Pretty much ever since we stopped using branches and twigs to build homes, we’ve thought of concrete and steel as the materials of choice when it comes to construction. But these materials are responsible for as much as a tenth of worldwide carbon emissions, so we have two choices: either we start producing steel and concrete in more energy-efficient ways, or we create new building materials to take their place.
Ask the US’ Defence Advanced Research Projects Agency (DARPA) or University of Cambridge bioengineer Michelle Oyen what they think the cities of tomorrow will be made of, and they might answer bone, bark, egg shells or spider’s silk.
DARPA and Oyen are part of a growing movement that sees biomimicry, or the principle of seeking sustainable solutions to human challenges by emulating nature’s time-tested patterns and strategies, as the future of construction.
The benefit of letting nature guide our construction techniques is obvious. For example, despite knowing its cost to the environment we use steel because it’s really good at taking tension, but spider’s silk is stronger than steel and more flexible – because it is a perfectly designed composite of proteins. It makes sense then that we stop using steel and prop buildings up with spider’s silk; apart from anything else who wouldn’t want to live in a city that looks like Spiderman has had a particularly busy night of webslinging. The reason we don’t is because the construction industry is set in its ways, and we believe we can ‘green’ steel. But why bother when nature has already given us a better alternative?
“The construction industry is a very conservative one,” said Oyen in a statement. “All of our existing building standards have been designed with concrete and steel in mind. Constructing buildings out of entirely new materials would mean completely rethinking the whole industry. But if you want to do something really transformative to bring down carbon emissions, then I think that’s what we have to do. If we’re going to make a real change, a major rethink is what has to happen.”
If we want to move to a more sustainable future then some of our preconceptions about construction are going to have to be disrupted. The principal assumption that has to change is: just because we can make buildings out of concrete and steel, doesn’t mean we have to or we should. The cement industry, for example, is one of the world’s most polluting, accounting for 5% of man-made carbon-dioxide emissions each year, as making and transporting concrete puts a massive burden on the environment.
There seems to be little desire to change. Retrofitting old kilns to improve thermal efficiency could lower concrete manufacturers’ energy usage by two-fifths, according to the Carbon Disclosure Project, but even this would only represent symbolic greening.
What is needed is drastic change, and what could be more dramatic than replacing concrete and steel with bone? While bone cities may seem haunting at first glance, bone is stronger than steel, and just one cubic inch of it can bear a load four times greater than concrete. Bone gets its strength from having a roughly equal ratio of proteins and minerals – the minerals give bone stiffness and hardness, while the proteins give it toughness or resistance to fracture. Bones also have the advantage of being self-healing, which is another feature that engineers are trying to bring to biomimetic materials.
DARPA’s living materials
The US’ research agency, DARPA, has already realised that living materials provide many advantages, as they can be grown where needed, self-repair when damaged and respond to changes in their surroundings. The agency has recently launched the Engineered Living Materials (ELM) programme to create a new class of materials that combine the structural properties of traditional buildings with the added benefits that living systems provide.
Imagine that instead of shipping finished materials, we can ship precursors and rapidly grow them on site using local resources
“The vision of the ELM programme is to grow materials on demand where they are needed,” said ELM programme manager, Justin Gallivan. “Imagine that instead of shipping finished materials, we can ship precursors and rapidly grow them on site using local resources. And, since the materials will be alive, they will be able to respond to changes in their environment and heal themselves in response to damage.”
Being able to construct with living materials could offer significant benefits; however, DARPA has commenced its ELM programme because it concluded that scientists and engineers are currently unable to easily control the size and shape of living materials in ways that would make them useful for construction. But Oyen and her team at the Oyen Lab (which came into being in 2006 at Cambridge University’s Engineering Department) have been constructing small samples of artificial bone and eggshell, which they believe could be scaled up and used as low-carbon building materials.
“What we’re trying to do is to rethink the way that we make things,” said Oyen. “Engineers tend to throw energy at problems, whereas nature throws information at problems – they fundamentally do things differently.”
Oyen cites eggshells as an example of nature doing something totally different that we can mimic. “If you look at a chicken, they go from zero to eggshell in 18 hours,” said Oyen in an interview with the Guardian. “It’s almost a millimetre thick, 95% ceramic and it has this organic component that makes it very tough. The whole thing has been put down in an extremely short period of time, at an ambient pressure and at body temperature, barely above ambient temperatures.”
Nature has already given us an idea of the kinds of resilient and sustainable materials that could be used to build the cities of the future. Oyen’s eggshells are already much more resistant to fracture than manmade ceramic. The experiments being carried out by Oyen and DARPA will hopefully contribute to the construction industry taking the way nature creates sustainable structures and putting this knowledge into practical use. Then we may well see skyscrapers made out of bone and eggshell.
“From a timeline perspective,” said Oyen, “for the last 10 years we’ve been trying to figure these things out. We’ve probably still a few more years to go and then maybe the following decade will be taking all the things we’ve learned and being able to apply them to making new materials.”