A vast amount of our built environment is made of concrete. It’s largely affordable, durable and easy to make. It’s also responsible, by some estimates, for roughly 8% of global CO2 emissions.
But the U.S. is also facing a significant housing demand shortage, and since concrete is one of the primary building materials for houses and apartments, scientists are working to make it more sustainable to produce.
Late last year, a research lab at Oregon State University made a breakthrough when it created a more environmentally friendly concrete derived from soil instead of cement. Besides emitting less CO2 during production, it’s strong, dries fast and it can be 3D printed rapidly.
Devin Roach is an assistant professor of manufacturing and mechanical engineering at OSU. He joins us to share more about how the concrete was made, why it’s useful and the possibilities for commercial use.
Note: The following transcript was transcribed digitally and validated for accuracy, readability and formatting by an OPB volunteer.
Dave Miller: This is Think Out Loud on OPB. I’m Dave Miller. A vast amount of our built environment is made of concrete. It is pretty durable, pretty affordable and pretty easy to make. It’s also responsible for about 8% of global CO2 emissions, which leads to a conundrum: how can the U.S. address our significant housing shortage in a more sustainable way? Researchers at Oregon State University say they may have part of an answer. They announced not long ago that they made a breakthrough in fast-drying, 3D-printable concrete that has a smaller carbon footprint.
Devin Roach is an assistant professor of manufacturing and mechanical engineering at OSU. He joins us now. It’s great to have you on Think Out Loud.
Devin Roach: Thank you very much for having me.
Miller: What is concrete traditionally made of?
Roach: Concrete is traditionally made of two things: one is aggregate and one is cement. Aggregate can be a combination of rocks, stones, things like that. Cement is limestone, clay, shale and some other natural ingredients, with some chemicals that are added in to give it some strength.
Miller: What makes it such that the concrete you’re describing has such a big carbon footprint?
Roach: To make the cement actually requires some very complicated processing in order to combine all the different raw materials, like limestone. These are typically heated to really high temperatures and they off gas, so they create a lot of gasses that generate a lot of CO2 during the production.
Miller: So what was the idea behind a 3D printer and a different recipe?
Roach: Currently, 3D printing is being used to quickly build infrastructure. There’s entire neighborhoods in Texas that are being 3D printed. There’s even a 3D-printed Starbucks. And right now, it’s allowing us to build infrastructure quickly when we have limited access to labor or the ability to build things fast enough to meet demand.
Miller: What were the challenges in using a 3D printer specifically to make concrete?
Roach: We can 3D print things using cement-based concrete. But typically what happens is, after you print let’s say five to 10 layers, the cement-based concrete starts to slump. It has a very slow curing time. You can’t print over gaps, you can’t make windows, you can’t make doors, and things like that, so it requires scaffolding. And this inhibits the entire point, which was speed and quick building of infrastructure.
Miller: If you were going to get the same properties as traditional concrete using a 3D printer, how long might it take?
Roach: It may take many, many months, maybe even up to a year to 3D print even a single-story home and get the same properties that you get from traditional poured cement-based concrete.
Miller: So that basically makes it completely unfeasible for the job at hand.
Roach: Totally unfeasible for our traditional materials. Exactly.
Miller: So what was your breakthrough?
Roach: So we figured out that, basically, if we add a different sort of curing agent or binding agent, we can actually cure regular concrete very, very quickly through a process called frontal polymerization. Essentially what this does is it cures the material directly as it comes out of the 3D printing nozzle. And one of the main things we did is we actually, instead of using cement-based concrete, we actually use soil as our primary material.
Miller: Can you describe what this would look like? If you were at a building site, say, for a single family home, what would it look like?
Roach: Well, you would have maybe only a few people standing around and they would be watching sort of a robot move around in the plot of the land, depositing material in the layout that you maybe designed with your designer. So primarily, it’s actually a giant robot doing this printing. And it’s essentially just extruding the material or sort of squeezing the material out of a nozzle as it moves along the plot of land.
Miller: And so it would be this robot nozzle, say, pouring a foundation, that would then cure in a matter of hours, as opposed to months or years?
Roach: Exactly. Yeah, so in our study we found that this new material could cure immediately after it came out of the nozzle. It could achieve about 3 megapascals directly after printing, which means it could print freestanding walls, it could make overhangs, and things like that. And then over the course of a week it could surpass 17 to 20 megapascals, which is the strength required for residential structural concrete.
Miller: I might not be the only person listening now who has never heard the phrase “megapascal.” What’s it a measure of?
Roach: A megapascal is a measure of strength. So when we think about building a structure, we want it to be able to withstand not only the roof, but also maybe earthquakes or other things like that. So we want around 20 megapascals.
Miller: Now, you mentioned that one of the changes here is that instead of using cement as the key binding ingredient, you use soil. What kind of soil?
Roach: Great question. We use something called kaolinite. It can be found in the wild, in nature, maybe even at your construction site. What you can do is you can take this soil, mix it with the binding material and create an infrastructure material.
Miller: Do you have a sense for the availability of that kind of soil around the country?
Roach: That’s a key point in our study, that this clay-based soil is incredibly abundant throughout different regions in the U.S. If you dig deep enough, you can find it in most parts of the world.
Miller: It’s the idea that people would be, say, at a construction site for this single family home or a coffee shop somewhere, that they’d be digging up some of this clay heavy soil and using it to actually put back in the form of concrete? Or they’d be bringing it in a dump truck?
Roach: What’s great about this is you can source your clay or source your soil directly at the location of building it. That’s one of the things that we believe is going to make this material much better than cement-based concrete, is you don’t have to transport it. That’s actually where a lot of the CO2 emissions are as well, is you make this cement-based concrete elsewhere and you transport it to the construction site. So here we can source it directly at the point of construction.
Miller: It seems like, as you’re pointing to there, there are a lot of different ways to calculate carbon emissions for this, so a lot of different factors that could maybe move in different directions. But broadly, what’s your understanding of the carbon footprint of this kind of printed concrete technology compared to traditional concrete?
Roach: We’re still looking to figure that out. We know for sure that when we produce the material, it is not carbon emitting. And we know that when we source the material, it’s not carbon emitting. So we can already cut out a lot of the emissions from the get-go. But after that, the curing and the complex chemical processes that happen during this rapid curing, we’re still trying to characterize how much emissions that causes.
Miller: What about price? What might this cost?
Roach: Another great question. Our material currently costs more than standard cement, so we definitely need to bring the cost down. That’s one of the main things that we’re working on in our lab. But at this point, we’re finding that if we can source soil locally, we can dramatically decrease the cost.
Miller: So what are the next steps? What all would have to happen before this could actually be truly scaled up and be a viable, regular old option for builders?
Roach: My wife works in construction, so she probably has an even better answer to this. But one of the things that we need to do is we need to follow the American Society for Testing and Materials Standards, the ASTM standards, and basically prepare a report for professional engineers and other construction engineers to review and approve the material before it can be included in construction projects
Miller: And make sure that you have enough megapascals?
Roach: Make sure you have enough megapascals, that’s right.
Miller: Devin, thanks very much.
Roach: Thank you.
Miller: Devin Roach is an assistant professor of manufacturing and mechanical engineering at Oregon State University.
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