In response to the environmental challenges posed by conventional expansive soil stabilization methods, this study investigates the low-carbon potential of industrial by-products-cement kiln dust (CKD) and calcium carbide slag (CCS)-as sustainable stabilizers. A comprehensive series of laboratory tests, including compaction tests, free swelling rate measurements, unconfined compressive strength (UCS) evaluations, and scanning electron microscopy (SEM) analyses, were conducted on expansive soil samples treated with varying dosages in both single and binary formulations. The results indicate that the binary system significantly outperforms individual stabilizers; for example, a formulation containing 10% CKD and 9% CCS achieved a maximum dry density of 1.64 g/cm3, reduced the free swelling rate to 22.7% at 28 days, and reached a UCS of 371.3 kPa. SEM analysis further revealed that the enhanced performance is due to the synergistic formation of hydration products-namely calcium silicate hydrate (C-S-H) and calcium aluminate hydrate (C-A-H)-which effectively fill interparticle voids and reinforce soil structure. These findings demonstrate that the dual mechanism, combining rapid early-stage hydration from CCS with sustained long-term strength development from CKD, offers a cost-effective and environmentally sustainable alternative to traditional stabilizers for expansive soils.

This study addresses the engineering geological disaster resulting from the degradation of mechanical properties of expansive soil due to changes in environmental humidity along the Middle Route of the South-to-North Water Transfer Project. Calcium carbide slag and slag are utilized as curing materials to improve the expansive soil. Comparative tests were conducted on the unconfined compressive strength, split tensile strength, and water stability of untreated and treated expansive soil to analyze the performance differences pre- and post-treatment. The strength enhancement mechanism of the calcium carbide slag-slag cured soil was investigated through the X-ray diffraction (XRD), electron microscope scanning (SEM), thermogravimetric analysis (TGA) test and nuclear magnetic resonance (NMR) test, revealing its microscopic mechanism of action. The results showed a significant increase in the overall strength and water resistance of the calcium carbide slag-slag composite modified cured soil with different slag dosage based on 6% dosage of calcium carbide slag, and a maximum value was reached when the slag dosage was 9%. Over time, the unconfined compressive strength and split tensile strength improved, while the water stability coefficient decreased notably. Hydration of calcium silicate hydrate (C-S-H) and calcium aluminate hydrate (C-A-H) generated by the hydration of calcium carbide slag-slag composite cured soil led to the formation of tightly bonded soil particles, enhancing the soil's pore structure distribution and strength. The evident effectiveness of the composite curing method for calcium carbide slag-slag treated soil suggests promising engineering applications.