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Living, Reproducing Concrete Created with Bacteria

Living building material

Sample of living building material (University of Colorado, Boulder)

16 Jan. 2020. Engineers developed a more sustainable type of concrete adding a form of bacteria to grow and reproduce the material under most conditions. A team from University of Colorado in Boulder describes its process and material in yesterday’s issue of the journal Matter.

Researchers from the Living Materials Lab led by Colorado civil engineering professor Wil Srubar are seeking construction materials with a greater ability for self-repair and less environmental impact than most of today’s concrete. Production of concrete contributes about seven percent of all global carbon emissions, which the industry acknowledges. And while other labs and companies are experimenting with adding bacteria to concrete, say the authors, many of these attempts failed since most bacteria have short life spans, and do not provide long-term benefits for self-healing or other desired functions.

“We already use biological materials in our buildings, like wood, but those materials are no longer alive,” says Srubar in a university statement. “We’re asking: Why can’t we keep them alive and have that biology do something beneficial, too?”

To meet these needs, Srubar and colleagues designed a process for supporting bacteria, in this case a marine bacteria of the synechococcus group, when mixed with concrete. Synechococcus bacteria use photosynthesis for adapting to changes in light and salinity, as salt water mixes with fresh water. The Colorado researchers combine synechococcus bacteria with sand and hydrogel, a water-based polymer, that provides a scaffold for the bacteria to form colonies. This bacterial matrix is then added to concrete.

The researchers discovered that through photosynthesis the bacteria absorb carbon dioxide and generate calcium carbonate, the primary ingredient in concrete, which both reduces the environmental impact of their new material and strengthens it at the same time. They also found their living building material or LBM, could reproduce and grow under the right conditions, for three generations.

The material incubates at 37 degrees C (98.6 F), human body temperature, and can be stored at 4 C (39 F), where the concrete solidifies. The team’s tests show nine to 14 percent of their LBM remains viable in at least 50 percent relative humidity for 30 days, a far greater percentage than previous attempts to add microorganisms to concrete that never reached 0.5%. Results also show LBM’s performance and viability continues in up to 100 percent humidity, suggesting its usefulness for high-humidity climates.

Their tests show as well that LBM gets tougher in dryer conditions, where humidity is less than 50 percent. The results indicate the mineralized gel makes the concrete more resilient as humidity lowers. But the findings show that in dryer conditions, the natural marine bacteria die, and thus stop reproducing. The authors say further studies should explore molecular additives to compensate for dry conditions.

The authors point out their process offers a platform technology that can be adapted for combining other microorganisms with concrete and reacting under various environmental conditions. This platform, say the researchers, could add other functions to building materials, such as sensing for toxic chemicals in the air.

“Though this technology is at its beginning,” adds first author Chelsea Heveran, now on the faculty at Montana State University, “looking forward, living building materials could be used to improve the efficiency and sustainability of building material production and could allow materials to sense and interact with their environment.”

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