Freeze-thaw response and macro-micro evolution of saline soil stabilized with lime and fly Ash

초록

Freeze-thaw cycles in cold regions often induce severe deterioration in saline subgrade soils due to their geological and environmental sensitivity. To address this, low-carbon, resource-efficient stabilization methods are urgently needed as sustainable alternatives to traditional cement-based solutions. In this study, industrial by-product fly ash and lime were utilized to stabilize saline soils, aiming to reduce environmental impact while enhancing frost resistance and durability. Unconfined compressive strength (UCS) tests, scanning electron microscopy (SEM), mercury intrusion porosimetry (MIP), and X-ray diffraction (XRD) were employed to assess both mechanical properties and microstructural evolution. The results indicate that lime-fly ash stabilization markedly increases UCS, with the highest improvement, approximately 34.2 times that of untreated soil, achieved using 20% fly ash after 28 days of curing. Freeze-thaw cycles (FTCs) induce microstructural changes, transforming larger inter-aggregate pores into smaller intra-aggregate pores (< 4 mu m) and reducing the dominant pore size, leading to a denser soil matrix. The addition of fly ash enhances hydration reactions, forming calcium silicate hydrate (CSH) and calcium aluminate hydrate (CAH) gels that improve the stability of soil under FTCs. Lime-fly ash stabilized soil exhibits greater strength retention and self-healing capabilities during FTCs compared to lime-stabilized soil. These findings provide insight into the long-term evolution of stabilized saline soils and offer practical implications for enhancing subgrade durability and environmental sustainability in cold-region infrastructure development.

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