Research on Mechanical Characteristics and Crack Resistance of Fly Ash Sandstone Tunnel Slag Cement Stabilized Material

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.