Production technology of mortar-based building materials from the Arch of Trajan and the Roman Theatre in Benevento, Italy

This research deals with the archaeometric study of mortars of two outstanding examples of Roman architecture in Benevento (southern Italy): The Roman Theatre and the Arch of Trajan. Mortars were analysed by means of a multi-analytical approach (i.e., polarized light microscopy, thermal analyses, infrared spectroscopy, scanning electron microscopy and energy-dispersed spectrometry) according to existing recommendations. Two different types of recipes were identified for the mortars of the Roman Theatre: a lime-based pozzolanic mortar and a hydraulic one, the hydraulicity of which, in both recipes, was due to the occurrence of natural pozzolanic admixture in air-hardening lime. As far as the Arch of Trajan is concerned, the investigated mortars are highly hydraulic as a consequence of the concomitant effect of a pozzolana-based aggregate and of a binder deriving from a marly-limestone-like stone. Although having the same function, the two different recipes identified for the bedding mortars of the Roman Theatre are clearly referred to different building phases of the monument associated to two out of the three documented construction phases.