To examine the effect mechanism of rubber and diatomite on asphalt as well as the performance of asphalt mixtures for road applications, various composite-modified asphalts are prepared using rubber and diatomite. The performance of modified asphalts with various proportions is analyzed, and the optimal dosage ratio of modifiers is determined via the response surface approach. The microstructure of rubber–diatomite composite-modified asphalt is methodically examined using Fourier transform infrared spectroscopy and scanning electron microscopy. The road performance, aging resistance, and long-term stability of asphalt mixtures are evaluated through Marshall tests, wheel tracking tests, aging wheel tracking tests, freeze–thaw splitting tests, and cyclic freeze–thaw drying aging splitting tests. The obtained results reveal that asphalt with 22% rubber and 4% diatomite exhibits the best overall performance. The composite-modified asphalt essentially demonstrates the physical blending between rubber powder, diatomite, and base asphalt. The asphalt built from them formed a uniform and stable overall structure. Compared with rubber asphalt and rubber–SBS composite-modified asphalt, rubber–diatomite composite-modified asphalt exhibits superior road performance, including better aging resistance and long-term water stability in asphalt mixtures. This study can promote the further extensive application of rubber–diatomite-modified asphalt in road engineering, while providing new ideas for cost-saving and environmentally friendly asphalt modification.

To investigate the influence of fly ash on the mechanical and crack resistance properties of cement stabilized materials, the aggregate gradation was determined based on the stepwise filling method and the i-method. The mechanical strength test, drying shrinkage test, and dry-wet cycle test were conducted to study the crack resistance characteristics of cement-stabilized tunnel slag gravel and cement-fly ash stabilized tunnel slag gravel with varying fly ash contents. A crack resistance coefficient was proposed to evaluate the crack resistance capability of cement stabilized materials. The results showed that the incorporation of fly ash affected the early unconfined compressive strength and splitting strength of cement stabilized materials—the higher the fly ash content, the lower the early strength. The addition of fly ash benefits the long-term mechanical strength.At 90 days, the mechanical strength of fly ash cement stabilized materials increased by 8–27% compared to conventional cement stabilized materials. The optimal fly ash content was approximately 9%. The incorporation of fly ash significantly reduced the early drying shrinkage of cement stabilized materials, decreasing the likelihood of shrinkage cracks. By introducing a crack resistance coefficient to evaluate the crack resistance performance of cement stabilized materials, it was found that at 28 days, the crack resistance coefficient of fly ash cement stabilized materials was 61% higher than that of conventional ones, indicating that fly ash can improve early crack resistance. In the dry-wet cycle test, the shrinkage strain of each cycle was greater than that of the initial (0th) cycle. After the fifth cycle, the crack resistance coefficient of the fly ash cement stabilized material increased by 27% compared to the conventional material, indicating that the presence of fly ash can mitigate the adverse effects of dry-wet cycles.