined to determine the cause, extent, and potential further development of defects. In the absence of an accurate determination, additional inspections should be planned and performed.