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Monday, 27 January 2020

Researchers have developed "living concrete" capable of self-regeneration

Example of self-regenerating concrete. | Genie-inc.com


American researchers have developed a “living” building material, incorporating many photosynthetic bacteria. The material thus acts like a living organism: it is capable of developing and regenerating at an impressive speed.

“Living concrete”, as it is now called in the press, consists essentially of a mixture of gelatin, sand and cyanobacteria. Developed and tested by scientists at the University of Colorado at Boulder (United States), the resulting structure was able to regenerate three times after being cut, suggesting a potential breakthrough in the emerging field of self-healing materials.



The innovative material, developed in partnership with DARPA (Defense Advanced Research Projects Agency), presents a khaki green color after manufacturing. The initial coloring then fades as the bacteria die.

"It really looks like Frankenstein-like material ," Will Srubar told the New York Times , engineer and project manager at UC Boulder.

An arch molded with living and self-regenerating building material, in the laboratory of Dr. Srubar. Credits: CU Boulder College of Engineering & Applied Science

Even when the color fades, the bacteria survive for several weeks and can be rejuvenated - causing further growth - under the right conditions. The results of the study were published Wednesday in the journal Matter .

"The new material represents an exciting new class of low carbon designer building materials ," said Andrea Hamilton, construction expert at the University of Strathclyde, Scotland.

To develop it, the researchers first tried to introduce cyanobacteria into a mixture of hot water, sand and nutrients. The microbes then absorbed the light and began to produce calcium carbonate, gradually cementing the sand particles together. But the process was slow, and DARPA (the research arm of the Ministry of Defense and the project funder) wanted construction to take place very quickly. This need then accelerated the birth of this new, more efficient version of the material.


Gelatin added to the “mixture”

Dr. Srubar has worked with gelatin in the past, a food ingredient that, when dissolved in water and cooled, forms special bonds between its molecules. It is important to note that gelatin can be used at moderate temperatures which are mild to bacteria. Srubar therefore suggested adding gelatin to strengthen the matrix built by cyanobacteria, intriguing his team, which was impatient to try.

The researchers then bought gelatin (Knox brand) from a local supermarket and dissolved it in the solution containing the bacteria. When they poured the mixture into molds and cooled it, the gelatin formed its bonds. In other words, gelatin had just strengthened the structure and helped the bacteria to do their job, making the material more resistant and accelerating its self-regeneration / development.

The structure of living building material (LBM) is supported by the physically crosslinked hydrogel as well as by precipitation of bacterial calcite. In the event of a drop in humidity, the mechanical properties of the structure are improved. Conversely, the higher the humidity, the more the self-regenerating capacities of the material increase. Credits: University of Colorado (Boulder)

After about a day, the mixture made it possible to form concrete blocks with any mold used by the group, including 5 cm cubes, blocks the size of a shoe box and pieces of trellis. with spacers and cutouts.

The individual 5 cm cubes were strong enough for a person to stand on, although the material was brittle compared to most conventional concrete. The blocks the size of a shoebox, however, have shown that it is possible to make real constructions.


Potential use in space

DARPA is particularly interested in a self-cultivation material that could be used to assemble structures in remote desert areas, even potentially in space. Living concrete could also be useful in harsher environments than the driest land deserts, such as on Mars for example.

If live concrete can reach this level of use, it could reduce the quantity - and the weight - of materials that space agencies will have to send into orbit. " There is no way to transport building materials into space, " said Srubar. " So we will bring biology with us ."


Bibliography:

Biomineralization and Successive Regeneration of Engineered Living Building Materials
Chelsea M. Heveran, Sarah L. Williams, Jishen Qiu, Juliana Artier, Mija H. Hubler, Sherri M. Cook, Jeffrey C. Cameron, Wil V. Srubar III

Published:January 15, 2020

DOI:https://doi.org/10.1016/j.matt.2019.11.016

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