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

Abstract

Bituminous sub-ballast in railway track-bed can mitigate the variation of the moisture content in the subgrade and 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 are related to the environmental and economic issues. This research work joins the worldwide effort towards a paradigm shift in civil engineering devoted to assess the sustainability of infrastructures at the design stage. With this 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 a Life-Cycle Assessment (LCA). In comparison with a traditional bituminous sub-ballast the Crumb Rubber Modified (CRM) mixtures showed higher impacts due to the treatment of the rubber as well as the higher amount of bitumen employed in the mixture. In turn, when RAP is used, the LCA results report an improvement of all the indicators considered. The reduction of the impacts is even higher when full blending between the aged and the virgin binder is assumed because it allows reducing the amount of virgin bitumen employed. The results are intended to be used by engineering experts and practitioners to make more assertive judgments on the advantages and disadvantages associated with the use of emerging and commonly called sustainable strategies and practices for railway track-bed.

Assessment of Eco-Friendly Pavement Construction and Maintenance Using Multi-Recycled RAP Mixtures

“…It has the biggest contribution to 12, 11, 11, 9 and 10 impact categories for LCS0, LCS1, LCS2, LCS3 and LCS4, respectively. This result was in line with the results obtained in other studies [11,78,[82][83][84]. Transport and mixture production had the biggest contribution to only one, two or three categories, depending on the scenario.…”

Crumb Rubber Modifier in Road Asphalt Pavements: State of the Art and Statistics

“…These two phenomena contribute to increase the heterogeneity of the rubber modified bitumen and the difference in density between bitumen and rubber granulate becomes significant. For these reasons the rubber particles have a tendency to fall to the bottom, decreasing the storage stability [64]. Several attempts have recently been made to overcome this problem.…”

Vertical Deformation and Ballast Abrasion Characteristics of Asphalt-Scrap Rubber Track Bed

“…However, the use of slab tracks requires very high development costs, which is two times greater than conventional railways. Therefore, a new idea emerged regarding modification of ballast layers with asphalt mixtures which are expected to produce the higher quality of railways compared to conventional railways but with lower costs compared to slab tracks [3], [4], [5], [6], [7], [8].…”

“…Also, scrap rubber as waste materials could be utilized for ballast structures mixtures [13], [14], [12], [15]. Based on the results of several previous studies, the use of excessive rubber (a large percentage) can reduce the stiffness and increase the instability of the rail track which is characterized by the high vertical deformation [16], [7], [17], [8], [14], [15]. Rubber also has properties that are not resistant to temperature heating because rubber is categorized as a thermoplastic material [18].…”