## 4 Conclusions  
In this research, the effect of high content of waste tire rubber and sulfur on the aging behavior of bitumen was investigated. Tests related to bitumen, such as frequency sweep tests, temperature sweep tests, MSCR tests, ATR-FTIR test, RTFOT, and PAV, were carried out. The main conclusions were drawn as following:  
* The addition of sulfur to HCRMB leads to an increase in G*, R0.1, and R3.2 and a decrease in \(\delta\), Jnr0.1, and Jnr3.2, resulting in an improvement in the elasticity of HCRMB. Moreover, in the low temperature region, the G* master curves of 70# are higher than that of the HCRMB with different amounts of sulfur;
* The elasticity of 70# and HCRMB with different amounts of sulfur increases with aging. In addition, the RTFOT aging resistance and the PAV aging resistance of HCRMB is better than that of conventional RMB, and the increase in the amount of sulfur can improve the RTFOT aging resistance and the PAV aging resistance of HCRMB;
* The carbonyl group of conventional RMB is less affected by aging than that of HCRMB. Under the influence of aging, conventional RMB is more easily desulfurized than HCRMB, and sulfur cannot reduce the degree of oxidation of HCRMB after aging, but can inhibit the degree of desulfurization of HCRMB. Furthermore, the aging process of HCRMB with different amounts of sulfur is dominated by the degradation of polybutadiene, whereas there is a certain CR desulfurization in conventional RMB aging. \begin{table}
\begin{tabular}{c c c c c c c c c c} \hline \hline \multirow{2}{*}{**Sample**} & \multicolumn{2}{c}{**20 TB\_0.25 ul**} & \multicolumn{2}{c}{**20 TB\_0.45 ul**} & \multicolumn{2}{c}{**40 TB\_0.25 ul**} & \multicolumn{2}{c}{**40 TB\_0.45 ul**} \\ \cline{2-10}  & **I\({}_{\text{Si-O-Si}}\)** & **\(\Delta\)I\({}_{\text{Si-O-Si}}\)** & **I\({}_{\text{Si-O-Si}}\)** & **I\({}_{\text{Si-O-Si}}\)** & **I\({}_{\text{Si-O-Si}}\)** & **\(\Delta\)I\({}_{\text{Si-O-Si}}\)** & **I\({}_{\text{Si-O-Si}}\)** & **\(\Delta\)I\({}_{\text{Si-O-Si}}\)** \\ \hline Unaged & 0.225 & - & 0.290 & - & 0.443 & - & 0.438 & - \\ RTFOT aging & 0.331 & 0.106 & 0.328 & 0.038 & 0.464 & 0.021 & 0.450 & 0.012 \\ PAV aging & 0.335 & 0.110 & 0.357 & 0.067 & 0.476 & 0.034 & 0.442 & 0.004 \\ \hline \hline \end{tabular}
\end{table} 
Table 4: I\({}_{\text{Si-O-Si}}\) of HCRMB with different amounts of sulfur before and after aging. \begin{table}
\begin{tabular}{c c c c c c c c c c c} \hline \hline \multirow{2}{*}{**Sample**} & \multicolumn{2}{c}{**70\#**} & \multicolumn{2}{c}{**20 TB\_0.25 ul**} & \multicolumn{2}{c}{**20 TB\_0.45 ul**} & \multicolumn{2}{c}{**40 TB\_0.25 ul**} & \multicolumn{2}{c}{**40 TB\_0.45 ul**} \\ \cline{2-10}  & **I\({}_{\text{CA}}\)** & **\(\Delta\)I\({}_{\text{CA}}\)** & **I\({}_{\text{CA}}\)** & **\(\Delta\)I\({}_{\text{CA}}\)** & **I\({}_{\text{CA}}\)** & **\(\Delta\)I\({}_{\text{CA}}\)** & **I\({}_{\text{CA}}\)** & **\(\Delta\)I\({}_{\text{CA}}\)** & **\(\Delta\)I\({}_{\text{CA}}\)** \\ \hline Unaged & 0.049 & & 0.024 & & 0.016 & & 0.008 & & 0.015 & \\ RTFOT aging & 0.126 & 0.077 & 0.046 & 0.022 & 0.052 & 0.036 & 0.059 & 0.051 & 0.073 & 0.058 \\ PAV aging & 0.249 & 0.200 & 0.179 & 0.156 & 0.180 & 0.164 & 0.174 & 0.166 & 0.184 & 0.169 \\ \hline \hline \end{tabular}
\end{table} 
Table 3: I\({}_{\text{CA}}\) of HCRMB with different amounts of sulfur before and after aging. **Author Contributions:** Conceptualization, S.W. ; methodology, S.W. ; validation, W.H. ; investigation, X.L. ; writing--original draft, S.W. ; writing--review and editing, P.L. ; visualization, P.L. ; supervision, S.W. ; formal analysis, S.R. and Y.L. All authors have read and agreed to the published version of the manuscript. **Funding:** This research was developed within the Projects of National Natural Science Foundation of China under Grant number 51978518 and China Scholarship Council (CSC No. 202106260114). **Institutional Review Board Statement:** Not applicable. **Informed Consent Statement:** Not applicable.