Optimizing the Compressive Strength of Sodium Alginate-Modified EICP-Treated Sand Using Design of Experiments

Biological soil improvement techniques, such as enzyme-induced calcium precipitation (EICP), have attracted increasing attention as a sustainable and durable solution for ground improvement. However, recent life-cycle environmental assessment studies of EICP ground improvement have shown that enzyme stabilizers such as nonfat milk powder have a significant environmental impact. Hence, this study explores the potential of using sustainable biopolymer [sodium alginate (SA)] as a modifier in EICP cementing solution. The interaction effect between different EICP cementing solution constituents (calcium chloride, urease enzyme, urea, and SA) on the performance of sand-treated specimens is investigated. Response surface methodology (RSM), a design of experiments (DOE) approach, is utilized to design the testing program. In addition, RSM is adopted to model the effect of different constituents on the performance of EICP-treated soils. An optimal mix is suggested for the EICP-SA modified cementing solution with a maximum unconfined compressive strength of 1,762 kPa, compared with 460 kPa of the EICP-milk treated specimens. Moreover, the practical considerations of the SA-modified EICP solution are investigated through scanning electron microscopy, energy dispersive spectrometry, and water retention. Notably, the study demonstrated that SA-modified EICP specimens have superior water retention characteristics compared with regular EICP-treated soils due to the inclusion of SA in the EICP solution. Additionally, a set of durability tests revealed the promising performance of the SA-modified EICP-treated specimens under wetting–drying cycles, with results complying with ASTM standards. These findings suggest that the SA-modified EICP approach offers a potent and environmentally friendly alternative for soil stabilization and improvement.