Suitability of recycled materials as a composite sleeper: A scoping review

Abstract

The railway transportation system is the most convenient transportation system due to its easy accessibility and construction mode. Sleeper is the most important and vulnerable part of the railway transportation system due to its load-bearing and load distribution characteristics. Several types of materials are used nowadays as sleeper materials, such as timber, concrete, and steel. Each type of sleeper has some disadvantages and is sometimes harmful to the environment. For that reason, a composite sleeper with different materials has recently been developed by other sleeper manufacturing companies. Different composite sleeper materials are geopolymer concrete, recycled polymer, and CarbonLoc composite. The use of plastic can be an excellent alternative to conventional sleeper material. Still, the only use of recycled plastic as a sleeper material cannot be suitable due to less stiffness, higher cost, voids formation, porosity, spike loosening, and permanent deformation due to creep and less modulus of elasticity. The structural properties of this type of sleeper can be improved by using recycled rubber, fibre reinforced foamed Urethane (FFU), and epoxy polymer resin as a composite material. Composite sleepers with recycled and reinforced materials can be a good alternative for the railway track with critical locations such as crossings, switches, bridge transom, and areas with constraint clearance. Though composite sleeper has been used for several decades in different parts of the world, it is not gaining popularity due to the lack of standards and confusion between buyers and sellers based on acceptance criteria and qualifications. Therefore, this scoping review will give some idea about different composite sleeper types and review the significant features based on the mechanical, physical, and structural properties. Finally, it will highlight other comparative characteristics of composite sleepers with recycled and reinforcing materials and their properties.