A comparative life-cycle assessment of asphalt mixtures for railway sub-ballast containing alternative materials

Bituminous sub-ballast in railway track-bed can mitigate the variation of the moisture content in the subgradeand reduce vertical stiffness variations of the track leading to a more durable infrastructure. Nevertheless,durability is only one of the aspects that affects the sustainability of an infrastructure. Other relevant aspects arerelated to the environmental and economic issues. This research work joins the worldwide effort towards aparadigm shift in civil engineering devoted to assess the sustainability of infrastructures at the design stage. Withthis in mind, in this study different alternative bituminous sub-ballast mixtures containing recycled materials,namely crumb rubber (CR) and reclaimed asphalt pavements (RAP) were compared by means of the results of aLife-Cycle Assessment (LCA). In comparison with a traditional bituminous sub-ballast the Crumb RubberModified (CRM) mixtures showed higher impacts due to the treatment of the rubber as well as the higher amountof bitumen employed in the mixture. In turn, when RAP is used, the LCA results report an improvement of all theindicators considered. The reduction of the impacts is even higher when full blending between the aged and thevirgin binder is assumed because it allows reducing the amount of virgin bitumen employed. The results areintended to be used by engineering experts and practitioners to make more assertive judgments on the advantagesand disadvantages associated with the use of emerging and commonly called sustainable strategies andpractices for railway track-bed.