Cyclic Stress–Strain Response of Biopolymer-Treated Fly Ash

The inherent low-plasticity and fine-grained characteristics of fly ash (FA) often result in its susceptibility to failure under cyclic loading. This study investigates the potential of guar gum (GG) biopolymer as sustainable additives to enhance the cyclic stress–strain response of FA. A series of cyclic triaxial tests was performed on untreated FA (UFA) and GG-treated FA (GFA) to assess the effects of varying GG dosages (0.20%, 0.30%, 0.40%, and 0.50%) and curing periods (7, 14, and 28 days). The test results indicate a significant improvement in the cyclic stress–strain response of FA under consolidated undrained conditions with the inclusion of GG. The GFA samples exhibited steeper hysteresis loops, signifying enhanced stiffness, which was attributed to interparticle bridging and bonding between the GG and FA particles. Optimal performance was observed at a 0.50% GG dosage, with dynamic shear modulus increases of 188% and 284% after 7 and 28 days of curing, respectively. The damping ratio also improved, showing increases of 262% and 364% for 7 and 28 days of curing, respectively, after 50 loading cycles, due to the viscoelastic properties of GG. GG treatment further reduced shear modulus degradation, increasing the degradation index from 0.74 (7 days) to 0.85 (28 days) after 50 cycles. Additionally, the energy dissipation capacity of the FA improved by 191% under optimal conditions. These findings highlight the efficacy of GG in enhancing the dynamic properties and cyclic response of FA, thereby presenting a promising eco-friendly solution for geotechnical applications.