Building with wood makes an important contribution to climate protection. By combining wood and concrete, the Fraunhofer Institute for Wood Research Wilhelm-Klauditz-Institut WKI in Braunschweig aims to significantly expand the range of applications for timber constructions. A new type of bonding technology enables the accelerated production of wood-concrete composite elements (HBV elements). The aim is to establish construction with HBV elements in multi-storey building construction as a competitive alternative to pure prefabricated reinforced concrete elements.

Material Properties of Wood and Cconcrete optimally combined

According to the WKI, wood-concrete hybrid components optimally combine the specific material properties of wood and concrete. Due to its low weight and high tensile strength, wood is ideal for lightweight construction. The combination with concrete improves the load-bearing capacity, fire resistance and sound insulation, while at the same time enabling a slim component design.

Increased uUse of renewable Raw Materials as a Goal

The new joining technology, which the Fraunhofer WKI is developing in collaboration with two research partners and with major support from industry, is intended to improve the structural properties, cost-effectiveness and recyclability of wood-concrete composite elements and thus contribute to the increased use of renewable raw materials in solid construction. The researchers are also taking into account the use of hardwood as a regionally available source of raw materials.

Alternative bonding Technologies

"We are developing a standardized process for the production of long-term resistant HBV components under practical conditions. In addition to hot bonding technology, we are working with our project partners from the Technical University of Braunschweig and the University of Kassel to test and analyze alternative bonding technologies for joining wood and smooth concrete components. During the research work, attention is also paid to a practical application for factory and construction site production of the components," reports Malte Mérono, project manager at the Fraunhofer WKI.

Guide as a Planning Basis

The research results are summarized in a practical guide that presents the specific implementation steps and relevant criteria in a user-friendly way. This guide is intended to serve as a planning basis and make it easier for small and medium-sized enterprises (SMEs) in particular to produce HBV elements safely.

First successful Use in Practice

The development by Malte Mérono and his partners has already passed the practical test. In collaboration with fischerwerke GmbH & Co. KG, a bonded HBV element was successfully used as a suspended ceiling in a multi-storey building project. The company is now seeking building authority approval for the suspended ceiling. "The approval of the bonded suspended ceiling brings us a big step closer to our goal of being able to use wood in multi-storey buildings. This is an important contribution to the ecological turnaround in the construction industry, which is dominated by reinforced concrete," says Malte Mérono.

Broad iInterest in new Process

The topic of “bonded timber-concrete composite elements” is generally meeting with great demand in the industry. Construction companies, engineering firms, adhesive manufacturers and architects are all interested in this construction method. "We are experiencing a high demand in Germany, but also from abroad, on the one hand for tests by our ‘Structural Bonding’ test center and on the other hand for the qualification of the industry in the area of ‘Proof of suitability for the execution of bonding work for the production of load-bearing timber components and glulam’, the colloquially known ‘glue approvals’. However, detailed questions and new bonding methods in the field of glued laminated timber are constantly being developed and brought to us. The industry is pushing this type of construction very strongly," reports Harald Schwab, Head of Department at the Fraunhofer WKI.

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