Optimum Mixing Ratio and Shear Strength of Granulated Rubber–Fly Ash Mixtures

Studies on shredded waste tires mixed with sand for fill applications are well documented. In this study, a new composite material from mixture of shredded tires and fly ash as fill material is explored. Shredded waste tires with nominal size equal to 9.5 mm (granulated rubber), and fly ash generated from two thermal power plants are used in the study. The composite material is obtained by mixing different proportions of granulated rubber and fly ash. Granulated rubber content equal to 0%, 10%, 30%, and 60% (by weight of fly ash) in the mixture are tested. Compaction characteristics, optimum mixing ratio, and shear strength properties of the mixtures are determined. The maximum dry unit weight and the optimum water content values ranged between 15%–22.5% and $12.6–14.6\mathrm{kN}/{\mathrm{m}}^3$, and 10%–27% and $10.5–11.6\mathrm{kN}/{\mathrm{m}}^3$ for mixtures prepared with fly ashes from two sources. Large-size direct shear apparatus is used to obtain the angle of shearing resistance and apparent cohesion of mixtures at both peak state and at near end-of-test. The shear strength of fly ash and granulated rubber mixture is found to be higher than that of fly ash alone or granulated rubber alone, and the maximum shear strength of the composite material is observed for granulated rubber contents equal to about 60% (by weight of fly ash). The peak shear strength parameters of mixtures, apparent cohesion and friction angle, are found to be in the range 14.9–46.0 kPa and 37.5°–50.1°, respectively. Based on minimum void ratio, optimum mix proportions of granulated rubber and fly ash from two sources ranges between 54%–100% and 81%–185% (by weight of fly ash). Based on shear strength testing, fly ash-granulated rubber mixtures are found to perform better than sand-granulated rubber mixtures.