Polymer-assisted soybean crude urease carbonate precipitation technique for soil improvement

Abstract

This study presents a sustainable approach to soil improvement by integrating polyvinyl alcohol (PVA) into the Soybean Crude Urease Carbonate Precipitation (SCU-CP) technique. The research aims to enhance SCU-CP, which utilizes soybean-derived urease to precipitate calcium carbonate, bonding soil particles and increasing strength. Challenges such as low solution viscosity and inconsistent carbonate precipitation are addressed by incorporating PVA, a biodegradable polymer that improves viscosity and retention. Comprehensive evaluations reveal significant findings: increasing PVA concentration enhances solution viscosity and results in higher calcium carbonate precipitation. Water retention assessments show that the PCP-1% treatment increases saturation water content (w_s) to 0.263 compared to 0.217 for untreated soil, while also reduces the air-entry value (α). Unconfined Compressive Strength (UCS) tests indicate substantial improvement for PCP-1%, achieving approximately 140 kPa, with values reaching 179 kPa after 28 days. Calcium carbonate content measurements reveal that SCU-CP exhibits a variable distribution (standard deviation of 1.13), while PCP-1% demonstrates a more uniform distribution (standard deviation of 0.60), indicating improved effectiveness. Durability assessments through wet-dry cycling show that SCU-CP experiences a mass loss of 36.5%, while PCP-1% retains only 5% mass loss and maintains a UCS values. SEM images indicate that SCU-CP forms spherical structures, whereas PCP-1% produces a more diverse and crystalline morphology, suggesting better nucleation and distribution. Overall, the polymer-assisted SCU-CP technique (PCP) demonstrates significant potential for effective soil improvement.