Large-scale direct shear testing of waste crushed rock reinforced with waste rubber as pavement base/subbase materials

Construction and demolition (C&D) waste and scrap tires contribute to huge portions of the waste generated worldwide. One of the most effective and practical ways to eliminate the need to send C&D waste and scrap tires to landfills is to recycle and reuse them in civil and construction projects. On the other hand, the shear behavior of the granular aggregates has a significant influence on the performance of pavement layers. Unbound granular aggregates such as crushed rock have high compressive strength but low tensile strength. One way to improve the aggregates’ tensile weakness is to introduce crumb rubber into the unbound granular materials. This study explored the possibility of using the blends of waste crushed rock (WCR) and waste rubber, as a low-carbon and economically viable solution, for pavement base/subbase application. Little research has been done to study the shear strength properties of mixed waste materials. This study is the first to evaluate the shear behavior of WCR reinforced by varying sizes & percentages of waste rubber using a large direct shear testing (LDST) device. The experimental results show that an introduction of waste rubber to WCR increased the shear capacity of the blends. Mixtures of WCR with rubber in two sizes (coarse/fine) and at three distinct percentage inclusions (0.5, 1 and 2%) all satisfy the shear strength requirements for aggregates in pavement base/sub-base applications. In addition, a straightforward non-linear model was developed in order to facilitate easy estimation of the shear capacity of rubberized WCR. The outcomes of this study can provide practical guidance on the application of rubberized waste crushed rock as pavement base/subbase materials.