Stabilization of an expansive clay containing sulfate with Soma fly ash

Date

2025-09-01

Author

As, Mehmet
Çokça, Erdal

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Stabilization of an expansive soil containing sulfate with lime fails to effectively mitigate the swelling behavior of these soils as a result of the occurrence of ettringite, a highly expansive mineral. This study evaluated the effectiveness of utilizing15% Soma fly ash (SFA) as an alternative to 4% lime (L) in enhancing the stability of expansive soil containing sulfate (SO4) against swelling. Maximum allowable SO4 content for the stabilization of the expansive sulfate clay with SFA wasinvestigated to achieve the greatest reduction in swell potential and simultaneously inhibit the formation of ettringite. Index, swelling, and unconfined compressive strength (UCS) tests, together with scanning electron microscope (SEM)views and X-ray diffraction (XRD) analysis, were used to assess the impact of fly ash on the behavior of sulfate-bearing expansive soil.SO4 concentration exhibited varying effects on the swell potential of treated specimens. A noticeableincrease in the swell potential of expansive sulfate clay was observed when treated with 4% L, but no significant increase was observed when treated with 15% SFA. The UCS of the expansive sulfate clay specimens treated with both additivesgenerally decreased. A significant reduction in strength was recorded for expansive sulfate clay treated with 15% SFA and exposed to 27,000 ppm SO4 when cured at 10 °C, primarily due to ettringite/thaumasite and thenardite formation. Theresults indicated that 15% SFA can be safely used for stabilizing expansive soils containing SO4 without causing heave or durability problems, provided that the SO4 concentration of the expansive soil is below the threshold level of 6750 ppm.

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https://hdl.handle.net/11511/117332

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Department of Civil Engineering, Article