Abstract
Seasonal freeze-thaw (FT) cycles cause progressive subgrade deterioration in cold-region pavements, reducing bearing capacity and long-term structural integrity. This study investigates an organosilane-based engineered water repellency (EWR) treatment to improve hydrophobicity, moisture stability, and freeze-thaw durability of frost-susceptible subgrade soils. A high-frost-susceptibility silt from Fairbanks, Alaska, treated at a 1:40 organosilane-to-soil ratio, was subjected to repeated FT cycling under closed-system conditions. Laboratory characterisation included contact angle measurements, water drop penetration tests (WDPT), and unconfined compressive strength (UCS) evaluation at 0, 5, 10, and 15 FT cycles. EWR treatment substantially enhanced hydrophobicity, with contact angles exceeding 125 degrees and WDPT times greater than 3600 s, classifying treated soil as extremely water repellent, and durability confirmed after 21 days of humid conditioning. Untreated soils experienced strength loss of up to 12% after ten cycles due to ice formation and pore expansion, while treated soils exhibited incremental gains of 2.7% under identical conditions. Air-dried treated specimens achieved a 333% strength increase relative to optimum moisture-compacted untreated samples, retaining strength after moisture exposure. These findings demonstrate that EWR limits water ingress, preserves unsaturated pore conditions, and mitigates FT-induced degradation, highlighting its potential for resilient pavement design in cold regions.