Synergetic Effect of Calcinated Coal Gangue and Xanthan Gum in Enhancing the Geotechnical Properties of Dispersive Soil for Subgrade Application

Abstract Dispersive soils present considerable difficulties in pavements due to their elevated exchangeable sodium percentage (ESP) and low electrolyte concentrations, often resulting in subgrade failures and surface distress. In the current study, a synthetic dispersive soil was created to maintain consistency and control by incorporating 0.16% sodium carbonate at the soil’s liquid limit. This research explored the effectiveness of calcinated coal gangue (CCG) and xanthan gum (XG) in stabilizing dispersive soils, both individually and in combination. The testing scheme included the crumb test, differential free swell index (DFSI), unconfined compressive strength (UCS), and California bearing ratio (CBR) over various curing durations (up to 28 days) and different CCG (1%, 3%, 5%, 7%, and 10%) and XG (0.5%, 1%, 1.5%, and 2%) dosages. Additionally, microstructural analysis and carbon footprint assessment were carried out. The untreated soil exhibited high dispersivity and a swell index of 820%. The addition of <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline" overflow="scroll"> <mml:mrow> <mml:mi>CCG</mml:mi> <mml:mo>≥</mml:mo> <mml:mn>5</mml:mn> <mml:mo>%</mml:mo> </mml:mrow> </mml:math> along with XG of 1.5% rendered the soil as nondispersive, thereby lowering the swell index to 100%. The UCS improved from 65.7 to 600 kPa with the 5% CCG dosage and surpassed 2 MPa with 2% XG. The CBR increased from 0.92% to 3.13% with 5% CCG and attained 13.4% with 2% XG. The synergetic effect of CCG and XG attained UCS and CBR values greater than 2 MPa and 18% respectively, thereby surpassing the individual effects of the additives. The combined carbon emissions of CCG and XG revealed a reduction by 1.5 and 2.1 times compared to those of cement stabilization and lime stabilization, respectively. These findings demonstrate that the combination of CCG and XG offers a potential solution for controlling the dispersive behavior in pavement subgrade.