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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, its high tendency to warp has meant that engineers have had to look for alternatives in some areas where wood is traditionally used.
(Published on May 2005 – JEC Magazine #17)
Eslon Neo Lumber FFU is an extremely dimensionally stable composite material made from Baydur® 60 grade reinforced with long glass fibres 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, due either 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 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 (Fibre reinforced Foamed Urethane) is produced 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. 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 polyurethaneglass fibre compound, they absorb only a minimal amount of water. Due to the material’s fibre 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 it a very reliable material, even when exposed to long-term weathering. Unlike natural wood, it loses none of its favourable mechanical properties even after long-term service in the open air. The polyurethane-glass fibre composite is also superior to concrete thanks to its low weight and simple machinability onsite. 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, polyurethane sleepers are used on bridges but also in tunnels 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.