How to grow concrete and other building materials

When a radio talk show host last year insisted you could grow concrete, he was mercilessly ridiculed on social media. While his argument was misinformed, does bioengineering mean that it might one day be possible to “grow” concrete on a small scale?

Concrete is the most widely used man-made material, second only to water as the most consumed resource on Earth. Incredibly, 7.3 billion cubic meters of concrete are poured each year, which accounts for 8% of carbon dioxide emissions.

While greener concrete can help limit some of the environmental damage caused by our favorite building material, we’re likely to need more of it. After all, our growing world population, which is expected to reach 9.7 billion by 2050, will need new homes, and we will also need efficient ways to maintain current homes and infrastructure.

Self-healing concrete is part of the solution to this global challenge. Engineers have developed forms of it that contain capsules that release a healing agent to repair cracks when they are opened. Using this miracle new material could save millions of pounds each year in maintenance costs, not to mention the disruption caused by repairs to tunnels, bridges and other concrete infrastructure.

The problem with conventional reinforced concrete is that the stress gradually creates small cracks, allowing water and oxygen to penetrate the steel into the concrete, causing it to corrode. This in turn could cause serious damage to the structure.

Hendrik Jonkers, a professor of bio-adaptive and sustainable building materials at Delft University of Technology in the Netherlands, discovered a special ingredient that allows concrete to heal itself: bacteria commonly found in stone . He managed to create self-healing organic concrete by incorporating bacterial spores, which are like seeds for bacteria, into a concrete mix.

When cracks start to appear in the bio concrete, water and oxygen seep into them and activate the spores, causing the bacteria to multiply. This ensures a wide diffusion of bacteria inside the crack. The widely dispersed bacteria will begin to convert the nutrients in the spores into calcium carbonate, or limestone, which will eventually seal the crack. This essentially “cures” the concrete using a natural process called biomineralization – the same process that often causes plaque to form on your teeth.

“What makes these lime-producing bacteria so special is that they are able to survive in concrete for over 200 years and to intervene when the concrete is damaged,” says Professor Jonkers. The use of this new material in construction gives buildings real longevity.

The technology, which was developed and patented in collaboration with Delft University of Technology, has been commercialized. Basilisk Self-Healing Concrete sells an admixture suitable for building new structures, as well as two other products that can be applied to existing buildings to increase their durability.

Basilisk’s self-​healing products have been used by a Dutch railway company and in the construction of the Port of Rotterdam, while JP Concrete’s Sensicrete is the first self-​healing concrete available in the UK and the company hopes see the material being used in new construction and infrastructure in the country soon.

The only prohibitive factor is cost. “Self-healing concrete is not the kind of thing that would, at least currently, be considered economically viable for normal construction. These are typically critical infrastructures, where the benefits of the material’s long-term robustness far outweigh the upfront costs,” says Martyn Dade-Robertson, professor of emerging technologies and co-director of the Hub for Biotechnology in the Built. Environment at the University of Newcastle.

However, he believes that biotechnology will revolutionize the construction industry and wants to use the ability of microorganisms to sense and react to their environment, as well as add their own structures to it.

“The concept behind our project, Thinking Soils, is that you have bacteria in the soil that can sense mechanical pressure,” says Dade-​Robertson. This could trigger biomineralization, which is the same process used by self-healing concrete. “We could create a self-constructed foundation simply by exerting the right pressure on the ground, eliminating the need for costly excavations and reinforced concrete slabs.”

Unsurprisingly, making this a reality is difficult. His team has identified genes in certain bacteria that activate in response to pressure. “We want to engineer those answers,” says Dade-Robertson, who, through synthetic biology, used genetic engineering to engineer bacteria that glow under pressure.

The next step is to make an enzyme responsible for the biomineralization process. “It’s a very complicated enzyme to make, but what we’re trying to do is get an engineered system that will lead to the creation of the enzyme in response to the bacteria’s genetic ‘switch’ triggered by a load.” The researchers are “very close” to managing this, but putting together different processes will be a challenge. They intend to create a demonstrator where they can load a material and from it produce calcium carbonate crystals, essentially using its pressure-sensing ability to trigger biomineralization. Dade-Robertson admits the project is ambitious, but says it’s about creating a new class of materials.

Growth of small scale deposits to bind particles together and fill cracks is neat. But could we ever grow materials into ready-to-build shapes and structures, essentially “growing” parts of a house? Professor Dade-Robertson says it’s probably not too far.

An American company is already making decorative “stone” using biomineralization, while a British start-up called Biohm is soon planning to make insulation blocks from mycelium, which is the root network of a fungus.

These biotech feats are impressive, but the next step is to engineer living materials that can be used in construction. For example, biodegradable microbial cellulose materials can be “grown” to replace plastic, such as in eco-friendly food packaging. What if you could turn the material’s ability to biodegrade on and off? According to Dade-Robertson, if this were possible, it could one day be used to construct environmentally friendly buildings. For example, once someone is done living in a cellulose-based dwelling, the biodegradable switch could be “turned on” and the building would disappear.

The development of materials that retain their realistic properties takes this idea even further. For example, instead of drying out the mycelium to produce insulating bricks, the roots of fungi could be kept alive. “It might get thicker in the winter to keep you warm,” Dade-Robertson muses.

In fact, NASA wants to know if mycelium could be a good material to use to build on Mars. “Since mycelia normally excrete enzymes, it should be possible to bioengineer them to secrete other materials on demand, such as bioplastics or latex to form a biocomposite,” says Lynn Rothschild of Nasa Ames Research Center. “A mycotectural building envelope could significantly reduce the energy required for construction, because in the presence of food and water storage, it would expand on its own.”

A group at MIT has developed materials made of layers of bacterial spores and latex that can change shape in response to water. While they focused on garments, Dade-Robertson’s group is investigating whether this method could be used to make building membranes that could “sweat” as indoor humidity increases, eliminating the need for ventilation systems. mechanical air conditioning. “Using latex membranes coated in bacteria spores, the material will flex and open pores – like sweat glands – allowing air to flow through the walls,” he says.

Elsewhere, others are also working to create living building material. Wil Srubar, a professor of architectural engineering and materials science at the University of Colorado Boulder, used photosynthetic cyanobacteria – the green microorganisms that grow on the walls of aquariums – to help grow a building material which can be kept alive.

Cyanobacteria use carbon dioxide and sunlight to grow and can create biocement, which Srubar’s team used to help bind sand particles together to form a brick.

“By keeping the cyanobacteria alive, we were able to make building materials exponentially. We took a live brick, split it in half and grew two solid bricks from the halves,” he says. Such a technique could certainly be useful on a construction site and could also save energy.

While the manufacture, transport and assembly of building materials accounts for 11% of global CO2 emissions, living building materials such as cyanobacteria bricks could sequester CO2.

An expandable home might even be on the cards. “Imagine having a building that starts pushing bricks for expansion as your family grows, so your house grows with you,” says Dade-Robertson. While he acknowledges that these are “big things,” there is basic research going on that could lead us in that direction, making science-fiction-worthy ideas a reality.

If he’s right, our green homes will be a far cry from the futuristic glassy skyscrapers of “Minority Report” or the swanky apartments of “Blade Runner,” instead taking inspiration from nature. Self-healing concrete and mushroom bricks are amazing, but we’ve only scratched the surface of the potential of bio-engineered building materials. Organisms could contribute living functions to building blocks, such as reacting to temperature or pressure, self-healing, or even lighting up. As Professor Srubar says: “If nature can do it, living materials can also be modified to do it.

Innovation

Cultivate other building materials

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