| Summary: | Geopolymer (GP) has recently emerged as a novel and environmental friendly alternative to conventional soil stabilization products like lime and Ordinary Portland Cement (OPC), which adversely affect the environment. This article emphasizes GPs produced from high calcium class C fly ash (CFA) and an alkali activator comprising sodium hydroxide and sodium silicate solution for sand stabilization. The experimental program includes a series of unconfined compressive strength (UCS), flexural strength, tensile strength, and microstructural analyses using scanning electron microscopy. Results revealed that UCS, flexural strength, and tensile strength of GP-treated soil were in the range of 2–10, 0.5–2.0, and 0.4–1.2 MPa, respectively (depending on the ratio of fly ash and activator). These strengths were even higher than those of cement-stabilized soil. The microstructural analysis revealed that the formation of dense calcium–sodium alumina–silicate hydrated gel (C, N–A–S–H) is the reason for strength improvement. According to the findings of this study, using a CFA-GP binder for soil improvement is a viable alternative to OPC in geotechnical applications.
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