Eco-Friendly Biopolymers for Improving Strength and Durability Characteristics of Fly Ash Deposits

Despite its potential as a geomaterial, fly ash (FA) has limitations in geotechnical applications because of its low strength, high deformability, and poor durability, necessitating sustainable improvement strategies. This study investigated the strength and durability enhancement of FA stabilized with two biopolymers, xanthan gum (XG) and guar gum (GG), at varying dosages, curing periods, curing methods, and mixing techniques. Unconfined compressive strength (UCS) tests were performed to evaluate the strength development in XG- and GG-treated FA (XFA and GFA), along with their durability, assessed by wetting and drying (WD) strength. Test results indicate that both biopolymers significantly improved the strength and durability of FA, with GFA consistently outperforming XFA. At the optimal dosages of 0.75% XG and 0.50% GG, the UCS of XFA and GFA increased by 1,029% and 1,282%, respectively, with GFA exhibiting 105% higher strength than XFA. The strength gain was more prominent during early curing (7 days), with GFA and XFA achieving improvements of 619% and 378%, respectively. Wet mixing with air curing enhanced the UCS by up to 97% (XFA) and 76% (GFA) compared to moist curing. Dry mixing further enhanced the UCS, especially under moist curing conditions, where XFA and GFA exhibited 65% and 57% higher UCS than their wet-mixed counterparts. After 12 WD cycles, GFA retained 58% of its UCS, outperforming XFA, which retained 50.7%, indicating better long-term durability. Furthermore, microstructural analyses revealed enhanced particle binding, bridging, and distinct bonding mechanisms in the XFA and GFA.