Effect of cement kiln dust on expansive subgrade stabilised with alkali-activated fly ash

Expansive subgrades are problematic soils due to their poor load-bearing performance and high-volume change capacity. This study explored the effect of cement kiln dust (CKD) on the behaviour of a laboratory-prepared highly expansive subgrade, consisting of a bentonite–kaolin blend treated with alkali-activated fly ash (FA), through several experimental tests. A series of laboratory tests was performed, and the performance of the treated specimens was evaluated against that of conventional cement-treated specimens. An artificial neural network (ANN) model was constructed to predict unconfined compressive strength (UCS) of soil samples. Alkali-activated soil samples exhibited improved strength characteristics compared to cement-treated specimens under laboratory conditions. The CKD further increased the mechanical performance of specimens. Swelling and water absorption (WA) were reduced by over 99% and 97%, respectively, after 28 d of soaking. Microstructural analyses suggested the development of a more compact and less porous structure. The proposed stabilisation method showed promise as a potentially more sustainable alternative to cement, achieving up to 30% lower CO2-e emissions. The ANN exhibited superior predictive performance, highlighting its potential as a cost-effective tool for geotechnical applications. Additionally, a multi-factor analysis of variance (ANOVA) revealed that bulk density (BD), swelling, WA and UCS were predominantly influenced by CKD (%), FA (%) and molarity.