Strength Improvement of Black Cotton Soil With Cement and Waste Glass Powder for Subgrade Stabilization

Expansive soils cause volume changes because they swell and lose strength when wet and shrink when dried. Light buildings and pavements constructed over such soils will not last long due to settlement and cyclic volume changes. Therefore, the purpose of this study was to blend black cotton soil with cement and waste glass powder (WGP) in order to enhance its performance as a subgrade material. Cement was mixed with the soil in ratios of 2%, 4%, 6%, 8%, and 10%, while WGP was added in proportions of 3%, 6%, 9%, and 12%. WGP is a nondecomposable solid waste collected from local drinking vessels. Three samples of black cotton soil were taken at a depth of 1.5 m from a road segment. The glass was crushed using a Los Angeles Abrasion Test Machine and passed through sieve number 200 (75 µm) to be mixed with the soil. The physical characteristics and strength parameters of both native and treated soils were tested in the laboratory. The American Association of State Highway and Transportation Officials (AASHTO) classification identified the soil as A7‐5, and the Unified Soil Classification System (USCS) classification classified it as CH. Results showed that increasing cement and WGP content enhanced the maximum dry density (MDD), California bearing ratio (CBR), and unconfined compressive strength (UCS), while reducing the liquid limit (LL), plasticity index (PI), free swell index (FSI), optimum moisture content (OMC) and CBR swell. The PI dropped from 44.59% to 14.92%, the FSI decreased from 115% to 46.5%, and the OMC dropped from 26.5% to 21.75%. Meanwhile, the MDD increased from 1.459 g/cm 3 to 1.62 g/cm 3 , the CBR increased from 0.92% to 13.52%, and the UCS increased from 23.7 kPa to 112.95 kPa when the optimal dosages of 4% cement and 12% WGP were added. In conclusion, the combination of cement and WGP significantly enhanced the properties of black cotton soil.