Effect of crushed glass on the mechanical and microstructural behavior of highly expansive clay subgrade

Expansive soils swell when they absorb water and shrink by losing water. This process causes significant volume changes in highly expansive clay soils. Clay soil foundations have caused problems for various civil engineering projects, including pavements, railroads, embankments, and foundations worldwide. Besides, the accumulation of huge amounts of waste glass is responsible for several environmental issues. Although the idea of using waste glass for pavement application is not new, the adoption of waste glass for the treatment of highly expansive clay soil as the pavement subgrade has been rarely studied. Previous studies in this area mainly adopted powdered glass, glass fine, glass residue, and soda-lime glass powder, which are costly to produce. In this study, 5 mm minus crushed glass was added to the expansive clay subgrade at different percentages (0%, 5%, 10%, 15%, and 20% by dry weight of the clay). Comprehensive series of mechanical and microstructural analyses have been conducted in this research. The results show that the inclusion of crushed glass into expansive clay, as a pavement subgrade material, significantly improved the mechanical properties (i.e., unconfined compressive strength, California bearing ratio, and resilient modulus) and reduced the swelling and shrinkage potentials and improved the soil-water retention properties of the clay. Crushed glass also enhanced the flexibility/deformability of the subgrade expansive clay soil. The improvement of the properties of the clay subgrade with crushed glass was also supported by the X-ray micro-tomography and SEM analyses. According to the test results, the addition of 10-15% glass was found as the optimum content.