Shear Resistance of Tire-Derived Aggregate Using Large-Scale Direct Shear Tests

This paper presents a large-scale direct shear testing of tire-derived aggregate (TDA) of large sizes (25–75 mm). The objective of this research is to obtain and compare the shear resistances of large-sized TDA and TDA in contact with sand, concrete, and geosynthetics. TDAs are pieces of processed and shredded waste tires that can be used as lightweight and quick fills for embankments, subgrades, and retaining walls. A large-scale direct shear apparatus was designed and constructed. The shear box dimensions were 79 cm wide, 80 cm long, and 122 cm tall. The lower shear box was driven by a hydraulic piston, while the upper shear box remained stationary. The horizontal shear forces, shear displacements, and vertical forces were recorded by an automatic data acquisition system. Three normal loads were applied on the TDA to simulate overburden pressures of 24, 48, and 96 kPa (or 500, 1,000, and 2,000 lb/ft2). Duplicate tests were performed to verify the repeatability. The control tests using sand proved that the equipment could obtain comparable and slightly conservative shear strength. The Mohr-Coulomb failure criterion was used to obtain the cohesion (or adhesion) and friction angles of the TDA. The shear testing revealed the difference of failure mechanisms of TDA and sand. For TDA, no peak shear resistance was observed during the entire shearing, and shear resistance continued to increase until the test was terminated at sufficient shear displacement. Further analysis revealed that the shear strength parameters of TDA increase with shear deformation; this represents a challenge in selecting the design parameters of TDAs. The shear strengths of TDA and TDA in contact with other materials are dictated primarily by friction. The friction angles of TDA, TDA on sand, and TDA on concrete are very similar (in a range of 35–39°).