## 4 Results and Discussion
### G-R Index Results
At 15 \({}^{\circ}\)C, while the bitumen shows more stiffness than at higher temperatures, the phase shift angle still reflects more flexibility than the 4% SBS sample, keeping it out of the block cracking region for a longer range. This suggests that the additional SBS content improves the bitumen's capacity to withstand low-temperature cracking, although the material's performance under extreme low-temperature conditions still requires consideration. Figure 3: G–R index animal bone ash modified samples (**a**) 4%, (**b**) 5%, (**c**) 6%. In summary, the progression from 4% to 5% SBS shows a clear enhancement in the bitumen's flexibility and resistance to block cracking. The 4% SBS sample offers significant improvement in elasticity at higher temperatures, but some risk of cracking remains at low temperatures, particularly under high stress. The 5% SBS sample demonstrates superior performance, maintaining flexibility and avoiding the block cracking region across both temperature settings and stress levels. The higher SBS content improves the bitumen's ability to deform under stress, reducing the risk of cracking, making it the most effective concentration for improving bitumen performance, particularly in high-stress and low-temperature environments. In the 4% animal bone ash sample (Figure 3a), the bitumen shows a noticeable shift toward the block cracking region, particularly at the lower temperature of 15 \({}^{\circ}\)C and higher stress levels of G-R = 600 kPa. The grey curve at 15 \({}^{\circ}\)C indicates that the material behaves stiffly under these conditions, increasing its susceptibility to cracking. At 25 \({}^{\circ}\)C, the bitumen shows improved flexibility, remaining mostly in the no block cracking zone, but as the stress increases, the curve begins to shift toward the damage zone, indicating that the bitumen still risks cracking under higher loads, despite the improvement in flexibility at warmer temperatures. The phase shift angle (8) at lower temperatures reflects more  
Figure 4: G–R index WCO modified samples (**a**) WCO 3%, (**b**) WCO 4%, (**c**) WCO 5%. solid-like behavior, making the bitumen more prone to block cracking under stress when using 4% animal bone ash. For the 5% animal bone ash sample (Figure 3b), the material exhibits similar behavior to the 4% sample but with slightly increased stiffness. At 15 \({}^{\circ}\)C, the bitumen moves further into the block cracking region under G-R = 600 kPa, showing that the addition of more bone ash increases stiffness, reducing the bitumen's ability to deform under stress. At 25 \({}^{\circ}\)C, the bitumen shows relatively better performance, staying in the no block cracking zone for a longer range. However, under high stress, it still approaches the damage zone, although the material demonstrates more rigidity than the 4% sample. This suggests that while animal bone ash improves the material's structural integrity at higher temperatures, it increases the risk of block cracking at low temperatures and high stress levels due to the increased stiffness. The 6% animal bone ash sample (Figure 3c) displays the most pronounced shift toward stiffness among the three samples. At 15 \({}^{\circ}\)C, the material moves even deeper into the block cracking region, indicating a significant reduction in flexibility due to the high concentration of animal bone ash. The bitumen becomes highly prone to cracking under stress, particularly at low temperatures. At 25 \({}^{\circ}\)C, the bitumen retains some flexibility but begins to approach the damage zone sooner under high stress, reflecting the fact that the increased rigidity from the bone ash modifier affects its performance, even at higher temperatures. While the 6% bone ash sample provides enhanced stiffness, this increased rigidity limits the bitumen's ability to absorb stress without cracking. In summary, the progression from 4% to 6% animal bone ash demonstrates increasing stiffness and reduced flexibility, especially at lower temperatures.