# Aging Characteristics of Rubber Modified Asphalts in Different Environmental Factors Combinations
## 4 Conclusions  
Based on the experimental results from the three kinds of asphalts influenced by different environmental combinations, the following conclusions can be drawn:  
1. Conventional property tests, including softening point, viscosity, creep stiffness, creep rate, and fatigue cracking factor, were conducted on asphalt samples. Results demonstrate that the aging characteristics of two kinds of rubber-modified asphalts improve with different pertinences, unlike virgin asphalt. Firstly, the resistant ability to high temperature of asphalt rubber rarely declines under water molecule action, whereas TOR asphalt rubber effectively avoids the degradation in resistance to high temperature induced by ultraviolet radiation. Secondly, the low-temperature resistance of asphalt rubber remains relatively stable under either water action or air pressure. Thirdly, asphalt rubber has superior resistance to traffic loading under ultraviolet radiation. In addition, TOR asphalt rubber has strong resistance to traffic loading in a water environment.
2. Chemical analyses contribute to the determination of aging mechanism. The SEM images illustrate that the detrimental effects of multi-factor combinations lead to the rough surfaces of two kinds of rubber modified asphalts, and these correspond directly to asphalt decays. According to thermogravimetric analysis, the good thermal stability of three kinds of asphalts are confirmed by the similar TG curves observed in most environmental combinations. Based on the IR spectra, new characteristic functional groups are not detected during the different aging processes. Furthermore, the oxidation degrees of two kinds of asphalt rubbers change relatively slightly throughout each aging process, thus demonstrating the outstanding antioxidant properties of them.
3. Lastly, aging characteristics in different environments can be reasonably considered in the rational application of asphalts. Asphalt rubber is suitable for hot and humid areas or low temperature areas, meanwhile TOR asphalt rubber is appropriate to intensive ultraviolet radiation regions and heavy traffic areas.  
\begin{table}
\begin{tabular}{c c c c c c c} \hline \hline
**Sample** & **Index** & **A** & **B** & **C** & **D** & **E** & **F** \\ \hline \multirow{2}{*}{Asphalt P} & \(I_{C=O}\) & 0 & 0.018289 & 0.031278 & 0.070536 & 0.082277 & 0.095618 \\  & \(I_{S=O}\) & 0.024649 & 0.043078 & 0.088656 & 0.150342 & 0.131924 & 0.141804 \\ \hline \multirow{2}{*}{Asphalt R} & \(I_{C=O}\) & 0 & 0.051451 & 0.071577 & 0.096944 & 0.111945 & 0.128721 \\  & \(I_{S=O}\) & 0.041658 & 0.073521 & 0.075599 & 0.126110 & 0.115765 & 0.124667 \\ \hline \multirow{2}{*}{Asphalt T} & \(I_{C=O}\) & 0 & 0.046519 & 0.070505 & 0.090220 & 0.098583 & 0.109545 \\  & \(I_{S=O}\) & 0.036079 & 0.072126 & 0.073580 & 0.093736 & 0.099961 & 0.114495 \\ \hline \multicolumn{7}{c}{The integral range of C=O is [1640 cm\({}^{-1}\), 1740 cm\({}^{-1}\)]; the integral range of S=O is [985 cm\({}^{-1}\), 1070 cm\({}^{-1}\)]; the integral range of C–H is [1400 cm\({}^{-1}\), 1500 cm\({}^{-1}\)].} \\ \end{tabular}
\end{table}
Table 9: Values of C=O and S=O indices.  
**Acknowledgments:** The authors would like to acknowledge the financial support from the National Natural Science Foundation Committee of China (no. 51178409 and no. 51578480) and thank the Engineering Testing Centre of Yangzhou University for their supports in the experiment.  
**Author Contributions:** [PERSON] and [PERSON] conceived and designed the experiments; [PERSON] and [PERSON] performed the experiments; [PERSON] and [PERSON] analyzed the data; [PERSON] wrote the paper; and [PERSON] modified and provided comments on the paper.  
**Conflicts of Interest:** The authors declare no conflict of interest. The founding sponsors had no role in the design of the study; in the collection, analyses, or interpretation of data; in the writing of the manuscript, and in the decision to publish the results.