FAVRE — recycling concrete protects the environment and saves resources

Why do we need this new technology?

Concrete is the most commonly used material worldwide. However, cement production generates carbon dioxide (approximately 700 kg of CO₂ per metric ton of cement), and sand suitable for use as a raw material is in increasingly short supply. In some areas of the world, mafia-like structures are already forming, illegally extracting sand from coastlines and riverbeds. Each year, some 40 billion metric tons of sand and gravel are used to produce concrete. That’s enough sand to build a wall with a width and height of 27 meters, stretching around the entire Equator.

More than 218 million metric tons of inorganic waste was generated in Germany alone in 2018, according to Kreislaufwirtschaft Bau, an initiative working toward a circular economy in the construction sector. In principle, it should be possible to recycle the raw materials involved in this human activity. But so far, there has not been a suitable method for reclaiming sand and other raw materials for cement production from construction debris on a large scale. Just eight percent of this waste is currently recycled. Some 70 percent of waste concrete is used in roadbeds.

“But that’s not recycling, it’s downcycling,” says Dr. Volker Thome, head of the Inorganic Materials and Recycling department at the Fraunhofer Institute for Building Physics IBP. It would only be genuine recycling if the waste concrete were reused to produce not only aggregate but also raw materials for new cement production. “Even if we only reclaimed the high-quality aggregates from waste concrete, that alone would be enough to achieve something like a tenfold increase in the recycling rate, pushing it up to as much as 80 percent.”

In the FAVRE project, Thome and his team are working on a new method of recycling construction debris for industrial application. The researchers have succeeded in using “ultra-short flashes” to break down waste concrete into its elements and process it so those fractions are available as substitute materials for production of cement, thereby helping to protect the climate and conserve resources.

Who will benefit from the new technology?

The technology from the FAVRE project could make an important contribution to climate action and significantly reduce worldwide resource use. For the construction industry, it would ease the tense situation involved in purchasing raw materials. It would also make mafia trafficking of sand and illegal exploitation no longer attractive. At the same time, the environmental footprint of concrete construction would be massively improved: The secondary lime produced through recycling is carbon-neutral — unlike the primary lime that is conventionally used in cement production.

How does the new solution work?

The process of breaking down construction debris is known as “electrodynamic fragmentation.” Pieces of old concrete are placed in a water bath, where “ultra-short electrical pulses” break them down into their constituent elements. The high-voltage pulses are generated by a Marx generator, which is capable of producing ultra-short pulses lasting less than 500 nsec.

Thome, a mineralogist, explains the mechanism: “When the electrical pulse hits the concrete, the predischarges always follow the path of least resistance — which is along the grain boundaries. These predischarges weaken the concrete along its phase boundaries. The first predischarge to be grounded leads to an electrical breakdown that produces shock waves. This ultimately separates the individual elements of the concrete from each other. It’s almost like the material is being pulled apart, since unlike in mechanical methods, the only force that needs to be overcome is the material’s tensile strength.”

The basis for the technology was developed back in the 1950s, but it went unused for a long time. The reason was that previous applications were not cost-effective due to their high energy use and low throughput of only about one metric ton per hour. The researchers at Fraunhofer IBP have now succeeded in developing an energy-saving method for industrial use. A skillful arrangement of multiple electrode pairs combined with a new type of generator makes it possible to break down large amounts of material per unit of time.

What makes the project unique?

The technology being developed by the researchers working on the FAVRE project is to enable construction debris recycling on a large, industrial scale for the first time. This innovation from Fraunhofer IBP significantly reduces the energy consumed by the recycling process as compared to conventional methods, making recycling a cost-effective alternative. Electrodynamic fragmentation enables genuine recycling of waste concrete without any loss of quality. In addition, the new fragmentation system can also separate composite materials that are difficult to process. These composite materials (such as reinforced concrete) cannot be fully broken down using the mechanical processing methods customary today. This unique aspect is also reflected in the project’s name: FAVRE stands for “Fragmentierungs-Anlage für Verbundwerkstoff-Recycling,” German for “Fragmentation System for Composite Material Recycling.”

Why is the Fraunhofer Future Foundation supporting this project?

In FAVRE, the Fraunhofer Future Foundation is supporting a technology that can contribute to a significantly more efficient circular economy to enhance sustainability. Recycling waste concrete is a highly effective way to conserve resources and counteract the shortage of raw materials already affecting the construction sector. This technology can also contribute to climate action: The secondary lime produced through recycling is carbon-neutral — unlike the primary lime that is conventionally used in cement production.

Bundesverband Baustoffe – Steine und Erden e. V. (2021): Mineralische Bauabfälle Monitoring 2018: Bericht zum Aufkommen und zum Verbleib mineralischer Bauabfälle im Jahr 2018.

Fraunhofer IBP (2014): Recyclingtechnologie mit Potenzial. Presseinformation zur Auszeichnung »Ausgezeichneter Ort im Land der Ideen«.

Fraunhofer IBP (2012): Wenn der Blitz im Labor einschlägt - innovative Recyclingverfahren mittels elektrodynamischer Fragmentierung. In: Forschung im Fokus Februar 2012.

Hans Otto Film GbR (2019): Volker Thome ist der Sandmann. Vimeo, 7. Februar 2019, Web.