Faster and more environmentally friendly construction with wood-concrete composite elements

Ceilings of residential or office buildings are usually poured from fresh reinforced concrete. This is very cheap, but bad for the environment. Concrete production causes billions of tons of CO2 emissions every year. In addition, the wet concrete is not optimal to install: Among other things, the fresh concrete carries unwanted moisture into the structure. Researchers at the University of Kassel, together with partners in the SpeedTeCC project, have found out how to do this more efficiently using a bonding technique.

Wood can be the solution

In the newly developed fast bonding technique, wooden beams are joined to precast concrete elements. The concrete slab lies flat on the beams. The incorporated wood means that up to 70 percent less concrete is needed for a building ceiling. The composite method is new: For this, the researchers use a metal grid that is placed between the glued joints of the wood and the precast concrete element. Electricity is connected to both ends of the metal grid so that the composite joint is heated and bonded in a targeted manner.

This makes the process particularly practical. "It is often cold on the construction site, and components cannot be bonded well in this way. Our goal was a simple, manageable process for practical use. With the SpeedTeCC process, we are no longer dependent on the outside temperature. This makes it possible to bond wood and precast concrete components even at low temperatures," explains Jens Frohnmüller from the Department of Building Preservation and Timber Construction. He supervised the project together with department head Prof. Dr.-Ing. Werner Seim at the University of Kassel.

Applicable in practice

The process can save a lot of time on the construction site. By working with precast concrete elements, a house can be built in a short time. Reinforced concrete, on the other hand, must first cure and dry.

The researchers started with small samples for statistical evaluation, increasing one scale in size with each test to check the load-bearing capacity and durability of the adhesive bond. These tests can ensure that the adhesive bond between the wood and concrete will remain durable for the life of the eventual building, not just the short term. "The icing on the cake is our 1:1 ceiling tests. We produced twelve ceiling elements using our new method," says Frohnmüller. These components are 6 meters long and 1.30 meters wide. The test was successful. The components were convincing in the tests on load-bearing, deformation and vibration behavior. This makes the fast bonding technology suitable for multi-story timber construction.

The new rapid bonding technology for wood-concrete composite elements should find its way into practice as quickly as possible. "With the follow-up project, we would like to bring the process further towards market maturity and into series production," says Frohnmüller. The focus here is to be on a manufacturing method that is as simple and robust as possible.

The University of Kassel has been working on SpeedTeCC together with the Technical University of Braunschweig, the Institute for Joining and Welding Technology (IFS) and the Fraunhofer Institute for Wood Research, Wilhelm-Klauditz-Institut (WKI). The cooperation partners are currently working on a guide to make the method available to industry. This documentation will be available in the next few months on the homepage of the International Association for Technical Wood Issues (iVTH) in Braunschweig, which supervised the project funded by the Industrial Cooperative Research IGF, AiF e. V. and BMWi.

Contact:
Jens Frohnmüller M. Eng.
Tel.: 0561 804 - 2685
E-mail: frohnmüller@uni-kassel.de