Secrets Of Ancient Concrete, And… Data Centers In Space?

IRA FLATOW: Hi, I’m Ira Flatow, and you’re listening to Science Friday. If you’ve listened to this show for a while that one of my favorite topics is concrete, really. And some of my favorite examples of the long term durability of concrete are from the Romans. Take the Pantheon and all those famous aqueducts built thousands of years ago and still standing.

But how exactly was this concrete made, and what ingredients went into the cement? That knowledge hasn’t been very solid. Well, late last year, scientists discovered an actual cement mixing site in Pompeii preserved in the volcanic ash. And it might hold clues to how we can improve our concrete today. Here to uncover those secrets is Dr. Admir Masic, Associate Professor of Civil and Environmental Engineering at MIT and one of the co-authors on that study. Dr. Masic, welcome to Science Friday.

ADMIR MASIC: Thank you for having me.

IRA FLATOW: Nice to have you. So you go to Pompeii and you make a discovery there that changes about how they made their concrete.

ADMIR MASIC: Yeah. So the context of Pompeii is fascinating. If you think about a city that, 2,000 years ago, was literally frozen in time by this eruption of Mount Vesuvius and then stayed preserved until we excavated it offers an incredible snapshot of what they were up to. And interestingly, a year ago, archeologists excavated a construction site, including a very well-organized construction materials like roof tiles or bricks and tools.

So imagine literally an active construction site that allowed us to walk through and understand from the raw materials how they were mixed and prepared to be then used in construction. So imagine people were building a house at the moment of eruption, and the literally stop the operations and froze that scene. And it felt literally like entering into Pompeii 2,000– so it was for me, a time travel, literally.

IRA FLATOW: Wow. Right. From what I understand, the Romans left all of this concrete behind. But did they leave behind the recipe for making this cement that becomes concrete?

ADMIR MASIC: Yeah, that’s a great question. It’s interesting in that ancient time, there were these scholars, architects, and scientists that did document a lot of what they were up to. Some of notable ones are, of course, Vitruvius and Pliny the Elder. And both of them describe recipes for making this magic material.

Vitruvius, in his de architectura, talks about the magic powder. He says, quote, “This substance, when mixed with lime and rubble, not only lends strength to buildings, but even when pieces of it are constructed in the sea, they set hard underwater.” So they document this recipe of mixing volcanic ash, lime, and then they notice this fantastic property that it hardens underwater.

IRA FLATOW: Now, did you discover that the ways that they made their concrete was different than the ways we make ours?

ADMIR MASIC: So what these scholars, ancient scholars suggest is that lime, not the lime that we use in our cocktails, but the processed limestone, so you take the stone, you create a kiln, and the product of this is quicklime, calcium oxide. And what these ancient scholars suggested is that this quicklime would first be mixed with water to make the reaction and create slaked lime, and then added to the volcanic ash to make concrete.

What we found in Pompeii is something slightly different. Ancient Pompeians would take these calcined stone, grind it, mix it dry with volcanic ash, and then add water. And that makes a slight difference. We call hot mixing because mix heats up because of the reactions of quicklime with water within the mix. Temperatures that can go up to 200 degrees in some hot spots.

Vitruvius says first slaked lime and then mix it. Nevertheless, in Pompeii, there is clear evidence that the raw materials were premixed dry and then water was added, at least in this specific case of the Roman Villa in Pompeii.

IRA FLATOW: And why is it that these ancient Roman structures are still so able to stand up for thousands of years? What’s different about the cement in them than the cement we use?

ADMIR MASIC: Yeah, great. I mean, we are talking about a self-healing concrete. Because of this way of hot mixing that when the microcrack is formed, basically are dissolving and recrystallizing in cracks that cannot be met with our modern analogs.

IRA FLATOW: That’s amazing. I want to ask you what it was like standing in this workshop that’s thousands of years old for the first time for you.

ADMIR MASIC: Oh, personally, for me was outstanding in the sense that together with my team at MIT, we came up with this theory based on the research that was done on ancient Roman walls in little town in Priverno. Of course, analyzing post mortem concretes in the sense that they were already mixed and all our crazy hypothesis that indeed, Romans used hot mixing. Many of my colleagues criticized these arguments simply because it’s difficult to think that this process might have been applied by the Romans because Vitruvius says, hey, do this.

So for me, finding a pile of premixed dry volcanic ash and quicklime was incredible. I got emotional. And of course, my archeologist friends made fun of me saying, Admir, I mean, there are beautiful frescoes around you, and you get emotional and cry by looking at a pile of dirt. But you see, for me, that pile of dirt was years of waiting to really confirm quite the challenging hypothesis.

IRA FLATOW: Well, as someone who loves to talk about concrete, I can see how you can get emotional–

ADMIR MASIC: Great.

IRA FLATOW: –about that also. Well, let me return to one question that’s fascinating about this self-healing quality of the concrete that they made. You say modern concrete does not have this self-healing quality. Is it possible to put that into modern concrete somehow?

ADMIR MASIC: Yeah, that’s exactly what we are up to now. And we were able to patent some of these ideas. And companies are starting to offer self-healing, Roman-inspired concretes out there.

IRA FLATOW: That’s great. Thank you, Dr. Masic, for taking time to be with us today.

ADMIR MASIC: Thank you very much for having me.

IRA FLATOW: You’re welcome. Dr. Admir Masic, Associate Professor of Civil and Environmental Engineering at MIT.

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After the break, we’re going to move from something concrete to something still on the drawing boards. How realistic is it to move data centers to space? Stay with us.

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As tech companies build up data centers for AI, they are also searching for new ways to supply the immense electrical power necessary to run them, like reviving old nuclear reactors, for instance. But lately, tech leaders like Google CEO Sundar Pichai, former Amazon CEO Jeff Bezos, and OpenAI CEO Sam Altman have been thinking not only outside the box, but out of this world.

SUNDAR PICHAI: How do we, one day, have data centers in space so that we can better harness the energy from the sun?

JEFF BEZOS: these giant training clusters, those will be better built in space because we have solar power there 24/7.

SAM ALTMAN: The world needs a lot more processing power. If that looks like tiling data centers on Earth, which I think is what it looks like in the short term, or we do go build them in space. I don’t know. It sounds cool to try to build them in space.

IRA FLATOW: Yeah, it does sound cool, but you know what? The devil is in the details, right? What resources and money would it take to move these enormous structures into space? And does this mean we could start seeing more of our infrastructure move into orbit in the next few decades?

Here to beam us up is Dr. Benjamin Lee, Professor of Electrical and Systems Engineering at the University of Pennsylvania in Philadelphia. He studies microprocessor design and how to make them more efficient in data centers. Welcome to Science Friday.

BENJAMIN LEE: Thanks so much. Wonderful to be here.

IRA FLATOW: Nice to have you. So in those clips we just heard, it sounds like that power is the main draw. Is it as simple as that? There’s more energy available in space, so let’s put stuff up there.

BENJAMIN LEE: That’s certainly the starting point. As many of us already know, finding the energy on today’s grids is increasingly difficult, especially given the size of our data centers. We’re talking about 1,000 megawatts, 2,000 megawatts. And grid capacity is scarce. And certainly, many of the hyperscaler data center operators are having difficulty finding sites that can support those power loads.

The second issue really is about where the energy is coming from. There has been a lot of interest in carbon efficient energy, so solar is certainly one of those. But solar energy on Earth is clearly intermittent. You can’t compute with solar energy in the middle of the night, and launching data centers into space could solve that problem. We could put data centers in sun synchronous orbit and get solar energy exposure on those solar panels pretty much continuously. So I think energy is definitely the starting point for orbital data centers.

IRA FLATOW: Well, let’s look into those devils in the detail. How big would the solar panels have to be to capture that much power?

BENJAMIN LEE: Right. So we’re talking about kilometers of solar panels if we’re talking about these giga scale data centers. If you’re talking about gigawatt or two, those panels end up being fairly significant. And the size of it is one thing, but the launch costs, the weight of those panels and sending that all up to space, it would be certainly another.

IRA FLATOW: Yeah, and when you have panels or anything in space that big, don’t you have risks from, well let’s say, space debris for these massive structures?

BENJAMIN LEE: Certainly. And reliability and repair is an ongoing challenge for anything we send into space. We know that, especially for these larger data centers, components will fail occasionally. And we will need a strategy to replace and address that. And that’s true for the hardware components that perform the compute. But it’s also going to be true for the solar panels and other infrastructure that goes up.

IRA FLATOW: Well, on Earth, these data centers are cooled by water. How would you cool them up there where there is no water.

BENJAMIN LEE: That’s right. And so the fact that space is cold is one thing, but it doesn’t really help our ability to extract the heat from the processor chips and send it out into the ambient. Normally, on Earth, what we do is we rely on blowing cold air or flowing cool water over the compute, and then eventually, releasing it out into the atmosphere.

Without an atmosphere in space would need to rely on radiative cooling, and radiative cooling really relies on yet more panels and larger surface area that would allow us to radiate that heat out into space. So not only are we talking about the surface area for the solar panels, we’re also talking about surface area for the cooling.

IRA FLATOW: OK. So let’s say you’ve got these data centers in orbit around the Earth and they’re crunching a lot of data. How do you effectively communicate with them at high speed sending the data back and forth?

BENJAMIN LEE: Right We might be able to send on the order of 10 gigabits per second up into space using radio frequencies. But the difficulty is really about moving large volumes of data. So in one of the earlier clips you aired, there was a discussion of training large AI models in orbit. The difficulty is that training requires massive data sets, essentially all of the internet’s data, and getting all of that data up into space would be challenging. We would essentially have to launch that data up into space, along with the compute.

There’s an old joke in computer science where we say that if we wanted to send a large amount of data quickly, maybe from the East Coast to the West Coast, the easiest thing to do, the fastest thing to do would be to put a disk in the mail. And I think that’s certainly true when we’re talking about sending things into space as well.

IRA FLATOW: Well, you’ve mentioned all the negative parts about doing this, all the challenges of putting data centers in space. Why not just make data centers on Earth be more efficient in how we make power and how they process data?

BENJAMIN LEE: That’s right. And I think right now, we know that we are somewhat wasteful in how we are consuming data center resources. We are pursuing, first and foremost, better and better AI models. And we’re willing to pay whatever energy cost it takes to get that new capability, that new application. We don’t want to worry whether or not if we had just thrown an additional 100 megawatts at the problem, that we could have gotten something we didn’t have before.

So right now, when we think about the AI models, they are equipped to answer any possible query that any possible user could pose to it. And that, generality really is computationally expensive. If, however, you knew that you wanted a model for finance or you wanted a model for medicine or for education, you could come up with specialized models that could give you an answer that is just as good, but require far fewer calculations.

The reason why we haven’t done this yet is because we don’t know what those really compelling applications are, the ones that will change the way we live and work. But once we figure those out, I think there will be plenty of opportunity to reduce the energy cost and improve energy efficiency.

IRA FLATOW: Because what you’re talking about, what these guys are talking about going into space that’s not going to happen this year or 10 years from now, is it? And in that time, who knows what kinds of efficiencies we might have?

BENJAMIN LEE: That’s right. And going back to your other point, I would also say, it’s very hard to what the energy landscape in the United States will look like in 10 or 15 years, whether we will have much more battery capacity, much more solar capacity, small modular reactors. All of that is also possible within the next 10 or 15 years. And that may change how we view the relative merits of doing one of those things versus sending data centers into space.

IRA FLATOW: Do you still think, though, that we should be thinking about sending data centers into space as more than just a thought, as a possibility?

BENJAMIN LEE: I think replacing these massive terrestrial data centers with orbital data centers is really ambitious and potentially a long-term goal. But in the near term, I think there are really interesting fundamental research questions going back to some of the things we had just talked about– radiation hardening, thermal management, power delivery.

I would also say that the challenges associated with data movement also means that there is an opportunity to do more compute in space. Maybe we have satellites collecting massive amounts of data, image data, or other kinds of data from orbit. Instead of sending that all down to Earth for processing, you can imagine doing more of that compute in space. I think that would be really great application of orbital computing without going to this end goal of replacing massive terrestrial data centers.

IRA FLATOW: So you do think we should expect to see more of our infrastructure moved into orbit.

BENJAMIN LEE: Yes. And I think that is a natural progression from where we are today, where we are seeing, with SpaceX and other private space companies, significantly reducing the cost of launches and also with the advent of these constellations of communication satellites like Starlink. I think putting some amount of compute to complement that communication would be really exciting and would make a lot of sense, but maybe not at the scale of 1,000 megawatts of data center capacity.

IRA FLATOW: Thank you, Dr. Lee. Terrific!

BENJAMIN LEE: Thank you so much. I really enjoyed it.

IRA FLATOW: Dr. Benjamin Lee, Professor of Electrical and Systems Engineering at the University of Pennsylvania in Philadelphia. This episode was produced by Dee Peterschmidt. I’m Ira Flatow. Thanks for listening.

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