Effect of Clay Mineralogy on the Extent of Ettringite-Induced Heaving in Lime-Treated Sulfate-Rich Soils

Lime is often used as a traditional calcium-based stabilizer to improve the engineering properties of clayey soils that do not have acceptable engineering properties. However, lime stabilization is usually counterproductive for stabilizing sulfate-rich soil due to ettringite formation and associated heaving. The extent of ettringite-induced heaving primarily depends on the soil type, stabilizer type and dosage, and curing period. This research work aims to study the role of clay mineralogy and curing period on the extent of ettringite-induced heaving. Two different sulfate-rich soils with kaolinite and montmorillonite as the predominant clay minerals were treated with lime and subjected to strength tests, both with and without exposure to capillary soaking, and one-dimensional free swell tests to assess the extent of ettringite-induced heaving after different curing periods. Besides strength and swell testing, the soil water characteristic curves for treated soil groups were also obtained to gauge the soil specimens’ affinity for water. Supplementary mineralogical and microstructural analyses using X-ray diffraction, scanning electron microscopy imaging, energy-dispersive X-ray spectroscopy, and thermal analysis were used to understand the reasons behind the observed engineering test results. Test results indicate that ettringite forms quickly in montmorillonite-rich sulfate soils than in kaolinite-rich sulfate soils. However, the magnitude of ettringite-induced swelling is greater in kaolinite-rich soil compared to montmorillonite-rich soil.