This study addresses the use of alkali activated fly ash-based binder to improve engineering characteristics of soils, and as a substitute to usual high-carbon footprint stabilisers such as lime and Ordinary Portland Cement. In particular, it examines the use of a calcium-rich fly ash from coal combustion binder activated by a sodium-based alkaline solution for kaolin treatment. The global aim is to explore the feasibility of using this binder as a potential soil stabiliser. To do so, a multi-scale analysis that conjointly explores the physicochemical evolution of the system, its microstructure and mechanical performances was carried out.At a particle level, calcium-rich particles from fly ash constitute the reactive part of the mix. Their dissolution releases calcium that subsequently combines with silicon and potentially aluminium to form chains whose structure resembles the one of Calcium Silicate Hydrate encountered in Portland Cement and responsible of a mechanical improvement. At a microstructural level, a denser material is consequently formed overtime because of the filling of pores by the new compounds. Different heterogenous matrices of various porosity and arrangement are however observed across the material and owed to the high heterogeneity of fly ash whose particles locally react differently.Finally, at a macroscopic level, those changes lead to an improvement of the treated soil resistance to compression and shear forces. The maximum stability is achieved after 28 days for 10 % of added binder, and with an effectiveness suitable for field applications. This study hence confirms a positive feasibility potential of using calciumrichfly ash-based alkali activated binder for kaolin soil stabilisation.