This article presents a comprehensive study on the efficacy of xanthan gum (XG) biopolymer as a green construction material in treating problematic expansive subgrade. The soil was treated with various concentrations of XG (0, 0.5, 1.0, 1.5, 2.0, and 5.0%) considering long-term aging period (0, 4, 7, 14, 28, 60 and 365 days). The results showed a reduction in soil plasticity at a higher aging period with the increase in XG content. At 1.5% XG content the unconfined compressive strength, elastic modulus, resilient modulus, unsoaked and soaked CBR values of treated soil were notably increased by 5–10 orders of magnitude and regarded as optimum. Meanwhile, microstructural studies coupled with elemental analysis highlight the bridging of soil particles with stiff XG-hydrogel formation that contributes to strength development. Overall, XG-treatment exhibits an economical and sustainable solution for the treatment of problematic expansive subgrade.

An earthwork design requires to consider the influence of severe climatic conditions on enduring performance of soils treated with chemical additives. This study was focused on investigating the mechanical behavior of a lime and cement-treated cohesive soil under the effects of repeated cycles of wetting and drying. The soil samples were prepared by adding different concentrations of cement (2, 6, 10, 12, 16, 20%) and quicklime (2, 4, 6, 8, 10%). Due to low-plastic nature of the host soil, the effectiveness of cement to reduce the plasticity of soil was relatively higher compared to lime-treatment. Likewise, an increase in optimum moisture and decrease in maximum dry unit weight was observed for both the additives and these effects were significant for lime treated soil compared to cement. Moreover, an increase in strength from 0.57 MPa to 12.9 MPa at 20% cement and from 0.57 MPa to 2.03 MPa at 2% lime was observed in unconfined compressive strengths (UCS) tests on soil samples. To investigate the durability characteristics of the treated soil, the samples were subjected to 12 cycles of wetting and drying with each cycle consisting of 5 hours of immersion in potable water and subsequent drying in oven for 43 hours. The compressive strength, volume change and weight loss of soil samples were determined at the 1st, 3rd, 6th, 9th and 12th cycle. It is observed that the durability behaviour of treated soil is multipart due to parallel processes of positive aging (hydration process associated with binding agents) and negative aging (induced weathering). For a sustainable mechanical performance of the treated soil, an optimum dose of 6% lime or 16% cement is recommended and some correlations are proposed to quantify the effects of repeated wetting and drying.