Microcracking of granite feldspar during thermal artificial processes

Abstract

Granite is one of the most widely used building stones and is a main component in many heritage buildings.  Thermal changes are responsible for decay, especially in granites exposed to weathering. Feldspars are an important component of granites, which are susceptible to microcracking, which causes the disintegration of these crystals. Microcracks generated in feldspars during thermal processes such as freeze-thaw and thermal shock were studied to understand the decay process of granite buildings due to weathering. Using petrographic study techniques of optical microscopy and fluorescence, microcracks propagation (inter- and intracrystalline) was studied in feldspars (potassium feldspars and plagioclases) of two widely used building heritage granites. Potassium feldspars and plagioclases developed different mechanisms of microcracking due their microstructures. The propagation of microcracks occurred predominantly in pre-existing microcracks, contact between minerals and crystallographic planes where they exist as twins and cleavage directions. The compositional zoned plagioclase in both studied granites also generated concentric microcracks.