Hydromechanical responses of bentonite-based superabsorbent polymer improved silt under freeze-thaw cycles

Moisture migration-induced frost heave significantly undermines subgrade integrity in cold regions, yet existing soil amendments struggle to simultaneously regulate water redistribution and maintain mechanical stability over extended freeze-thaw cycles. This study addresses this gap by developing a bentonite-based superabsorbent polymer (BT-SAP) and quantifying its multifunctional mechanism through integrated experimentation. Controlled unidirectional freezing tests reveal BT-SAP extends rapid cooling duration by 18%-22%, decelerating freezing rates while stabilizing 35 cm freezing fronts under -15 °C/5 °C thermal boundaries. The material suppresses capillary-driven moisture migration by 63%, reducing the saturation of freezing front from 32.2% to 23.5%, and enhances cohesion by 30% while confining post-cycling strength loss is less than 9.7% through gel-facilitated interparticle bonding. Critically, hydrogel networks establish dual moisture barriers at subgrade interfaces, forming a dense hydraulic seal at the base that impedes upward flux, and immobilizing 85% of pore water against freezing suction at the crown to minimize ice-lens formation. Optimal mitigation was observed for improvement layer thicknesses of 30-40 cm and BT-SAP contents of 0.5%-0.75%, which achieved substantial reductions in frost heave and preserved 92% of pre-cycle strength. The mechanisms revealed here support design guidelines for composite subgrade systems using BT-SAP and provide quantitative parameters for field-scale implementation.