Designs, Application and Performances of Asphalt/Bituminous Trackbeds in European, Asian, and African Countries
Résumé
International rail authorities in several countries, primarily in Western Europe and Asia, have been actively involved with the development and application of asphalt trackbeds for more than 40 years. In this paper, representative activities and standards for trackbeds in countries involved with significant asphalt trackbed design and construction are described. The most common identified use of this technique consists of building asphalt subballast layers as a (partial) replacement for unbound granular material (UGM) subballast. This has been primarily associated with the construction of new high-speed lines (HSL), where the used asphalt mix is similar to those used for highway base courses. Most countries specify a layered design for the track support layers. This involves setting specific standards for individual layer thickness and bearing capacity depending on traffic characteristics. Some other identified uses include asphalt slab tracks and even sleeperless and ballastless track systems where the rail is embedded in an asphalt slab. The presented use cases in this paper account for the advantages and important considerations in relation to the use of asphalt in layered track designs. Even though some countries have adopted asphalt layers as a standard component of their track systems, more information is needed to develop a rational and optimized design method and maintenance protocols of asphalt subballast layers; thus, the importance of the data collected from instrumented track sections and information introduced in this paper.