Shear Strength of Tire Derived Aggregates

Research Overview

The California Department of Resources Recycling and Recovery (CalRecycle) has been working for more than 15 years to develop technology to promote the use of Tire-Derived Aggregate (TDA) in civil engineering applications in California.  During that time, CalRecycle has designed and constructed numerous successful project incorporating TDA. To complete the designs for these projects, material properties are needed for TDA. One of the most important of these properties is the shear strength, as it is critical in the design of the light-weight fill applications (e.g., embankments, light rail foundation, landslide repair, and retaining walls). 

The shear strength of TDA has been typically determined through standard soil testing procedures (e.g., ASTM D3080). This is generally acceptable for crumb rubber and some types of small size (Type A) TDA material with a particle size range of 3 to 4 inches according to ASTM D6270. For large-size (Type B) TDA, with a particle size of 3 to 12 inches according to ASTM D6270, standard soil testing devices are too small to achieve the required strain/displacement for peak strength measurement. Type B TDA requires less processing and is therefore more cost effective than Type A TDA for earth fill applications. However, because larger strength testing devices generally have not been available until recently, designs using Type B TDA have been based on conservative estimates of shear strength, potentially making TDA less competitive as an alternative fill material for construction projects. To address this concern in a previous testing program for CalRecycle reported by McCartney et al. (2016), UCSD constructed a large combination direct shear/simple shear machine to measure shear strength properties for Type B TDA. This machine in direct shear mode is shown in Figure 1.1(a) and in simple shear mode is shown in Figure 1.1(b). The details of the machine in these two modes are reported in detail in Fox et al. (2018). Further, the direct shear/simple shear machine shown in Figure 1.1 was used to perform a comprehensive testing program on the internal shear strength of Type B TDA and concrete-Type B TDA interface shear strength, reported in detail by Ghaaowd et al. (2017), and the cyclic shearing response of Type B TDA, reported in detail by McCartney et al. (2017). The shear strength data obtained from these studies is applicable for the design of field projects involving beneficial reuse of this material in reinforced walls, slopes, and embankments, while the cyclic shearing response of Type B TDA is applicable for seismic analyses of TDA structures.