Recovered plastic and demolition waste blends as railway capping materials

The sustainable utilization of plastic and demolition waste as an alternative civil construction material has garnered increasing interest in recent years. Usage of these sustainable recycled products in the civil construction industry will reduce the demand for quarry materials, costs associated with landfilling as well as reducing the carbon footprint of future infrastructure projects. This study is focused on the usage of recovered plastic (RP) blends with demolition aggregates, namely recycled concrete aggregates (RCA) and crushed brick (CB) as railway capping materials. RP used in this research is the mixture of various types of waste plastics, which neither can be separated nor recycled into new products. The influence of RP inclusion in RCA and CB was evaluated based on tests that incorporated the evaluation of particle breakage, compressibility behavior, stiffness and strength parameters of the blends. Resilient modulus, (M-r) of the recycled products was determined based on a proposed Repeated Load Triaxial (RLT) testing protocol, based on the range of relevant applied stresses to capping materials. Two types of conventional capping materials (CCMs) currently used as railway capping materials were also evaluated under similar testing conditions. The responses of the blends were evaluated against the range of results of CCMs to determine the optimum percentage of RP. It was determined that the inclusion of waste plastic in demolition aggregates could enhance the degradation resistance and energy absorption characteristics of blends. Inclusion of RP with 5% in RCA and 3% in CB was found to be the optimum blend, which furthermore was found to enhance the energy-absorbing capacity of this alternative recycled railway capping layer product.