Sustainable approach to mitigate freeze–thaw damage in collapsible soils using nano-scale iron oxide

Loess soils in cold regions are highly susceptible to freeze–thaw-induced deterioration, which can significantly affect the durability and stability of geotechnical structures. However, the coupled effects of nano iron oxide (NIO) stabilization and repeated freeze–thaw cycles (FTCs) on the mechanical and shear behavior of loess soils have not been sufficiently investigated. This study evaluates the influence of NIO stabilization on the mechanical, durability, and shear behavior of loess soil subjected to FTCs. Unconfined compressive strength (UCS), ultrasonic pulse velocity (UPV), direct shear, and accumulated mass loss tests were conducted on loess specimens containing different NIO contents under various FTC conditions. The results demonstrated that the inclusion of NIO significantly enhanced the mechanical performance and freeze–thaw resistance of loess soil. The optimum performance was observed at 1.5% NIO content, where the UCS increased by approximately 32% compared with untreated soil after 14 days of curing, while the corresponding UPV increased by approximately 27%. After 12 FTCs, specimens stabilized with 1.5% NIO maintained UCS values approximately 60% higher than untreated loess and exhibited the lowest accumulated mass loss (5.7%) compared with untreated soil (8.2%). Moreover, the reductions in UPV, cohesion, and internal friction angle after 12 FTCs were limited to approximately 23%, 14%, and 12.3%, respectively, indicating improved resistance against freeze–thaw-induced structural degradation. The improved behavior of stabilized loess was mainly attributed to nanoparticle-induced densification, pore filling, and enhancement of interparticle bonding within the soil matrix. Overall, the findings indicate that nano iron oxide can be considered a promising stabilizer for improving the mechanical performance and freeze–thaw durability of loess soils in cold-region geotechnical applications.