Strengthening potential of xanthan gum biopolymer in stabilizing weak subgrade soil

This article presents a comprehensive study on the efficacy of xanthan gum (XG) biopolymer as a green construction material in treating problematic weak subgrade soil (i.e., expansive soil). In this regard, a wide range of geotechnical properties i.e., compaction, unconfined compressive strength (UCS), elastic modulus (E₅₀), energy absorption capacity (E_v), soaked and unsoaked California bearing ratio (CBR), swelling potential, consolidation parameters along with microstructural studies of untreated and treated soils were investigated. The soil was treated with varying percentages of XG (i.e., 0, 0.5, 1.0, 1.5, 2.0, and 5.0%) considering the long-term aging period (i.e., 0, 4, 7, 14, 28, and 60 days). Results showed a slight decrease in the maximum dry density of treated soil with increased optimum moisture content. At an optimum XG content of 1.5%, the strength parameters, i.e., UCS-value, E₅₀, E_v, soaked and unsoaked CBR, were significantly increased by 1.8–9 orders of magnitude, transforming the weak subgrade into a hard-quality subgrade for pavement construction. In addition, compression and rebound indices were significantly reduced by 83 and 82%, while swell percentage and pressure were decreased by 79 and 86%, respectively. The microstructural studies showed the cross-linking and binding of soil grains by cementitious hydrogel, which is responsible for ameliorating geotechnical parameters. Based on the findings, XG biopolymer was found to be a promising green construction material for the amelioration of problematic weak subgrade soil.