## 4 Conclusions  
In this study, diatomic and crumb rubber particles were used to reinforce the properties of asphalt mixtures. According to the rutting test, low-temperature trabecular bending test, freeze-thaw splitting test, and uniaxial compression creep test, the effects of rubber particle and diatomic on the road performance and creep characteristics of asphalt mixtures were analyzed, and their creep characteristics were studied by the Burgers model and the modified Burgers model. Through the convolution integral and creep test data, the relaxation moduli of compound modified asphalt mixtures were calculated, and their relaxation characteristics were evaluated by using the second-order extensive Maxwell model and the Scott-Blair model. Based on the above analytical results, the following conclusions can be achieved:  
1. The addition of rubber particle and diatomic can improve the high temperature stability and low-temperature crack resistance of asphalt mixtures, but the improvement effect is weaker than that of SBS. This is because rubber particle and diatomic are mainly used for physical blending to strengthen asphalt mixture, and its effect is weaker than the chemical modification of SBS. Diatomic and rubber particles have a negative impact on the water stability of asphalt mixture, while the negative effect of rubber particles on water stability become relatively weak when using SBS modified asphalt. While when using SBS modified asphalt, the negative effect of rubber particles on water stability is relatively weak.
2. The improvement effect of rubber particle and diatomic on the high and low temperature performance of suspended dense asphalt mixture is better than that of skeleton dense asphalt mixture. After the addition of rubber particles, the skeleton extrusion of skeleton dense asphalt mixture is destroyed and the local weak area is introduced, which can reduce the enhancement effect of rubber particle and diatomic on the high and low temperature performance of asphalt mixtures.  
3. The addition of rubber particle and diatomic can improve the ability of instantaneous elastic deformation, viscoelastic deformation, and irreversible permanent deformation. SBS modified asphalt has high bonding performance which can promote the strengthening of rubber particle and diatomic. The improvement effect of suspended dense matrix asphalt mixture is higher than that of skeleton dense asphalt mixture.
4. Diatomite and rubber particles can increase the relaxation modulus of asphalt mixtures, but the improvement effect is not as good as SBS modified asphalt; under the combined action of diatomaceous earth, rubber particles, and SBS modified asphalt mixture, the relaxation characteristics of asphalt mixture are the best. The effect of rubber particle and diatomite on the relaxation and solid elastic properties of the suspended dense asphalt mixture is obviously better than that of the skeleton dense asphalt mixture.  
Conceptualization, C.L. and Z.G.; methodology, C.L., Z.G. and H.Z.; validation, C.L., H.Z. and X.X.; formal analysis, H.Z.; investigation, J.H.; supervision, C.L.; writing--original draft preparation, H.Z.; writing--review and editing, C.L., Z.G., X.X. and J.H.; project administration, C.L.; funding acquisition, C.L. All authors have read and agreed to the published version of the manuscript.  
This research was funded by the Science and Technology Project of Jilin Provincial High Class Highway Construction Bureau, Contract No. 2018 ZDGC-9-1.  
We gratefully acknowledge the financial support of the above project and the researchers of all reports cited in our paper.  
The authors declare no conflict of interest.