Potential for improving the environmental performance of railway sleepers with an outer shell made of recycled materials

An innovative sleeper with a pre-stressed reinforced concrete inner structure wrapped by an outer shell manufactured with end-of-life tires powder and recycled plastics has been recently designed by the Greenrail company. The external protection is aimed at increasing its lifetime and reducing the maintenance requirements of the railway lines. This study evaluates the environmental performances of this sleeper, under different operational conditions, in comparison with traditional pre-stressed reinforced concrete sleepers, using the Life Cycle Assessment methodology. The assessment includes 16 environmental, energy, and human health impact categories. It is performed considering the following functional unit: 1 railway sleeper, including the fastenings of the rail to the sleeper and the portion of the track bed underneath it, over one year of operation. The evaluated system includes the sleeper production, its installation, the railway maintenance, the sleeper removal at its end-of-life and the final recovery. Moreover, the ballast is included in the analysis considering its mining and transportation to the railway line, the partial replacement during maintenance operations, the removal during a track renewal, and the end-of-life management. For the worst operational conditions of the Greenrail sleeper, the potential impacts between the two sleeper typologies differ by <10% for most of the examined categories, meaning that no significant environmental differences are observed. In the average conditions, impact reductions for the Greenrail sleepers result bigger than 10% for 7 out of 16 categories. Finally, for the best conditions, benefits are in the range 20% - 30% for 11 impact categories.