Behavior of a Mixture of Coal Wash and Rubber Crumbs under Cyclic Loading

The interest in the utilization of granular waste materials as construction fills in lieu of quarried natural aggregates has been increasing recently, resulting in more sustainable and cost-effective industry practices being adopted. This study proposes a mixture of coal wash (CW; a by-product of coal mining) and rubber crumbs (RC; shredding of waste rubber tires) as a potential capping composite for railways. A series of cyclic triaxial tests mimicking typical rail traffic loads were conducted on CWRC mixtures with and without rest periods to gain an insightful understanding of the deformation mechanism of rubber particles. It is found that the inclusion of RC increases the axial permanent strain, the volumetric strain, and the damping ratio, and it reduces the resilient modulus, the shear modulus, and the breakage index (BI). Also, it is found that the mixture with RC recovers part of its energy dissipation efficiency after a rest period is applied, reducing the breakage index further even when the number of load cycles increases. Accordingly, a modified equation is proposed to determine the void ratio, capturing the deformation of the rubber.