An Integrated Analytical Approach to Define the Compositional and Textural Features of Mortars Used in the Underwater Archaeological Site of Castrum Novum (Santa Marinella, Rome, Italy)

摘要

This paper aims to carry out an archaeometric characterization of mortar samples taken from an underwater environment. The fishpond of the archaeological site of Castrum Novum (Santa Marinella, Rome, Italy) was chosen as a pilot site for experimentation. The masonry structures reached the maximum thickness at the apex of the fishpond (4.70 m) and consisted of a concrete conglomerate composed of slightly rough stones of medium size bound with non-hydraulic mortar. After sampling, for a complete characterization of selected mortar fragments, different and complementary techniques (stereomicroscopy, polarizing optical microscopy, and X-ray powder diffraction analysis) were carried out in order to: a) define the minero-petrographic features; and b) investigate their state of conservation. The obtained data allowed the determination of the main constituents of mortars from a compositional point of view. The raw materials, in fact, were quite homogeneous, as well as the ratio in which they were mixed, confirming the typical "recipe" used in Roman times to manufacture hydraulic-type mortars by adding pozzolana. At the same time, it was possible to identify the various degradation processes we were interested in, namely, biological colonization (bio-fouling) that develops differently according to environmental conditions. Based on characterization phase results, the research will help to develop adequate techniques for intervention (innovative tools and methods for the protection of underwater cultural heritage) with particular regard to cleaning and consolidating procedures to be carried out directly in situ.