Mechanical properties and microstructural evolution of fly ash stabilized loess: Insights from multiscale analysis and environmental impacts

Loess, widely distributed globally, is prone to geological hazards due to its metastable structure. Conventional stabilizers (cement, lime) improve its mechanical properties but cause high carbon emissions. This study investigates the effectiveness of fly ash as an eco-friendly stabilizer for loess via multiscale analysis and life cycle assessment (LCA). Unconfined compression tests (UCS) were conducted to evaluate mechanical performance. The UCS of loess stabilized with 20% fly ash increased by 330.4% compared with compacted loess. Microstructural evolution is characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), and X-ray computed tomography (CT). The results show that fly ash particles can fill the inter-aggregate pores, leading to the transformation of macropores and mesopores into small pores and improving cementation. Three-dimensional CT analysis further confirms that with the addition of fly ash, the microstructure becomes denser and the pore morphology evolves toward spherical shapes. LCA demonstrates that compared to conventional stabilizers, fly ash stabilization significantly reduces global warming potential (GWP) and primary energy demand (PED). Compared to stabilization with lime and cement, using fly ash for 1 m³ of loess reduces CO₂ eq emissions by 288.01 kg and 43.09 kg, and decreases PED by 1750.84 MJ and 300.44 MJ, respectively. These findings confirm fly ash as a sustainable stabilizer, supporting geotechnical applications and low-carbon soil improvement. • 330.39% UCS increase in loess stabilized with 20% fly ash. • Fly ash fills the inter-aggregate pores, optimizing the microstructure. • 3D CT reveals denser, uniform pore network after fly ash stabilization. • LCA shows stabilizing 1 m³ loess with fly ash reduces 288.01 kg CO₂ eq and 1750.84 MJ vs. lime.