Compositional analysis of the stones and ancient mortars of the Nora medieval tower fortification (south Sardinia, Italy)

The medieval Nora tower, still active in 1607, is located on a promontory on the south-western Gulf of Cagliari (Sardinia), near to the Coltellazzo Island and the Punic-Roman archaeological area of Nora. The tower structure is a truncated cone about 11 meters high and 12 meters in diameter at the base. Inside, it has a double ribbed vaulted dome, supported by a central pillar. Aims of this research are studying the building materials used for the construction of the tower, addressed to define: i) the different stones (mainly volcanic and sedimentary rocks) used for construction; ii) the compositional characteristics of ancient mortars and the mixture proportions of binder and aggregate; iii) the provenance from territory of the raw materials; iii) chemical and physical decay processes. Several chemical, physical, mineralogical and petrographic investigations are made on samples taken from the tower masonry, using different analytical methods such as XRF, XRD, polarizing light microscope, helium pycnometer, and mechanical tests.