Читать книгу Monument Future - Siegfried Siegesmund - Страница 268

Increasing temperatures associated with global warming are an imminent threat to European countries, where many historical items or edifices composed of stone are important to their cultural heritage. Repetitive cycles of heating and cooling by solar radiation generate large thermal stresses and increase the possibility of microcrack formation in stone and subsequent weathering. However, there are many unsolved questions regarding the relation among the rate of temperature change (RTC), microcrack detection and extension, and weathering processes. Accordingly, herein, we estimated thermally induced weathering of stone via nondestructive monitoring of acoustic emission (AE) concurrently generated with microcrack formation. Rock types that have frequently been used for stone items or edifices important to cultural heritage are granite, marble, and sandstone. The strain and AE of specimens composed of these rock types were measured in a temperature-controlled chamber programed with a heating–cooling range of 4–84 °C and RTC of ±2 °C/min. As a result, we confirmed strain changes and detected the AE amplitude in the specimens associated with temperature changes. This AE signal is considered to correspond to stress waves when microcracks form at grain boundaries. Microcrack formation in the stone and deterioration may be estimated using a system for monitoring strain and AE.

Keywords: thermal weathering, acoustic emission, microcrack, cultural stone