Early-age microstructural characteristics and improvement mechanisms of cement–fly ash stabilized dispersive soil

Abstract

Dispersive soil is highly susceptible to erosion and seepage failure, posing significant risks to hydraulic and geotechnical structures. This study evaluates the effectiveness of a fly ash–dominated cementitious stabilization system for improving dispersive soil. A series of dispersibility, permeability, SEM, EDS, and XRD tests were conducted on soils treated with different cement and fly ash contents after 72 h of curing. C1F4 is the minimum dosage required to achieve a non-dispersive classification. The results show that the combined use of cement and fly ash effectively suppresses soil dispersivity. The permeability coefficient decreases by 20.4%–83.4% compared with untreated soil, indicating a substantial improvement in seepage resistance. Microstructural analysis reveals significant pore refinement, with the average pore diameter decreasing from 2.09 \(\mu\) m to 0.50 \(\mu\) m (approximately 76%). EDS and XRD results indicate that hydration reactions generated calcium-rich amorphous cementitious products, which filled pores and enhanced particle bonding. These findings demonstrate that the fly ash–dominated stabilization system provides an effective and sustainable approach for reducing dispersivity, improving impermeability, and enhancing the microstructural stability of dispersive soils.