Research Matters

Sriramya Duddukuri Nair on green concrete and 3D printed buildings - Research Matters S2E6

• Cornell University • Season 2 • Episode 6

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In this episode of Research Matters, we speak with Sriramya Duddukuri Nair, assistant professor of civil and environmental engineering in the Cornell Duffield College of Engineering, about the enormous — and often invisible — impact of construction materials on our climate and daily lives. From reimagining “green concrete” to experimenting with 3D-printed buildings made from local, in-situ materials, Nair explains how engineers are working to build faster, cleaner and more resilient infrastructure for a warming world. It’s a wide-ranging conversation about innovation under pressure — and why the future of climate solutions may be hiding in the concrete beneath our feet. Watch here.

Sriramya Nair:

The more larger companies invest in 3D printing, the more we can push this forward. Printing single-story houses, by their 100th house, they've learned a lot more about, how to build these.

Laura Reiley:

Yeah, I'll take the 100th. Not the first.

Sriramya Nair:

Not the first, yes.

Laura Reiley:

Welcome to Research Matters, the Cornell Video Podcast where we speak with the scientists and researchers who are tackling some of the most pressing, real world challenges. I'm your host, Laura Reiley. Today, we're talking about something that touches every part of our lives, though most of us never give it a second thought: the materials that form the buildings around us, the roads, the bridges, the infrastructure of daily life. Our guest today is Professor Sriramya Nair, assistant professor in the School of Civil and Environmental Engineering at Cornell University. She's an expert in sustainable construction materials, green concrete and the emerging frontier of 3D printed building materials. Her research at Cornell explores how we can build safer, greener and more efficiently, and what happens when traditional materials can't keep up with the demands of a rapidly changing world. Sriramya, it's so good to have you here.

Sriramya Nair:

Hi. Thank you.

Laura Reiley:

All right. So I guess we'll start with some very basic questions. Why do the building materials matter and what, what should be greener about them?

Sriramya Nair:

Building materials matter because of the amount of materials that we use in the world. If you think of construction of new infrastructure in emerging countries or in developed countries, we are still constructing a lot in cities, or a lot of our infrastructure is old and we have to replace them. So the amount of materials we need is astronomical. And of those materials, concrete is commonly used because it is economical. It's really cheap, but it can form any shape that you would like it to take. And it's also a structural material. You can build high-rise buildings. You can build bridges. It can take, sustain a lot of load.

Laura Reiley:

So can you quantify like how much concrete do we use. Like in a in a year, say.

Sriramya Nair:

Yes. Emeritus faculty Professor Hall, he was in civil engineering. In one lecture he put it this way. He said if you take all the amount of concrete that we use in the entire world and divide it up to the population, it ends up being that each person is consuming about four four-liter Coke bottles. You know, so if you think of these large, Coke bottles, so four liters, four of them, so 16 liters per person.

Laura Reiley:

Per day?

Sriramya Nair:

Per day. 

Laura Reiley:

Wow. That's... I'm consuming a lot of concrete. All right. And I...This is going to reveal my ignorance, but can you just back up and describe what is concrete versus cement?

Sriramya Nair:

So cement is a powder. It's manufactured. So we take materials that are in the ground and we heat it up. And then we make this powder where when you mix it with water, there's a chemical reaction that's happening. And it goes from a powder and a liquid-like material with introduction of water to something that's solid and that can take load. But we don't build just with the cement paste. We typically add aggregates to them. So rock, sand and so concrete is a mixture in that simplest form it'll have cement sand, rocks, water. But today's concrete is not that simple. It's a very complex mixture.

Laura Reiley:

So what is not green about concrete as we produce it most of the time.

Sriramya Nair:

Yeah. Even though cement is only a small part of the pie chart, it leads to the most carbon emissions. So manufacturing of cement, like I mentioned, you have to heat it to 1400 degrees Celsius. We are also burning calcium carbonate because of which CO2 is being emitted. So all of it typically, again, it depends on the plant and how they're manufacturing it. But for every kilogram of cement that's produced we are producing about 0.9 kilograms of CO2. So there's high emissions of cement, but that's just cement. But if you think of concrete because we're using so little cement, overall, you're not actually placing as much material. So it all depends on how much cement do you have in your concrete. But we have to remember that we don't need concrete though, just because we think the emissions are so high, we shouldn't stop using it. Because like I said, it's really cheap. It's easy to make it. You can make it anywhere in the world. But there are ways we can do to reduce our carbon footprint. But we shouldn't say concrete is bad because it emits a lot of CO2. It has a lot of benefits we get from it, as well.

Laura Reiley:

So what are some of the ways that we can reduce the carbon footprint of... either one.

Sriramya Nair:

Yeah. So the first main thing is the pie chart that I was talking about that the concrete is, by changing those percentages in that pie chart you can change the strength of concrete. So whether it is, 20 megapascal concrete or 100 megapascal concrete for high strength, for example. So depending on the application, you need to change the composition of that pie chart. So you have to use a concrete that's specific for that application. So that means that you are using only the amount of cement you truly need for that strength. So if you're always over designing your concrete for like ten megapascals more than what you need...

Laura Reiley:

Do we do that? Is that kind of a common occurrence that we over design?

Sriramya Nair:

Absolutely. Over design is very common because that's the easiest way to definitely meet the metrics of construction. So let's say the structural engineer says they want 5,000 psi for a specific structural element. Then, just to be on the safe side, the contractor or the ready-mix supplier might shoot for 7,500 PSI so to get to that higher strength, just to make sure you definitely have 5,000. So that factor of safety that we are using ends up being we are over designing. And the structural engineer might have already over designed it to get to 5,000. So it's being cognizant of it. So let's say we are saying cement, any kilogram is a kilogram of CO2 of cement. And that roughly adds up to... we are responsible for 8 to 9% of CO2 emissions worldwide.

Laura Reiley:

Wow.

Sriramya Nair:

Yeah.

Laura Reiley:

That is incredible.

Sriramya Nair:

Yeah. So that means that if you're using 10% less cement...

Laura Reiley:

That's a big reduction in emissions.

Sriramya Nair:

Exactly. Yeah.

Laura Reiley:

What are the greener materials and what are the sources of those. And are they... are there kind of circular economies where it could be a byproduct of something over here that ends up, you know, that would be in landfill or whatever? I mean, what are the what are the options?

Sriramya Nair:

There is a lot of emphasis on for example, cement -- you have to post-process the material or manufacture it at 1,200 to 1,400 degrees Celsius. You have to grind it. You have to process it. But let's say there is a waste material that you have to process only to 600 or 700 degrees Celsius or 800 degrees Celsius. Then you are using less energy to make that material. So typically what we do is we... Previously for durability, we were already replacing cement with partially replacing it. But you know, just if you just use 100% cement by itself, there are some products that form within it that are not very durable. There's like a chemical transformation that might happen and it might your concrete might actually be weak. So a long time ago, people figured out that if you replace part of cement with flash, for example, it's been a few decades now. We found that it actually makes like a more durable product. So now we're talking about it from a sustainability perspective, but, in general, making something really durable so that lasts a long time so it doesn't crack. You don't have to replace it prematurely. All that is also green construction. So we already knew that replacing cement partially is important. So with coal plants shutting down, there was, worry in the industry that we might not have access to as much fly ash in the future.

Laura Reiley:

So that is a byproduct of the coal industry.

Sriramya Nair:

Exactly. So then, from then we've been looking at there's a lot of clays. There's things called natural pozzolans like volcanic ash or, how do we process them? Because some of them, if you just mix cement with them, they might not be reactive. So then the science here is what can we do to these materials, like minimal processing, to make them reactive so that we can replace cement with them. And if you think of it, flash is a great resource if you have it accessible regionally. But if you have to ship it from across the country...

Laura Reiley:

Then you're adding the cost of that or the, you know, the emissions cost.

Sriramya Nair:

Exactly. So then it's all about what kind of, landfill, material is locally available to you. For example, I visited a site. It's a place called Miwell. So it's like five hours up north from here, and they have these huge piles of, mining tailings they used to extract iron ore. So they had this whole amount of material that's in, like, huge mountain, but it's like a manmade mountain of waste material. So then the question is, can we clean up such landfills and use them beneficially to make cement? So then the question is what is the composition and how can we, like I said, minimal processing. That is also a way of bringing in new revenue for the companies, new jobs, because you can set up new plants and process those materials.

Laura Reiley:

So I can imagine that persuading the building, the construction industry to adopt some of these new materials, may be tricky just because, I mean, we've seen in, you know, in recent years horrible failures in terms of bridges, I mean, that, that Surfside.

Sriramya Nair:

Yes.

Laura Reiley:

You know, condo, condo in Florida, you know, and that has caused a lot of, kind of retrofitting or at least kind of hand-wringing about building materials in the 60s or 70s. So are these new materials a hard sell for, or are there are there kind of regulatory hoops that you have to jump through to get them approved?

Sriramya Nair:

Yeah. So I think that's a two-part answer. So the first part is, American Society of Civil Engineers, they rate all our infrastructure. So every few years, every four years there's like new ranking that comes out for infrastructure. So the bridges we drive on to go from our house to the work all of them are rated. And, in general, most of the reviews for... So that's like dams, bridges, anything that you think of infrastructure is like a huge number of categories. Most of them are like a C, C minus. So a mid...

Laura Reiley:

Not too good. Why is that not shocking somehow?

Sriramya Nair:

But in general. Like we need a lot of money for maintaining the infrastructure and we only have limited resources. So then the question becomes the resources that a county has, for example. What are they going to spend those, you know, dollars on? How are they going to prioritize what needs to be fixed? So that's when it becomes challenging to figure out or predict this is the next building that's going to fail, or this is the next bridge that's going to fail. When you have 100 bridges that are all at a C minus and you only have, let's say, $1 million.

Laura Reiley:

Yeah. What's the triage there? How do you where do you prioritize.

Sriramya Nair:

S o that's like the tricky part because majority of our infrastructure is failing and we need a lot of maintenance to keep up with that infrastructure. So that's one of the biggest challenges. But you asked a question about, what kind of changes are happening in the industry so that we can use more green concrete, for example. In the last five years, especially, I would say there's a huge boom in startups. There is so much innovation that's happening in the space of trying to reimagine how what is concrete, like alternative binders or we've been doing this a certain way, but is there a different way of how do we how do we even make the cement? Or what goes into that pie chart that makes concrete? There are significant innovations that have come up in this space. And, the industry is changing. There've been some trial experiments took place, for example, Minnesota D.O.T. placed a whole pavement where they use ten different types of green concrete to understand how different their placements are. How long will they last? Previously to get to that stage would have taken much longer. But as a community, we have taken on this challenge to make better concrete, cleaner concrete, sustainable concrete, more durable concrete to just reimagine what we can do. And there's a lot of changes that have come, and we've embraced it.

Laura Reiley:

So is net zero. Is that... is that a just a complete pipe dream, or is that a conceivable goal for, for concrete?

Sriramya Nair:

So the Global Cement and Concrete Association has a vision for how do we get to net zero? Net zero obviously, it isn't one thing that's going to get us to net zero. It's a different mindset. And it's also the technological advances that are going to come up, in the near future. Like I said, we've invested a lot in new technologies recently. Obviously, some are going to fail, but there are quite a few that are very promising. So if we stay the course and get to the finish line and we do little, little and everything adds up, then net zero is possible because right now we are at 10% CO2 emissions. And it is achievable because we are thinking it all the way through, right? From who's producing the cement to who's specifying what — What type of concrete do we need? How are we making the concrete? And this circularity of how are materials being used and where are they going to end up in the end. So we are keeping that whole thing in mind when we are thinking about concrete. So it is definitely achievable. This is a global problem and the solutions are also global, and that the global community is coming together to solve this problem.

Laura Reiley:

So I know you've done some work in concrete repair and and using magnetize. I don't know exactly how to term it. Magnetized materials? What does that look like and how how how does that solve the problem?

Sriramya Nair:

Yeah. Like I said, a majority of our infrastructure is failing. Repair is one way to use the least amount of material, because if you have to tear it down and construct again, that's a lot. So, in the recent past, we've worked on the concept of adding magnetic particles to the repair materials, because most repair materials, what happens is they are a surface treatment. You can't actually infill the cracks to the depth. Most of the repair happens very close to the surface. So that's good for, not wanting unwanted chemicals to go into concrete. And, you know...

Laura Reiley:

Cosmetically repairing. Yeah.

Sriramya Nair:

Yeah, yeah. But you actually want to improve the strength of your structural element, let's say, because it's load-bearing. Then you want to infill it all the way to the depth of the crack. So then we develop this technique where... and sometimes you might only have access to the surface of the concrete. So we developed this technique where you inject magnetic particles with the solution that can heal your cracks. But what it does is you can push the fluid away from the surface. Typically materials want to go towards a magnet. They attract towards the magnet. But we designed a system such that it can push away from the system, and that way you can infill deeper than you could without.

Laura Reiley:

So you're pushing kind of with a magnetic...

Sriramya Nair:

Yes.

Laura Reiley:

...force pushing something, a material, in.

Sriramya Nair:

Exactly. Yeah. So that's been really exciting to see the potential to fill cracks that would have been harder to fill otherwise.

Laura Reiley:

Wonderful. And I know another big part of the research that you do is in 3D printing. You know, we've all watched those mesmerizing videos on, you know, on YouTube or whatever of a building being constructed with these big robotic arms. What does that look like and how and how does that kind of compare, in terms of greenness or sustainability?

Sriramya Nair:

So we do have a large-scale robotic arm in our lab, too. So when people walk up to it, it's just like amazing. So all the students that are taking classes, they'll walk by the lab, they're just very mesmerized by it. Woah, look at that robotic arm. So it has an effect on most people that walk by the lab. And, I'm amazed when I stand by it every time we print something new in the lab. So when we think of 3D printing with concrete, all the things we talked about, green concrete and the mixture design, we are applying the same concepts, but it's just that this is a flowable material where the material gets placed through a robotic arm. So concrete can take the shape of any formwork that you place. But here there's no formwork. So that means that's also less waste, because typically formworkers are wood-based that might end up in the landfill, especially if you're doing customized shapes for an architectural feature. But now with a robotic arm, you can actually print any shape that you want without any formwork. So this opens up opportunities for, for example, in our lab we are exploring infill patterns, let's say gyroids where we worked with an...

Laura Reiley:

And is that something that will have more structural integrity because of the, the kind of crisscross shapes?

Sriramya Nair:

Yeah, they're basically like if you think of like a sine curve.

Laura Reiley:

Yep.

Sriramya Nair:

It's more like a sine curve in 3D. That's the easiest way to think of it.

Laura Reiley:

Sure. OK.

Sriramya Nair:

So it's like this wavy structure inside. But what what it does is it's really good in compression in all directions because concrete typically is really good in compression. So we're choosing shapes that play to that strength. Because it's weak in tension we want to minimize the regions where concrete would be in tension and where it is in tension, we typically place rebar. That's why it's called reinforced concrete. But here in our lab in the beginning, we were mostly doing unreinforced concrete. For example, we printed steps in our lab.

Laura Reiley:

Oh, I saw those. I saw those on the website. They're very cool looking. Kind of cross-sectionally.

Sriramya Nair:

Yes, exactly. And then we try to use... because arches are good under compression. So all the load gets transferred through the arch. I know the span is small but it sells the idea that with 3D printing you can reimagine what structural elements or shapes could look like. So if you think of those steps, we illuminated so much material in the steps by using that shape optimization.

Laura Reiley:

But is there more structural uncertainty with 3D printing? And I mean, obviously you're doing things that are layered essentially... how, how does that in, you know, impact longevity of the building or even, load?

Sriramya Nair:

Absolutely. Those are questions we're all asking. Those are all existing challenges, because the answer is it depends. It depends on your material. It depends on the temperature conditions that day, the humidity, how well it'll bond with each other like the layers that you're placing. Or it could be based on the printer setup that you have. So just because I get good printability and good bonds to it doesn't mean you get it too, because we are all learning as a community. So we still have to have standards, which is also something a lot of the organizations are working towards setting up standards, saying that these are metrics that you have to meet with 3D printing because there's no standards right now. So for, printing single-story houses, they're printing larger elements than what's needed to make sure they're strong enough. So let's say if you say a four-inch wall is enough, then you're printing a six-inch wall, let's say. But it's just to make sure that... and also like I can for example, they've printed the 100 homes in Texas and by, by their hundredth house, they've learned a lot more about, you know, how to build these.

Laura Reiley:

Yeah, l'll take the hundredth, n ot the first, for sure.

Sriramya Nair:

Yes. No. But, the more we build, the more, larger companies invest in 3D printing, the more we can push this forward.

Laura Reiley:

So I think you recently got a fast grant for AI and and 3D printing. I imagine AI could be employed just to kind of deal with the thorny problems that might crop up in what you just described. How, how could it help you?

Sriramya Nair:

Yeah. So in the past, most of my work is experimental, which means that we never really had that many data points to do AI. I know you can do machine learning and AI with smaller data sets, but that's not what AI truly is for. But now, with robotic construction and having so much control over your structural elements and how you're placing them and where you placing them, we can collect a lot of data. So all of a sudden, in my research group, we've gone from we don't have as much data to we actually do have a lot of data. So how can we use this knowledge that we are gathering during printing and after printing to make better informed decisions? And that could also translate to large scale. Like you said, there might be uncertainty and you might not have, like, you know, like I'm printing, but is it the same over here and there, like quality control...

Laura Reiley:

Would this be kind of open source so that everybody could contribute data...

Sriramya Nair:

Once I figure out how I can use AI, absolutely. We publish everything. Right. So yes, that is the goal. This is my first venture into AI, and that's what a seed grant is, right? Atkinson has been great that way to give us opportunities to collaborate across campus with different faculty and, you know, start a new line of research. So I'm really excited to see where that's going to be headed.

Laura Reiley:

So I do want to talk a little bit about funding because I know that's something that's that is a challenge. And that, you know, we have kind of priority changes that, that shift our commitment as a country, as a as an administration, for infrastructure reinforcement. How has that affected you and how are you seeing the way forward?

Sriramya Nair:

In the past few years, we have been extremely fortunate as a community where we've seen huge investments from the federal government to support, the research that we do both from, longevity, durability, but also reimagining how we make the cement. And what do we want to put in this pie chart? So there's been a huge range of thought processes that have gone into it from different researchers. So it's like I said, it's, we've been very fortunate and, but with the recent changes in the priorities, including me, a lot of people have lost a lot of, federal funding. So, but I truly believe that we have learned some really good ways of making better concrete. It's like the next generation concrete. And there's a lot more to happen in this space. And even though the federal priorities have changed, we need to keep pushing our knowledge forward so that way we don't reverse back to, you know, how we did things 15 years ago, ten years ago. And also with automation and with robotics that are going to come up, there is going to be a lot of changes that happen in the industry in terms of what is feasible, and we need to embrace those changes, along with green concrete, to make infrastructure better.

Laura Reiley:

So it's seems like is Europe kind of leading the way right now? I know there's that is it LC3 Concrete? Are there centers in the world where there's real forward movement that we should all be emulating?

Sriramya Nair:

Yeah, LC3 is a great example of, a material that's been globally accepted and it's going to have an immediate impact in the near future, like right now, of how... what materials we could put into that pie chart. It's it's all about that pie chart. And LC3 is just one such example. There are so many other because they mainly focus on limestone and calcine clays, but there are so many other materials that are really promising and have a good future. Even in the US, we've spent a lot of time, like collectively as a community on calcine clays. But we are also interested in other material systems, as well.

Laura Reiley:

With these podcasts, I love to... if there is something that you can give advice about, for, for home home buyers or consumers, is there anything they can do to make better choices in their own lives in terms of building materials or, you know, home projects that will move, move the needle a little bit in terms of, you know, in a green direction.

Sriramya Nair:

Absolutely. I think the first thing would be is, don't be afraid to, you know, consume your four four-liter Coke bottles of concrete, because, we need it in our everyday lives. Like, infrastructure makes our lives better and concrete is a structural material. It's not just a material that can hold its shape and take load, but it's a structural material that can take significant amounts of load. So if you think from that perspective, concrete has a very important role to play. And it's not that expensive.

Laura Reiley:

So, Sriramya, this has been really fascinating. I actually saw you speak about concrete at a, at a bar at a nerd night at a bar downtown, and I thought I did not know how fascinating concrete was. So that's why why you're here today. Obviously this is about climate change, but it also hits, you know, home construction and transportation and all of the infrastructure around us. But it really underscores kind of how much innovation is still needed. And the work you're doing is obviously heading us in the right direction there. You want to learn more about Dr. Nair's work or Cornell Engineering's research in sustainable infrastructure, you can visit nair.cee.cornell.edu. I'm Laura Reiley, and we'll see you next time right here on Research Matters.