Pozzolanic mortars for restoration of sacred tuff masonry structures

Recent earthquakes have shown the seismic vulnerability of the Italian Architectural heritage and the need of interventions. The restoration design should take into account not only assessment and rehabilitation, but also the need of fruition of the cultural assets. These aspects have been considered in the last Italian seismic codes, a performance-based set of technical requirements to be addressed in the design process. In this framework, the requirements that the materials, meant to repair or replace historic ones, should fulfill are a key issue. In particular, for tuff masonry structures, the evaluation of the mechanical characteristics of the mortar is essential. Tests performed directly on samples withdrawn on site are perhaps the most reliable tools to determine the strength characteristics of a mortar to be used for restoration. Unfortunately, the possible dimensions of the samples are not compatible with the minimum required for a reliable mechanical test, so that the characterization of the old mortars and their historic context can be made obtaining information by the treatises of the time: components and their proportions, together with curing operations are often reported in the manuals. In particular, in the Middle Age the Roman knowledge about pozzolanic mortars was somewhat lost, and the results can be seen in the durability problems of several monuments of the period. These last considerations are the motivations of this paper, in which a study of the pozzolanic mortars in tuff masonry structures is provided. As a case study, the tuff masonry structures of the Paleocristian Basilica in Cimitile are considered and examined.