Geomechanical Behaviour of Clay Stabilised with Low-Calcium Fly Ash and Alkali Activation

Abstract

This study examines the geomechanical behaviour of clay stabilised with alkali-activated fly ash and non-activated fly ash to improve the geotechnical properties of clay soils. Class F fly ash and its alkali-activated form were employed as stabilisers to provide a sustainable alternative to traditional binders like cement and lime. Laboratory experiments, including one-dimensional consolidation and consolidated-undrained triaxial tests, were conducted on clay samples treated with varying fly ash contents and curing durations. The results indicated that alkali-activated fly ash significantly improved the mechanical performance of clay by reducing compressibility, swelling, and permeability during curing. Triaxial test results showed that alkali activation increased strength parameters and altered the stress–strain behaviour of the soil from ductile to brittle. Specifically, clay treated with 25% alkali-activated fly ash and cured for 28 days achieved nearly a ninefold increase in maximum deviator stress compared to untreated samples. Both fly ash types improved shear strength and critical state parameters, though non-activated fly ash resulted in lower effective cohesion than the control. Overall, the findings demonstrate that untreated Class F fly ash has limited binding capacity, while alkali activation substantially enhances the stabilisation effect, offering a promising and sustainable alternative for geotechnical soil improvement.