Research of correlations between NDT and DT to assess mechanical properties of soft stone in ancient masonry

A deep knowledge of the physical and mechanical properties of the constituent materials of ancient masonries is of crucial importance in the choice of the proper intervention techniques. In case of historical buildings sustainable diagnostic procedures responding to the conservation constraints, should have the lowest degree of intrusion and the fullest respect for their physical integrity. The extraction of samples from existing structures for laboratory tests is one of the major problems in the field of the diagnosis of ancient buildings and this has moved the scientific community to propose alternative non-destructive techniques to evaluate the mechanical and physical properties of building stones. In the present work, non-destructive (NDT) and destructive (DT) tests have been investigated as tools for assessing the compressive strength of "Lecce stone", a soft calcarenite used as traditional building material in the Southern Italy. Ultrasonic pulse velocity and Schmidt hammer test have been compared with standardized mechanical destructive tests on cubes in order to research correlations between the results. The final aim is to assess the reliability of the non-destructive investigated methods in describing the mechanical performance of the stone, limiting the use of destructive analyses on masonries. Compressive strength on microcores, reducing at least the intrusion of the sampling for mechanical test in laboratory conditions, was also determined and good correlation was found with the strength results obtained by the standard compressive test.