## 4 Conclusions  
From the outcomes of this study, the following conclusions can be drawn:  
With the addition of 4% CRM, the increase in viscosity is more than two times the viscosity of the neat asphalt, and about 31% and 34% more than the addition of 4% of PP and TPS, respectively. Thus, to enhance the viscosity in an asphalt binder, use CRM, as it is the preferred additive for improving rutting resistance and fatigue/reflection cracking resistance in flexible pavement, followed by PP and TPS modifiers.  
The results showed that significant reduction in ductility occurred by the addition of CRM, PP, and TPS modifiers. Moreover, TPS-modified asphalt binder was found to have a high ductility and thus TPS is more flexible. Further, it concluded that TPS behaves differently from both CRM and PP for all concentrations.  
The results of the toughness and tenacity test concluded that the maximum force increased linearly with the increase of CRM, PP, and TPS concentrations. The consequences indicated that the maximum strength obtained from the addition of CRM is better than those derived from PP and TPS modifiers. The significant dissipated energy during the fracturing process was achieved by adding CRM. Outcomes also showed that CRM has a small value of tenacity. Thus, CRM is the most appropriate modifier for enhancing the mechanical properties of the asphalt binder behavior.  
The DSR test results showed that the G*/sin(\(\delta\)) and G* values increased with the modifier content and decreased when the temperature increased. The values obtained from the CRM-modified bitumen  
Figure 9: G* (left) and \(\delta\) (right) serving as a function of temperature for modified binders: (**a**) CRM; (**b**) PP; and (**c**) TPS.  
binders were higher than those of the PP- and TPS-modified binders. Thus, CRM-modified asphalt binders were the most preferable for enhancing the medium and high-temperature performance and permanent deformations.  
The DSR stress-strain relationship results indicate that the medium- and high-temperature features (stress) increased when CRM content increased. However, in the case of PP and TPS, the properties increased at 2% and 3.5% of PP and the stress decreased considerably at 4% of PP. Further, the properties increased at concentrations of 2% and 3% TPS and the stress reduced substantially at 3.5% and 4% TPS. Because the CRM-modified binder has a wide linear viscoelasticity area, CRM is the most appropriate modifier to enhance medium- and high-temperature performances.  
Note that this study investigated only medium- and high-temperature effects. In future studies, the authors will investigate the low-temperature properties of asphalt binders modified by CRM, PP, and TPS, as well as the effect of these modifiers on the physical properties and the low-temperature performance (mechanical performance) of the modified asphalt binders, in order to prove which additive is preferable when enhancing bitumen binders.  
[PERSON] conceptualized the paper, designed experiments, manufactured the specimens, and performed and analyzed the experimental investigations. [PERSON] oversight the research and contributed to the review and construction of the manuscript.  
This research received no external funding but, the author would like to thank the Jiangsu Tiannuo Advanced Material Technology Co., Ltd./China, for patronizing this research study.  
The authors have no conflict of interest to report.