Fungal mycelium as a construction material, ecofriendly concrete and smart recycling solutions pave the way for climate neutrality.
© Fraunhofer / Marko Priske
Fungal mycelium as a construction material, ecofriendly concrete and smart recycling solutions pave the way for climate neutrality.
© Fraunhofer / Marko Priske
Fungal mycelium as a construction material, ecofriendly concrete and smart recycling solutions pave the way for climate neutrality.
© Fraunhofer / Marko Priske
Fungal mycelium as a construction material, ecofriendly concrete and smart recycling solutions pave the way for climate neutrality.
© Fraunhofer / Marko Priske
Fungal mycelium as a construction material, ecofriendly concrete and smart recycling solutions pave the way for climate neutrality.
© Fraunhofer / Marko Priske
Web special Fraunhofer magazine 4.2024
Everyone knows the story of the three little pigs. Each of them wanted to build himself a house. The first little pig was a bit lazy, so he built his house out of straw. The second was a harder worker, so he used wood. But the third little pig went to all the effort of using brick. In the fable, which dates back to 19th-century England, the big bad wolf comes and blows down the houses made of straw and wood, calling out, “Then I’ll huff and I’ll puff and I’ll blow your house down.” But the wolf is no match for the brick house and ultimately ends up getting burned in the chimney. The three little pigs live happily ever after, safe and sound in the third house.
But what does all that have to do with this article? Well, from the story we learn that it is worthwhile to put some effort into building – and that brick is a very dependable construction material. Similar materials have been used in Germany for generations. Of the more than 19 million homes in Germany, the majority are built out of natural stone, brick or concrete. It is a tradition that dates back to antiquity, as sturdy walls afforded protection from storms, fire and invaders. German builders still emphasize stability and durability to this day. Besides that, stone also has natural heat-insulating properties, so it reduces energy consumption.
But it also has its drawbacks. Both natural stone and cement can sometimes contain substances that harm the environment or even human health. Water-soluble chromates in cement can trigger allergies, for example. Cement is also highly alkaline, which can irritate the skin and mucous membranes. Some kinds of natural stone, like granite, contain radioactive substances such as uranium, thorium and radium. At high activity concentrations, these substances release small amounts of radon, a radioactive gas that is considered harmful to health and increases people’s risk of developing lung cancer. On top of that, natural stone is often treated with chemicals to polish or protect it from weathering. Some of these sealers and surface treatments release volatile organic compounds (VOCs), which can reduce air quality inside enclosed spaces.
As part of the new German Federal Climate Change Act (Klimaschutzgesetz, KSG), the German federal government stipulated that all existing buildings in Germany be made climate-neutral by 2045 − a massive project, but also a source of tremendous opportunities in terms of the future viability of German industry. Construction and use of buildings has been responsible for about 30 percent of CO₂ emissions in the country to date. The construction industry is facing the challenge of rethinking and reshaping the entire process, from the use of materials through to disposal.
Meeting climate targets requires fundamental change in a form just as complex as construction itself. On the journey toward climate neutrality, sustainable construction materials and intelligent recycling concepts are two factors that could revolutionize the industry. Numerous Fraunhofer institutes are researching these key technologies, which combine to empower a climate-neutral building sector. The Fraunhofer institutes offer solutions for the entire building value chain, from raw materials to the final product and from new construction to renovations. “Conventional construction products use a lot of energy in the manufacturing process, plus they are often made from petroleum, which is a finite resource,” says Dr. Henrik-Alexander Christ from the Fraunhofer Institute for Wood Research, Wilhelm-Klauditz-Institut, WKI. “Disposal and recycling are also difficult with these products. In many cases, incineration is the only option, but it also releases large amounts of carbon.” Experimental sustainable construction materials are a promising answer to the environmental challenges facing the construction industry. These innovative materials are designed to lower carbon emissions, conserve resources and minimize waste.
When it comes to fungus in the walls, most people tend to think of unsightly and potentially harmful mold and mildew. Christ and his colleague Dr. Steffen Sydow aim to change that. They are researching fungal mycelium, which they hope to use as a bio-based adhesive for hot-pressed construction and insulation materials. Fungal mycelium consists of long, thin cells that form a complex three-dimensional network. The network works its way through the substrates used, which can include substances like woody residue from hemp plants, wood chips and other plant fibers, and turns them into composites with favorable technical properties. “Mycelium is like a biological form of glue, if you will, making it an alternative to conventional petroleum-based products,” Christ says. To intensify the natural bonding properties of the fungus, the mycelium is inactivated during hot pressing and the material is reinforced and dried.
But even beyond that, fungus also has true super powers when it comes to building: Mycelium is often lighter in weight than many traditional construction materials, plus it is extremely adaptable and can be molded into almost any shape. It also has high compressive strength and thermal and acoustic insulating properties. In tests, its thermal conductivity was similar to that of wood fiber insulation board. “Fungus has impressive capabilities that can be harnessed through biotechnology,” says Lina Vieres, a research scientist in the Product Development department at the Fraunhofer Institute for Environmental, Safety and Energy Technology UMSICHT. Knowing that fungus can take fantastic shapes with extreme stability, she and biodesigner Julia Krayer started researching fungus-based materials five years ago.
In the FungiFacturing project, they cooperated with a team from the Fraunhofer Institute for Building Physics IBP to inject a paste of residual materials with a fungus growing through it. Working in their fungus lab, the researchers used a ceramic 3D printer to process the mass into sound absorption materials. Sawdust, brewer’s grains from beer production or straw, all plant-based residues, serve as the nutrient-rich substrate for growing the fungi. The fungal mycelium grows inside an incubator, hardening the printed object until it is rock-hard. “Not all fungi are suitable for this. Fungi that break down wood, such as bracket fungi and tinder fungus, are especially good candidates.”
To acquire this knowledge, Vieres worked extensively with the mushrooms. She is scheduled to do a continuing education course for certification as a mycology specialist next year. “My friends are no longer surprised to find me crawling off into the bushes looking for interesting mushrooms,” Vieres says. She is certain of one thing: “The super powers of fungus can be used on a much more far-reaching basis than before.”
Even with all its benefits, there is one important construction material that fungal mycelium cannot fully replace: concrete. No other materials have yet been able to match its high stability and compressive strength, which are needed for load-bearing structures, or its durability and fireproof properties. The issue is that concrete is not especially ecofriendly, primarily because cement production is CO₂-intensive, generating about eight percent of worldwide greenhouse gas emissions.
“Limestone is burned at high temperatures,” says mineralogist Dr. Sebastian Dittrich, Group Manager Processing and Recovery at Fraunhofer IBP. “That requires a lot of energy, uses up fossil fuels like coal or natural gas and releases chemically bound carbon dioxide.” Producing concrete also consumes huge volumes of sand, gravel and limestone, which adversely affects natural ecosystems and jeopardizes biodiversity: Trees are cut down, rivers polluted and animal habitats destroyed in the process of extracting these materials.
To address these issues, various Fraunhofer institutes are working on more-sustainable versions by finding substitutes for the materials used to make concrete. Researchers at the Fraunhofer Institute for Ceramic Technologies and Systems IKTS and the Fraunhofer Institute for Electron Beam and Plasma Technology FEP are putting their hopes in bacteria. They are working on a biogenic construction material based on cyanobacteria as an alternative to concrete. These tiny organisms multiply in a nutrient solution and use photosynthesis to bind aggregates such as sand or basalt into solid structures reminiscent of stone. Unlike conventional concrete production, the process generates no harmful carbon emissions. Instead, the material actually binds the gas inside, where it cannot contribute to climate change.
Christina Haxter from Fraunhofer WKI, for her part, is taking a different tack involving woven materials. Natural fibers derived from flax, a well-known material in Germany, are woven together on a huge loom at Fraunhofer WKI and used to reinforce concrete. Potential uses include floor slabs in buildings or applications in road construction. “The conventional steel rebar used in concrete can corrode, but flax can’t,” Haxter says, pointing out just one advantage. What is more, the bio-based version of the reinforcing material is lightweight, sturdy and resilient, making it an ideal material for long-lasting and yet also sustainable construction projects. Other scientists are taking still other approaches. Dr. Sebastian Dittrich and his team at Fraunhofer IBP are working on a new formulation for concrete in the BAUSEP joint research project. To that end, they are using secondary raw materials such as ash from household waste incinerators and slag from steel mills. The particular properties of concrete are maintained even when the materials used to make it are changed.
The ash undergoes ultrasonic cleaning to remove any clinging foreign materials, and glass is sorted out. The new formulations make it possible to reduce the proportion of primary raw materials used. “The approach we have developed can help significantly reduce resource consumption in the construction industry,” Dittrich says. The project is still in the testing phase; the team has produced some 150 square meters of paving stones so far. “We firmly believe the new concrete will have its uses in road and building construction and in civil engineering,” Dittrich notes.
Industrial waste materials aren’t the only thing that can be reused in new construction, either; mineral construction and demolition debris can, too. Each year, Germany produces about 220.6 million metric tons of these materials, a large portion of all the waste generated in the country. Reuse and recycling are important in order to conserve natural resources and use less energy. Many projects in progress at various Fraunhofer institutes are looking at recycling in the construction sector. For example, Fraunhofer IBP is producing construction materials from recycled materials such as concrete, brick and asphalt. These secondary raw materials can then be reused in building construction. This reduces waste while also lowering the use of primary raw materials, thereby extending the life cycle of construction materials. Another project, BauCycle, is developing a method of sorting construction debris by dividing it into valuable recycling materials and secondary raw materials for use in construction − one route to circularity in the building sector.
Expanded polystyrene (EPS) is another of the construction and demolition materials that are generated in large volumes but have thus far mostly been simply thrown away. Commonly used in insulation, EPS is 98 percent air, which gives it extreme insulating properties. It also does not require much energy to produce or transport. “It’s a really exciting material,” says Dr. Patrick Taschner from Fraunhofer Austria, “but only 26 percent of the building material and 56 percent of the expanded polystyrene used for packaging is recycled in Austria.” To tackle this imbalance, Taschner and a consortium from the EPSolutely research project, consisting of 13 partners, worked together to devise a concept for efficiently collecting, processing and reusing old expanded polystyrene nationwide. Some 5,000 collection bags with QR codes have already been distributed to partner companies. Construction firms use an app to quickly and easily send a message when the bags are full and ready to pick up. “Then we can grind it up, clean it and use it to make new insulation board.” The process emits 80 percent less CO2.
If the construction industry and all existing buildings are to be made climate-neutral by 2045, we also need to change the way we think about renovation and refurbishment. “These processes are often lengthy and resource-intensive,” explains Dr. Simon Schmidt, head of the Hygrothermics department at Fraunhofer IBP. Researchers from seven Fraunhofer institutes aim to change that in the BAU-DNS flagship project. Schmidt explains: “Renovations could be completed about ten to 15 percent faster, and the gray energy of these material streams could be cut in half through bio-based materials and other approaches.” A faster pace would be made possible, for instance, by systemic and functional development of sustainable renovation and rehabilitation modules, one of the areas of focus for BAU-DNS. The modules are to be industrially prefabricated and assembled on site, which will also help construction firms cope with the shortage of skilled workers. Schmidt knows what he is talking about, as he comes from a family of tradespeople and apprenticed as a carpenter himself. Now, as a structural engineer, he is focusing on the needs of construction companies. He views sustainability as especially important. “This is the only way to take the construction sector into the future.”
Fraunhofer-Gesellschaft
