Author of original text: Amos Zeeberg
Source: https://www.nytimes.com/2020/01/15/science/construction-concrete-bacteria-photosynthesis.html?fbclid=IwAR0m7LZK76O_mhR4VKSNcXm2SIb4A4L9Y4vZWs8CDLWbhBEoAyx0o85V48I
"Frankenstein's Material"
...teeming with photosynthetic microbes and eventually made from them. And it can reproduce.
Wil Srubar, on the left, a construction engineer at the University of Colorado, Boulder and a materials science and engineering student. Sarah Williams holds bricks made of building materials made from cyanobacteria and other materials.
For centuries, builders have been making concrete in roughly the same way: mixing hard materials like sand with various binders and hoping it stays strong and stiff for a long time.
An interdisciplinary team of scientists from the University of Colorado, Boulder, has now created an entirely different kind of concrete – one that is alive and can even reproduce.
The minerals in the new material are not deposited chemically, but by cyanobacteria, a common class of microbes that capture energy through photosynthesis. The photosynthetic process absorbs carbon dioxide, unlike the production of conventional concrete, which emits massive amounts of greenhouse gases.
Photosynthetic bacteria also give the concrete another unusual feature: a green color. "It really looks like Frankenstein's material," said Wil Srubar, a construction engineer and leader of the research project. (When the material dries, the green color fades.)
Other scientists have worked on incorporating biology into concrete, particularly concrete that can heal its own cracks. According to its creators, the main advantage of the new material is that instead of adding bacteria to conventional concrete – an inhospitable environment – their process is focused on the bacteria: obtaining them to build concrete and keeping them alive for later use.
The new, living concrete
...described in the journal Matter, "represents a new and exciting class of low-carbon, designer building materials," said Andrea Hamilton, a concrete expert at Strathclyde University in Scotland.
In building living concrete, scientists first tried to put cyanobacteria into a mix of warm water, sand, and nutrients. The microbes eagerly absorbed light and began producing calcium carbonate, gradually bonding the sand particles. However, this process was slow – and Darpa, the speculative research arm of the Department of Defense and project donor, wanted construction to proceed very quickly. Necessity, happy accident, and born invention.
An arch made of living building materials in Dr. Srubar's lab
Dr. Srubar had previously worked with gelatin, a food ingredient that, when dissolved in water and cooled, forms special bonds between its molecules. Importantly, it can be used at moderate temperatures gentle to bacteria. He suggested adding gelatin to strengthen the matrix formed by cyanobacteria, and the team was intrigued.
The scientists bought Knox-brand gelatin at a local supermarket and dissolved it in a solution with bacteria. When he poured the mixture into molds and cooled it in a refrigerator, the gelatin formed its bonds – "just like when you make Jell-O," Dr. Srubar said. The gelatin provided greater structure and worked with the bacteria, helping the living concrete grow stronger and faster.
Within about a day, the mixture formed concrete blocks in the shape of any mold the group used, including two-inch cubes, shoe-sized blocks, and pieces of roofing with braces and cutouts. The individual two-inch cubes were strong enough for a person to stand on, though the material is weak compared to conventional concrete. The shoebox-sized blocks showed potential for actual construction.
Initial experiments
"When we first created a large structure using this system, we didn't know if it would work; we scaled up from this small size to this large brick," said Chelsea Heveran, a former postdoctoral researcher with the group – now an engineer at Montana State University – and the lead author of the study. "We pulled it out of the mold and held it – it was beautiful, bright green, and the word 'Darpa' was written on the side." (The mold had the name of the project donor.) "It was the first time we had the scale we had envisioned, and it was truly exciting."
When the group brought small samples to a regular check-in meeting with Darpa representatives, they were amazed, Dr. Srubar said: "Everyone wanted one on their desk."
Stored in relatively dry air at room temperature, the blocks reach their maximum strength over days, and the bacteria gradually begin to die. But even after several weeks, the blocks are still alive; when exposed again to high heat and humidity, many bacterial cells back up on their own.
The group can have one block, cut it with a diamond tip, place half back in a warm tub with a larger amount of raw materials, pour it into a mold, and start making concrete again. Each block could thus bring three new generations, thus obtaining eight descendants.
The Department of Defense is interested in exploiting the reproductive capacity of these "LBM" - living building materials - to support construction in remote or barren environments. "You don't want to drive to the desert with a lot of materials," said Dr. Srubar.
The advantage of the blocks is
.. that they are made from various common materials. Most concrete requires virgin sand from rivers, lakes, and oceans, which is insufficient worldwide, particularly due to the huge demand for concrete. The new living material is not so picky. "We are not committed to using a specific type of sand," said Dr. Srubar. "We could use waste materials like ground glass or recycled concrete."
The research team is working on making the material more practical by strengthening the concrete; increasing the bacteria's resistance to dehydration; changing the arrangement of materials so they can be packed flat and easily assembled like a plasterboard sheet; and finding another type of cyanobacteria that do not require the addition of gel.
Dr. Srubar said that synthetic biology tools could dramatically expand the field of possibilities: for example, building materials that can detect toxic chemicals and respond to them or that light up to reveal structural damage. Living concrete could help in environments harsher than the driest deserts; other planets, such as Mars.
"There is no way to transport building materials into space," said Dr. Srubar. "We are bringing biology with us."