Hybrid alkaline-lime treatment for swelling and microstructure of expansive soil

Addressing the challenges posed by expansive soil, which undergoes significant volume changes with variations in moisture content, is crucial for ensuring the durability and reliability of civil engineering infrastructure. Traditional calcium-based stabilisers raise environmental concerns and may trigger secondary swelling. This study explores a novel approach to soil stabilisation by directly activating aluminosilicates in a synthetic soil simulating the mineralogical composition of residual Bringelly Shale using sodium hydroxide (NaOH), without additional precursors. The experimental program involved synthesising artificial soil samples and treating them with NaOH solution at various molarities, lime alone, and hybrid use of lime and NaOH solution, respectively. Swelling potential, microstructural analyses, and mineralogical composition were assessed using the swelling tests, scanning electron microscopy, X-ray diffraction, Fourier transform infrared spectroscopy, and thermogravimetric analysis. The findings indicate that the direct alkali activation technique has the potential to substitute lime binders partially or completely, ensuring stability in swelling potential while minimising the environmental impact and cost. The curing effects on hybrid-treated soil were investigated over 7, 14, and 28 days, showing promising long-term outcomes. In addition, a design formula has been designed to help practitioners choose the optimum lime-to-alkaline ratio for achieving the desired swelling control.