NOISE REDUCTION: The German Association of Railway Engineers held a symposium in Berlin to examine the Duraflex system of noise reduction for ballasted track developed by Frenzel-Bau, Bayer MaterialScience and Hennecke.

Ballast cavities are filled with elastic polyurethane foam, preventing movement under the load of passing trains. This increases the durability of the superstructure and absorbs structure-borne noise at the point where it is usually generated.

Duraflex was demonstrated on a section of track used for testing at the Wedding depot of Berlin urban transport operator BVG. This has wood and concrete sleepers and tight curves, and is subjected to high loadings during acceleration and brake testing.

‘We used a mixing head to inject the liquid polyurethane system directly into the cavities between the ballast stones´, said Dr Andreas Hoffmann, polyurethane specialist at Bayer MaterialScience. ‘To achieve the desired durability and noise reduction, it was sufficient to apply the foam to the ballast in the sleepers´ load transfer area. After a short time, the polyurethane system had completely cured, and the track was ready for operation again.´

Durflex has been tested on a 300 m section of main line at Uelzen, where it cut vibrations by 40% and airborne noise by between 1·5 dB and 3 dB, depending on the train.