One cubic meter of robinia wood stores just under 1,300 kilograms of CO2, whereas the production of one metric tonne of steel in Germany releases – with the current energy mix – around 1,500 kilograms of CO2. The potential savings in harmful greenhouse gases are therefore enormous. Taking a bridge as an example, this means that for a bridge span of approximately 25 meters, around 14 tonnes of steel girders are required for the load-bearing structure, which corresponds to an emission of 21 tonnes of CO2. A comparable bridge with a load-bearing structure made from glulam would require around 10 tonnes of wood and would bind 18 tonnes of carbon dioxide over a long period of time.
Load-bearing building structures in exterior and damp areas must fulfill stringent climatic and mechanical requirements. With spruce wood, this is only possible to a very limited extent. In addition, it requires a high material and biocide input in order to achieve the necessary stability as well as resistance to wood pests. As a result, tropical wood is often used for such demanding wooden structures, as well as for simpler wooden construction products for outdoor use, such as decking planks. Sometimes wood is used that has been extensively modified, for example thermo pine, or radiata pine that has been acetylated with acetic acid and has to be imported from New Zealand. Robinia, in contrast, does not require any form of biocidal treatment whatsoever and has excellent inherent mechanical properties.
As a result of its high strength and durability, robinia wood could also be used for redensification in cities. Many locations feature low buildings that could be extended upwards, such as supermarkets. These buildings are, however, often not designed to withstand additional floors of steel and concrete. With lightweight structures made from robinia wood, this could nevertheless be achievable in many cases.
Due to the fact that robinia, as a leguminous and drought-resistant species, also grows in sandy or nutrient-poor soils, it can cope better with the new climatic conditions than spruce and other European coniferous and deciduous tree species. The increased cultivation of robinia as a source of construction wood therefore serves not only direct climate protection through the binding of CO2, but also future-proof forest conversion and the recultivation of former open-cast brown-coal mines. Plus: Whilst a spruce needs around 80 years to reach harvesting maturity, the robinia can be felled for timber production after just 30 to 40 years. A shortening of the transport routes for the wood is also a goal of our project, as the existing robinia stocks originate primarily from Southern and Eastern Europe, in particular from Hungary.
With the development of an approved construction product, we are ensuring that the climate-resistant “tree of the future” robinia can be used as efficiently as possible (cascade utilization). This means that the wood is initially used as high-quality construction timber for many years. After the structure has been demolished, it can – depending on its condition – be further processed into other products, such as decking planks. Thermal utilization (energy generation through incineration) or biological utilization (composting) only occur at the very end of a long chain of multiple usages.
Fraunhofer Institute for Wood Research 
