# Rheological Performance of Bio-Char Modified Asphal with Different Particle Sizes
## 5 Results and Discussions
### Dynamic Shear Rheometer Test  
#### 5.3.1 Putting Resistance Analysis  
From Figure 4a, the rutting indexes of 2% BL, 4% BL, 8% BL, 2% BS, 4% BS, and 8% BS increased by 4.55%, 17.49%, 45.72%, 23.61%, 31.70%, and 58.40%, on average, as compared to that of the control asphalt binder within a 52 \({}^{\circ}\)C to 76 \({}^{\circ}\)C temperature range. This meant that bio-char modified asphalts had better resistance to rutting at higher temperatures than the control asphalt binder. This was partially attributed to the stiff volume-filling particles, such as the bio-char particles. The other reason might be that the porous structure of bio-char led to a higher surface area which, accordingly, led to the higher adhesion between the bio-char and the base asphalt binder. With the increasing of bio-char content, the rutting resistance became stronger. The enforcement of interaction among the bio-char particles might be a contributor to the higher rutting resistance. With the increase of bio-char content, stiff porous particles came into contact with each other, and a skeleton framework could be formed when the bio-char content increased to a higher amount. The higher rutting resistance also could be explained by the higher viscosity. The conclusions were consistent with the above conclusions about the viscosities.  
From Figure 4b, after the RTFO aging, the rutting indexes of bio-char modified asphalts were higher than those before RTFO aging, because of the aging. Additionally, the bio-char modified asphalts still had higher aging resistance than the control asphalt binder. It was evident that bio-char modified asphalts, with larger-sized particles, had a more obvious change than those with smaller-sized particles. The rotational viscosities of 2% BL, 4% BL, and 8% BL were 5.80%, 3.09%, and 4.16% higher than those of 2% BS, 4% BS, and 8% BS, respectively, after the RTFO aging, while they were 15.36%, 10.76%, and 8.01% lower, respectively, before the RTFO aging. This could be attributed to the relatively weak aging resistance of bio-char modified asphalts with larger particle sizes. These conclusions were consistent with the above conclusions about the anti-aging properties.  
Figure 3: Aging indexes of control, graphite modified and bio-char modified asphalts.  
The rutting indexes of the control asphalt binder, 4% GS, 4% BL, and 4% BS, before and after RTFO aging, are displayed in Figure 5. Before the RTFO aging, the rutting indexes of 4% GS, 4% BL, and 4% BS increased by 2.32%, 17.49%, and 31.70%, on average, compared to that of the control asphalt. Therefore, the graphite modified asphalt had a similar rutting index to that of the control asphalt, and bio-char modified asphalt has better rutting index than that of the graphite modified asphalt. After the RTFO aging, the rutting indexes of 4% GS, 4% BL, and 4% BS increased by 7.07%, 20.59%, and 16.98%, on average, compared to that of the control asphalt binder. This indicated, to a large extent, that the bio-char modified asphals had better aging resistance than the graphite modified asphalt, especially, for the bio-char modified asphalt with smaller-sized particles. The higher number of stiff particles and the fibrous and porous structure of the bio-char contributed to the form of a biochar-binder matrix.  
Figure 4: (**a**) Rutting indexes (G*/sin\(\delta\)) of original control and bio-char modified asphals; (**b**) rutting indexes (G*/sin\(\delta\)) of control and bio-char modified asphals after RTFO aging.