Efficacy of Crustacean and Protein-Based Biopolymer Inclusion on the Strength Characteristics of Organic Soil.

The current study evaluated the potential of crustacean polysaccharide and protein-based biopolymers, namely, chitosan and casein, in ameliorating a low organic soil. The inclusion of these biopolymers will ensure the reusability and recyclability of waste materials derived from the marine industry and dairy industry, respectively. The unconfined compressive strength and consolidated undrained shear parameters were investigated at varying dosages of chitosan and casein (0.5%, 1%, 2%, and 4%) and curing periods (up to 90 days). The compressive strength increased with an increase in the curing period and dosage and led to maximum values of 4.39 and 3.13 MPa for chitosan- and casein-treated soils, respectively, for 4% dosage and 90 days of curing. The effective cohesion (c′) and friction angle (ϕ′) improved after including chitosan and casein. The scanning electron microscopy images revealed that the filler characteristics of chitosan led to strength improvement up to 60 days and developed bond strength via fiber bridging after 60 days of curing at higher dosages. In contrast, the casein–soil mix revealed a higher fibrous structure after a curing period of 28 days, which resulted in strength improvement. This contributed to the highest effective friction angle of 21.57° for the 2% and 60-day-cured casein–soil mix. Casein outperformed chitosan in imparting higher effective shear parameters at 1% and 2% dosages. Fourier transform infrared analysis validated the absence of any new compounds within the soil structure. The research findings on chitosan and casein from the current study recommend the application of these materials for addressing the issues of unstable slopes and pavement subgrade. Practical Applications: The ground improvement industry must shift from environmentally harmful materials to sustainable and nontoxic materials to reduce carbon footprint. Biopolymers are innovative materials derived from various bacteria, plants, and other animals and can impart the required properties for the soils tested (Fatehi et al. 2021). Chitosan and casein are two biopolymers that satisfy the sustainability requirement by being environmentally safe products of waste materials (Chang et al. 2018; Kannan and Sujatha 2023). Applying casein and chitosan has imparted significant improvement in strength to the studied soil. The compressive strength achieved for the fine-grained soils treated with chitosan and casein lies in the range of 0.75–4.39 MPa. Thus, the strength obtained for the treated soils affirms the suitability of these biopolymers in pavement subgrade. The significant improvement in the effective cohesion (c′: 72–179 kPa) and friction angle (ϕ′: 10.57°–21.57°) of amended soils renders the chitosan- and casein-amended samples as excellent shallow foundation materials. Additionally, based on the higher undrained shear strength (125–400 kPa) obtained from consolidated undrained tests, the biopolymers can be recommended for unstable slopes. [ABSTRACT FROM AUTHOR]