The utilization of high-quality curing agents to improve loess filler can not only use local materials to cut down the project cost, but also diminishes the amount of traditional binders such as lime and cement, which is of great significance for carbon reduction. In order to explore the mechanical properties and durability of composite improved loess using CG-2 curing agent and cement, a series of tests are conducted, including triaxial shear tests, unconfined compressive strength (UCS) tests, freeze-thaw cycle tests, and water stability tests. Furthermore, the microscopic pore structure of the composite improved loess is studied by SEM NMR and XRD tests. The findings indicate that the maximum dry density and optimal water content of the composite improved loess show a trend of increasing first and then decreasing with the increase of cement and curing agent dosage (DCA), and the maximum value is obtained when a cement dosage is 6 % and a DCA of 0.020 %. The shear strength and UCS of the composite improved loess are significantly higher than those of the cement improved loess (CIL), and the greater the amount of curing agent, the higher the strength. On the premise of reaching the same strength standard, the addition of curing agent can significantly reduce the amount of cement. With the increase of the DCA and cement dosage, the durability of composite improved loess is significantly improved than that of the CIL. The addition of curing agent can also reduce the spacing of mineral crystal planes of the composite improved loess, enhance the cementation characteristics of soil particles, change the contact mode between particles, and then improve the physical and mechanical properties of the improved soil. It is recommended to use a cement dosage of 6 % and a DCA of 0.020 % for the improvement of loess filling materials of secondary and below highway base, which can achieve the optimal improvement effect.

In order to study the improvement effect of the CG-2 curing agent and cement on loess, a series of physical and mechanical property tests and microstructure tests were carried out on loess improved with different dosages of curing agent and cement to study the physical and mechanical properties, durability and microscopic pore characteristics of the CG-2 curing agent and cement-improved loess. The results show that the unconfined compressive strength of improved loess increases gradually with the increase in curing agent and cement dosage, and the higher the compaction degree and the longer the curing age, the higher the unconfined compressive strength. In the case of the same cement content, the higher the dosage of curing agent, the more the unconfined compressive strength of improved loess increases. Under the condition of reaching the same unconfined compressive strength, the addition of curing agent can significantly reduce the amount of cement. The more the content of cement and curing agent, the less the unconfined compressive strength decreases after a certain number of freeze-thaw cycles, and the higher the dry-wet cycles index after a certain number of dry-wet cycles, indicating that the addition of curing agent can significantly improve the ability of the sample to resist freeze-thaw cycles and dry-wet cycles. According to the microscopic test results, it is found that the addition of curing agent can reduce the porosity of soil particles, change the contact and arrangement mode between soil particles, and enhance the agglomeration and cementation characteristics between soil particles, and obviously improve the physical and mechanical properties of soil. The research results can provide new ideas and methods for the improvement technology of loess.