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Researchers at TU Berlin have developed a technique to make current construction methods for ceilings more climate-friendly, efficient, resource-saving and inexpensive. Anyone looking to build ceilings with spans of seven meters or more through climate-friendly methods today can replace standard 25 to 35 centimeter-thick, CO2-intensive reinforced concrete ceilings with environmentally friendly ceiling constructions made of a composite of 20 centimeters of wood and only ten centimeters of concrete.
Research on the new wood-concrete composite was conducted in the Peter Behrens Halle, the civil engineering experiment test hall at TU Berlin. In this process, wood and concrete are glued together. In the foreground are the wooden elements on which a granulate chip has been applied. The concrete is then poured onto this. The result is a very strong bond. Image credit: TU Berlin / Chair of Hybrid and Composite Structures
Until now, the two materials have been screwed together or connected with each other using a joint. In the new process, concrete and wood are actually stuck together. “Adhesive is applied to the wood. Coarse chippings are placed on top. Once the adhesive has hardened, fresh concrete is applied in a second step. The fresh concrete interlocks with the chippings protruding from the adhesive layer. This creates a rigid bond with a very high load bearing,” explains Professor Dr.-Ing. Volker Schmid. He researched and developed this granulate chip bonding process working with Melf Sutter, research associate at the Chair of Hybrid and Composite Structures at TU Berlin (headed by Volker Schmid) and Baden-Wuerttemberg company Lignotrend.
The bonding technique is much stiffer than is the case with bolting. This results in better vibration and deformation behavior, which makes it possible to reduce the concrete layer from ten centimeters to eight centimeters without reducing the load-bearing capacity. Since the production of both concrete and steel has been extremely CO2-intensive up to now, every ton of concrete and steel saved helps protect the climate.
While the production of conventional wood-concrete composite ceilings is very labor-intensive, the innovative bonding technology is highly efficient: It is easy and robust to handle, has a low susceptibility to faults and a high degree of prefabrication. This means that the wood-concrete ceiling elements bonded with granulate chippings can be completely prefabricated in a company and installed on a construction site quickly and regardless of the weather. “The producer also has the option, however, of only manufacturing semi-finished elements, in other words only gluing the chippings onto the wood elements. The concrete is then applied at the construction site,” says Volker Schmid. The process thus allows for flexible applications.
The research project was funded by the Federal Ministry of Economics as part of its central innovation program for SMEs. The new technology has already been successfully used in the construction of a kindergarten in Sissach, Switzerland.
Source: TU Berlin
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