Three-Dimensional Digital Reconstruction and Archaeometric Approaches for Hydroxyapatite-Based Restoration of Sacidava Roman Fortress

This study presents an integrated digital and archaeometric investigation of the Roman fortress of Sacidava, located in Dobrogea, Romania. Combining 3D digital reconstruction and advanced material analysis, the research explores both the original architecture and the preserved state of the site. Using Autodesk Fusion 360, a complete 3D model was developed, digitally restoring the fortress as it likely appeared in the 4th century AD and enabling the generation of precise plans, sections, and photogrammetric elevations. Mortar samples from the eight towers of the Sacidava fortress were examined through scanning electron microscopy with energy dispersive spectroscopy (SEM-EDS), atomic force microscopy (AFM), and confocal laser scanning microscopy (CLSM), revealing phyllosilicate-rich matrices, carbonated lime residues, and heterogeneous microstructures. The most severe degradation was found in the towers facing the Danube (E2, F, G), which was strongly influenced by humidity and salt crystallization, while the southern towers (A–C) retained more stable textures. Hydroxyapatite (HAp) treatments visibly improved the surface condition by reducing roughness and sealing active pores. For the first time, chromatic parameters were correlated with environmental factors, such as pH, moisture, and salt content. ImageJ-based pseudo-computed tomography (pseudo-CT), principal component analysis (PCA), and dendrogram analyses confirmed a clear pattern of deterioration near the ancient port area, where increased acidity and moisture coincided with darker surface coloration and deeper microstructural alteration.