Mineral, Chemical and Petrographic Characterization of Hydraulic Mortars & Chronological Building Correlation of the Baths of Porta Marina in Ostia Antica (Italy)

Abstract

The Baths of Porta Marina were an imperial public complex located in the maritime suburban district of Ostia, the city harbor of Rome. During its large period of use from the 2nd century AD until the 6th century AD, several modifications of capacity and thermal path took place, resulting in architectural modifications. Previous studies based on archaeological evidence, written sources, architectural and stratigraphic analyses have provided thorough chronological data for construction phases. Characterization of hydraulic coatings and bedding mortars has been carried out focusing on waterproofing processes of antique hydraulic facilities and to propose a timeline of raw materials uses for this particular building and for others hydraulic facilities preceding the thermal complex (1st century AD). Mineralogical, chemical, and petrographic analyses were performed on several mortar samples from pools and cisterns from different construction phases of the Baths of Porta Marina. They confirm that mortars of Roman waterproof coverings, made with pozzolanic aggregates, show a persistent composition over centuries, hardly distinguishable macroscopically. Nonetheless, petrographic examination has been an interesting tool to highlight differences among the mortars. Some distinctive features of volcanic aggregates allow us to identify different depositional units from Alban Hills volcanic district as sources.