Anti-fouling additives for the consolidation of archaeological mortars in underwater environment: Efficacy tests performed on the apsidal fishpond of Castrum Novum (Rome, Italy)

This paper deals with the formulation of innovative mortars for the consolidation of archeological structures in underwater environment. The research was conducted within the frame of the MaTaCoS project (Advanced materials and technologies applied to the conservation of underwater cultural heritage) funded by MISE (Italian Ministry of Economic Development). The project concerns the design of advanced tools and methods for the protection of Underwater Cultural Heritage, through specific cleaning and consolidating procedures to be applied directly in situ. The fishpond of the archaeological site of Castrum Novum (Santa Marinella, Rome, Italy) was chosen as a pilot site for experimentation. It is a structure on the coastline, composed of only one tank, with an average immersion of 0.37 m below the sea level, and developing with an NE/SW orientation. The masonry structures reach the maximum thickness at the apex of the fishpond (4.70 m) and consist of a concrete conglomerate composed of slightly rough stones of medium size bound with non-hydraulic mortar. Selected mortars' fragments taken from the fishpond were characterized by means of minero-petrographic technique in order to define their main constituents from a compositional and textural point of view and also to identify the various degradation processes, mainly biological colonization. Starting from the acquired information, innovative mortars were formulated with the addition of two different anti-fouling additives aimed to slow down the above-mentioned degradation. The efficacy of the anti-fouling products was tested on specimens settled in laboratory environment (artificial marine environment). This information could be useful both for the definition of restoration interventions and for planning preservation protocols to be applied in this peculiar environment.