The Use of Ultrasonic Pulse Velocity Test for the Diagnosis of Historic Masonries: the Influence of Frequency and Applied Load

The ultrasonic pulse velocity (UPV) method can be conveniently used to check the quality of stones and also for material characterization. Both the intrinsic characteristic of the stone (porosity, grain size, anisotropy, etc.) and the external factors (humidity, stress, temperature, presence of cracks) may affect the elastic wave propagation, thus in order to correctly estimate the ultrasonic behavior of the investigated material it is important to know in what manner and how much the variation of the experimental conditions may modify the characteristics of the waves being measured. This aspect is of crucial importance when in situ measurements are made. In this work the attention is focused on two parameters: the wave frequency used in the measurements and the application of an external load. In the present work the effect of loading on the UPV has been investigated for the Lecce stone varying the wave frequency and the specimen geometry. Results provide further knowledge about the response of soft stones to UPV propagation, evidencing that, as for concrete and mortars, UPV are not influenced so much by the application of load before that crack damage occurs. This result supports the possibility of using ultrasonic pulse velocities to characterize physical and mechanical properties of the stone within a building.Moreover, the obtained results suggest that when UPV are employed to assess the quality of stones or their mechanical and physical properties, it would be a good practice to use more than one frequency of measurement.