Compact limestones as historical building material: properties of the Trani stone (Apulia, Southern Italy) and preliminary study for self cleaning treatments

In this paper we deal with an experimental activity aimed to the characterization of a compact local limestone, named Trani stone. Compact limestones are very common materials used in the monumental and historic built heritage. In particular, with reference to the Apulian region (Southern Italy), they are the constituent stones of the numerous Romanesque Cathedrals, as well as of many other important monuments such as the UNESCO site of Castel del Monte. They have also been employed for the building of the fortified towns and norman-swabian castles facing the sea. The study reports mineralogical-petrographical and physical features, with particular reference to the behaviour with respect to the water. Ultrasonic tests have also been performed as indirect tool for the qualification of the stone in dry and wet conditions. A superficial treatment with photocatalytic titania (in water and alcoholic solution) has also been applied to the stone, in order to study the potential use of self-cleaning and antipollution nanotitania coatings for stone surface protection; a preliminary assessment of the morphology and distribution of the titania films on the stone surface and related colour changes has been carried out.