## 3 Results and Discussion
Ultrasound velocities gradually decrease from room temperature to 200-300 \({}^{\circ}\)C, followed by a rapid fall in velocity values from 400 \({}^{\circ}\)C to 800 \({}^{\circ}\)C, as reported before (Figure 13). Figure 12: Scatter plots of different ultrasound velocities among heat-treated groups. Scatter plot of P-wave velocity values between PUNDIT and GEOTRON devices (**left**). Scatter plot of P-wave and S-wave velocity (GEOTRON device) values (**right**). Temperature elevation tends to alter the physical properties of the specimens, as previously shown. PUNDIT P-wave velocity shows a high exponential correlation with Duroskop values (Figure 14). P-wave velocity and Duroskop show exponential correlation with an R-value of 98%. As P-wave velocity shows the best way to indicate the physical changes inside the samples and Duroskop value changes of the surface hardness change, the high correlation of these two parameters suggests that physical changes occur inside and outside the specimens. Figure 14: Scatter plot of Duroskop value vs. P-wave velocity. Figure 13: Comparison of P-wave velocity values of heat-treated granite samples in the literature and this paper. From room temperature to 250 \({}^{\circ}\)C, 500 \({}^{\circ}\)C and 750 \({}^{\circ}\)C mass decrease slightly, volume values at 250 \({}^{\circ}\)C increase then decrease at 500 \({}^{\circ}\)C and increase significantly at 750 \({}^{\circ}\)C. From these results, bulk density values show similar changes as volume changes in the specimens at elevated temperatures. Duroskop values decrease slightly at 250 \({}^{\circ}\)C and 500 \({}^{\circ}\)C, then significantly at 750 \({}^{\circ}\)C. P- and S-wave velocity values decrease continuously. The percental changes and comparison of all measured physical parameters can be seen in Figure 15. Percental changes of mass, volume, bulk density, PUNDIT and GEOTRON P- and S- wave velocity, and Duroskop values represent the percentage changes between untreated room temperature and heat-treated values and not between consecutive temperatures. P-wave velocity, bulk density, and Duroskop value changes together show a correlation in parameters in terms of multi-modal comparisons. Heat-treatment processes induce significant bulk density, surface strength-, and ultrasound velocity decreases. These physical changes tend to correlate exponentially (Figure 16). Figure 7:0 Bar plot of mass-, volume-, bulk density-, P-wave velocity (PUNDIT), P-wave velocity (GEOTRON) between groups, S-wave velocity (GEOTRON) between groups and Duroskop percental changes between untreated room temperature and heat-treated values. Physical parameters change slightly between room temperature and 500 \({}^{\circ}\)C and significantly between 500 \({}^{\circ}\)C and 750 \({}^{\circ}\)C, as shown in Figure 7:1 Mineral alterations and related expansions (such as \(\alpha\)-quartz to \(\beta\)-quartz inversion at 573 \({}^{\circ}\)C) and the thermal expansion difference of the main rock-forming minerals cause micro- and macro cracking inside and on the outer surface of the specimens between 500 \({}^{\circ}\)C and 750 \({}^{\circ}\)C [14; 15; 52; 53]. This cracking development increases volume significantly and permanently while decreasing bulk density-, P- and S-wave velocity-, and Duroskop surface strength values. For further research, heat-treatment between 500 \({}^{\circ}\)C and 750 \({}^{\circ}\)C is essential in order to increase the examination of the physical decrease of the host rock.