## 4 Conclusions  
In China, many researchers are confronted with two sets of indicators in evaluating SBS-modified asphalt, Chinese test methods and Superpave test methods, which are random in practical application. In order to make the evaluation of SBS-modified asphalt performance more reliable and targeted, this paper evaluates the adaptability of each indicator through the quantitative analysis of laboratory tests. The research results provide theoretical support for unifying the performance evaluation index of SBS-modified asphalt, and provide suitable evaluation index for the selected SBS modifier which is development by a materials company and widely used in Shaanxi province, China. Some conclusions are as follows:  
(1) According to the performance evaluation tests conducted in China and other countries, the addition of SBS modifier can significantly improve the high-temperature performance of asphalt, and can also significantly reduce the temperature sensitivity of asphalt. In addition, it increased the viscosity of asphalt at high temperatures, and increased the difficulty of mixing and compaction of the asphalt mixture.  
(2) For SK70# and SK90# matrix asphalt, the addition of the SBS modifier can reduce the penetration of asphalt binder in a certain extent, but the effect was not obvious, and the penetration index of asphalt binder had no obvious trends between different modifier contents. In addition, the swelling effect of SBS modified asphalt might lead to great variability of penetration test results, so the penetration test was not recommended to evaluate the performance of SBS modified asphalt.  
(3) The addition of SBS modifier can significantly improve the softening point of asphalt binder, and this conclusion was in line with the dynamic shear rheological (DSR) test results in Superpave. Therefore, the softening point can be taken as an evaluation index for the high-temperature performance of SBS modified asphalt. The variance analysis shows the effects of SBS modifier on the softening point of SK90# matrix asphalt were significantly better than that of SK70# matrix asphalt.  
(4) SBS modifier can considerable enhance the ductility and elastic recovery of asphalt binder, which was in line with the bending beam rheometer (BBR) test results in Superpave. The analysis of variance showed that the influence of SBS modifier on the ductility and elasticity recovery of 70# asphalt was greater than that of 90# asphalt, and the influence of SBS modifier on stiffness was greater than that of the ductility. Therefore, in the study of the influence of SBS modifier on the low temperature performance of asphalt binder, the effect of BBR test was more obvious than the low temperature ductility test. In addition, the low temperature ductility value of SBS modified asphalt was small. Therefore, the possibility of error was greater during the test. Thus, it was recommended to using the BBR test to evaluate the low-temperature performance of SBS modified asphalt.  
[PERSON] and [PERSON] conceived and designed the experiments; [PERSON] performed the experiments; [PERSON] and [PERSON] analyzed the data; [PERSON] and [PERSON] contributed reagents/materials; [PERSON] wrote the paper; [PERSON] and [PERSON] reviewed and edited the paper.  
This research was funded by the research project of the National Natural Science Foundation of China (NSFC) (no. 51578075, 51878063), the Open Fund of Key Laboratory of Special Environment Road Engineering of Hunan Province (Changsha University of Science & Technology) (KFJ180503), and the Scientific Research Foundation of Xi'an Aeronautical University (2018 KY0212).  
The authors declare no conflict of interest.