Evaluation of marble thermal-induced decay by ultrasonic pulse velocity and Leeb hardness

Marble has a great importance in the field of cultural heritage and, therefore, it is important to quantify the decay level of the marble to implement at the right time restoration plans aimed at safeguarding as much as possible cultural heritages. The degradation of the marbles with consequent loss of mechanical properties is correlated to an increase in porosity; this increase in porosity is the result of the loss of cohesion among the grains and the formation of micro-cracks. When it is not possible to remove samples to be analysed in the laboratory or when are needed instant check, the role of non-destructive and operable in situ methods is fundamental. In this study, by using portable instruments, correlations were obtained between the variation in the ultrasonic pulse velocity (UPV), the variation in surface hardness Leeb (HL) in relation to the variation in porosity open to water. This porosity was obtained by subjecting two varieties of marble (from Apuan Alps, in Italy, and from Paros Island, in Greece) to artificial thermal degradation of varying intensity from 100°C up to 500°C, at ambient pressure. As the intensity of degradation increases, more and more porosities open to water are generated.