Nondestructive characterization of ornamental rocks with ultrasound

Abstract

Because of their esthetic, mechanical and thermic properties, marble and granite are the most used ornamental rock for the construction of buildings. In the last years the characterization of these materials received a high scientific and practical attention. Yet the actually disposable methods of inspection are sometimes inadequate, expensive and destructive. Under all the newly developed methods the ultrasound method appears to be the most attractive because it allows to determine the physical properties of marble and granite in a nondestructive, nonexpensive and practical way. For this purpose we used two identical piezoelectric transducers with a central frequency of 5 MHz in order to measure the transmission of ultrasound through rock samples for determing their ultrasound parameters, i.e. the longitudinal and transversal velocity as well as the damping of ultrasound waves inside the rock samples. We present also a discussion of the factors, which are responsible for the variation of the velocity and the damping of the ultrasound waves. We also studied, if it would be possible to use the dispersion of Lamb modes as a new alternative for replacing the ordinary destructive tests used by geologists (thin sections, electron microprobe, rock powder etc.) with a nondestructive ultrasound technique in order to classify rocks. Our work confirmed that the velocity and damping of ultrasound waves in marble and granite might be used efficiently as criteria for estimating the mechanical properties of these materials.