The use of a layer of asphalt within railway trackbeds has steadily grown since the early 1980s in the United States. Its primary use has been for maintenance and rehabilitation applications in existing tracks, particularly at special trackworks, to improve trackbed performance, and to a lesser extent for new trackbed applications where the projected long-term performance of the asphalt trackbed is anticipated to be economically justified. Normally the asphalt layer is 6 in. (150 mm) thick, placed on a prepared subgrade or granular subballast, and is subsequently topped with a layer of typical ballast. Accepted highway/railway construction practices are adhered to, including adequate preparation and compaction of the support layers. In addition, surface and sub-surface drainage aspects are evaluated on a site-specific basis and improvements are specified based on accepted engineering practices. This application does not deviate significantly from conventional all-granular trackbed designs, except the asphalt layer is substituted for a portion of the thickness of the granular subballast and ballast support materials.
Described herein are 1) typical trackbed designs, 2) in-track applications, and 3) long-term performance evaluations for various types of major applications on several U.S. Class I railroads, namely NS, UP, CSX, and BNSF, and a limited number of Shortline railroads. Specifically addressed are rehabilitation applications for special trackworks — tunnel floors/approaches, wheel impact load detectors, bridge approaches, rail-highway crossings, turnouts, rail crossings, and rail crossovers — plus descriptions for a limited number of new double-tracking open-track installations. Brief descriptions are provided for international applications in six countries.
Particular detail is given to factors affecting the economic justification for utilizing this technology based on long-term performances and historical evaluations of numerous installations. Details are provided relative to unique conditions and logistics related to the application of the layer of asphalt within the trackbed support for the special trackworks and selected open-track installations. Several specific installations are highlighted.