When working on conservation projects of historical masonry structures, the main challenge is to ensure its structural safety having little information about the existing building. Uncertainties may concern materials, geometry and existing damage. The success of any structural retrofitting measure, which needs to fulfill the criteria of minimum intervention and compatibility with cultural heritage values, essentially depends on our ability to properly understand the structure. Moreover, the inspection is further limited due to the need of following a non-invasive approach that does not harm the valuable fabric.
The present paper proposes new systems and methods to inspect the interior of historical masonry walls. The system is based on a technique called tomography, which is an imaging technique that can produce images of the cross-section of an object based on the transmission of any kind of penetrating wave. The system designed and fabricated by the research team is meant to obtain images of the interior of historic walls based on acoustic wave propagation. Multiple acoustic waves are generated by means of hitting the wall surface on multiple points. At the opposite side, a remote sensing laser vibrometer measures vibrations from a distance on different points, recording the acoustic signal when it reaches the opposite surface.
The technique is fully non-destructive. The research has specifically aimed to automate the inspection, which, currently, is typically performed manually, consuming much time at operational and processing level. That is why their use is limited in practice. The research acknowledges that detailed information about the interior of heritage structures obtained (inner geometry or damage) is essential for conservation purposes and for making decisions on how to intervene. The system has been tested in six masonry walls at the laboratory and shows that the acoustic wave propagation is clearly influenced by the geometric characteristics of the cross-section.
Acknowledgments
The authors would like to specially thank and dedicate this work to the memory of the stonemason Rodrigo de la Torre Martín-Romo, who built the masonry walls and whose insight and expertise was essential to decide the most appropriate masonry typologies that are most representative of historical masonry constructions