Improving expansive soil subgrade using sustainable green polymer-based admixture

The damage to road infrastructure caused by expansive soils due to seasonal drying and wetting has been widely reported in many countries. Cement and lime are commonly adopted to enhance the properties of problematic clay soils. However, environmental concerns arise from chemical soil stabilizers like lime and cement, particularly regarding the greenhouse gas emissions associated with their manufacturing processes. Polymer-based admixtures offer a viable option for improving the engineering properties of problematic soils. This paper investigates the feasibility of using a polymer-based admixture, Renolith emulsion, as a standalone binder for stabilizing expansive clay soil in pavement subgrade applications. Various contents of Renolith (i.e., 0%, 0.5%, 1%, 1.5%, and 2% by the dry soil weight) were added to the expansive clay soil, and a comprehensive series of laboratory experiments was performed to assess the geotechnical feasibility of Renolith emulsion-stabilized expansive clay soil. These experiments included mechanical tests, such as repeated load triaxial (RLT), swell-shrinkage tests, standard compaction, unconfined compression strength, soaked California bearing ratio (CBR), direct shear (DS), and soil water retention curve (SWRC), and microchemical analyses such as XRD, XRF, thermogravimetric, and scanning electron microscopy. The geotechnical assessments revealed that incorporating 1% Renolith emulsion yielded the most favorable results for stabilizing expansive clay soil, resulting in substantial enhancements in the soaked CBR, resilient modulus, and cohesion by 170.1% (from 2.61% to 7.05%), 40.2% (from 58.17 MPa to 81.55 MPa), and 44.2% (from 48.66 kPa to 70.15 kPa), respectively. Additionally, the introduction of 1% Renolith reduced the soil swell-shrinkage index by 18.3% (from 3.71 to 3.03%/pF).