Sustainable Improvement of Clays Using Low-Carbon Nontraditional Additive

Nontraditional low-carbon additives are widely used in the sustainable treatment of problematic soils for construction and pavement materials. This study investigated the mechanical and microstructural properties of white kaolin (low strength clay) and green bentonite (high swelling clay) treated with a low-carbon sodium silicate-based liquid additive. The mechanical tests included unconfined compressive strength (UCS), direct shear and one-dimensional compression tests. Microscale assessments, including a field emission scanning electron microscopic (FESEM) test, nitrogen-based Brunauer, Emmett, and Teller (N2-BET) surface area analysis and particle size analysis (PSA), were performed on the treated specimens to investigate the modification of soil structure, including soil fabric and interparticle forces. The performance of the proposed additive is demonstrated by the improvement of shear strength and compressibility of both tested soils. The optimum additive content was found to be 6%, and a significant improvement occurred in the first 7 days of curing. The mechanical property improvement is attributed to the formation of cementitious products and, subsequently, the modification of the soil structure. These cementitious products filled the pores and bonded the soil particles, resulting in an increase in interparticle forces. The sodium silicate-based additive can offer a low-carbon alternative to traditional additives such as cement and lime, which is significant from the engineering and environmental perspectives.