Cementation processes of Roman pozzolanic binders from Caesarea Maritima (Israel)

A multi-analytical characterization study was performed on the pozzolanic binding composites used for the construction of Sebastos harbor in Caesarea Maritima, comparing underwater concretes to on-land mortars. Historically dated to the 1st Century BCE, the structure was erected by King Herod the Great as the largest ancient artificial harbor in the open sea. The combined interpretation of the results obtained through petrographic, mineralogical, spectroscopic, and microstructural/microchemical analyses indicated the use of different binder recipes, related to Roman and Phoenician-Punic technological practices, employing both natural volcanic pozzolans and artificial pozzolanic additives derived from the combustion of organics. Furthermore, the study unraveled the complex cementation processes of the binding composites, influenced by diversified chemical-physical-biological conditions of the precipitating environment such as water salinity and bacterial activity, leading to the formation of unconventional carbonates, as well as peculiar hydrated calcium aluminosilicate (C–A–S–H) and magnesium aluminosilicate (M–A–S–H) phases. The results constitute a relevant contribution to the understanding of the reactive pathways of ancient and modern pozzolanic systems.