Efficacy of expansive soil stabilisation using un-calcinated Kaolinite-Based Alkali-Activated binders

In recent years, alkali-activation and geopolymerisation have emerged as sustainable alternatives for stabilising expansive soils, traditionally treated with lime or cement. While most studies focus on high-temperature-processed materials such as fly ash, slag, and metakaolin, this study investigates the potential of using un-calcinated kaolinite as a precursor to produce an alkali-activated binder (U-KAB) slurry for expansive soil stabilisation. The U-KAB slurry, prepared by mixing un-calcinated kaolinite with NaOH solution, was applied at dosages ranging from 1.6% to 9.6% to a synthetic expansive soil composed of kaolinite, montmorillonite, and quartz. Two phases of experimental testing and characterisation provided valuable insights into its stabilisation potential, highlighting a new pathway for the development of cleaner soil stabilisation binders by avoiding the high energy consumption and carbon emissions associated with thermal calcination. The paper also emphasises the critical importance of carefully monitoring NaOH dosage and allowing for an adequate curing period—incorporating both sealed curing and air-drying—to enhance stabilisation effectiveness. Furthermore, while the results underscore the stabilisation potential of the U-KAB slurry, they also highlight the potential presence of excess unreacted alkali when aiming to achieve well effective dissolution of aluminosilicates at higher dosages. Unreacted alkali can adversely affect the stabilisation process, particularly in causing unsought swelling or negative swelling (consolidation) in the treated soils depending on the curing conditions. This indicates there may be a need in some cases to further optimise U-KAB mix design to mitigate these issues. The goal is to achieve an optimised U-KAB slurry with effective dissolution of the precursor to enhance geopolymerisation while ensuring adequate workability for mixing to stabilise the expansive soil.