Synergistic Effect of Nano-TiO2 and CNTs on the Mechanical and Microstructural Properties of Cement–Silica Fume Stabilized Soils under Freeze–Thaw Cycles

Abstract

Soft clay soils with high water content and low bearing capacity pose serious challenges for geotechnical infrastructures, particularly in cold regions where repeated freeze-thaw cycles accelerate structural degradation. Although various nano-additives have been utilized  to enhance soil stabilization, the synergistic effect of nano titanium dioxide (nano-TiO2) and carbon nanotubes (CNTs) in cement–silica  fume systems has not yet been systematically evaluated. In this study, the combined influence of nano-TiO2 and CNTs on the mechanical and durability properties of cement–silica fume stabilized soils was investigated through an extensive experimental program involving 243 specimens prepared with 12% cement and varying silica fume (5−20%), nano-TiO2 (1−5%), and CNT (0.15−0.45%)  contents, cured for 7, 28, and 56 days. The specimens were subjected to 25 freeze–thaw cycles at a constant moisture  content of 40%, exceeding the liquid limit of the soil.Results indicated that the silica fume–cement mixtures improved unconfined  compressive strength (UCS) by an average of 85% compared to cement alone, while the incorporation of nano-TiO2 and CNTs further  increased UCS by up to 142%. Water absorption decreased by approximately 85%, and strength loss under freeze–thaw cycles was  minimal. These findings highlight the novelty and practical significance of the nano-TiO2–CNT composite in enhancing both the mechanical strength and frost durability of cement-stabilized soils, providing a sustainable approach to subgrade stabilization in cold climates.