SEM-EDS characterization of historic mortar as a tool in archaeometric study: an updated analytical protocol tested on the Roman theatre of Aosta (NW Italy)

The archaeometric study of ancient mortars can provide important information relating to the raw materials used and their provenance. A mineralogical and petrographic study based on optical and electron microscopy on mortars from the Roman Theatre of Aosta (NW Italy) was carried out. The construction of the theatre is believed to have taken place a few decades after the foundation of Augusta Praetoria , the ancient city of Aosta, in 25 BC. Both original and mortars belonging to four different subsequent restoration interventions were studied. It was possible to detect the areas of origin of the materials used for the historical mortars, which were of local provenance, being characterized by abundant metamorphic minerals, typical of Alpine orogeny. X-ray element maps were also created to better define the distribution of aggregate, binder and porosity. The characterization of the binder was obtained by creating two-dimensional maps of the hydraulic index. These made it possible to distinguish aerial mortar from the Roman age samples and hydraulic mortars for subsequent restorations.