Spatial Variability of Roman Mortar Properties: Physicochemical Characterization and GIS Analysis in the Colonia Augusta Achaica Patrensis

The study of Roman mortars provides critical insights into ancient construction technologies and long-term material degradation processes. However, the spatial variability of their physicochemical properties remains insufficiently explored, particularly in complex urban archaeological contexts. This study aims to investigate the relationship between material properties and spatial distribution of Roman mortars from the Colonia Augusta Achaica Patrensis (modern Patras, Greece). A total of 22 mortar samples from different monuments were analyzed using a combination of physicochemical characterization techniques, including X-ray diffraction (XRD), scanning electron microscopy (SEM), X-ray fluorescence (XRF), Fourier transform infrared spectroscopy (FTIR), and thermogravimetric analysis (TGA). In parallel, a geospatial database was developed, and GIS-based spatial analysis was applied to identify patterns in the distribution of material properties. This integrative approach enables the exploration of spatial correlations between composition, microstructure, and environmental context. The results reveal significant spatial variability in both chemical composition and microstructural characteristics across the study area. The mortars exhibit predominantly mesoporous structures (mean pore diameter ~25 nm) with relatively low pore volume, while the specific surface area is mainly associated with amorphous aluminosilicate phases. At the Roman Aqueduct (AQD) site, a marked decrease in calcite content is observed in samples collected closer to the ground, attributed to capillary rise and progressive dissolution of calcium carbonate, as confirmed by XRF, XRD, and TGA analyses. The spatial analysis demonstrates that these variations are not randomly distributed but are linked to local environmental conditions and construction practices. Furthermore, the relatively high calcite content observed in several samples, combined with the absence of natural pozzolanic materials, suggests adaptation of construction techniques to local geological resources. Τhe study highlights the importance of integrating material characterization with spatial analysis, proposing a comprehensive framework for understanding the technological variability and degradation processes of Roman mortars in archaeological contexts.