Compaction, degradation and deformation characteristics of an energy absorbing matrix

The reuse of waste materials as an alternative to natural aggregates is becoming more popular in engineering projects. It offers a sustainable and economical solution to address the environmental concerns arising from the scarcity of natural quarries as well as the increase in waste generation. Coal wash (CW) and rubber crumbs (RC) are industrial by-products that could potentially be used in railway substructures. In this study, different RC levels are introduced into CW (i.e. CWRC mixture) to reduce potential breakage of CW and increase the ductility and energy absorbing capacity of the matrix. The compaction and degradation characteristics of CWRC mixtures to be used as a construction fill are investigated under five energy levels ranging from standard to modified Proctor compaction. An optimum compaction energy is determined so as to minimize breakage but still yield an acceptable void ratio (compact packing) to avoid excessive settlements. The compressibility of rubber particles and the induced change in the volume of solids is addressed with regard to the overall void ratio of the matrix. Furthermore, the results of triaxial tests on four CWRC mixtures compacted to the same void ratio under three different confining pressures (25, 50 and 75 kPa) are presented, and the effect of RC content on the stress-strain relationship is elucidated.