Читать книгу Monument Future - Siegfried Siegesmund - Страница 281

The reason for the high sensitivity of calcitic marbles can be found by the pronounced anisotropy of the thermal expansion coefficient of the calcite single crystals (Fig. 1a). Temperature changes lead to anisotropic volume changes of the crystals, resulting in microstresses and microcracks. Even moderate repetitive temperature changes can cause significant deterioration. The extent of the local stresses and the resulting cracks are controlled by grain size, grain-to-grain misorientation as well as type and contact of grain boundaries (Rüdrich 2003, Shushakova 2013).

Figure 1: Schematic sketch of the thermal dilatation of calcite (modified after Rüdrich 2003). a) Coefficients of thermal expansion in different directions. b) Sketch of a single calcite crystal in its initial state. Volume change due to c) heating and d) cooling.