Hydro-thermal-mechanical characteristics and sustainability of geopolymer solidified soils incorporating nano-silica in cold regions

Abstract

Geopolymer has being emerged as a promising alternative to traditional Portland cement in geotechnical engineering, particularly for subgrade applications in cold regions, owing to its eco-friendly and high-performance characteristics. However, exposing geopolymer solidified soils (GSSs) to cold environments can deteriorate the mechanical properties. Hence, it is crucial to improve the mechanical properties and freeze-thaw resistance of the GSSs. In this study, the unconfined compressive strength (UCS), hydro-thermal-deformation characteristics, and microstructure of the nano-silica geopolymer solidified soils (NSGSSs) were experimentally investigated, and the sustainability of the NSGSSs was assessed. The results showed that under the same strain condition, the stresses of the NSGSSs were larger than those of the GSSs. Besides, the UCS of the NSGSSs firstly increased and then decreased with nano-silica (NS) content, with the GSSs containing 3 wt% NS demonstrating the highest peak stress. The UCS loss rate increased with the freeze-thaw cycles (FTCs) and then stabilized, with the first FTC having the most significant impact on the UCS of the soil samples. During the FTCs, the NSGSSs exhibited a larger amplitude of soil temperature variation and residual volumetric unfrozen water content compared to the GSSs. However, the vertical deformation, frost heave and thaw settlement rates of the NSGSSs were markedly smaller than those of the GSSs. After the 9th FTC, the NSGSSs with 3 wt% NS content showed a denser structure and excellent freeze-thaw resistance. Moreover, although adding NS to GSSs increased carbon emissions and costs, the low values of the carbon emission index and economic efficiency index indicated that the substantial improvement in mechanical properties outweighed these negative aspects, particularly for the NSGSSs exposed to the FTCs. This study would provide valuable insights into the development of new eco-friendly materials and offers a novel approach for frost heave prevention and control in cold region geotechnical engineering.