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HFA-Projekt: Suche nach möglichen Alternativen für Kreosot zur Imprägnierung von Bahnschwellen aus Holz

Die Holzforschung Austria (HFA) betreut das Forschungsprojekt „Bahnschwelle 2020“. Ziel ist es, Alternativen für das derzeit wegen der guten Langzeiterfahrungen noch unverzichtbare Schutzmittel Kreosot (Steinkohlenteeröl) zur Imprägnierung von Bahnschwellen aus Holz zu finden.

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Ecological benefits of the wooden sleeper

Around the world, wood is the most important and most frequently used renewable resource.

The woods used in Europe for the production of wooden sleepers originate entirely from sustainably managed forests – which is frequently documented by an FSC or PEFC certification.

In the environmental categories primary fossil energy needs and global warming potential of its non-wood competitor products, wood has numerous ecological advantages compared to other materials. This is because of the fact that during the biological production of the wood – i.e. the growth of the tree – regenerative primary energy is stored in the wood and later in the product which is made out of it, until the primary energy can be recovered finally, at the end of the product’s life. Likewise, during the growth of the tree, large quantities of carbon or carbon dioxide are stored in the wood and are bound there for the entire time of the product’s use. They are only released again at the end of its life.

In this connection, a life cycle assessment study (Life cycle assessment of railway sleepers – Comparison of railway sleepers made from concrete, steel, beech wood and oak wood) by EMPA from the year 2009 said among others:
Taking thermal utilisation into consideration, compared to sleepers made of other materials, in all impact categories with the exception of the impact category over-fertilisation, wooden sleepers perform the best. In some impact categories the avoided emissions achieved in the substitution effect – by replacing fossil energy sources – through energy recovery from the wooden sleepers are larger than the direct emissions from their life cycle, especially in the case of climate change (in case used in a combined heat and power generation plant), but also partly in abiotic consumption of resources, stratospheric ozone depletion, or photosmog.

The study also determines that the eco-profiles of the beech and oak sleepers hardly differ from one another at all.
The conversion to impregnation oil type C pursuant to EN 13991 and its introduction in accordance with the German standard DIN 68811:2007-01 have lead to the fact that the use of impregnation oil, compared to earlier studies, now plays a subordinate role for the eco-profile of the wooden sleepers.

Energy recovery for the sleepers typical today due to the Waste Wood Ordinance proves itself to be essential for a profitable eco-profile of the wooden sleepers.

Over their service life wooden sleepers store roughly the same amount of CO2 as carbon, as greenhouse gases are released from fossil sources throughout their life cycle, including track construction, maintenance and servicing. Around 132 kg CO2 is stored in each wooden sleeper. Extrapolated to the entire German railway system, that is 3.78 million tonnes CO2 which is stored in the wooden sleepers today.

If waste sleepers are used properly thermally – preferably in combined heat and power generation – through the substitution of fossil energy sources roughly just as much CO2 will be avoided as is emitted over the life cycle of the wooden sleepers, including track construction and maintenance. So, in sustainable forest management, wooden sleepers are not only CO2 neutral with respect to their biogenic carbon dioxide, but are also “first choice”.with respect to the CO2 from fossil sources.

Thus the use of wooden sleepers is also a valuable contribution to climate protection!