干湿-冻融循环作用下地聚物固化黄土力学特性及微观结构研究

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

摘要

【目的】西北寒旱区输水明渠黄土长期受干湿交替与冻融循环耦合作用影响，易发生孔隙扩展、结构松散和强度衰减。为揭示地聚物固化黄土在干湿-冻融循环下的力学劣化机制与微观结构演化规律，提升明渠黄土边坡长期服役稳定性，开展地聚物固化黄土耐久性研究。【方法】以新疆某输水明渠黄土为对象，制备0%、5%、10%和15%地聚物掺量固化黄土试样，开展0~12次干湿-冻融循环试验，采用X射线衍射、扫描电镜-能谱分析和核磁共振技术，表征矿物组成、微观形貌及孔隙结构变化。【结果】地聚物显著提高了黄土强度和抗干湿-冻融劣化能力，其中10%掺量效果最优。循环前10%地聚物固化黄土无侧限抗压强度达1.405 MPa,较未固化黄土提高248%;12次循环后强度损失率为37.12%,明显低于未固化黄土的62.53%。微观结果表明，地聚物反应生成的C—S—H和C—A—H凝胶可填充孔隙、胶结土颗粒，使土体由松散絮凝结构向致密胶结结构转变；干湿-冻融循环会削弱凝胶胶结作用，促进小孔隙向大孔隙转化，导致强度持续衰减。孔隙结构关联分析表明，大孔隙数量对无侧限抗压强度劣化影响最显著。【结论】地聚物可通过凝胶填充、颗粒胶结和孔隙细化协同提升黄土抗干湿-冻融循环性能，10%掺量可实现强度提升与耐久性改善的较优平衡。研究结果可为地聚物固化黄土在明渠工程的应用提供科学依据。

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.

关键词

地聚物固化黄土 / 干湿-冻融循环 / 输水明渠 / 无侧限抗压强度 / 变形模量 / 孔隙结构 / 微观结构 / 劣化机制

Key words

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

基金资助

国家自然科学基金项目(52204201)