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13 Sep 2004  -  Germany

On the right track with new composite material

Leverkusen, Germany

Wood, one of the oldest materials known to man, is also one of the most fascinating. By the same token, however, this familiar material does have its limits in terms of its uses. For example, being a natural raw material, wood is not resistant to weathering. Also, the high tendency of the material to warp has meant that engineers have had to look for alternatives in some areas where wood is traditionally used.

"Eslon Neo Lumber FFU" is an extremely dimensionally stable composite material made from Baydur® 60 grade reinforced with long glass fibers produced by Sumika Bayer Urethane Co. Ltd., a subsidiary of Bayer MaterialScience AG. The Japanese company Sekisui Chemical has successfully sold this product for over 20 years as a construction material in the Asian market where the sophisticated composite material has proved successful in a wide variety of fields. Specifically, it is used for applications where it is not possible to use wood, either due to technical or economic reasons but where wood would have been the material of choice based on how easy it is to process. The most common applications of the composite material are pools for fish farming, silos, walkways, soil anchors (in this instance as a substitute for concrete) and above all railway sleepers. The tracks for the Japanese high-speed train Shinkansen for instance have been laid on polyurethane sleepers.

Now the versatile composite material has made its debut in Europe. As part of a renovation project, for the first time ever the tracks on the Zollamt bridge in Vienna have been laid on sleepers made from polyurethane.

"Eslon Neo Lumber FFU is particularly suited to use on bridges as it offers clear advantages over wood", says Michael Schwittlinsky from Sekisui Chemical Germany. "Temperature changes, UV radiation and in particular the permanent moisture in the air mean that wooden sleepers weather more quickly here than in other areas of application. The problem is that making structural improvements to railway tracks involves not only considerable inconvenience but also high costs." Consequently, in these and similar areas of application, materials which have a long life in these conditions soon pay for themselves.

Eslon Neo Lumber FFU (FFU stands for fiber reinforced foamed urethane) is produced at Sekisui in almost any required length using the pultrusion process. It looks like wood and combines all positive attributes of the natural product with those of a modern composite material. The Eslon Neo Lumber sleepers can be screwed together, nailed or sawed using conventional woodworking tools and also adhere together superbly, with even a stronger bond than that which wood produces. Other positive features are a low linear coefficient of thermal expansion and low thermal conductivity values. Thanks to the closed cell structure of the light polyurethane-glass fiber compound they absorb only a minimal amount of water. Due to the material's fiber reinforcement, its high compressive and tensile strength place it among the current top high-tech construction materials.

The material's good resistance to hydrolysis, greases and oils is another quality which makes the "polyurethane wood" a very reliable material, even when exposed to long-term weathering. Unlike natural wood, Eslon Neo Lumber FFU loses none of its favorable mechanical properties even after long-term service in the open air. The polyurethane-glass fiber composite is also superior to concrete thanks to its low weight and simple machinability on-site. Bridges which date back to an earlier period in particular often require individual solutions when it comes to installing sleepers. The statics of these bridges generally also only allow lightweight materials to be used.

In Japan not only are polyurethane sleepers used on bridges but also in tunnels that are situated close to the sea where they are often washed by seawater and exposed to an aggressive microclimate. Due to the limited amount of space available in such cases, work is very difficult and costly. Consequently, the polyurethane option, which is light and resistant to salt water, is generally preferred.

Sleepers of varying length are used for the manufacture of points. When concrete sleepers are cast, a separate mold is needed for each length. With the pultrusion process on the other hand, it is easy to make any individual length. Polyurethane sleepers are significantly lighter than concrete. This is a particular advantage with points sleepers which can be up to 10 meters long. They also do not break as easily.

The excellent electrical insulation properties which the plastic sleepers possess proves effective in the winter when the points have to be heated in order to prevent them from freezing. The material is also resistant to frost and deicing salt.