Freeze-Dried ß-Glucan and Poly-γ-glutamic Acid: An Efficient Stabilizer to Strengthen Subgrades of Low Compressible Fine-Grained Soils with Varying Curing Periods.

The freeze-drying of biopolymers presents a fresh option with greater potential for application in soil subgrade stabilization. A freeze-dried combination of ß-glucan (BG) and γ-poly-glutamic acid (GPA) biopolymers was used to treat low compressible clay (CL) and low compressible silt (ML) soils in dosages of 0.5%, 1%, 1.5%, and 2%. The California bearing ratio (CBR) test for the treated specimens was performed under three curing conditions: (i) thermal curing at 60 °C, (ii) air-curing for seven days followed by submergence for 4 days, and (iii) no curing, i.e., tested immediately after mixing. To investigate the influence of shear strength on the freeze-dried biopolymer-stabilized soil specimens and their variations with aging, unconfined compressive strength (UCS) tests were conducted after thermal curing at 60 °C for 3 days, 7 days, and 7 days of thermal curing followed by 21 days of air curing. The maximum CBR of 125.3% was observed for thermally cured CL and a minimum CBR of 6.1% was observed under soaked curing conditions for ML soils. Scanning electron microscopy (SEM), infrared spectroscopy, average particle size, permeability, and adsorption tests revealed the pore filling, biopolymer adsorption and coating on the soil surface, and agglomeration of the soil along with the presence of hydrogen bonds, covalent amide bonds, and Van der Waals forces that contributed to the stiffening of the stabilized soil. Using three-dimensional (3D) finite element analysis (FEA) and layered elastic analysis (LEA), a mechanistic-empirical pavement design was carried out for the stabilized soil and a design thickness catalog was prepared for the maximum CBR. The cost reductions for a 1 km section of the pavement were expected to be 12.5%.

Crustacean polysaccharides for the geotechnical enhancement of organic silt: A clean and green alternative.

Biopolymer-based soil stabilization offers a clean alternative to conventional stabilizers like cement and lime. This study investigates the possibility of using shrimp-based chitin and chitosan for stabilizing low plastic silt with organic content by investigating their effect on pH, compaction, strength, hydraulic conductivity (HC) and consolidation characteristics. X-ray diffraction (XRD) spectrum shows that no new chemical compounds were formed in the soil on additive treatment; however, results of scanning electron microscope (SEM) analysis indicate the formation of biopolymer threads that bridge the voids in the soil matrix leading to a stiffer soil matrix, with increased strength and lower HC. Chitosan showed nearly 103 % strength enhancement after 28 d of curing with no degradation. However, chitin failed as a soil stabilizing additive as it showed degradation owing to fungal bloom after 14 d of curing. Chitosan can therefore be recommended as a non-polluting and sustainable soil additive.

ß-Glucan as a Sustainable Alternative to Stabilize Pavement Subgrade.

Beta glucan (ß-Glucan), a polysaccharide biopolymer, is used to improve the subgrade strength of clayey soils in an attempt to advocate a sustainable, carbon-neutral, and eco-friendly stabilizer. A design thickness catalog was developed for a three-layered flexible pavement using 3D finite element analysis (FEA) and layered elastic analysis. The analyses were performed for ß-glucan-treated fine-grained soils with varying traffic intensities based on a mechanistic design philosophy conforming to IRC: 37-2018. Genetic programming (GP) was employed to obtain equations governing the rutting and fatigue failure in pavements. Thirty-nine datasets were used in the determination and analysis of critical strains governing the failure of a flexible pavement. Energy-dispersive X-ray spectroscopy (EDS), Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), Zetasizer analysis, and pH tests of the ß-glucan-treated soil revealed the mechanism of strength improvement of the fine-grained soils. The savings in cost for a 1 km stretch of the pavement were estimated to be 14.3%.

An appraisal of the hydro-mechanical behaviour of polysaccharides, xanthan gum, guar gum and ß-glucan amended soil.

The study aims to investigate the hydro-mechanical behaviour of the polysaccharide amended sand-clay mixture and analyse the soil - biopolymer interaction. Parameters like permeability, strength and heavy metal attenuation capacity of the amended soil were characterized and studied particularly for its use in landfill applications. The permeability of the soil was investigated for a period of one year. The results of the investigation show that all the selected polysaccharides significantly reduce the permeability and improve the heavy metal adsorption capacity of the sand-clay mixtures. The biopolymer also contributes to the increase in the strength of the soil. The improved mechanical properties of the amended soil can be ascribed to the bio-clogging through gel plug formation and bonding action of the biopolymers. Xanthan gum amended soil showed the least permeability, highest strength and adsorbed the selected heavy metals almost entirely, showing the best performance as a liner material.