In this episode, host Daniel Raimi talks with Mahmoud Taha, a professor and chair of the University of New Mexico’s Department of Civil Engineering. An expert on cement, Taha walks through how and where the “magic glue of construction” is made, and why it produces such a sizable amount of CO₂ emissions. Taha notes that cement can be manufactured with more environmentally sustainable materials, but these cement alternatives often are less durable and thus are not appropriate for all construction projects. To complement those efforts, Taha says the US government could offer more funding for research and development and could incentivize cement manufacturers to shift their business practices toward less environmental impact.
Listen to the Podcast
- Environmental hazards of cement: “Cement production is actually known today to be one of the most highly polluting sources, in the sense of emissions of CO₂. About 8–10 percent of the CO₂ we emit from industrial resources or in general to the atmosphere is coming from cement manufacturing.” (6:31)
- Using new materials in cement comes with trade-offs: “[With low-carbon cement alternatives], there are trade-offs related to time and strength, and there are trade-offs related to the long-term durability of the material … We wouldn’t get a final product as good as the [cement] we have now … but if the issue is that we need things fast, and we need them to be as strong, then engineering-wise, we could find solutions.” (20:32)
- More government support can help expand low-carbon technologies: “The government has been trying to make efforts in the area of research and development, so there has been moderate funding from the National Science Foundation, the US Department of Energy, and others … but making a dent in [cement emissions] needs a very concentrated effort. I don’t think what’s been done has been concentrated and orchestrated enough … The typical [strategy] we’ve seen in the research and development sector is to fund research that hopefully develops some intellectual property. But this is very slow, and we don’t have a lot of time.” (24:28)
Top of the Stack
- Good Economics for Hard Times by Abhijit V. Banerjee and Esther Duflo.
- “Sweden’s HYBRIT starts operations at pilot plant for fossil-free steel” in Reuters.
The Full Transcript
Daniel Raimi: Hello, and welcome to Resources Radio, a weekly podcast from Resources for the Future. I'm your host, Daniel Raimi. This week, we talk with Mahmoud Taha, professor, Regents’ Lecturer, and chair of the Department of Civil Engineering at the University of New Mexico.
Mahmoud is an expert on many things related to material science, but today I'll ask him about cement, which he calls the “magic glue of construction.” We'll focus on the greenhouse gas footprint of cement options for reducing that footprint and how the use of new materials might affect the cost and performance of cement. We'll also touch on government policies that can help spur innovation and speed deployment. Stay with us.
Mahmoud Taha from the University of New Mexico. Thank you so much for joining us today on Resources Radio. It's a real privilege to have you with us.
Mahmoud Taha: Thank you, Daniel.
Daniel Raimi: So, Mahmoud, we're going to talk today about cement making and, in particular, the possibility of low carbon emissions cement. But before we do that, we always ask our guests how they got interested in working on related topics. So can you tell us how you got interested in working on environmentally friendly cement?
Mahmoud Taha: Well, thank you again, Daniel, for the invitation and for being here. Well, I need to say that I'm a bridge engineer by training. I'm a professor at a university. Most of my career has been working on the cement concrete polymers and related things. As a professional, I wouldn't call myself an environmentalist. I always was interested in—of course—whenever we produce things to have them be environmentally friendly, making sure we produce sustainable structures and things like this.
So I actually grew up in Cairo, Egypt, where 20 million people live in the metro area, and I moved to North America 25 years ago. So, the issue of environmental concerns 25 years ago wasn't as it is today. I would say the key change to my vision of the topic started a few years ago and became especially more impactful when I was visiting southern Colorado. I live in New Mexico, and I visited southern Colorado a few times.
My wife is from South Colorado, and we go for family visits. Usually, when I visited Colorado before, the big difference between Colorado and New Mexico was the forests and the very green areas. In the last few years, as you visit, you see that you're losing this. That is, more of the things are getting to be a high desert. There is less water. There is less snow. With these changes, you start feeling, "Oh, it's in my backyard. It's not something I'm just reading in the news.” So, that actually changed a lot of my view of things. And then opportunities emerged through colleagues where we could look at environmentally friendly materials ... I personally have seen the changes happening in New Mexico and in Colorado, and in many beloved places that I enjoyed visiting, that now see fires and hurricanes and things like that.
Daniel Raimi: Well, that's really interesting. It makes a lot of sense. I think many of us are seeing changes like that play out in our lives and the places that we love. But let's talk now about cement. So, I'm hoping we can start with the very basics. Cement is one of the most widely used materials in the world. And yet—speaking for myself before starting to look into this topic a few months ago—I didn't really know how it was made. I imagine many of our listeners don't know much about how it's made. So can you give us a really quick primer about how most cement currently gets produced?
Mahmoud Taha: Cement is the magic glue we use in construction. So how it's made is simple. Basically, we mix silica sand with limestone, and we mix them at very high temperatures. When we say very high, I'm talking about 1400–1500 degrees Celsius; that's about 2,500 degrees Fahrenheit. So it's a very high temperature. We mix them at this temperature. We grind them together, and we produce that material that makes the core of that magic glue that's called clinker. Whenever you add water to it, it makes the rock-like material that's the concrete or the hardened cement. We basically add to this material only these two materials—the silica and limestone—and what happens is that actually limestone at a very high temperature basically makes lime.
Then the lime reacts with the silica, and it makes this clinker material. We just add to them, after this, a little bit of gypsum just to get the reaction to be a little slow so that when you add water to cement, it doesn't harden immediately. But that's pretty much what the process is: it is the limestone and silica together at a very high temperature. And the process of making the lime is called calcination, and that's actually where most of the carbon dioxide goes out because limestone is calcium carbonate and you make from quicklime, which is calcium oxide.
Daniel Raimi: Right. So can you say a little bit more about that, about where exactly in the process the CO₂ emissions come from? You mentioned a very high heat. So obviously, there's going to be some fuel combustion. I would imagine that's involved in that, and then the calcination process as well. Can you help us understand the ratio of where the CO₂ emissions are coming in particular?
Mahmoud Taha: Cement production is actually known today to be one of the most highly polluting sources—polluting in the sense of emissions of CO₂. About 8-10 percent of the CO₂ we emit from industrial resources or in general to the atmosphere is coming from cement manufacturing. So it's quite a high amount of carbon dioxide. Actually, about 50 percent of the carbon dioxide comes from the calcination, which is a big number, and it can tell you right away that … 50 percent comes from just making the limestone to lime.
About 40 percent comes from making the high temperature burning fuel to make a high temperature. Which, as I said, it’s a considerably high temperature: about 1500 degrees Celsius. And so that's a very high temperature, and that takes a lot of fill and a very large amount of CO₂. Another 10 percent comes from other things like, for example, transportation of the material, because you don't usually have the cement manufacturing at the same location, you have the raw materials—but the most of the CO₂ emissions comes from the calcination and from burning fuel to make cement.
Daniel Raimi: I mentioned around the world. There are different fuels that are used in different parts of the world, which brings me to the next question, which is: Can you help us understand where the largest producers and consumers of cement are geographically speaking? Also, I'm wondering if there's widespread international trade of cement, the way that there's widespread international trade of, let's say, petroleum products.
Mahmoud Taha: There is. The largest amount of production of cement worldwide is in China, and China produces about 50 percent of the world’s cement. But not all of it is used in China. So there’s a considerable amount that's produced in China, but used elsewhere. I would say close to 25-30 percent is produced in many developed areas like the United States, Europe, and India. So they produce close to 25-30 percent, but of course, in some many cases, this is not enough. So China is representing a good source of cement for them. And the rest is the other 20 percent—a world production or worldwide.
With the fact that a huge amount of development is happening in developing countries, they don't produce as much cement to make these developments. So a lot of the cement produced in China and in India and other places goes to developing countries. So, of course, there is a big international trade of cement. In my opinion, we cannot blame the producer of the cement, only because of the fact that China's producing 50 percent of the cement.A lot of pollution occurs during production, but there is a worldwide demand on the material. That’s like anything else. So, worldwide it is being used. The 50 percent is not only used in China.
Daniel Raimi: Right. Great. Those are great points. I'll just point listeners to a large body of research out there on estimating emissions on a production basis, which is where are fuels consumed and where do emissions occur. Versus a consumption basis, which is where do the end-use products end up, whether that's cement or toys that our kids play with or televisions or anything else.
Mahmoud Taha: That's correct.
Daniel Raimi: And they come up. You see very different answers there. So let's move on now from the very basics of cement and talk a little bit more about some of the more environmentally friendly processes that you've become more interested in. So obviously, there's a lot of interest in trying to reduce carbon dioxide emissions from the cement making process. Can you give us a brief overview again for the non-expert of what some of those major options are, including the use of alternative materials to the silica in limestone better so commonly used today?
Mahmoud Taha: So, if we think about reducing the largest percent of carbon dioxide that we emit to the atmosphere, the reduction can happen in two basic ways. That's what, worldwide, the efforts are. Number one is to make more efficient use of the cement in concrete. In other words, if you are using a specific amount of cement in producing a cubic yard of concrete, we will say, "Can you use less cement to make the same cubic yard?" There is, and actually, there has been research in this area since I would say the 1970s, using the materials known as pozzolans. Just for you to know, the pozzolans stem from the idea of the volcanic ash. The Romans built hundreds of years ago with volcanic ash.
So, the pozzolans are natural materials that are highly rich in silica. When you add them to water, they react like cement, but they take a much longer time to build their strength and their integrity. So there's been work since the 1970s on replacing cement in concrete, in the typical concrete to use in driveways and highways and bridges and everywhere with a pozzolan material. Some of these pozzolan materials actually are waste materials coming from industrial plants or like fly ash, coming from the coal industry power plants. There is a silica fume that comes from the iron industry. So all of these are waste materials. So its use is good for the environment, and they are highly rich in silica. When you add them to the cement, they act like cement, but again they do not provide the same strength quickly.
So this is one way—to reduce the cement. I think we as the research community worldwide have cut a good shot on this. We did a lot of work on this, and people for years did this, and we can replace actually 25 to 30 percent of the cement in the concrete, or maybe more, with those materials. There are other materials that are more recent that are called, for example, the geopolymers. These are silica materials you can activate using the sodium hydroxyls. They can be used to replace typical Cement. There are special types of cement-like magnesium cement. Sulfur eliminates cement. The issue is those other products. The alternative cement is they are not as mature in the market like Portland cement. But they can be used, and their use can be expanded to replace cement.
So that's the first way is to actually use less cement in the concrete and use some of those alternative cements. Another way is to actually reduce the amount of the material that gets you a lot of the carbon dioxide when you are making cement. So, if we have a specific percentage of the clinker ... and we go through with the grinding of the silica, this material is the basic responsible material for the large emissions that we need all the temperature to produce.
So if we can produce cement with the least materials through mixing some of the supplementary materials—as I said, fly ash or slag with the cement—during production, that's another way to produce cement that has the least of the effective material that results in the larger emissions of CO₂. Canada has lots of work in this, and they produce what we call slag cement, and there are other countries as well. But that was since early 2000; they produced cement that has a considerable percentage of it as slag, and it works well for different construction purposes. So, these are the two basic ways for reducing the CO₂ emissions in cement.
Daniel Raimi: That's really interesting. One of the questions that came to my mind as you were just answering that is that we did an episode a few weeks ago on low-carbon steelmaking. And one of the topics that our guests Chris Bataille mentioned was recycling steel and how steel recycling could be an overly useful way of reducing the production of virgin steel. Is there anything equivalent for cement? Is there large-scale cement recycling that takes place today?
Mahmoud Taha: There is. The idea is there, but the amount of recycled cement and concrete is not at the scale necessary to make a dent in emissions because you have to have a significant amount of recycling. What is common today and happening at a good scale, in many places worldwide, is the recycling of the aggregate, the gravel and the sand that is used in concrete. So we used old concrete that we can recycle to make the new concrete. But cement recycling hasn't been that common or at large enough volume to allow it to make a meaningful effect. But also ... for cement production, changing the type of fuel is an option, because we talked about how the CO₂ emissions come because of the high temperature you need.
Mostly it's coal that is used on it or petroleum resources. So one way to reduce this is to use alternative thin materials or alternative fuel. People for a while used recycled tires, for example. There is research being done on using recycled papers and recycled other materials to actually achieve the high temperature without resulting in the same amount of carbon dioxide being emitted. A very nice initiative was done in Brazil using biomass. Basically, when you burn biomass, because there is a considerable amount of CO₂ already put into the atmosphere to produce the biomaterials, then burning it does not emit additional CO₂ to the atmosphere. So biomass has been very successfully used in Brazil and in other places to produce cement that has a lower emissions of CO₂ but, in the meantime, still can produce at that high temperature.
Daniel Raimi: Got it. That's really interesting. Then we could, of course, get into the discussion about carbon capture and sequestration, which is another pathway for reducing emissions. But let's go on now, and I wanted to ask you about one of the issues you raised just a moment ago, which is about the potential trade-offs between reducing CO₂ emissions and affecting the quality of the product itself. So you mentioned the time it might take for some alternative materials to be used effectively, relative to gypsum or some of these other materials. I'm totally out of my depth here, so I apologize if I'm mainly going to get the technicalities, but can you just give us an overview of what some of the trade-offs might be between using new materials or other techniques to reduce emissions and how that might affect the quality of the actual performance of the cement?
Mahmoud Taha: That's a good question. The two key trade-offs for the construction industry are: how fast the cement hardens and how strong it becomes. I think both of the typical solutions can be overkill. I'm trying to use a tractor to move a 25-gallon bucket. That's typically what we do. While you could move the bucket using a dolly, you can move it using some other means that is not as heavy as the tractor. I think that's what's happening because we can't wait too long to open the road. And we can't wait too long for the material to gain strength.
That is what is hurting in the trade-offs. Many of those materials could reach a similar strength to the current cement. On many occasions we might not need that strength. The metrics we are using and the specifications we are using worldwide were not necessarily developed at a time where we need to use less material in this cement. I think a good revision of this could take care of a lot of the trade-offs because, in many occasions, we might be giving you concrete to put on your driveway that is way stronger and is way faster to harden than what you really need. I think that applies to many things.
So there are trade-offs as I said, related to time and strength, and there are trade-offs related to the long-term durability, which is basically the longevity of the material. But for many of them we have technical solutions that can take care of them. We wouldn't get a final product as good as the one we have now, but it's the issue that we need things fast, and we need them to be as strong as we think they need to be. But engineering-wise, we could find solutions for this.
Daniel Raimi: That’s really interesting. I bet various economic pressures and other pressures are probably incentivizing people to use materials that just might be overkill.
Mahmoud Taha: It is. Many times, it's not driven by the needs. It is driven by the market. It's driven by, as you said, other factors.
Daniel Raimi: So on a related note, can you help us understand one other thing? You mentioned some experiments that were done in Brazil in previous years. I'm wondering if there are other large-scale efforts that are currently underway that you're aware of that really try to deploy these new technologies, particularly if they're trying to deploy them at scale. At the same time, I'm wondering about their viability in the marketplace. Is it economically viable to try to use some of these new materials and really make a dent in emissions?
Mahmoud Taha: There are large efforts. I would say there are a lot of research efforts trying to make use of materials like geopolymers. As we've talked about, biomass is a very interesting alternative that's being tried in many countries. The largest effort might be happening now is not on the cement making itself, but more on the carbon capture and storage that you mentioned. That basically is trying to realize the fact that if you are going to produce cement, even with the alternative materials, you still are going to produce a considerable amount of carbon dioxide.
If we can incorporate in the production methods for capturing the carbon, storing it, and sequestering it after for use in other construction materials, or storing it in the ground at some deep formations, these are the biggest efforts now—carbon capture and storage. Some of them are really taking off, and there are some companies, and some industries growing to do this because it will help the cement industry, and it will also help in reducing carbon dioxide. I don't think we are shy of innovations in this area, but I think we are really shy of implementation and having markets for those products.
Daniel Raimi: One of the ways that the government might be able to intervene here is trying to support the development of those markets, which brings us to another question I wanted to ask about government policy. I know governments have been pretty involved in supporting research and development for some of these technologies. I'm wondering if you also see the need or what you see out there in the marketplace of whether governments are being active in supporting the deployment of these new technologies and materials. If so, what are you seeing that might be particularly promising out there in the world?
Mahmoud Taha: I agree with you. I think the government has been trying to make efforts in the area of research and development. So there has been moderate funding from the National Science Foundation, the US Department of Energy, and others, and worldwide in the area of research for alternative cementing materials and trying to reduce it. But the problem, as I see it, is we've been trying to reach the moon. 8 percent is a very large number, and making a dent in it needs a very concentrated effort. I don't think what's been done has been concentrated and orchestrated enough. It is a good effort to develop some of those materials, but the typical way we've seen in the industry or in the research and development sector, which is basically you fund research that hopefully develops some intellectual property and that can come to some startups that make an industry.
This is very slow, and we don't have a lot of time to get the 8 percent down because, by 2030, or 2040, you can reach the 1°Celsius increase, which will have very dramatic effects. I think that there is a need from the governments to realize, number one, that the typical technology development method might not be the most effective. Governments need to realize that the way to do this is by actually coming into play with some interference to create that economy that would enforce the CO₂ emissions issues. For example, I think that governance might need to involve a carbon dioxide tax or credit, in other words, into projects. For example, federal government buildings could have a tax credit embedded to the materials used in projects.
If you are achieving a carbon tax, a carbon credit, a CO₂ credit, you could have points. There were similar things done years ago in the area of sustainability that incorporate other measures and metrics for sustainability. The government needs to think about this and to think of policies, implement policies for this, and might also need to interfere with the cement manufacturing too, so that the CO₂ reduction will be an integral part of the business model for cement manufacturing, because the amount of CO₂ now produced is very high and the carbon dioxide levels needs to be reduced. So I think the government needs to interfere to create that circular economy that can support new materials that are coming from reducing the CO₂ emissions.
Daniel Raimi: Very interesting. We're very aware at Resources for the Future of different ways that governments are trying to implement those ideas and send those price signals through the market. So it'll be really fascinating to watch. Just a quick data point, I was doing a little bit of math while you were speaking and realized that if cement was its own country, it would probably be the third-largest emitter of all nations of the world behind only China in the United States in the neighborhood of all the CO₂ emissions from the country of India.
Mahmoud Taha: Which is huge. Very large.
Daniel Raimi: Enormous. So, wow. Mahmoud Taha from the University of New Mexico, there are so many more questions I want to ask you to dig in deeply on this, but hopefully, we've whetted our audience's appetite, and they can follow up and do more research themselves on this really fascinating topic.
Now I'd like to go to our last question that we ask all of our guests, which is asking you to recommend something that you've read or watched or heard that you'd recommend to our audience or something that's on the top of your literal or metaphorical reading stack. And I'll start just with a really quick recommendation of some news that came across my screen today, we're recording on August 31, 2020, and there was just news out of Sweden of the first pilot plant that is producing zero fossil fuel steel, from Sweden.
Steel is another part of the economy that's very difficult to fully decarbonize, but there are new technologies using electricity and other technologies to produce steel with virtually no emissions. So, it's really exciting to see that, and I’ll be hopeful that we'll see similar developments in the cement world in the years to come. But how about you, Mahmoud: What's on the top of your literal or metaphorical reading stack?
Mahmoud Taha: There's a number of things, but a very nice book that I recently came across, not in my area, really, but I think it strongly relates to this discussion and to a lot of the thinking I've been recently doing on this topic and the reading, by two of the Nobel Prize winners in Economics in 2019, Abhijit V. Banerjee and Esther Duflo, from MIT. The title of the book is Good Economics for Hard Times. What I really liked about the book is that well, first of all, I'm not an economist. But I like the fact that the book is for the normal person, someone who is interested to read and learn about what's happening around us. The book is fascinating and discusses economics and everything.
There was an interesting argument, the counter-argument of the idea for immigration, for example, when they say, "Immigration is not going to result in a reduction in the economy; actually it makes its own economy." And they actually address the issue of climate change. What I liked about it is their discussion on the fact that if we think that funding R&D, which is the typical idea, that funding R&D is going to get us a solution for climate change, and we are going to make economic growth, and we also are going to solve the problem—that is actually a wishful thinking. The fact is that there is no free lunch. We’ve got to pay for this. We have to think: how can we create an economy that is based on less CO₂ emissions?
As you just said—the example from Sweden—we can do it. We can create these technologies. We have to realize it's not going to be cheap, there is going to be a price we are going to pay, but we need to do it for ourselves and for the next generations. So, we need to think, how can we do this? I think there are a lot of good R&D work starting points, and with collective and orchestrated efforts. I think it can be done. So that's a fascinating book I really like. I think it's a good eye-opener for many issues.
Daniel Raimi: Fantastic. Well, that's really interesting. And coming from you with your extensive experience on these issues means a lot. So, I hope our audience will check that out. We'll close it out now, Mahmoud and say, thank you once again for joining us on Resources Radio and helping us understand the basics of cement and the basics of green cement. We've really appreciated your time.
Mahmoud Taha: Thank you very much. Pleasure.
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