Insights into the strength and microstructural characteristics of FA-RHA-stabilized dredged soil at high water content

This study presents a systematic experimental investigation on strength behavior and microstructural evolution of fly ash (FA) and rice husk ash (RHA) stabilized dredged clay at high water content. Five FA-RHA combinations with a fixed total binder content of 20% were evaluated at curing times of 3 hours, 7 days, and 28 days through direct shear (DS), unconfined compressive strength (UCS), and scanning electron microscopy (SEM) tests. The results demonstrate that the FA-RHA blend significantly enhances the strength performance of dredged soil, with an optimal binder combination of 5%FA + 15%RHA. At 28 days of curing, this mixture achieved a peak shear strength of 290.5 kPa under a normal stress of 200 kPa, accompanied by the maximum cohesion of 143.4 kPa, internal friction angle of 35.6°, and UCS of 356.6 kPa. Microstructural observations reveal that the superior performance of the optimal blend is attributed to the synergistic interaction between early-hydration from FA and sustained pozzolanic reactions from RHA, leading to extensive cementitious gel formation and pore refinement. The results provide clear mechanistic insight into the strength development of FA-RHA-stabilized dredged clay and demonstrate that this binary binder system offers an effective and sustainable alternative to conventional cement-based stabilization for dredged soil reuse.