This photo shows recycled tire rubber in the novel sub-ballast for train tracks.
This photo shows recycled tire rubber in the novel sub-ballast for train tracks.

Researchers from the Polytechnic University of Valencia (UPV), the rail company AZVI and the University of Seville, all in Spain, have developed a material for use in the sub-ballast layer of train tracks that incorporates shredded rubber from used tires. Combined with crushed limestone, this type of mixture has already been used to good effect in asphalt mixtures and roadside embankments, but its use in the rail sector is relatively unexplored.

This novel material has already been tested along a section of the Almoraima-Algeciras ADIF line in Andalusia, Spain, where it has been assessed by UPV technicians. Not only does the material promote the wholesale recycling of used tires, a large and problematic source of waste, but it offers several other interesting advantages over traditional materials used for train tracks. It can absorb the vibrations from moving trains, reducing noise pollution from rail traffic, and can also increase the resistance of the crushed limestone to abrasion and fragmentation.

"There are multiple benefits to using this material," explains Pablo Martínez Fernández, researcher at the UPV's Institute of Transport and Territory (ITRAT). "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 tire recycling companies. It revitalizes 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 tires."

As part of this project, the team worked on the design, development and evaluation of different compositions and blends of the material, varying only the amounts of waste rubber used each time. "From our laboratories at the Departamento de Ingeniería del Terreno (DIT), we analyzed the response of the new material, with different concentrations of used tire rubber, in order to find the best composition," says Carlos Hidalgo Signes, also at the UPV.

Another advantage of this novel sub-ballast material 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," explains Hidalgo Signes.

This story is adapted from material from the Polytechnic University of Valencia, with editorial changes made by Materials Today. The views expressed in this article do not necessarily represent those of Elsevier. Link to original source.