Ultrasonic sound test on stone: comparison of indirect and direct methods under various test conditions.

In order to choose the best ultrasonic measurement method, in transmission mode, on different rock categories (marbles, limestones and sandstones), a series of ultrasonic tests (with direct and indirect method, with different frequencies, on dried and saturated specimens, with control of pressure) have been executed, taking into account the petrographic characteristics of the stones tested. After the definition of accuracy in the measurement methods, the influence of climate factors, both in laboratory and in situ tests, has been evaluated. The comparisons between the results of ultrasonic tests obtained on saturated and dried specimens, with transducers with different frequencies of measure (54kHz, 33kHz, 250kHz), and by means of control of pressure, have been executed. The results obtained have been correlated with the results of other technological test executed on stone (non-destructive and destructive). From all the results obtained the indirect method with 33kHz frequency seems to be the most appropriated in expeditions measurements both in situ and in laboratory.