Lime–fly ash binder composition controls freeze–thaw durability of stabilized clays

This study examines the effects of freeze-thaw (F-T) cycles on the unconfined compressive strength (UCS) of untreated and stabilized soils using fly ash, lime, and lime-fly ash mixtures (30% FA, 5% L, and 30% FA + 5% L). Specimens were subjected to 2, 4, 6, 8, and 12 F-T cycles. Fly ash-only mixtures showed a continuous reduction in UCS with increasing cycles, whereas lime and lime-fly ash mixtures exhibited higher resistance to F-T deterioration. Strength remained relatively stable up to six cycles, followed by a noticeable decline; however, lime-treated samples maintained higher UCS than untreated soils even after 12 cycles. For S30FA5L, S5L, and B5L mixtures, UCS increased by approximately 27-35% during the 2nd to 4th cycles. Lime-treated soils exhibited higher strength and more brittle behavior, while lime-fly ash mixtures showed more ductile responses. Although fly ash addition did not significantly enhance strength compared to lime alone, it improved ductility. Furthermore, strength enhancement became more pronounced when CaO > 7.7%, CaO/Al₂O₃ > 0.44, CaO/SiO₂ > 0.13, and CaO/(Al₂O₃ + SiO₂) > 0.10. These findings highlight the importance of oxide composition and calcium availability in governing freeze-thaw durability of stabilized clays.