## 4 Results and Discussion
### DSR Results  
Figures 7 and 8 depict the results of the dynamic shear rheometer (DSR) test conducted on unaged bitumen samples. The DSR test results indicate a remarkable modification in the rheological properties of lignin-modified bitumen under different blending conditions. The variation of \(\mid\)G\({}^{*}\mid/\sin(\delta)\) with temperature for bitumen with different Kraft lignin contents (0, 5, 10, and 20%) in different blending conditions is shown in Figure 7. The \(\mid\)G\({}^{*}\mid/\sin(\delta)\) parameter is, to some extent, an indicator of the rutting resistance of an asphalt binder. Furthermore, it is essential to note that the value of \(\mid\)G\({}^{*}\mid/\sin(\delta)\) in the DSR test should surpass 1.00 kPa for unaged asphalt binders, as specified by the Performance Grade (PG) standards for bitumen (_Ministere des Transports du Quebec_: 4101 standard). The results indicate an increasing trend in the value of \(\mid\)G\({}^{*}\mid/\sin(\delta)\) for all bitumen samples, compared to the VB sample. The samples without Kraft lignin show a significant increase in stiffness (\(\mid\)G\({}^{*}\mid\) value increasing) and in elastic behavior (\(\delta\) value reducing) during the blending process, which is noteworthy, with a rise, for the \(\mid\)G\({}^{*}\mid/\sin(\delta)\) parameter, from 1.55 kPa for VB to 1.81 and 2.37 kPa for VB-HSM and VB-MM, respectively, at 58 \({}^{\circ}\)C. As the addition of Kraft lignin results in an upward shift in \(\mid\)G\({}^{*}\mid/\sin(\delta)\), it indicates an increase, to a certain extent, in the rutting resistance. This increment is more prominent in MM samples than in HSM samples, which suggests that in the MM blending process, as previously discussed, more volatile and light components were lost and exhibited more stiffness (\(\mid\)G\({}^{*}\mid\)) and less viscous behavior (\(\delta\)) in general. Therefore, it can be concluded that the addition of Kraft lignin significantly enhances, to some extent, the rutting resistance of bitumen, and the blending process also affects the \(\mid\)G\({}^{*}\mid\) and \(\delta\). For more information on the effect of lignin on rutting resistance, refer to [PERSON] et al. (2023) [20]. For instance, the HSM samples exhibit increases of 32, 48, and 83% for the 5L-HSM, 10L-HSM, and 20L-HSM samples, respectively, for the \(\mid\)G\({}^{*}\mid/\sin(\delta)\) parameter, which is an indicator for rutting resistance. Figure 8 illustrates the norm of the complex shear modulus (\(\mid\)G\({}^{*}\mid\)) and the phase angle (\(\delta\)) of all samples, indicating a significant modification for the HSM and MM samples in different ways. An increase in the \(\mid\)G\({}^{*}\mid\) value indicates that the lignin-modified bitumen samples are becoming stiffer. A decrease in \(\delta\) values suggests that the samples are becoming more elastic and less viscous, as they are able to respond more quickly to the applied stress. Figure 7: Impact of Kraft lignin on the \(\mid\)G\({}^{*}\mid/\sin(\delta)\) of bitumen under two blending conditions (dotted line: minimum value to be obtained at 58 \({}^{\circ}\)C). Regarding the impact of Kraft lignin as an additive, the results show that adding Kraft lignin in the HSM samples leads to a significant increase in stiffness (\(\,\mid\)G*\(\,\mid\)), but does not have a significant effect on the viscous behavior (a small change in the \(\delta\) value) (Figure 8). Conversely, the MM samples exhibit less alteration in \(\,\mid\)G*\(\,\mid\) (stiffness), but remarkable changes in the \(\delta\) (viscous behavior). For instance, in HSM samples at 58 \({}^{\circ}\)C, the \(\delta\) value changes by \(-0.07\), 0.12, and 0.68% (less than 1%) for 5, 10, and 20% of Kraft lignin, respectively. All changes suggest that the addition of Kraft lignin using HSM does not have a remarkable impact on \(\delta\). However, the changes in \(\,\mid\)G*\(\,\mid\) are remarkable.