The Santa Croce wall structure of Cagliari's ancient fortifications (Sardinia, Italy): construction technologies and stone decay

Abstract

The research discusses a part of the modern fortification of Cagliari built since the XVI centuries: the bastion of Santa Croce. The Cagliari fortifications show the designs of "modern" technologies that around the middle of the XV century in Europe replaced the medieval walls, with several changes to the structures (i.e.: lowering of buildings, replacement of quadrangular medieval towers with lesser height cylindrical, increase of the thickness of the walls through the creation of embankments, etc.). For the boundary walls of Santa Croce, built between 1568 and 1578 and completed with additional outworks in the XVIII century, were used local carbonate rocks of Cagliari's geological Miocene formation. The main represented lithologies used in the wall structure are the Pietra Cantone, Tramezzario and Pietra Forte limestones. These rocks are also used in the La Concezione and San Guglielmo structure walls. Subordinately, in the bastion of Santa Croce (as well as in the curtain of San Guglielmo) there are the occasionally presence of volcanic ashlars belong to Asuni area (central-south Sardinia). These volcanic ashlars are used as materials for the recent consolidation and restructuring of the fortifications of Cagliari, implemented in the century before. Primarily, the study analyzes the relationships between the ancient construction technologies and the use of stone in these building walls. Secondarily, it analyzes the decay of geomaterials to define the chemical and physical processes in progress in the monument, and to identify how to intervene in the restore works, in order to consolidate the material where there is obvious static-structural criticality.