## 3 Results and Discussion
### Results of Rheological Properties at Low Temperatures  
The rheological characteristics of the asphalt binders were assessed at low temperatures using stiffness (measured in MPa) and m-value as the main parameters. The performance of pavement in cold climates is heavily influenced by these properties, as they play a crucial role in its ability to withstand cracking caused by thermal stresses. The stiffness results from Figure 6 and Table 8 demonstrate that the original PG64-22 binder possesses a stiffness of 186 MPa, which accurately reflects its fundamental performance. An incorporation of 10% Trinidad Lake Asphal (TLA) into the binder resulted in a slight decrease in stiffness, with a value of 178 MPa. This decrease indicates an initial enhancement in flexibility, most likely because of the more pliable characteristics of the organic asphalt in TLA. Nevertheless, when the TLA content was elevated to 20%, the stiffness experienced a substantial increase, reaching 253 MPa. The increase in stiffness can be attributed to the elevated levels of asphaltene in TLA, which leads to a more rigid binder structure. This enhances the material's ability to resist deformation but also increases its vulnerability to cracking. The function of SIS as a polymer modifier was also investigated. Upon adding 5% SIS to the binder that already contained 10% TLA, the stiffness was slightly decreased to 251 MPa. Figure 7 depicts the m-value results, which provide valuable information about the binder's capacity to alleviate stresses at low temperatures. The initial PG64-22 binder demonstrated a commendable m-value of 0.34, signifying favorable stress relaxation characteristics and consequently a reduced likelihood of thermal cracking. Nevertheless, when 10% TLA was introduced, the m-value dropped to 0.279, indicating a decrease in the binder's ability to relax. Surprisingly, increasing the TLA content to 20% resulted in a small enhancement in the m-value, reaching 0.294. This improvement could be attributed to the higher amount of resin in TLA, which might counterbalance the adverse impact on stress relaxation to some extent. The inclusion of SIS had an additional effect on the m-value. The addition of 5% SIS to the 10% TLA blend resulted in a decrease in the m-value to 0.257. Furthermore, increasing the SIS content to 10% led to a more significant reduction in the m-value, resulting in a value of 0.213. The binder with a composition of 20% TLA and 10% SIS exhibited the lowest m-value, which was measured at 0.184. These findings indicate that SIS increases the rigidity of the binder, but at the same time, decreases its capacity to release stress, which is essential for preventing cracking at low temperatures. The decline in m-value as the SIS content increases suggests that the polymer network created by SIS limits the relaxation mechanisms of the binder, thereby heightening the likelihood of thermal cracking in cold conditions. \begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline  & & & & & & & \\ \hline \multicolumn{1}{c}{\multirow{-2}{*}{**Combination**}} & \multirow{-2}{*}{**PG64-**} & \multirow{-2}{*}{**PG64-**} & \multirow{-2}{*}{**PG64-**} & \multirow{-2}{*}{**22+10\%TLA**} & \multirow{-2}{*}{**22+20\%TLA**} & \multirow  
In summary, the findings indicate that there is a reciprocal correlation between stiffness and m-value, implying a compromise between the ability to withstand deformation and the vulnerability to cracking. The inclusion of TLA and SIS improves the rigidity of the binder, making it better suited for high-temperature conditions. However, this also decreases the m-value, which increases the risk of cracking in low-temperature environments. Hence, it is crucial to strike a delicate equilibrium when employing SIS as a modifier, so as to guarantee that the advantages of enhanced rigidity are not achieved at the cost of diminished performance in low temperatures.