Improving CBR Parameter of Expansive Soil Using the Carbonate Precipitation Method with Tofu Waste as a Biocatalyst

Expansive soil is problematic from an infrastructural perspective, including the subgrade of pavement construction. The high swelling and shrinkage of this soil promotes subgrade imbalance, resulting in severe pavement construction problems. One potential soil improvement method is the carbonate precipitation method; however, this method requires a catalyst. This research aims to evaluate the use of tofu waste as a biocatalyst in the carbonate precipitation method to improve expansive soil. Several variations of tofu waste reacted with reagents (urea and calcium chloride) as treatment solutions. Soil identification, hydrolysis, precipitation, Atterberg limits, California bearing ratio (CBR), scanning electron microscopy (SEM), and X-ray diffraction (XRD) tests were performed. The results showed that the optimum tofu waste concentration was 40 g/L. The swelling ratio in the soil treated with carbonate decreased by 12.5%. The CBR value of the treated soil also increased by 23.9%. The SEM and XRD analysis results showed the formation of aragonite, calcite, and vaterite. Moreover, this study confirmed that tofu waste is a promising biocatalyst for carbonate precipitation.