A new material that incorporates rubber from used tyres has been developed researchers from the Polytechnic University of Valencia in Spain, the rail company AZVI and the University of Seville for use in the sub-ballast layer of train tracks.
The used tyres are combined with crushed stone and this mixture is already used in asphalt mixtures and roadside embankments, although its use in the railway sector is relatively unexplored.The new material was already tested along a section of the Almoraima-Algeciras ADIF line in Andalusia, Spain and has been assessed by UPV technicians.
Aside from allowing and even promoting the wholesale recycling of used tyres, it also provides insulation for urban environments with close rail traffic as it absorbs vibrations from the moving trains. The tyre rubber also increases the resistance of the crushed limestone to abrasion and fragmentation.
Pablo Martínez Fernández, researcher at the university’s Institute of Transport and Territory (ITRAT), explains: “There are multiple benefits to using this material. On the one side, it contributes to mitigating the vibrations caused by moving trains. But at the same time it opens up a new market for many of our quarries, particularly limestone quarries, as well as for tyre recycling companies. It revitalises both sectors, making better use of the available limestone, not normally fit for use as a sub-ballast because of its low resistance to fragmentation, and the rubber from used tyres.”
As part of the Compovía project, the team, led by Ricardo Insa, worked on the design, development and evaluation of different compositions and blends of the product, varying only the amounts of waste rubber used each time.
“From our laboratories at the Departamento de Ingeniería del Terreno (DIT) we analysed the response of the new material, with different concentrations of used tyre rubber, in order to find the best composition,” says Carlos Hidalgo Signes, also of the UPV.
Another of its main characteristics is that it does not incorporate any binding materials: “We simply mix the crushed stone with the waste rubber, which is what gives it its cushioning effect,” adds Signes.