Sodium alginate-enhanced microbially induced calcite precipitation for sustainable sand stabilization

The integration of biopolymers into Microbially Induced Calcite Precipitation (MICP) presents a promising advancement in sustainable ground improvement techniques. This study investigates the effect of sodium alginate (SA), a naturally occurring biopolymer, on the mechanical and microstructural properties of MICP-treated sandy soils. By leveraging the gel-forming properties of SA, the research aims to overcome critical limitations associated with conventional MICP, such as nonuniform calcium carbonate distribution, harmful ammonium byproducts, and low viscosity of MICP cementing solution grout. A comprehensive experimental program was conducted using silica sand treated with equimolar urea and calcium chloride solutions. The study varied cementing solution concentrations (0.25 M to 1.5 M) and treatment cycles (1, 4, and 8). The results demonstrate that SA-MICP significantly improves soil strength, achieving unconfined compressive strengths (UCS) in excess of 900 kPa, nearly three times that of control MICP-treated specimens. Microstructural analyses via X-ray diffraction (XRD) and scanning electron microscopy (SEM) reveal that SA promotes the formation of calcium carbonate, stabilizes nucleation pathways, and enhances the uniformity of CaCO3 distribution across soil specimens. Additionally, the SA-MICP treatment helps sustain chemical conversion efficiency (CCE) over successive treatment cycles, highlighting its role in enhancing bacterial retention and optimizing the microenvironment for calcite crystal growth. This research underscores the transformative potential of biopolymers in bio-cementation processes, offering improved strength and environmental compatibility for field applications. The findings pave the way for future studies on scalability, cost-efficiency, and long-term performance of SA-MICP in field applications.