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Author Topic: Concrete - CO2 Villain or Solution?  (Read 455 times)

Bob Wallace

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Concrete - CO2 Villain or Solution?
« on: July 18, 2017, 05:52:03 PM »
"The concrete industry is one of two largest producers of carbon dioxide (CO2), creating up to 5% of worldwide man-made emissions of this gas, of which 50% is from the chemical process and 40% from burning fuel." - Wiki

Is this fixable?  Or even as bad as is commonly believed?

Cement manufacturing is among the most carbon-intensive industrial processes, but an international team of researchers has found that over time, the widely used building material reabsorbs much of the CO2 emitted when it was made.

"It sounds counterintuitive, but it's true," said Steven Davis, associate professor of Earth system science at the University of California, Irvine. "The cement poured around the world since 1930 has taken up a substantial portion of the CO2 released when it was initially produced."

For a study published today in Nature Geoscience, Davis and colleagues from China, Europe and other U.S. institutions tallied the emissions from cement manufacturing and compared them to the amount of CO2 reabsorbed by the material over its complete life cycle, which includes normal use, disposal and recycling. They found that "cement is a large, overlooked and growing net sink" around the world - "sink" meaning a feature such as a forest or ocean that takes carbon dioxide out of the atmosphere and permanently tucks it away so that it can no longer contribute to climate change.

Cement manufacturing is considered doubly carbon-intensive because emissions come from two sources. CO2 molecules are released into the air when limestone (calcium carbonate) is converted to lime (calcium oxide), the key ingredient in cement. And to generate the heat necessary to break up limestone, factories also burn large quantities of natural gas, coal and other fossil fuels.

 Through a process called carbonation, CO2 is drawn into the pores of cement-based materials, such as concrete and mortar. This starts at the surface and moves progressively inward, pulling in more and more carbon dioxide as years pass.

More than 76 billion tons of cement was produced around the world between 1930 and 2013, according to the study; 4 billion tons were manufactured in 2013 alone, mostly in China. It's estimated that, as a result, a total of 38.2 gigatons of CO2 was released over that period. The scientists concluded, however, that 4.5 gigatons - or 43 percent of emissions from limestone conversion - were gradually reabsorbed during that time frame.

"Cement has gotten a lot of attention for its sizable contribution to global climate change, but this research reinforces that the leading culprit continues to be fossil fuel burning," Davis said.

https://www.eurekalert.org/pub_releases/2016-11/uoc--cjf111516.php


Adding basalt or olivine to the mix should increase CO2 absorption.  Basalt fibers are already added to some concrete in order to strengthen it.  Adding basalt fiber can reduce or eliminate the need for rebar (another CO2 source) and make the concrete less likely to crack. 

An advanced materials manufacturer in Calumet, Michigan, Neuvokas (Finnish for “resourceful”) blends purchased fiber and internally formulated resin at high speeds to produce lightweight basalt fiber-reinforced polymer that is cost-competitive with traditional steel counterparts and also preferable to ordinary fiber rebar. Similar in chemical composition to glass fiber, basalt fiber is stronger and highly resists alkaline, acidic, and salt deterioration. Basalt rebar can also tolerate higher temperatures and more abrasion. Lack of developed standards for the product have held up its general institution.

Here are some of the other advantages of the Neuvokas product:

100X increase in production speeds of basalt rebar compared to current FRP production,
Price parity with steel,
Immunity to rust,
Increased tensile strength,
7X weight reduction with basalt rebar, and
Capability of using 30% less concrete.

http://cleantechnica.com/2014/11/06/neuvokas-basalt-rebar-lighter-stronger-cost-steel/


Bob Wallace

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Re: Concrete - CO2 Villain or Solution?
« Reply #1 on: July 18, 2017, 05:53:46 PM »
a team of MIT researchers, led by senior researcher Roland Pellenq, decided to take a closer look at the cement mix, going down to molecular level.  They questioned the standard calcium to silica ratio of 1.7, which is commonly accepted as the one resulting in the most stable and strong cement.

After conducting a series of experiments, however, the team established that the optimal calcium-to-silica clay ratio should in fact be 1.5. Not only that the final product has incredible mechanical resistance , which is double the one achieved with a ratio of 1,7, and it is much less prone to fracturing, but also the team estimated a reduction in carbon dioxide emissions from the manufacturing process of up to 60%.

https://www.greenoptimistic.com/mit-researchers-cook-eco-friendly-cement-20140929/#.WW4lyYjyvIV

Bob Wallace

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Re: Concrete - CO2 Villain or Solution?
« Reply #2 on: July 18, 2017, 06:11:32 PM »
And now, in a new paper in Science, representatives of Reykjavik Energy and a team of scientists from a large number of universities, including the University of Southampton in the U.K. and the Lamont-Doherty Earth Observatory at Columbia University, show not only that the process of injecting carbon dioxide into basalt rock at the Iceland site works, but that moreover, the carbon dioxide is mineralized, or turned into rock, very rapidly. In two years, they report, over 95 percent of injected carbon dioxide had become mineral.

“We demonstrate that by using this method, you can permanently remove the CO2, store it in the rock, and the rock isn’t going anywhere, it stays there for geological timescales,” adds Edda Aradottir, who works with Reykjavik Energy and is also an author of the study. “So I would hope that other types of industries would be interested in this method.”

The finding could be quite important because of the ubiquity of basalt in the world. The researchers say that 10 percent of the rocks that make up continents are basalt, and so is “most of the ocean floor.”

https://www.washingtonpost.com/news/energy-environment/wp/2016/06/09/scientists-in-iceland-have-a-solution-to-our-carbon-dioxide-problem-turn-it-into-stone/?utm_term=.82b8b505be24


Hefaistos

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Re: Concrete - CO2 Villain or Solution?
« Reply #3 on: July 18, 2017, 09:56:13 PM »
"The concrete industry is one of two largest producers of carbon dioxide (CO2), creating up to 5% of worldwide man-made emissions of this gas, of which 50% is from the chemical process and 40% from burning fuel." - Wiki

An additional aspect of concrete, is that after its use in building things, it starts to carbonate, i.e. it takes up CO2 in a process that lasts for decades.
"The carbonation depth is approximately proportional to the square root of time. For example, if the carbonation depth is 1mm in a one-year-old concrete, it will be about 3mm after 9 years, 5mm after 25 years and 10mm after 100 years."

http://www.understanding-cement.com/carbonation.html

"...the concept that the world’s concrete infrastructure could provide the single largest human-made carbon sink has genuine scientific merit."
However, the extent of carbonation is less understood, it remains to be quantified how much CO2 concrete actually absorbs over its lifecycle.

http://www.sustainableconcrete.org.nz/page/co2-absorption.aspx

Hefaistos

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Re: Concrete - CO2 Villain or Solution?
« Reply #4 on: July 18, 2017, 10:00:43 PM »
Here are some interesting results from research on concrete carbonation, showing that more than 50% of CO2 emitted during production of cement is later absorbed during the lifecycle of concrete.

The CO2 balance of concrete in a Life Cycle perspective
by K.O. Kjellsen (Norcem), M. Guimaraes (Aalborg Portland) and Å. Nilsson (Cementa), published by Danish Technological Institute, Denmark

Abstract
The amount of atmospheric carbon dioxide absorbed in Nordic concrete structures over a 100 year period has been calculated. The CO2 uptake, or carbonation, occurs gradually and was calculated for an initial service life period of 70 years followed by a 30 year post-demolition period. The processing of demolished concrete to recycled concrete aggregates increase the CO2 uptake, this was taken into account in the calculation of the total CO2 uptake.

Over 100 years, one year of Nordic concrete construction is calculated to absorb 0.34, 0.22, 0.24 and 0.021 million metric tons of CO2 in Denmark, Norway, Sweden and Iceland, respectively. These are quite notable numbers, and imply that about 0.5% of the total national CO2 emissions will be re-absorbed in concrete in Denmark, Sweden and Norway. The corresponding number for Iceland is about 1%. The calculations show that up to 30% of the total CO2 emission from cement production, or up to 57% of the CO2 emission from the so-called calcination process in cement manufacturing, is re-absorbed when the cement is utilized in concrete construction in the Nordic countries.

https://www.dti.dk/reports-on-co2-uptake-from-the-carbonation-of-concrete/co2-balance/18487,6

Bob Wallace

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Re: Concrete - CO2 Villain or Solution?
« Reply #5 on: July 18, 2017, 11:29:24 PM »
Much of the CO2 problem seems to come from heat processing materials.  Currently fossil fuels are used for the heat source.  I wonder if we could have electric furnaces processing the limestone?

...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.

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.

https://phys.org/news/2015-09-technique-cement-carbon-neutral.html#jCp

Aluminum smelters operate at 960 °C.  And they use electricity, not FF.




TerryM

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Re: Concrete - CO2 Villain or Solution?
« Reply #6 on: July 19, 2017, 01:20:13 AM »
Here are some interesting results from research on concrete carbonation, showing that more than 50% of CO2 emitted during production of cement is later absorbed during the lifecycle of concrete.

The CO2 balance of concrete in a Life Cycle perspective
by K.O. Kjellsen (Norcem), M. Guimaraes (Aalborg Portland) and Å. Nilsson (Cementa), published by Danish Technological Institute, Denmark

Abstract
The amount of atmospheric carbon dioxide absorbed in Nordic concrete structures over a 100 year period has been calculated. The CO2 uptake, or carbonation, occurs gradually and was calculated for an initial service life period of 70 years followed by a 30 year post-demolition period. The processing of demolished concrete to recycled concrete aggregates increase the CO2 uptake, this was taken into account in the calculation of the total CO2 uptake.

Over 100 years, one year of Nordic concrete construction is calculated to absorb 0.34, 0.22, 0.24 and 0.021 million metric tons of CO2 in Denmark, Norway, Sweden and Iceland, respectively. These are quite notable numbers, and imply that about 0.5% of the total national CO2 emissions will be re-absorbed in concrete in Denmark, Sweden and Norway. The corresponding number for Iceland is about 1%. The calculations show that up to 30% of the total CO2 emission from cement production, or up to 57% of the CO2 emission from the so-called calcination process in cement manufacturing, is re-absorbed when the cement is utilized in concrete construction in the Nordic countries.

https://www.dti.dk/reports-on-co2-uptake-from-the-carbonation-of-concrete/co2-balance/18487,6


So - - - We will save, and have been saving between .005 and .01 of the CO2 emitted in some of the smaller cold countries because of concrete reabsorption. Why doesn't this give me a warm feeling of relief?


Terry

Bob Wallace

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Re: Concrete - CO2 Villain or Solution?
« Reply #7 on: July 19, 2017, 02:23:11 AM »
up to 57% of the CO2 emission from the so-called calcination process in cement manufacturing, is re-absorbed when the cement is utilized in concrete construction in the Nordic countries.

I read that as concrete being only half as bad as we thought it was.  If we could use RE for the heat source during manufacturing we might be able to get concrete down to carbon neutral.

I'm not sure that Nordic has anything to do with the larger picture.  It's just where the study was run.  I don't see how location would increase carbon uptake unless heat is a catalyst.  And that suggests that things might be better in hotter locations.


Tor Bejnar

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Re: Concrete - CO2 Villain or Solution?
« Reply #8 on: July 19, 2017, 03:23:37 AM »
By corollary, I think (I know a little about olivine, not concrete), a warmer climate will likely make it faster.
Arctic ice is healthy for children and other living things.

ghoti

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Re: Concrete - CO2 Villain or Solution?
« Reply #9 on: July 19, 2017, 05:37:44 AM »
There's been some hype about a process to add CO2 back into concrete when it is mixed to capture the carbon and strengthen the concrete. Not clear how much extra carbon storage this can account for.


http://carboncure.com/


johnm33

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Re: Concrete - CO2 Villain or Solution?
« Reply #10 on: August 05, 2017, 01:00:51 PM »
From https://www.geopolymer.org/news/visit-airport-eco-building/
This project marks a very significant milestone in engineering – the world’s largest geopolymer concrete project. BWWA was built with approximately 40,000 m3 (100,000 tonnes) of geopolymer concrete making it the largest application of this new class of concrete in the world. The geopolymer concrete developed by the company Wagners, known as Earth Friendly Concrete (EFC), was found to be well suited for this construction method due to its high flexural tensile strength, low shrinkage and workability characteristics. Heavy duty geopolymer concrete, 435 mm thick, used for the turning node, apron and taxiway aircraft pavements, welcomes a heavy 747 cargo for regular air traffic between Toowoomba-Wellcamp BWWA airport and Hong Kong. For technical details read the paper by Glasby et al. (2015), EFC Geopolymer Concrete Aircraft Pavements at Brisbane West Wellcamp Airport, in our Library, Technical paper #23 GP-AIRPORT. Technical Paper on Geopolymer Aircraft Pavement
 They make a clear distinction between geopolymer and alkili activated materials, and for anyone interested in historic building techniques, or new possibilities, valuable insight. I'm not in a position to judge but their approach appears to be far less energy intensive and with a superior product, exploring the use of natural materials to a greater extent.
https://www.geopolymer.org/