Document Type : Original Research Paper
Authors
1 Faculty of Civil Engineering, Shahrood University of Technology, Shahrood, Iran
2 Associate Professor, Faculty of Civil Engineering, Shahrood University of Technology, Shahrood, Iran
3 Faculty of torbat heydarieh university
Abstract
This study investigates the mechanical performance of clayey soil (CL) and sandy soil (SP) stabilized using Bagheran Natural Pozzolan (BNP)-based geopolymer binders activated with sodium hydroxide (NaOH) and sodium silicate (Na₂SiO₃). The novelty of the study lies in the systematic comparison of BNP-based geopolymer systems in two contrasting soil matrices and the identification of soil-dependent activator mechanisms under ambient curing conditions. An experimental program was conducted including unconfined compressive strength (UCS) testing at 7, 28, and 90 days, supported by scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX), and X-ray diffraction (XRD) analyses. The results showed that alkali activation substantially improved the UCS of both soils compared with untreated, pozzolan-only, and cement-stabilized specimens. For clayey soil, NaOH activation produced 90-day UCS values of 4100–4600 kPa, while the incorporation of 5% microsilica increased the 90-day UCS to 6700–10200 kPa. The highest clay strength was obtained for the 30% P+NaOH+Si mixture. For sandy soil, NaOH-activated mixtures reached 6469–8100 kPa at 90 days, while NaOH+Si mixtures reached 6500–11659 kPa. The highest strength in sandy soil was obtained using sodium silicate activation, with the 20% P+Na₂SiO₃ mixture reaching 24000 kPa at 90 days. Microstructural observations supported the UCS trends by showing matrix densification, pore refinement, and improved interparticle bonding in alkali-activated specimens. Overall, under the tested laboratory conditions, BNP-based geopolymer stabilization showed strong potential as an alternative to cement stabilization, with NaOH+microsilica being more effective for clayey soil and Na₂SiO₃ activation being more effective for sandy soil.
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