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Public Radio's Environmental News Magazine (follow us on Google News)

Green Cement

Air Date: Week of

New research suggests the pyramids may have been made out of a concrete similar to green cement. (Wikipedia Commons)

Concrete is one of the most widely used materials in the world. It also accounts for five percent of the world’s carbon dioxide emissions. But researchers at Drexel University are trying to change that with a cool new cement that doesn’t need heating, just mixing. Drexel engineering professor Alex Moseson sat down with host Bruce Gellerman to tell us more about the process.


GELLERMAN: It's Living on Earth, I'm Bruce Gellerman.


GELLERMAN: Okay class, it’s pop quiz time. Keep your eyes on your own paper. Multiple choice, one question. Here we go. Water is the most widely used material in the world. What is the second most widely used material? Is it, A) Plastic, B) Steel, or C) Concrete? Alex Moseson, you're the smartest kid in the room, you teach Mechanical Engineering and Mechanics at Drexel University, what’s the answer?

MOSESON: It is concrete, produced on the order of about two tons per person per year.

GELELRMAN: Oh! That’s a lot of concrete!

MOSESON: It is indeed. Actually when you take a look at it, it doesn’t look like all that much, that’s on the order of a couple of slabs of sidewalk.

GELLERMAN: But it makes lots of tons of carbon dioxide, which is a greenhouse gas!

MOSESON: It does. It produces up to about five percent of the world’s greenhouse gas emissions in total from the CO2 released from making, not just the concrete, but really just from the cement that is used as the glue, the binder, that makes concrete possible.


Professor Alex Moseson (Courtesy of Alex Moseson)

GELLERMAN: So, how does that happen? Where does this CO2 come from in making the cement for the concrete?

MOSESON: Materials are typically mined in grand operations and brought to a giant kiln and then these rocks are essentially melted at 1500 degrees C. You can imagine it will take a lot of energy to melt rocks and you’re burning fuel, so that creates CO2 and other emissions. The rest of it comes from the chemical process that turns limestone into lime, which we need for cement.

GELLERMAN: And typically we call that Portland cement.

MOSESON: Right. So that stuff that goes through the kiln to come out the other end, have a couple of little things added to it and then we call that Portland.

GELLERMAN: So that’s where you and your research come in. You’ve developed something called Green Cement.

MOSESON: Indeed. So, we work on alkali-activated cement, and the beauty of it is we can take things that don’t need to go through a kiln in order to make them cement. So one of our investors had said: "Hey, it sounds like you figured out how to bake bread without an oven." Which is right!

GELLERMAN: So, you make Coolcrete.

MOSESON: You could say that.

GELLERMAN: Well, I just did! (Laughs.)

MOSESON: (Laughs.)

GELLERMAN: So, I don’t understand. What’s the stuff, what’s the magic sauce in making the cement without the heat and the CO2?

MOSESON: Any cement - you’re taking rocks, you’re turning it into a powder, and then you’re turning it back into rocks, and that’s an interesting process. In order to convince the chemicals involved to do that, you need something that is very caustic. Another way to do that is with an alkali chemical, something like soda ash, which happens to be very similar to baking soda, and it is widely available.

The idea is: we have a pinch of that alkali, and then we need something to activate. What we’re using are generally industrial byproducts, the leftovers from making iron out of iron ore, or the ashes left over from making power from coal.

GELLERMAN: So, by using fly ash or this slag, you can bake bread, make concrete, without the oven!

MOSESON: That’s right, and of course the next logical question is - well is it any good? Well, it’s not only just as good, it’s better in some ways.


MOSESON: In some ways. We’re looking at important metrics that everyone is familiar with such as strength and durability and things like that. There are some things that matter more to construction people, resistance to things like acid attack, resistance to the salt attack if you’re in a marine environment. There’s also interesting features that it’s better at containing waste, even things all the way up to nuclear waste, better than Portland.

GELLERMAN: What about cost, Professor? Is it competitive cost-wise, do you think?

MOSESON: Absolutely. If you’re going to say Product A, Portland cement, needs to be burned in a giant kiln which requires I don’t know how many millions of dollars to build and then millions more dollars of fuel to run, all you need to make ours is - mix it in a bucket.

GELLERMAN: Wow! So you built a better mix of cement, or concrete. Has the world beaten a path to your door?

MOSESON: Well, even though we have mega-scale recycling, we’re competitive in cost and strength, it has a longer life, it’s more durable, it’s more versatile, it is going to be certified, it’s even whiter, which is a big premium, (takes a deep breath) no. And that’s for three reasons. And I’ll tell you what the three reasons are.


MOSESON: The first reason is the variation in the feedstock materials. When we’re telling someone that we want to do something with your trash it’s hard to say: ‘Hey, person making iron, could you please tweak this so that your trash comes out better?’ And the second issue is, like with any product, we need all of its features to be working at the same time.

For example, getting it to set slowly enough and also having a high enough early strength. And when we pass those, we’ll be able to pass the standards required to overcome step three - and that is regulatory acceptance. So, we’re looking at making sure the cement is safe to use and that it does last as long as we think it’s going to. And this is a real issue to overcome because the cement that we know and love has been used for 100 years. So, we want to introduce this into the marketplace in the right way.

GELLERMAN: Good thing that the ancient Egyptians didn’t have these issues, because I understand that they actually built the pyramids using cement similar to the stuff that you’ve whipped up.

MOSESON: Indeed. And that is the excellent work of my colleague, Professor Barsoum, in Materials Science. He did some research into the origins of the pyramids and originally laughed at the idea that the pyramids could be re-constituted blocks. That they were carrying piles of rubble and making a rudimentary cement out of the ubiquitous limestone that they had there. We’ve done some tests ourselves and I can certainly say that it is at least as plausible as the other idea out there, except for ones that involve aliens, as the way they came to be.

GELLERMAN: So, what happens now, Professor?

MOSESON: We are trying to overcome the technical hurdles and we have a number of interested parties looking to help us take this into the real world.

Professor Alex Moseson’s video on Green Cement

GELLERMAN: Well, good luck!

MOSESON: Thank you very much!

GELLERMAN: Alex Moseson is an assistant teaching professor at Drexel University in Philadelphia. And by the way, the good professor says his process for whipping up green-crete reduces the emission of CO2 by 95 percent. And that is a hard



Website of Professor Alex Moseson


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