Acoustic Emission and Anisotropic Expansion when Heating Marble

Types of failure such as bowing, increased surface absorption, and loss of strength can frequently be observed on facades even a few years after installation if crystalline calcite marble is used. The investigation discussed evaluated the processes taking place in the structure of marble that lead to such damage. By means of a dilatometer the anisotropic thermal expansion of a coarse-grained marble type was measured systematically under temperatures between 20 and 200°C. The thermal expansion coefficient α amounted to between 15 ± 2$\dot{s}$10⁻⁶ K⁻¹ and 0 ± 2$\dot{s}$10⁻⁶ K⁻¹, depending on the orientation of the specimens, thus showing an extremely pronounced anisotropy. Special attention was paid to residual dilatation in the marble specimens that remained after the first heating-cooling cycle of the individual specimen (hysteresis). The dilatometric measurements were compared with investigations of acoustic emission (AE), which were carried out during the dilatometric measurements. These AE measurements provided information about the phase in the heating-cooling cycle during which the marble structure was damaged most by microcracks at the grain boundaries. The results proved that measuring AE signals is a suitable method of determining and analyzing thermal microfracturing of marble.