Ground-penetrating radar and microwave tomography to evaluate the crack and joint geometry in historical buildings: some examples from Chania, Crete, Greece

Diagnostics of historical buildings is crucial for the definition of a reliable restoration project or in the study of the seismic behaviour of a building. This was one of the objectives of the international project 'Advanced techniques for Seismic RISK Reduction in Mediterranean Archipelago Regions' (SE RISK). In particular, in the framework of the project, the present work is concerned with the exploitation of GPR for the inspection of two historical buildings of Crete Island, Greece, the Prefecture of Chania and Venizelo's House. In particular, the surveys aim at gaining information about the structure of the floors fracture areas and structural joint zones via high-resolution measurements thanks to the use of a 1500 MHz nominal centre frequency antenna. With regard to the Prefecture of Chania, the specific aim of the survey was to detect and localize fracture areas and joint zones thanks to a scanning line acquired orthogonally to the 'defects visible' at the surface of the floors. In Venizelo's House, the aim was to detect and localize fracture areas in the stone masonry. Besides the classical time data processing, a microwave tomography based approach was applied to the data. The comparison between the two approaches has shown that the results of both the procedures are in good agreement suggesting both the reliability of the standard processing routine and the new microwave approach. In addition, the microwave tomographic approach provides more detailed and higher resolution images allowing an easier data interpretation. The microwave tomographic approach also offers the advantage of performing an automatic procedure, thus mitigating the risk of introducing subjective elements as in the case of the classical approach.