New technique could make cement manufacturing carbon-neutral

September 28, 2015
Gaurav Sant

Concrete surrounds us in our cities and stretches across the land in a vast network of highways. It's so ubiquitous that most of us take it for granted, but many aren't aware that concrete's key ingredient, ordinary portland cement, is a major producer of greenhouse gases.

Each year, manufacturers produce around 5 billion tons of portland —the gray powder that mixes with water to form the "glue" that holds concrete together. That's nearly three-quarters of a ton for every person on Earth. For every ton of cement produced, the process creates approximately a ton of , all of which accounts for roughly 7 percent of the world's .

And with demand increasing every year—especially in the developing world, which uses much more portland cement than the U.S. does—scientists are determined to lessen the growing environmental impact of portland cement production.

One of those scientists is Gaurav Sant of the California NanoSystems Institute at UCLA, who recently completed research that could eventually lead to methods of cement production that give off no carbon dioxide, the gas that composes 82 percent of .

Sant, an associate professor of civil and environmental engineering and UCLA's Edward K. and Linda L. Rice professor of materials science, found that carbon dioxide released during cement manufacture could be captured and reused. The study is published in the journal Industrial and Engineering Chemistry Research.

"The reason we have been able to sustain global development has been our ability to produce portland cement at the volumes we have, and we will need to continue to do so," Sant said. "But the carbon dioxide released into the atmosphere creates significant environmental stress. So it raises the question of whether we can reuse that carbon dioxide to produce a building material."

During cement manufacturing, there are two steps responsible for carbon emissions. One is calcination, when limestone, the raw material most used to produce cement, is heated to about 750 degrees Celsius. That process separates limestone into a corrosive, unstable solid—calcium oxide, or lime—and carbon dioxide gas. When lime is combined with water, a process called slaking, it forms a more stable compound called calcium hydroxide.

And the major compound in portland cement is tricalcium silicate, which hardens like stone when it is combined with water. Tricalcium silicate is produced by combining lime with siliceous sand and heating the mixture to 1,500 degrees Celsius.

Of the total carbon dioxide emitted in cement manufacturing, 65 percent is released when the limestone is calcined and 35 percent is given off by the fuel burned to heat the tricalcium silicate compound.

But Sant and his team showed that the carbon dioxide given off during calcination can be captured and recombined with calcium hydroxide to recreate limestone—creating a cycle in which no carbon dioxide is released into the air. In addition, about 50 percent less heat is needed throughout the production cycle, since no additional heat is required to ensure the formation of tricalcium silicate.

Sant said the method is analogous to how limestone cementation occurs in nature, where limestone forms the tough exoskeletons of coral, mollusks and seashells, and when microbes form limestone that cements grains of sand together.

Although scientists had examined this idea previously, Sant said it had never been demonstrated before with a view to carbon dioxide-neutral cement production—and that it actually worked faster than he and his colleagues expected. The cycle took just three hours to complete, compared with the more than 28 days needed for portland cement to react with water to near completion and reach its final hardest consistency.

The successful sample was very small, as required by laboratory conditions. But Sant said now that the process has been proven, it could, in time, be scaled up to production levels.

If cement manufacturers continue to operate as they currently do, and if proposed carbon taxes in the U.S. and other nations are eventually enacted, would be much more expensive than it is now. Were that to happen, a new method for producing cement with little or no environmental impact would be of even greater interest, Sant said.

Explore further: Crush those clinkers while they're hot

More information: "Direct Carbonation of Ca(OH)2 Using Liquid and Supercritical CO2: Implications for Carbon-Neutral Cementation" Ind. Eng. Chem. Res., 2015, 54 (36), pp 8908–8918 DOI: 10.1021/acs.iecr.5b02356

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MR166
3 / 5 (2) Sep 28, 2015
"If cement manufacturers continue to operate as they currently do, and if proposed carbon taxes in the U.S. and other nations are eventually enacted, cement production would be much more expensive than it is now. Were that to happen, a new method for producing cement with little or no environmental impact would be of even greater interest, Sant said."

Translation:

There is no real hope of this process ever becoming economically feasible without government interference in the free market.
gkam
1.4 / 5 (9) Sep 28, 2015
This is really great. Many folk do not know the CO2 burden put on us from calcining cement, and the amounts of heat required.

There is no "free market" if one is free to contaminate the air breathed by others. You will be "free" to clean up your act.

But it is the energy saved here which will drive the conversion.
Shakescene21
4.6 / 5 (5) Sep 28, 2015
I hope this research is carried to the next stage. Cement production accounts for a large enough fraction of CO2 emissions (7%) that we are unlikely to stop Global Warming without slashing the CO2 emissions from this sector. A technological breakthrough is needed here, either a less carbon-intensive production method or a substitute for cement that is less carbon intensive.
Since cement is a proven and well-understood building material, it would be preferable to find cleaner production processes than to make a large gamble on unproven substitutes.
katesisco
1 / 5 (1) Sep 28, 2015
What I see here is the reason why we want a carbon tax. The developing nations that need roads to grow economically need the concrete which needs the cement which is going to carry a tax the developed nations never had to pay. For which we will lend them money conditionally.
And i thought the discovery of the crushing of healthy economies in the Middle East cites to deny Europe growing markets was bad.
TheGhostofOtto1923
3.7 / 5 (9) Sep 28, 2015
This is really great. Many folk do not know the CO2 burden put on us from calcining cement, and the amounts of heat required.

There is no "free market" if one is free to contaminate the air breathed by others. You will be "free" to clean up your act.

But it is the energy saved here which will drive the conversion.
Thanks for restating the info in article. It gives the impression that you know something about the subject.

Tricks of the trade.

"They pick professions in which the requisite skills are easy to fake, the jargon is easy to learn, and the credentials are unlikely to be thoroughly checked. Psychopaths find it extremely easy to pose as financial consultants, ministers, psychological counselors and psychologists. And that's a scary thought."

IMO...
gkam
1.4 / 5 (9) Sep 28, 2015
Anyone who has worked with cement calciners can see how to do this, mostly by closing up the ends of the rotating calciner, instead of just operating as an open tube. The rest of industry has cleaned up their act, and it is time they found this way for the cement manufacturers.
antigoracle
3 / 5 (4) Sep 28, 2015
.... by closing up the ends......, instead of just operating as an open tube.

Could someone close up gskam ends and stop his noxious emissions.
Thanks.
MR166
1 / 5 (2) Sep 28, 2015
Am I the only one who cannot understand this process as written in the article?

One paragraph states that lime stone is processed, converted into lime and then converted into calcium hydroxide by the addition of water.

The next paragraph states that cement is produced by combining sand with lime. No calcium hydroxide is used.

The last paragraph combines the captured Co2 and combines it with calcium hydroxide to create limestone again.

So in essence they are taking limestone adding heat and and then water and creating calcium hydroxide. Then they take Co2 and create the original limestone again.

How is this not similar to one men digging a ditch and another right behind him filling it in?????
Uncle Ira
3.5 / 5 (11) Sep 28, 2015
Anyone who has worked with cement calciners can see how to do this,


When you were working with the cements stuffs what kind of senior engineer were you then?

Oh yeah, I almost forget. While you are answering that one, could you also tell me about what I asked about five or four times before. You know how you always are asking me to ask you something, well here ol Ira-Skippy goes. Why did the peoples over at the Walmart banneded you from coming in there? Was it just that one Walmart or does that mean you can not go to any Walmart anywhere?

Oh yeah, I almost forget another thing. Pressing my luck yet Cher? Okayeei, so I take it by the quality of all your comments, that you must have been to some sort of college for a diploma,,, did you and Sarah Palin go to the same colleges at the same time together and get the same kind of diplomas together too?
MR166
1 / 5 (4) Sep 28, 2015
You see, anyone working industries that are 100s of years old know that the processes in place make the most efficient use of energy an resources that is humanly possible. THAT is why they are still in business and paying salaries. Yup, every once in a long while someone reinvents the wheel and things change. Other than true breakthroughs, things change only due to changes in government regulations. Regulations can be emotional and are not necessarily based on reality.
EyeNStein
5 / 5 (1) Sep 28, 2015
This is not a new process at all. They have just re-produced the "Lime mortar" that the Romans invented. Albeit with a quicker process involving liquefaction and reintroduction of CO2. https://en.wikipe...e_mortar

Its not strong enough for tall concrete or cast block bridges but its an excellent match for the soft stone or terracotta constructions (like Romans built) which have lasted thousands of years.
TheGhostofOtto1923
3.7 / 5 (9) Sep 28, 2015
Anyone who has worked with cement calciners can see how to do this, mostly by closing up the ends of the rotating calciner, instead of just operating as an open tube. The rest of industry has cleaned up their act, and it is time they found this way for the cement manufacturers.
2 other threads where george pretended to know something about calcimers.
http://m.phys.org/comments/351861555/
http://m.phys.org/comments/334476569/

-They didnt go very well either.
denglish
2.6 / 5 (5) Sep 28, 2015
Banned from Walmart? really?
gkam
1 / 5 (9) Sep 28, 2015
Well, put me in a piro and call me a goober, . . is that what they told you and the Missus last time you got lost in Wal*Mart? I avoid Wal*Mart, as killers of free enterprise through brute economic force. But I guess you folk are impressed with the choice of gator-skin boots.

No, but it is a funny line, if you assume we are all alike.
gkam
1.4 / 5 (10) Sep 28, 2015
I will tell you once again, Toots. My work at PG&E was for the customer, not our own stuff, except in some special requests. I went into the facilities of our customers for energy services, giving in-depth energy analyses, arranging financing, and troubleshooting power problems. In our 94,000 square mile service territory we had everything. Ain't like the Bayou.

BTW, drop the Delta Goober act. The engineers with whom I worked at Mississippi Power, Alabama Power, Gulf, Georgia Power, Southwest Electric Power, and others were some of the best I have seen, and would be embarrassed to see you try that tourist stuff.
Uncle Ira
3.9 / 5 (11) Sep 28, 2015
I will tell you once again, Toots.


Well you did not need to say that because we knew you would. Those letters you wasted because you could have used them to not answer the questions asked and tell us all about you.

My work at PG&E BUNCH OF BRAGGING AND STRUTTING GOES HERE.


Here we go again with more of that silliness and foolishment.

How come you can write all those words when you are talking about you and only one line bumper sticker slogans when you talk about the articles? Why that is Cher?

So I guess you are not going to tell us why you got the boot at the Walmart? I really wanted to hear about that one if you are going to be talking about you anyway.
KeithMcC
not rated yet Sep 28, 2015
Am I the only one who cannot understand this process as written in the article?

Me too. (The article is aUCLA press release.)
http://newsroom.u...-neutral
MR166
2.3 / 5 (3) Sep 28, 2015
A UCLA press release eh! No wonder college graduates are unable to find work.
TheGhostofOtto1923
3.7 / 5 (9) Sep 29, 2015
BTW, drop the Delta Goober act. The engineers with whom I worked at blahblah
BTW drop the expert act. Did you tell those engrs you allegedly worked with that you were an engr as well? Did you get fired from that job as well?

This is after all how causality works. Too bad you're incapable of appreciating it.

You've been found out here. You're a liar and a cheat. You lied about your degree and many other things didn't you?

As long as you participate here readers will be reminded of the kind of lowlife you are. And they will be shown the evidence that you yourself have posted, which demonstrates this.

Pretend all you want. We know what you are and what you are capable of.
gkam
1 / 5 (8) Sep 29, 2015
417 nm light?

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