Study on mechanical properties and microstructure of geopolymer solidified loess under dry-wet-freeze-thaw cycles

Abstract

[Objective] Loess in open water conveyance channels in cold and arid regions of northwest China is commonly subjected to the coupled effects of dry-wet alternation and freeze-thaw cycles, which can induce pore expansion, structural loosening and strength degradation. To reveal the mechanical deterioration mechanism and microstructural evolution of geopolymer solidified loess under dry-wet-freeze-thaw cycles, and to improve the long-term service stability of loess slopes in open channels, the durability of geopolymer solidified loess was investigated. [Methods] Loess collected from an open water conveyance channel in Xinjiang was used as the research object. Geopolymer solidified loess specimens with geopolymer contents of 0%, 5%, 10% and 15% were prepared and subjected to 0 to 12 dry-wet-freeze-thaw cycles. X-ray diffraction, scanning electron microscopy-energy dispersive spectroscopy and nuclear magnetic resonance tests were conducted to characterize the mineral composition, micromorphology and pore structure evolution. [Results] Geopolymer significantly improved the strength and resistance of loess to dry-wet-freeze-thaw deterioration, with the 10% geopolymer content showing the best performance. Before cycling, the unconfined compressive strength of the 10% geopolymer solidified loess reached 1.405 MPa, which was 248% higher than that of untreated loess. After 12 cycles, its strength loss rate was 37.12%, markedly lower than the 62.53% of untreated loess. The microstructural result showed that C—S—H and C—A—H gels generated by geopolymerization filled pores and cemented soil particles, transforming the soil from a loose flocculated structure into a dense cemented structure. Dry-wet-freeze-thaw cycles weakened the gel cementation effect, promoted the transformation of small pores into large pores and led to continuous strength degradation. Correlation analysis of pore structure indicated that the number of large pores had the most significant influence on the deterioration of unconfined compressive strength. [Conclusion] Geopolymer can synergistically improve the dry-wet-freeze-thaw resistance of loess through gel filling, particle cementation and pore refinement. A geopolymer content of 10% achieves a favorable balance between strength enhancement and durability improvement. The results provide a scientific basis for the application of geopolymer solidified loess in open channel engineering.

Keywords

geopolymer solidified loess / dry-wet-freeze-thaw cycles / open water conveyance channel / unconfined compressive strength / deformation modulus / pore structure / microstructure / deterioration mechanism