Environmental performance analysis of bitumen stabilized ballast for railway track-bed using life-cycle assessment

Bitumen stabilized ballast (BSB) is a novel and promising construction or maintenance strategy of traditional ballasted track-bed that consists in the use of bitumen emulsion (BE), which is poured or sprayed at ambient temperature onto the ballast. The bound aggregates show high resistance to degradation and allows increasing intervals between both minor and major maintenance activities. This paper presents the results of a life cycle assessment (LCA) undertaken to compare the potential environmental impacts associated with the use of bitumen stabilized ballast (bound with BE) with those associated to traditional ballast (unbound aggregates) layers. Afterwards, for a more comprehensive understanding of the advantages related to the use of BSB, the complete structure of the track-bed, which in addition to the ballast layer also includes other components, such as sleepers, fastening systems and rails, has been considered. Furthermore, multiple analyses were performed by considering different scenarios involving the comparison of different maintenance timing of BSB and traditional ballast depending on traffic level and/or standard deviation limit (SD) of track irregularities. When the analysis considers the life cycle of the complete structure of the track-bed one can conclude that, overall, the use of BSB contributes positively to the reduction of the environmental impacts, independently of the track quality level and the cumulated traffic values considered. Indeed, the higher durability of BSB allows reducing the frequency of replacement of the elements composing the track-bed leading to considerable improvements in the life cycle environmental performance of the entire infrastructure.