The influence of rubber crumbs on the cyclic deformation behaviour of waste mixtures

The practical application of waste materials such as steel furnace slag (SFS) and coal wash (CW) is becoming more prevalent in many geotechnical projects. While the inclusion of rubber crumbs (RC) from recycled tyres into mixtures of SFS and CW not only solves the problem of large stockpiles of waste tyres, it can also provide an energy-absorbing medium that will reduce vibration and track degradation on railroads. However, the high compressibility of rubber materials may subject rail track systems to increased deformation if they are included, which is why an engineering insight into the effect that rubber crumbs have on the cyclic deformation of SFS+CW+RC mixtures is imperative. In this study the influence of RC composition on the cyclic deformation of rail subballast materials, i.e. total and resilient deformation, was investigated using drained cyclic triaxial tests. The results reveal that with the inclusion of RC, the total axial strain increases, the volumetric strain becomes more contractive, and the resilient deformation of the SFS+CW+RC mixture increases while its resilient modulus decreases. By comparing with traditional subballast, the waste mixture with 10% RC was found to be the optimal waste matrix for subballast in view of controlling deformation while maintaining sufficient resilient modulus.