## 6 Conclusions  
Based on the average annual amount of UV radiation in China in the most recent 30 years and the characteristics of the UV aging of asphalt, the climatic zoning of UV radiation of asphalt in China was proposed. A variety of base asphalts and styrene-butadiene-styrene block copolymer (SBS) modified asphalts were selected to carry out the UV radiation test, and the relationship between UV radiation amount and viscosity, low-temperature performance, and rheological properties of asphalt were studied. The equivalent aging indexes of asphalt during UV radiation were selected, the UV aging equation of asphalt was proposed, and the equivalent UV aging relationship among different UV climate zones was established. The prevention and control strategies of UV aging of asphalt among different zones were proposed, and the above theory was verified using a trial road.  
The main conclusions are shown as follows:  
* The asphalt UV climate zone I is the area with annual UV radiation less than or equal to 69.4 kW\(\cdot\)h/m\({}^{2}\) in the most recent 30 years, zone II is areas with annual UV radiation of 69.4-81.4 kW\(\cdot\)h/m\({}^{2}\) in the most recent 30 years, and zone III is areas with annual UV radiation more than or equal to 81.4 kW\(\cdot\)h/m\({}^{2}\) in the most recent 30 years;
* The greater the amount of UV radiation, the greater the loss rate of penetration and ductility. For the same kind of asphalt, there is a relatively stable functional relationship between the loss rate and the amount of UV radiation.
* For asphalt, the G\({}^{*}\) increases and \(\delta\) decreases with increasing UV aging time, which indicates that the elastic component of the asphalt response becomes more dominant and the viscous component less dominant with UV aging.
* The penetration loss rate and ductility loss rate of asphalt can be used as equivalent UV aging indexes of asphalt.
* Under the same outdoor UV irradiation time, if asphalt wants to achieve the same technical performance as in zone I, the anti-UV ability of zone II needs to be improved by more than 5%, and that of zone III needs to be improved by more than 10%.  
Figure 14: Representative disease photos of the trial sections.  
It is necessary to state that the aging of asphalt mixtures is not only directly connected with UV aging of the binder but also with its composition and with humidity variations; the aging progress is different within the different thicknesses of asphalt mixtures and this progress is not related just to the type of binder [47; 48]. This paper intended to contribute to a more informed choice of the asphalt to use for surface courses constructed in different regions of China, by helping to address the aging issue on the asphalt mixtures themselves.  
Conceptualization, Z.L. and W.Z.; data curation, H.X. and W.Z.; funding acquisition, L.Z.; investigation, Z.L. and Y.C.; methodology, L.Z., M.L. and W.Z.; project administration, W.Z.; resources, W.Z.; software, H.X.; supervision, M.L.; writing--original draft, L.Z. All authors have read and agreed to the published version of the manuscript.  
Please add: This research was funded by \"National Key R&D Program of China, grant number 2018 YFB1600100\", \"Key Laboratory of Transport Industry of Road Structure and Material (Research Institute of Highway, Ministry of Transport), China, grant number 2019-Keji-271\" and \"Zhangdian District Science and Technology Bureau, China, grant number 9001-118232\".  
Not applicable.  
The data presented in this study are available on request from the corresponding author. The data used to support the findings of this study are from previously reported studies, which have been cited. This manuscript does not contain previously published Figures, Tables, and Charts, so all Figures, Tables, and Charts of this manuscript are original.  
We thank [PERSON], [PERSON] and [PERSON] for the help in the experiment.  
The authors declare no conflict of interest.