Modification of silty clay subgrade filler with red Pisha sandstone and carbide slag in seasonally frozen regions

Proper utilization of lower cost waste materials and industrial by-products for subgrade filling soil stabilization is an avenue of resource conservation and environmental protection. In this study, red Pisha sandstone (RPS) and carbide slag (CS) were selected to stabilize silty clay. The improvement effects of RPS–CS-stabilized soil with different admixture contents were evaluated through strength and durability tests. In addition, the mechanism of the improvement was investigated. The results indicate that the triaxial compressive strength of silty clay stabilized with 15 wt.% RPS and 15 wt.% CS was 81–136% times that of the unstabilized silty clay. After 20 freeze–thaw cycles, the strength loss ratio was 0.4–4.7% and the compression coefficient increased from 0.053 to 0.069 MPa −1 . More sand-size particles are beneficial to the adequate agglomeration and hydration reactions of RPS and CS. Large amounts of small rounded and plate-like calcium silicate hydrates (C–S–H gels) filled the soil’s pores and the number of isolated pore fractures in the samples decreased, which was responsible for the excellent mechanical properties of the RPS–CS-stabilized silty clay. The results of this study provide a reference for the utilization of red Pisha sandstone and carbide slag as sustainable stabilizers in embankment applications in seasonally frozen regions.