Heat-related Changes of Density, P-wave Velocity, and Surface Hardness of Granite

Low-and intermediate-level radioactive waste is stored in the National Radioactive Waste Repository in Bataapati in Hungary. The repository is located in the Carboniferous Moragy Granite Formation. This paper focuses on heat-related changes of physical properties such as bulk density, P-wave velocity, P-wave modulus, and Duroskop surface hardness of the dominant lithology: monzogranite. Cylindrical specimens were tested at laboratory conditions (22 degrees C) and were heat-treated up to 250 degrees C, 500 degrees C, and 750 degrees C. The properties were measured before and after the thermal strain. After heat-treatment, the monzogranite samples became brownish, and at 750 degrees C, cracks appear at the surface of the specimens. Laboratory test results show that bulk density values slightly decrease from room temperature to 250 degrees C treatment and further dropped at 500 degrees C and especially at 750 degrees C. P-wave velocity values and the connected P-wave modulus tend to decrease from room temperature to 750 degrees C significantly. Duroskop rebound values show slight declines in the surface strength of the specimens until 500 degrees C, and then a drastic decline at 750 degrees C. Heat treatment tends to alter the physical properties of the monzogranite. From room temperature to 500 degrees C, a slight but apparent decrease between 500 degrees C and 750 degrees C significant reductions in the bulk density, P-wave velocity, and Duroskop values. Behind the physical alterations are the different thermal-induced expansion of minerals and mineral alteration at elevated temperatures.