XRD and PCA analysis of historic mortars from the Venetian Fortress of Bergamo (Italy)

Mortars from the 16th-century Venetian Fortress of Bergamo (Italy) were investigated using X-ray diffraction (XRD). Samples were taken from the bastions of San Pietro and Valverde, areas affected by severe degradation and targeted in a recent conservation initiative. XRD qualitative phase analysis and semi-quantitative analysis were performed on 59 samples collected from 9 cores extracted at different locations. XRD analysis identified calcite, hydrocalumite- and hydrotalcite-type compounds, brucite, aragonite, plombierite, and a substantial amorphous fraction in the binder, while aggregates consist mainly of quartz and carbonate-rich sands. The large dataset of abundances of phases in the 59 samples was analyzed via principal component analysis (PCA). PCA results indicate a homogeneous distribution of mineral phases across the dataset, with no significant clustering by depth or sampling location, supporting the interpretation of a consistent binder composition throughout the investigated sections.