Fraunhofer researchers have developed a novel method for creating biogenic construction materials based on cyanobacteria. These bacteria, driven by photosynthesis, multiply in a nutrient solution, forming green concrete.
Rock-like solid structures are produced by adding aggregates and fillers such as sand, basalt, or renewable raw materials. Unlike traditional concrete production, this process does not emit any carbon dioxide. Instead, CO2 is absorbed and incorporated into the material, creating a green concrete that is environmentally beneficial.
The construction sector is grappling with a major challenge as cement, a key ingredient in concrete, significantly contributes to CO2 emissions. The German Environment Agency (UBA) reported that in 2018, cement production in Germany alone led to around 20 million metric tons of CO2 emission, representing roughly 10% of all industrial emissions.
Within the framework of the “BioCarboBeton” project, scientists from the Fraunhofer Institute for Ceramic Technologies and Systems (IKTS) and the Fraunhofer Institute for Electron Beam and Plasma Technology (FEP) have developed an environmentally benign, biologically induced process for creating biogenic building materials. This innovative process avoids emitting carbon and utilizes and sequesters the climate-damaging gas within the material.
The core of this new method is cyanobacteria, also known as blue-green algae. These bacterial cultures are capable of photosynthesis. They form limestone structures known as stromatolites when provided with light, moisture, and temperature. These biogenic structures, which have existed in nature for 3.5 billion years, demonstrate the durability of this biological process. CO2 is captured from the atmosphere during mineralization and is bound in the biogenic rock, a process the Fraunhofer researchers have successfully replicated technologically.
Under the direction of Dr. Matthias Ahlhelm, Fraunhofer IKTS is developing materials and processes, selecting potential fillers and binding agents, and providing form and structure. Meanwhile, Dr. Ulla König’s team at Fraunhofer FEP is working on cultivating the cyanobacteria, conducting microbiological analysis, and scaling up biomass production.
From Bacterial Solution to Solid Green Concrete
Cyanobacteria are first grown in a nutrient solution to produce the green concrete. The light source’s intensity and color affect the bacteria’s photosynthesis and metabolism. Calcium sources such as calcium chloride are added to facilitate the creation of stromatolite-like structures. Researchers then mix hydrogels with various fillers, like different types of sand, including sea or silica sand. Additional CO2 increases dissolved carbon dioxide levels, enhancing the process.
The bacterial mixture is stirred until homogeneous and then transferred to molds. The molds should be translucent to observe ongoing bacterial metabolic and photosynthesis processes. Subsequent mineralization leads to final solidification. The bacterial mixture can also be shaped through spraying, foaming, extrusion, or additive manufacturing, forming the basis for the final stages of mineralization.
Alternatively, porous substrates can be produced and treated with the cyanobacteria culture. “The developing solid structure remains porous during the process, allowing light to penetrate and drive the carbon dioxide fixation through limestone mineralization. We can halt the process by removing light and moisture or adjusting the temperature,” explains Ahlhelm. At this stage, the bacteria die off, leaving a solid product composed of biogenic calcium carbonate and fillers that can be used as bricks. The green concrete derived from cyanobacteria does not contain any toxic substances.
The BioCarboBeton project aims to identify the biogenic materials’ potential material and mechanical properties and scale up production processes. The researchers are exploring a circular process design, considering sourcing CO2 from industrial waste gases and using materials such as biogas, basalt, mine waste, and even milk residue from dairy operations as calcium sources. Sand, construction debris, and renewable resources are also being evaluated as fillers.
Applications for Green Concrete—from Insulation to Mortar
By carefully selecting fillers and managing the process and mineralization parameters, numerous products for different applications can be manufactured, including insulation materials, bricks, formwork fillings, and even mortar or stucco that hardens after application. Now that the Fraunhofer researchers have established and tested the process, they focus on scaling production and achieving the desired solid properties. The objective is to facilitate the production of environmentally friendly, bio-based construction materials at scale, efficiently, and economically.
Dr. Ahlhelm and Dr. König believe in the potential of this method: “Our process highlights the enormous potential of biologizing technology. The BioCarboBeton project represents a significant step towards a circular economy in the construction industry and beyond.”…LEARN MORE
