Recyclable timber-concrete composite construction

Concrete is an important material which is used in all areas of the construction industry. However, because one of the main ingredients is cement, large quantities of carbon dioxide are produced when manufacturing concrete. Furthermore, nearly two tons of gravel and sand is used to make one cubic metre of concrete. Many stakeholders in the construction industry are aware of the negative impact on the environment due to the extraction of raw materials. This underscores the need to use secondary raw materials and strategically manage these resources. After all, many buildings in Germany have been built using raw materials that should be considered as a resource. Brüninghoff is recognising and addressing this by making timber-concrete composite slab panels that can be removed and reinstalled.

 Preservation of resources 2.0 

The advantages of hybrid slab panels are clear: when the physical properties of timber and concrete are combined the result is extremely favourable structural and building-physical characteristics. While the economic benefits are considerable, the ecological value is extremely significant. Reducing the amount of concrete used preserves mineral resources and reduces CO₂ emissions. Brüninghoff knows about TCC elements and has been working intensively with them for over ten years. The company not only manufactures these elements at its own precasting plant, it also carries out the initial planning and subsequent assembly. As expert and Germany-wide pioneer in hybrid construction methods, Brüninghoff is dedicated to the development and ongoing improvement of hybrid slab panels and wall elements – while also taking ecological and economic aspects into consideration. To introduce a greater degree of sustainability into the resource-saving approach, the TCC elements are now geared even more closely towards a circular economy. The feasibility of removing the TCC slab panels was investigated using three test specimens under real life conditions during comprehensive trials, also taking reuse and recycling approaches into consideration. Prof. Dr. Anja Rosen, architect and DGNB Auditor at C5 GmbH, supported the removal trials with the Urban Mining Index she herself had developed and evaluated the results. 

 Reuse: reuse of entire elements 

The aim of the reuse approach is to reuse TCC slab panels previously recovered in other construction projects. From an ecological standpoint, this is the most favourable option as it uses the least amount of energy and retains all the original material characteristics. During the extensive trial carried out by Brüninghoff, three slab panels were successfully recovered and prepared for reinstallation, which highlights the suitability of this method for use in practice. Visible reinstallation of precisely these elements at the new premises of the firm Sesotec in Lower Bavaria gave two of the slab panels that were recovered during the trial a new installation location.  

 Recycling: accurate separation of materials 

If the elements cannot be reused, recycling provides a sustainable alternative. This involves accurately separating timber and concrete in a TCC slab panel connected by notches and anti-lift devices according to CEN TS 19103 so they can be used as raw materials for new products. When developing a removal concept, the anti-lift safeguard which, although a necessary feature, poses a particular challenge. This arises because the fully-threaded screws which are normally used when manufacturing the elements are screwed into the timber vertical to the floor/ceiling plane and cast in concrete. The removable connector was developed and used together with Reisser Schraubentechnik GmbH. Introducing the Reisser TCC connector has made the anti-lift safeguard easy to remove. This is because these connectors protect the screw thread and head or drive against concrete deposits which means the materials can be easily separated. While this guarantees straightforward disassembly, the notch also has been optimised for removal and allows the materials to be pulled apart more easily. The timber and concrete can therefore be easily pulled apart, which makes them easier to reuse and recycle. Its structural performance is therefore outstanding. Furthermore, the connection type is also particularly suitable for manufacturing fully prefabricated timber and concrete parts at the factory.  

All slab panel elements installed in the office wing of the new Sesotec construction project which has a total area of around 2,000 square metres were equipped with the removable TCC connectors. Adopting this approach when using the TCC slab panels saves resources and also establishes the circular economy of the installed materials. 

Tests in the field confirm the environmental benefits and cost-effectiveness of the technologies developed. By developing the TCC element, Brüninghoff is also demonstrating that the construction industry can also make a significant contribution to the circular economy by introducing innovative approaches and technologies.