Date of Award
12-1-2025
Degree Name
Master of Science
Department
Civil Engineering
First Advisor
Kolay, Prabir
Abstract
Highly plastic clays often pose significant engineering challenges due to their low undrained shear strength, high compressibility, high shrink-swell behavior, and can cause differential settlement due to volume instability when exposed to moisture variations. Traditional stabilizing agents like cement and lime, though effective, generate substantial environmental impacts, motivating research into eco-friendly alternatives. This study investigates Sodium Alginate (SA), a sustainable biopolymer extracted from brown seaweed, as a potential soil stabilizer for highly plastic clayey soil. The primary goal was to evaluate the performance of SA-treated soil at varying concentrations (0.25%, 0.5%, 0.75%, and 1.0% by dry weight of soil) with different curing periods (7, 14, and 28 days) and check its effectiveness towards stabilization. Laboratory tests, including Atterberg limits, miniature Proctor compaction, Unconfined compressive strength (UCS), Resilient modulus (RM), Ultrasonic pulse velocity (UPV), and Scanning electron microscopy (SEM), were systematically conducted to assess index, mechanical, compaction, and microstructural properties of treated clayey soil samples. The results indicated notable improvements in soil characteristics with increased SA content and prolonged curing periods. Specifically, significant enhancements were observed in UCS, reaching optimal values at 1.0% SA after 28 days, with a 57.53% improvement in strength relative to untreated soil, indicative of improved soil strength. UPV measurements corroborated these mechanical strength enhancements, exhibiting increased velocities corresponding to enhanced strength. With the addition of 1.0% SA cured for 28 days the pulse velocity increases from 1493.91 m/s (untreated clay) to 1726.70 m/s. Similarly, the RM test demonstrated that SA treatment markedly enhanced soil elasticity and reduced its susceptibility to deformation under repetitive loading. At the optimum concentration of 0.5% SA and 7 days of curing, the RM values increased from 178.3 MPa, 226.0 MPa, and 279.0 MPa to 366.8 MPa, 439.6 MPa, and 507.7 MPa at confining pressures of 13.8, 27.6, and 41.4 kPa, respectively, corresponding to increases of approximately 106%, 94%, and 82%. This improvement is critical for pavement design applications. Microstructural analysis through SEM further elucidated the interactions between clay particles and SA, highlighting a denser and more cohesive structure due to polymer bridging and pore filling, increasing aggregation and flocculation. This enhancement aligns with observed improvements in mechanical properties. In conclusion, this study confirms Sodium Alginate as a promising sustainable alternative to conventional soil stabilizers, demonstrating significant improvements in soil strength, stiffness, and overall performance. The results of this study contribute valuable insights toward sustainable soil stabilization practices, underscoring both engineering benefits and environmental advantages of employing biopolymer-based stabilization methods.
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