Niho Vegaliany Agnesia, Heriansyah Putra, Erizal, Muhammad Qarinur
The Soybean Crude Urease-Calcite Precipitation (SCU-CP) method offers a cost-effective alternative to Enzyme Induced Calcite Precipitation (EICP), which relies on pure urease, by utilizing soybean extract for soil improvement. However, its application is often hindered by challenges such as rapid hydrolysis leading to non-uniform calcite distribution and poor water retention in treated soils. This study investigates the modification of the SCU-CP method using skim milk and chitosan as environmentally friendly additives to enhance the shear strength of sandy soil. The experimental program evaluated the effects of varying concentrations of soybean extract (20, 60, and 100 g/L) modified with skim milk (3, 5, and 7 g/L) and chitosan (1, 1.5, and 2 g/L). The performance of the modified treatments was assessed through viscosity, water retention, unconfined compressive strength (UCS), and calcite distribution tests. Results demonstrated that the additives operate via distinct mechanisms. The addition of 7 g/L skim milk significantly increased the solution viscosity to 5.49 cP, promoting a more uniform vertical distribution of calcite with an average content of 1.98% and a low standard deviation of 0.03. Conversely, the addition of 2 g/L chitosan markedly improved water retention, achieving a low matric suction value of 13.07 kPa, and yielded the highest UCS of 23.37 kPa after 7 days of curing. The findings indicate that skim milk is optimal for achieving uniform treatment, while chitosan is superior for maximizing soil strength. These dual pathways provide tailored solutions for specific geotechnical applications of the SCU-CP method. © 2026 Elsevier B.V.
Department of Civil and Environmental Engineering, IPB University, Bogor, 16680, Indonesia; Civil Engineering Study Program, Universitas Negeri Medan, Medan, 20221, Indonesia
