فهرست نشریات علمی دسترسی آزاد ایران

This study explores the thermal behavior of four widely used Iranian granites - Khoramdareh,Nehbandan, Natanz, and Taibad - under temperatures ranging from 20°C to 1050°C. The investigationfocused on the evolution of microcracks and their impact on key physical properties such as porosity,water absorption, and P-wave velocity in both dry and saturated conditions. Using fluorescencemicroscopy, linear microcrack density (LMD), microcracks type, and width were analyzed in detail. At300°C, all granite samples showed an increase in inter-crystalline microcracks, leading to elevatedporosity and water absorption. At 600°C, the quartz phase transition at 573°C resulted in volumetricexpansion, causing a temporary decrease in porosity and an increase in P wave velocity. For example,the dry P wave velocities at 600°C were 4.77 km/s for Taibad, 4.71 km/s for Khoramdareh, 3.84 km/sfor Natanz, and 5.12 km/s for Nehbandan. Above 750°C, trans-crystalline microcracks becamedominant, significantly increasing porosity and water absorption while reducing P wave velocity.Nehbandan granite suffered structural failure at 600°C, whereas Natanz exhibited the highest LMD at750°C, indicating severe internal damage. The study highlights the importance of microcracks evolutionand mineralogical transformations, particularly quartz phase transitions, in controlling granite's thermalstability. Three critical thresholds (300°C, 600°C, and 750°C) were identified as turning points in thedeterioration process. Additionally, this research introduces a novel methodological approach,combining fluorescence microscopy with physical testing to achieve detailed characterization of thermaldamage. By extending the temperature range up to 1050°C, the study provides valuable insights intogranite performance in fire-prone and heat-exposed environments.