Mechanical, durability, and microstructure of soft clay stabilised with anionic biopolymer

This study examines the impact of incorporating sodium alginate (SA) biopolymer into soft clay using the deep soil mixing method (DSM). SA-stabilised samples were tested under high-moisture (A) and low-moisture (B) conditions to assess their mechanical properties, chemical attributes, freeze-thaw resistance, and microstructure. Results indicate that samples cured under condition A outperformed those in condition B, primarily due to enhanced biopolymer gel formation. In both conditions, increasing the SA content and curing time led to higher peak strength, stiffness, and pH. The higher SA ratio improved ductility in condition A but increased brittleness in condition B. At the 28-day mark, a 1.0% SA ratio and a pH range of 8.2–8.4 were crucial for specimen strength increase. Freeze-thaw cycles had minimal impact, with a modest reduction in compressive strength observed. Scanning electron microscopy showed face-to-face bonding between clay particles and the gel-like materials due to electrostatic attraction. After 14 days, ramifications occurred around the core structure, and after 28 days, high agglomeration structures appeared, attributed to clay particle flocculation. Energy-dispersive X-ray (EDX) analysis indicated an increase in the Si/Al ratio boosted sample strength, while X-ray diffraction (XRD) results showed no crystalline phase in SA-stabilised samples due to encapsulating clay minerals with gel-like materials. In summary, this study suggests that SA biopolymer offers an eco-friendly, sustainable option for enhancing soft clay with DSM.