Noise protection through foamed track ballast layer

Flexible track superstructure system with polyurethane proves its worth in rail traffic
Less noise pollution for residents / Extended maintenance cycles for track sections / Great potential for applications in local and long-distance traffic

Leverkusen, July 2008 – The passenger and freight traffic on rail is helping to prevent other transportation routes from becoming overloaded. It is also helping to conserve finite, natural energy resources, and thus to protect the environment. In terms of freight traffic alone, the transportation performance on the German rail network increased to 114.6 billion ton kilometers(1) in 2007, up 7.1 percent on the previous year. Conveying performance for passenger transportation, which came to 79.1 billion passenger kilometers(2) the same year, also demonstrates the growing popularity of rail traffic in Germany. However, the increase in the number of trains does not just raise demands on the stability and durability of the railway tracks – it also increases the noise pollution for nearby residents. In the past, rail network operators have tended to build noise protection walls to reduce noise levels. However, this solution is expensive and the walls themselves are often considered intrusive. What’s more, there is often no space to build noise protection walls in city centers.

FRENZEL-BAU GmbH & Co. KG, a specialist in rail engineering solutions headquartered in Freden, Germany, has teamed up with Bayer MaterialScience AG and Hennecke GmbH to devise a completely new solution to the problem – the innovative track superstructure system Durflex® with long-lasting flexibility. In this application, the cavities between the ballast stones in the track bed are completely filled with the Bayflex® elastic polyurethane foam system from Bayer MaterialScience. “This prevents the movement of the ballast stones, which occurs as a result of the dynamic forces generated when a train passes over them. This in turn increases the durability of the ballast superstructure considerably and absorbs the structure-borne noise at the point where it is usually generated,” explains Jürgen Frenzel, proprietor of FRENZEL-BAU. The system can be used both for building new sections of track and upgrading existing stretches.

New focus: “whispering ballast” in local public transport

Recently, participants at a symposium organized by the Verband Deutscher Eisenbahn-Ingenieure e.V. (VDEI, German Association of Railway Engineers) in Berlin were given the opportunity to see for themselves the benefits of the innovative Durflex® track superstructure system. This event for experts from railway infrastructure companies, planning offices, the German Federal Railways Authority and other institutions, focused on the application of the system in local public transportation. The symposium included a series of presentations on the topic and a practical demonstration of the system on a section of railway operated by the Berlin Transportation Company (Berliner Verkehrsbetriebe, BVG). The BVG operates an extensive rail network in the capital, covering some 350 kilometers of overground and underground tracks. Complaints from residents about the noise generated by the rail traffic was one of the factors that prompted the joint research project between BVG and FRENZEL-BAU.

Durflex® was implemented as part of the renovation work on a test track in BVG’s main workshop on Seestrasse in the Wedding district of Berlin. “As a result of the frequent acceleration and brake tests, the track is subject to extremely high dynamic loads on a regular basis. The maintenance and servicing costs are, therefore, equally high,” explains Ingolf Barthel, a manager in the Infrastructure division at BVG. The track section foamed with the polyurethane system is located right next to residential buildings, which means that noise reduction plays a key role here. The test track is fitted in sections with wooden and concrete sleepers and a switch. It also has two relatively tight curve radii.

A rail vehicle designed specially for applying the system was prepared on-site. “We used a mixing head to inject the liquid polyurethane system directly into the cavities between the ballast stones. To achieve the desired durability and noise reduction, it was sufficient to apply the foam to the ballast in the sleepers’ load transfer area,” says Dr. Andreas Hoffmann, an expert in polyurethane foam systems at Bayer MaterialScience. After a short time, the polyurethane system had completely cured, and the track was ready for operation again.

Results of the first pilot project are very promising

In the summer of 2007, this Durflex® technology was used on a 300-meter section of regular track on the Hamburg - Hannover high-speed line at Uelzen in Lower Saxony. imb Dynamik, a specialist in railroad track studies, performed extensive tests at Uelzen to determine the positional stability of the track, the base load, noise emissions and other relevant track superstructure parameters, and presented the results at the aforementioned VDEI symposium in Berlin. It turned out that Durflex® cuts the vibrations of the track system and, therefore, structure-borne noise emissions by around 40 percent compared with a standard ballast superstructure. Depending on the type of train – ICE, regional express or freight train – air-borne noise emissions are reduced by between 1.5 and 3 dB. Track sections foamed with Durflex® exhibit far less ballast compression, resulting in much more stable and durable track packing.

Overall, the new track superstructure system meets the high expectations of all the partners involved in the project, which was reflected in the positive feedback at the VDEI symposium and in the numerous inquiries received from rail network operators inside and outside Germany. Once again, BaySystems®, the umbrella brand for the global polyurethane systems operations of Bayer MaterialScience, has proved itself to be a professional system development partner for its customers, true to the Bayer slogan “Science For A Better Life”.