Analytical characterisation of 1st- and 2nd-century Roman mortars at the Utica archaeological site (Tunisia): Construction phases and provenance of the raw materials

The aim of this paper is to characterise the mortars from at the Roman site in Utica, Tunisia. In-depth knowledge of the composition of these Roman mortars is necessary to ensure the proper restoration and preservation of these ancient monuments. Despite the significance of this archaeological site, declared a UNESCO World Heritage Site in 1993, the Roman construction materials used there, particularly the mortars have never been analysed. The findings of this study allowed us to determine the particularities of the Roman mortars in Utica, highlighting the impact that local know-how, geological specificity and the history of the archaeological site had on the end product. The different mortars were analysed using petrographic (optical polarised and electron microscopes), mineralogical (X-ray diffraction), chemical and physical techniques. Three types of joint and coating mortars, associated with two different construction phases and a variety of uses, were identified. The mortars used in the city's first construction phase were low-hydraulicity calcium lime mortars containing inert quartz aggregates. Those related to the city's second phase of construction, are two types of mortar with a greater degree of hydraulicity by virtue of their artificial and natural pozzolanic aggregate content. The lime mortars containing artificial pozzolans (cocciopesto) were coated with lime mortars containing natural volcanic pozzolans. The foreign provenance of the natural and artificial pozzolans may be attributable to the amount of trade that passed through the Roman city’s port in the 1st and 2nd centuries AD.