Characterization of the carbonate rocks of the Calcari di Cagliari Formation using a combined petrographic, geomatic and geophysical approach.

Vienna, Austria

The methods and the tools aimed at characterizing and analysing the carbonate materials used in
the historic built heritage often follow different ways according to the different branches of
applied research involved in the knowledge process. In this framework, the 3D digital models both
of in situ architectural elements and of significative samples of rocks used as building materials
can play an important role in relating different data and disciplines aimed at the prevention and
conservation of the Cultural Heritage. Although the 3D geomatic and geophysical digital models
represent privileged tools of the diagnostic analysis, they must be supported by the knowledge of
the textural characteristics of the rocks under investigation with petrographic analyses. In order to
study the stone materials heavily used in the historic built heritage and analyse their vulnerability
to the conditions in their environment, it can be beneficial to study appropriately prepared
samples and make as many measurements as necessary with different techniques. Moreover,
some analyses are destructive and there is a limit to the number of samples that can be sacrificed.
For this reason, in the analysis of rock samples, non-destructive techniques are constantly being
improved. In this study, using a suitably implemented integrated methodology we analysed in
detail samples of the carbonate rocks of the Calcari di Cagliari formation represented by Pietra
Cantone, Tramezzario and Pietra Forte lithologies, mainly used in the past as construction
materials for the buildings of the Historical Centre of Cagliari (Italy). Our methodology is
represented by an integration of the geomatic survey carried out by structure-from-motion (SfM)
digital close-range photogrammetry and the seismic tomography normally used for the in situ
inspection adapted to laboratory tests on samples of the above lithologies using ultrasonic
frequency signals. The rigorous metric of the geomatic 3D models was used to implement the
ultrasonic survey by which internal characteristics and physical properties of the studied material
are detected thanks to the spatial variations of the longitudinal velocity obtained after the
tomographic inversion. The geomatic and geophysical data were complemented by an accurate
analysis of the above carbonate materials by optical and scanning electron microscopy in order to
detect their textural characteristics and especially the nature and distribution of their porosity. The microscopy analyses were integrated by mercury intrusion porosimetry (MIP) to obtain further
information on the pore network, particularly on the effective porosity, pores-throat
diameters/radii, permeability and tortuosity of the investigated materials. All the above
parameters were found to affect the geomatic and geophysical behaviour of the carbonate
materials. The integration of the multi-technique data produced in this study contributes to better
understand the interaction between the investigated materials and the environment.

Acknowledgements
This work was supported by Regione Autonoma dellaSardegna (RAS) (Sardinian Autonomous
Region), Regional Law 7th August 2007, no. 7, Promotion of scientific research and technological
innovation in Sardinia (Italy), Resp. Sc. S.Fais.