An investigation on the Roman mortars from the Palatine archaeological site

During the excavation of the Curiae Veteres area at the Palatine hill, mortars from different eras were sampled in order to understand how the production techniques changed through time, in particular from the early to the late Imperial age. A specific characterisation of the composition of the mortars sampled from different masonries was performed by different analytical techniques and the results were correlated to the archaeological studies with a multidisciplinary approach. The observation of thin sections through Optical Microscope (OM) and Electron Scanning Microscope associated to Energy-dispersive X-ray spectroscopy (SEM-EDS) allowed to identify the main mineral phases and to study the grain-size distribution of aggregates. The binder/aggregate ratio (b/a) was determined by Thermal Analysis (TGA-DSC), correlating the obtained results also with the information derived from Microscopic Observation. Furthermore, a more extensive identification of the mineral phases was done by X-ray Diffraction (XRD) and by Attenuated Total Reflection Infrared Spectroscopy (FTIR-ATR). The obtained results underline a correlation between the use of specific materials and the structural function of the masonries they are related to. Typical roman red and black pozzolanas were always used as aggregate, even during the periods of crisis for the Roman empire, whenever the structure had a bearing function. Instead, a brown pozzolana, well-known as pozzolanella, with a weaker hydraulic behaviour, was used for minor constructions elements like dividing walls. The presence of a wide range of materials and their different applications correspond to the ability to understand their correct use, emphasizing the high technological knowledge of the Romans.