Technological and geochemical study of historical mortars from the Roman “Villa dei Quintili” (Rome, Italy)

This contribution is concerned with the study of historical mortars from the Roman archaeological site “Villa dei Quintili” (Rome, Italy). The monumental complex, dating back to the 2nd century A.D., owes its construction to the brothers Sextus Quintilius Condianus and Sextus Quintilius Valerius Maximus, in 151 A.D. The villa was used as imperial residence until the 6th century (PARIS 2002), after that, it gradually decayed and in 1986 became property of the State. The monumental villa consists of several edifices showing building techniques that can be referred to different construction phases. It is worth noting that near the Tepidarium, one of the thermal areas, a limekiln was discovered, which was probably in use until the Renaissance. The study regarded forty-six mortar samples, collected from different edifices within the monumental complex, i.e. the thermal area (Calidarium and Frigidarium), the Viridarium, the Nymphaeum and some residential areas. A multianalytical approach has been used in order to completely characterize the samples. Specifically, polarizing optical microscopy observations, along with morphological and microchemical analyses by SEM-EDS were carried out to investigate some specific technological aspects of the examined mortars, such as the composition and texture of binder and aggregate and the ratio between the two components. Punctual analyses of both binder (lumps) and aggregate were also performed through LA-ICP-MS to determine the concentration of trace elements and gain information about the provenance area of raw materials. The petrographic analysis of mortars permitted to distinguish two types of mortars on the basis of texture and compactness of binder and the ratio binder/aggregate (Fig. 1). Such different features seem to correspond to two diverse historical periods and two different construction phases, as supposed by archaeologists. SEM-EDS analyses of lumps revealed that aerial lime was used for the preparation of all examined mortars, except for five samples that resulted to be feebly-hydraulic. Therefore, the high idraulic index (0.30 to 2.90), which characterizes the binder of all samples, indicates that the hydraulicity of mortars was obtained through the addition of pozzolana. In fact, compositional profiles performed at the rims binder/aggregate revealed a deep transformation of the binder. With the aim of identifying the source area of the raw materials used, results obtained from microchemical analyses of the volcanic aggregate have been compared with literature data, thus allowing to better constrain the provenance area (BARONE et alii 2010). These studies refer to major and trace elements of pozzolana samples from the Alban Hills area and clinopyroxenes occurring within volcanic rocks of the Roman magmatic province (e.g. Conticelli et al. 2010; Dallai et al. 2004; Gaeta et al. 2006; Boari et al. 2009).