Fraunhofer: Breakthrough in recycling could meet construction material shortage

In an age of a construction boom, raw materials and supplies thereof are being placed under more and more supply pressure, while the environmental damage wrought by the leftovers of construction work is growing and growing.

Germany’s Fraunhofer institute has worked on a compromise solution to both these problems, in the form of a €3.3m research project over the past three years. The project has yielded promising results: In addition to aerated concrete from building rubble there are also acoustic building materials and components made of mineral granules.

The full findings will be presented at the BAU 2019 trade fair in Munich, held from January 14-19.

One of the key aspects of the research was to do something constructive with the around five million metric tons of fine-grained building rubble left behind during construction work in Germany each year – to give an idea, this is around 12.5% of Germany’s sand and gravel requirement for its construction industry.

Hitherto this high-value material has often ended up in landfills or roads, but the Fraunhofer Institutes for Building Physics IBP, for Material Flow and Logistics IML, for Environmental, Safety and Energy Technology UMSICHT, and for Optronics, Systems Technology and Image Analysis IOSB together have come up with the BauCycle process, which upcycles the waste into high-quality building materials.

The process has the ultimate aim of transforming the mix of minerals within construction waste into a sustainable resource and demonstrate potential applications in construction, while there is also a target of setting up a dynamic market platform where the raw materials are traded as commodities.

During the process, the rubble and other waste is sorted down to a size of 1mm. The researchers have developed an opto-pneumatic detector that enables fine fractions to be separated on the basis of the color, brightness and chemical composition of the particles; it is even capable of distinguishing sulfates from silicates. The technology involved can achieve a throughput of 1.5 metric tonnes per hour.

In the best-case scenario, four clean aggregates may be recycled and reused to produce aerated concrete, a light building material with good thermal insulation properties. It is suitable for building two-story houses and as indoor insulation. Another project finding was that a combination of bricks and recovered concrete can be used to make geopolymers, a cement-free building material that is strong and acid-resistant, much like concrete. Geopolymers have the added advantage of a very low carbon footprint. Further research has also yielded a prototype of a sound-absorbing, open-pored panel made of granulates which matches up to current market materials for sound-absorption.

All the materials will be on display at the Fraunhofer stand in January.

“The Fraunhofer Institutes have been involved in a huge number of technological breakthroughs across industry in 2018,” said Robert Herrmann, CEO of economic development agency Germany Trade & Invest.

“They are an integral part of one of Germany’s most prized assets, a vibrant R&D landscape with numerous pioneering institutes and research centres constantly driving for disruptive innovation.

“Over the past 20 years, the amount spent on R&D in Germany has doubled from around 1.5% of GDP to just over 3 per cent in 2016, a level of €92.2bn.

“Germany has become a place of innovation, where future solutions can be found and where solid investment in the future is rewarded. This breakthrough success in the construction industry is a perfect example of how Germany’s R&D landscape rewards shrewd investment. ”