A multidisciplinary approach for the diagnostics of the stone building materials of architectural structures

Vienna - Austria

The integrated use of non-destructive geomatic and geophysical techniques such as close-range
digital photogrammetry, laser scanner techniques, thermography, sonic and ultrasonic methods,
resistivity, etc... for the diagnostics of the stone building materials of architectural structures has
become increasingly dependent on the integration of different disciplines of applied research. As
is well known many historic monuments are characterized by severe damage due to temporal
degradation, problems caused by differential settlements of the foundations and various types of
natural hazards. Therefore it is of great interest to test and develop effective, integrated non
invasive procedures to detect the conservation state of the building materials of historic
structures, and identify and prevent their potential vulnerability in order to preserve their intrinsic
characteristics for a long time.
For extensive applications, as well as for investigations on monuments or large architectural
elements, scanning and digital high resolution images are particularly useful, thanks to their
limited cost, high production and relatively simple reproducibility of the tests. These techniques
give useful information on the shallow conditions of the investigated materials. Geophysical
techniques such as the ultrasonic and resistivity methods are non-invasive and are considered the
most appropriate to evaluate the internal structure and assess the quality of the stone materials
of the architectural heritage.
This paper presents an integrated approach that combines advanced geomatic survey procedures,
such as close-range photogrammetry (CRP) based on high resolution images and Terrestrial Laser
Scanner (TLS) techniques with a few geophysical techniques such as the ultrasonic and resistivity
ones in order to test the effectiveness of the integrated approach in providing an effective
diagnosis of stone building materials in the Basilica di San Saturnino (Cagliari – Italy). This Basilica
is the oldest monument of the town of Cagliari (Italy) and represents an interesting synthesis of
different construction techniques with heterogeneous stone materials of different origins. CRP
and TLS were applied to the investigated elements with the aim of obtaining a natural colour
texturized 2D-3D model with a calibrated scale and coordinates. The geometrical anomaly and
reflectivity maps derived from the data of the CRP-TLS survey show the presence of some
anomalies worthy of attention, but they were referred to the shallow materials. A further
investigation on site using the ultrasonic pulse velocity (UPV) and electrical resistivity techniques
were performed to investigate the materials in depth. The results of the CRP and TLS techniques
allowed the best design of the ultrasonic and electrical techniques and also proved to be useful in
the data interpretation phase.