The Climate in Emergency

A weekly blog on science, news, and ideas related to climate change

Sticking Together for the Climate

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Last night, the PBS NewsHour told the story of Ferrock, a climate-friendly alternative to cement invented by the aptly-named David Stone. It was a good story, well-told—almost.

The reason that traditional (“Portland”) cement needs an alternative is that it is currently responsible for 5% of carbon dioxide emissions globally. And since cement is the binding agent used in concrete, the preeminent building material in the world, the demand for cement is likely to grow.

How does all that carbon dioxide follow from cement? PBS Newshour correctly reported that making the material takes a huge amount of energy. The first step in the process involves making limestone and other ingredients to 2,800 F. in order to create clinker, essentially a new mineral. Clinker plus gypsum is Portland cement. Cooking enough clinker for one ton of cement requires 4.7 million BTUs of energy. If that energy comes from coal (as it often does) then a ton of cement is another ton of carbon dioxide in the atmosphere.

What the Newshour did not add is that the kilns are only responsible for about 40% of the carbon emissions of cement production. 5-10% more comes from transporting raw materials and finished cement and the energy necessary to run machinery. The rest, 50%, comes from the chemical creation of clinker itself.

Limestone is calcium carbonate. Clinker is mostly calcium oxide. Transforming the one into the other liberates carbon dioxide as an inevitable byproduct. Worse, that is carbon that had been sequestered back when the limestone was created, millions or even billions of years ago. As regards climate change, there is a fundamental difference between recently sequestered carbon and ancient carbon.

Releasing recent carbon, for example, burning wood or even breathing, does not change the global carbon budget any (although deforestation on a large scale does)—just like adding and subtracting grocery money from a short-term checking account does not alter a person’s retirement savings. But liberating carbon that has been sequestered for millions of years does change the overall carbon budget—and warms the planet. In that sense, baking limestone is as bad as burning coal.

Ferrock offers an alternative because it is chemically different from Portland cement. The Newshour did not provide any detail on this point, and since its report did not explain the chemistry of clinker production it could not make clear how a “different recipe” could make Ferrock superior to Portland cement. But the report did include a brief shot of some chemical formulae and did state what Ferrock’s primary ingredients are: iron, silica, and carbon dioxide itself–the material takes carbon in, rather than putting it out.

That the raw materials are the wastes of other industries (steel dust, which is typically landfilled, and post-consumer recycled glass) is an added benefit of the process. The Newshour spent a good chunk of time explaining how the glass was originally sourced through a recovering alcoholic who picked up litter as a kind of self-appointed service position—a charming tale, but one that rather emphasized how small-scale Ferrock was, at least in the beginning.

Scale is Ferrock’s problem, according to the Newshour, which interviewed Steve Regis, the owner of a large Portlantd cement production facility, who asserted that

“Dave’s idea, I think it has a good niche market for — for nonstructural block, yard art, benches. But consider the scale of that compared to a 200-mile six-lane freeway eight inches thick or a runaway.”

David Stone appears to concede the point, or, at least, the reporter concedes the point and does not quote any rebuttal by Dr. Stone. He does say that

“I’m doing my part, as best I can, to respond, so that when the time comes and the world wants to build with new materials that are carbon-neutral or carbon-negative, I will be able to step forward and say, yes, I have such a material.”

Dr. Stone’s quote ends the report, except for some concluding narration, but Mr. Regis was the last person to actually provide the audience with information on what Ferrock can and cannot do–for a competitor to be given such an authoritative last word in an ostensibly friendly profile is striking, especially given that Mr. Regis’ claim is hard to believe. There is no shortage of post-consumer recycled glass, and steel dust is an otherwise unclaimed byproduct of the steel industry and probably quite plentiful. And of course, we have a lot of carbon dioxide…. So, why can’t Ferrock be scaled up? Perhaps it actually can’t, but in that case the reporter should have insisted that Mr. Regis make his case more clearly. Why should he be able to condescendingly bad-mouth his competition with a questionable argument, unchallenged by a journalist?

Most probably, if Ferrock can’t scale up it is because the construction industry is conservative. Industry standards and even the law require Portland cement and those standards are not likely to change without outside pressure because of a big alternative-cement project does fail, people could die and careers could end.

And this is true even when the alternative cement has shown itself in laboratory testing, as Ferrock has, to be superior to Portland cement in certain critical ways—the stuff is blast-resistant, meaning that an explosion (whether accidental or deliberate) that could collapse a building made of standard concrete would leave a similar building made of Ferrock-based concrete damaged but standing.

Industry conservatism is the real bugaboo of David Stone—and a startlingly large number of other people.

I have not done an exhaustive survey, but just a few minutes online turned up the following list—for ease of comparison I’ve included Ferrock on the list.


A cement-alternative made, apparently without kiln-baking. It uses iron and silica (from glass) rather than limestone and is a carbon sink rather than a carbon source. Concrete made from Ferrock is five times stronger than Portland cement-based concrete. Among other advantages, it is blast-resistent.

Liquid Granite

Liquid Granite is a cement-alternative whose composition is a trade secret; it is said to be made from an “inorganic powder” that is up to 70% recycled industrial waste and to be “carbon-free,” although it is only offered as a way to replace “more than two-thirds” of the Portland cement in concrete mixes. Its strength is comparable to Portland cement but with superior heat-resistance. Portland cement does not burn, but it does crack and crumble in fires.


Novacem is not a substance but a London-based company that produces a cement-alternative based on magnesium silicates. Production requires lower temperatures and does not release carbon dioxide directly the way the creation of limestone clinker does. Over time, the material absorbs carbon dioxide and so becomes carbon-negative.


Calera is a company that produces calcium carbonate by bubbling flue gas through sea water. Flue gas is carbon dioxide created by gas-powered power plants (coal-fired plants would work as well). The sea water is a source of calcium and magnesium. The process adds nothing to the water, which can then be desalinated and used or released back into the sea. Waste heat in the flue gas is enough to dry the calcium carbonate, which is then used as a carbon-negative clinker.

This description confuses me because it is exactly the same chemical process by which sea animals create limestone in the first place—and limestone has to be stripped of its carbon in order to become clinker. So why Calera’s artificial limestone does not need to be cooked is not clear to me. Perhaps the process was simply not well explained in the source I found.

Carbon Sciences

Another company creating artificial limestone using flue gas, although Carbon Sciences derive their calcium and magnesium from waste water from mining operations. The company also uses flue gas to force the material to absorb carbon dioxide faster than curing cement normally does, although it is not clear to me whether this process actually increases carbon absorption overall.


Ceratech is a company using fly ash, a byproduct of coal combustion, as clinker. Although dependence of coal would be problematic for a large-scale, long-term replacement for Portland cement, until coal use stops fly ash can serve as clinker at no additional carbon cost. Fly-ash cement is also stronger than Portland cement, so engineers can use less concrete for the same job. It can take longer to set and sometimes contains toxins, however.


CSHub is not a production company but a research group. It is working to understand the chemistry of cement production which is, surprisingly, mysterious except in its general outlines. They are working on a way to reduce the processing temperature for limestone clinker. So far, the problem with the new material is that the raw material is much harder to grind, so the energy requirement and therefore the carbon footprint of initial processing goes up even as the cooking temperature comes down.

So, What’s the Story?

In pointing out details that The Newshour missed, I do not mean to attack PBS. I have discussed the shortcomings of various media outlets before, but I basically like and respect The Newshour staff. I am inclined to think well of them.

But in this case, they missed the story. What they presented as the work of a plucky, isolated inventor, someone who may someday make a different (a feel-good story that requires no public action) is actually just one example of a whole wave of potential solutions to a serious problem that cannot be implemented for want of supportive government policy—remember the legal standards that more or less mandate the use of Portland cement. This is a much more disturbing story, and one that does require public response.

So, the PBS report presented information, information I might not have encountered otherwise –I knew about the carbon footprint of Portland cement, but not that alternatives exist. PBS did not present that information in context so as to tell a story the public really needs to hear.

So, here—I’ll fill in the gap.

Alternative cement requires supportive policy in the same way that alternative energy does and for the same reasons. It is in the public good that these technologies develop to the point where these companies can compete for business on a level playing field. That does not mean that all cement alternatives will actually work as cement or that all cements presented as carbon-neutral actually are—we still need building standards. But we need standards that support the switch to a carbon-sane future rather than inhibiting it.

And we need to stop pretending that the transition is not being deliberately held up. We need to demand actual, committed progress.


Author: Caroline Ailanthus

I am a creative science writer. That is, most of my writing is creative rather than technical, but my topic is usually science. I enjoy explaining things and exploring ideas. I have one published novel and another on the way. I have a master's degree in Conservation Biology and I work full-time as a writer.

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