A non destructive testing method for masonry by using UPV and cross validation procedure

The paper presents a new procedure to assess the compressive strength of regular masonry starting from results of non-destructive ultrasonic pulse velocity tests (UPV) on the constituent materials. The procedure has been calibrated on a soft calcarenitic stone used in the heritage masonry of Southern Italy, and starts from the knowledge of the regression between UPV and the compressive strength (UCS) of the material, determined by means of a wide experimental campaign on different varieties of quarry samples. Through an improved cross validation technique, the proposed method allows to estimate the compressive strength of new samples by making only non-destructive measurements without the need to conduct compression tests. The quality of the procedure was assessed both at the block scale and at the wall scale by comparing the estimated results with those obtained experimentally. In particular, the experiments were performed using new quarry stone blocks and blocks taken from existing walls of two ancient buildings during restoration works. The proposed method has proven to be reliable for the investigated material and it is easy to apply also for other materials as soon as it is possible to carry out a preliminary calibration in the laboratory, which allows knowing the UPV-UCS relationship over a wide range of strengths.