## 4 Results and Discussion
### Functional Group Compositions Analysis  
In order to study the reaction mechanism and the changes of 50# base asphalt with bio-oil, the relative variations in the functional groups of 50# base asphalt, bio-asphalt with 30% bio-oil,  
Figure 14: The changes of different parameters with reduced frequency change for the RTFO-aged asphalt. (**a**) Complex modulus; (**b**) Rutting factor.  
Figure 13: The changes of different parameters with reduced frequency change for the unaged asphalt. (**a**) Complex modulus; (**b**) Rutting factor.  
and the bio-oil were analyzed. As shown in Figure 15, FTIR spectra were constructed, showing the changes of absorbance spectra with wavenumber.  
The absorbance spectra trends of 50# base asphalt, bio-oil, and 50# base asphalt with 30% bio-oil were different. Based on the absorbance spectra peaks, the functional groups were analyzed from the three kinds of binders. The functional groups were identified and listed in Table 4.  
As shown in Figure 15 and Table 4, there was an obvious difference between 50# base asphalt and bio-oil. For the 50# base asphalt, C-H bending was dominant, while bio-oil had a large amount of different functional groups, such as O-H stretching, S=O, C=O stretching, and C-O stretching. This was mainly attributed to a great deal of oxygen in the bio-oil; it contributes to the aging process of bio-oil and bio-asphalt with bio-oil [22].  
\begin{table}
\begin{tabular}{c c c c} \hline \hline
**Binder Types** & **Absorption Wave Number** & **Functional Groups** & **Class of Compounds [22; 23; 24]** \\ \hline \multirow{6}{*}{50\# base asphalt} & 788-842 & C-H plane bending & Aromatic compounds \\  & 1024 & S=O & Sulfoxide \\  & 1379, 1452 & CH3 & Aliphatic compounds \\  & 1602 & C=C ring stretch & Aromatic compounds \\  & 2852, 2925 & C-H stretching & Alkanes \\  & 3421 & O-H stretching, N-H stretching & Polymeric O-H, water, NH\({}_{2}\) \\ \hline \multirow{6}{*}{Bio-oil} & 763-827 & C-H plane bending & Aromatic compounds \\  & 1097 & S=O & Sulfoxide \\  & 1263 & C-O stretching & Phenol, esters \\  & 1379, 1452 & CH3 & Aliphatic compounds \\  & 1519 & -NO\({}_{2}\) stretching & Nitrogenous compounds \\  & 1602 & C=C ring stretch & Aromatic compounds \\  & 1706 & C=O stretching & Ketones, aldehydes, carboxylic acids \\  & 2852, 2924 & C-H stretching & Alkanes \\  & 3421 & O-H stretching, N-H stretching & Polymeric O-H, water, NH\({}_{2}\) \\ \hline \multirow{6}{*}{Bio-asphalt (50\# base asphalt with 30\% bio-oil)} & 769-839 & C-H plane bending & Aromatic compounds \\  & 1024 & S=O & Sulfoxide \\ \cline{1-1}  & 1379, 1452 & CH3 & Aliphatic compounds \\ \cline{1-1}  & 1519 & -NO\({}_{2}\) stretching & Nitrogenous compounds \\ \cline{1-1}  & 1602 & C=C ring stretch & Aromatic compounds \\ \cline{1-1}  & 1706 & C=O stretching & Ketones, aldehydes, carboxylic acids \\ \cline{1-1}  & 2852, 2952 & C-H stretching & Alkanes \\ \cline{1-1}  & 3307 & O-H stretching, N-H stretching & Polymeric O-H, water, NH\({}_{2}\) \\ \hline \hline \end{tabular}
\end{table}
Table 4: Functional groups identified of three kinds of binders.  
Figure 15: FTIR spectra of three kinds of binders.  
From the comparison of the three kinds of binders, it can be seen that there was an obvious peak with wavenumber 1263 cm\({}^{-1}\), representing the presence of esters and phenol in the bio-oil. However, this disappeared after the bio-oil was added to 50\(\#\) base asphalt. The peaks at 3421 cm\({}^{-1}\) in bio-oil and 50\(\#\) base asphalt disappeared in the bio-asphalt, and a new peak at 3307 cm\({}^{-1}\) appeared in the bio-asphalt. These illustrated that some chemical reactions occurred when the 50\(\#\) base asphalt was mixed with bio-oil.  
In addition, there are many different types of functional groups and compounds in the bio-oil and bio-asphalt, such as aldehydes, ketones, carboxylic acids, and phenol. Different compounds yielded different characteristics of the bio-asphalts with added bio-oil, as compared to conventional asphalt made from crude oil.