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.