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<p>Fly ash-based geopolymers (FA-BG) have emerged as a promising alternative to traditional binders for soil stabilisation. However, existing reviews remain primarily descriptive and provide limited quantitative or mechanistic insight into their geotechnical performance. This review synthesises current knowledge through a mechanism-driven and property-oriented framework, linking activator chemistry, curing conditions, precursor characteristics, and soil mineralogy to the engineering behaviour of FA-BG-stabilised soils. Particular emphasis is placed on unconfined compressive strength (UCS), California bearing ratio (CBR), shear strength, and durability envelopes derived from reported experimental datasets. Quantitative envelopes extracted from over two decades of studies indicate that FA-BG treatment typically increases unconfined compressive strength from 0.7 to 4.5&#xa0;MPa, enhances soaked CBR by 200–600%, reduces plasticity indices by 20–60%, and lowers hydraulic conductivity by one to three orders of magnitude. These improvements are governed by the formation and densification of N-A-S-H/C-A-S-H gels, pore refinement, and modified clay surface interactions. Durability assessments further show notable resistance to leaching, chemical attack, and thermal degradation, although inconsistencies arise from variability in precursor composition, activator concentration, and curing regimes. Critical analysis of conflicting results reveals persisting challenges related to standardised mix design, incomplete reporting of untreated soil properties, and limited long-term field validation. Unlike earlier descriptive reviews, this work provides an interpretive framework to guide optimised geopolymer soil stabilisation and future research directions.</p>

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Review of the engineering behaviour of fly ash-based geopolymers in soil stabilization studies

  • 期刊论文

  • 发表日期：

    2026年3月11日

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  • Humaib Nasir,
  • Davinder Singh

摘要

Fly ash-based geopolymers (FA-BG) have emerged as a promising alternative to traditional binders for soil stabilisation. However, existing reviews remain primarily descriptive and provide limited quantitative or mechanistic insight into their geotechnical performance. This review synthesises current knowledge through a mechanism-driven and property-oriented framework, linking activator chemistry, curing conditions, precursor characteristics, and soil mineralogy to the engineering behaviour of FA-BG-stabilised soils. Particular emphasis is placed on unconfined compressive strength (UCS), California bearing ratio (CBR), shear strength, and durability envelopes derived from reported experimental datasets. Quantitative envelopes extracted from over two decades of studies indicate that FA-BG treatment typically increases unconfined compressive strength from 0.7 to 4.5 MPa, enhances soaked CBR by 200–600%, reduces plasticity indices by 20–60%, and lowers hydraulic conductivity by one to three orders of magnitude. These improvements are governed by the formation and densification of N-A-S-H/C-A-S-H gels, pore refinement, and modified clay surface interactions. Durability assessments further show notable resistance to leaching, chemical attack, and thermal degradation, although inconsistencies arise from variability in precursor composition, activator concentration, and curing regimes. Critical analysis of conflicting results reveals persisting challenges related to standardised mix design, incomplete reporting of untreated soil properties, and limited long-term field validation. Unlike earlier descriptive reviews, this work provides an interpretive framework to guide optimised geopolymer soil stabilisation and future research directions.