Читать книгу Monument Future - Siegfried Siegesmund - Страница 275

AE amplitude was generated in three rock types resulting from a temperature change of from 4 °C to 84 °C, which is probably observed in the field. The generation of AE signals the formation of microcracks due to thermal stress acting on grain boundaries. A large AE amplitude occurs when the temperature gradient is > 1.5 °C/min. This means that microcracks are generated inside the stone even with normal temperature changes in the field. As these microcracks grow, the bond strength between minerals eventually weakens, leading to stone degradation.

The generation, frequency, and pattern of AE differ depending on the rock type. These depend on the mineral composition, structure, and physical and mechanical properties of the rock itself. Granite containing a large amount of quartz has the highest AE generation, followed by that of marble with a uniform mineral composition; the lowest AE generation occurred in high-porosity sandstone.

For cultural properties composed of these three rock types, maintaining a small temperature change will prevent microcrack occurrence, but it is difficult to do so. The expected temperature increase in the future due to global warming is likely to further increase the potential for thermal weathering of cultural properties.