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<p>Poorly graded sands, characterized by high porosity and very low bearing capacity, present a persistent challenge in geotechnical engineering. In recent years, geopolymers have gained increasing attention as sustainable, low-carbon binders and viable alternatives to conventional cement. This study investigates the mechanical behavior and microstructural evolution of poorly graded sand stabilized using a slag-based geopolymer, with performance comparisons made against conventional cement stabilization at cement contents of 5, 8, and 11 wt.%. The effects of slag content (10, 20, and 30 wt.%), alkaline activator-to-slag ratio (0.5, 0.75, 1.0, and 1.5), and curing time (7, 14, and 28&#xa0;days) on unconfined compressive strength, stress–strain behavior, and initial stiffness were systematically evaluated. Results indicate that increasing slag content, together with an optimal activator-to-slag ratio, significantly improves the mechanical performance of the improved sand. After 28&#xa0;days of curing, the mixture containing 30 wt.% slag and an activator-to-slag ratio of 1.0 achieved a maximum unconfined compressive strength of 28.6&#xa0;MPa. Direct comparison with cement stabilization showed that the optimum geopolymer mixture developed compressive strengths more than three times higher than those of samples stabilized with 11 wt.% cement at 7&#xa0;days, with this advantage maintained at 28&#xa0;days. Beyond strength enhancement, geopolymer-treated samples exhibited higher initial stiffness, a more uniform stress–strain response, and reduced brittleness compared with cemented specimens. Microstructural analyses using Scanning Electron Microscopy (SEM) imaging and X-Ray Diffraction (XRD) patterns confirmed the formation of a dense and continuous matrix dominated by N–A–S–H and C–(A)–S–H gels, which underpin the observed mechanical improvements. Overall, the findings demonstrate that slag-based geopolymers are an efficient, sustainable, and low-carbon alternative to cement for stabilizing poorly graded sands, particularly where high strength and deformation control are required.</p>

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Slag-Based Geopolymer Versus Cement for Stabilization of Poorly Graded Sandy Soils: Mechanical Performance and Microstructural Characteristics

  • 期刊论文

  • 发表日期：

    2026年7月9日

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  • Ashkan Gholipoor Noroozi,
  • Alireza Ardakani

摘要

Poorly graded sands, characterized by high porosity and very low bearing capacity, present a persistent challenge in geotechnical engineering. In recent years, geopolymers have gained increasing attention as sustainable, low-carbon binders and viable alternatives to conventional cement. This study investigates the mechanical behavior and microstructural evolution of poorly graded sand stabilized using a slag-based geopolymer, with performance comparisons made against conventional cement stabilization at cement contents of 5, 8, and 11 wt.%. The effects of slag content (10, 20, and 30 wt.%), alkaline activator-to-slag ratio (0.5, 0.75, 1.0, and 1.5), and curing time (7, 14, and 28 days) on unconfined compressive strength, stress–strain behavior, and initial stiffness were systematically evaluated. Results indicate that increasing slag content, together with an optimal activator-to-slag ratio, significantly improves the mechanical performance of the improved sand. After 28 days of curing, the mixture containing 30 wt.% slag and an activator-to-slag ratio of 1.0 achieved a maximum unconfined compressive strength of 28.6 MPa. Direct comparison with cement stabilization showed that the optimum geopolymer mixture developed compressive strengths more than three times higher than those of samples stabilized with 11 wt.% cement at 7 days, with this advantage maintained at 28 days. Beyond strength enhancement, geopolymer-treated samples exhibited higher initial stiffness, a more uniform stress–strain response, and reduced brittleness compared with cemented specimens. Microstructural analyses using Scanning Electron Microscopy (SEM) imaging and X-Ray Diffraction (XRD) patterns confirmed the formation of a dense and continuous matrix dominated by N–A–S–H and C–(A)–S–H gels, which underpin the observed mechanical improvements. Overall, the findings demonstrate that slag-based geopolymers are an efficient, sustainable, and low-carbon alternative to cement for stabilizing poorly graded sands, particularly where high strength and deformation control are required.