From the “settled science” department and the University or California Irvine, comes this inconvenient fact. For years we’ve been told by academics that cement is another nasty global warming contributor, because of CO2 released during production.
“Cement manufacturing is responsible for 5 to 8 percent of global CO2 emissions,” notes Del Gado, a theoretical physicist who is part of Georgetown’s Institute for Soft Matter Synthesis and Metrology. “Although there have been calls for creating so-called ‘green cement,’ the sustainability and science communities have yet to find a way to reduce CO2 emissions while retaining the efficiency, durability and cost efficiency of cement. Our study could help change that.”
Now, not so much.
Concrete jungle functions as carbon sink, UCI and other researchers find
Cement-based materials eventually reabsorb much of the CO2 released during creation
Steven Davis / UCI
Irvine, Calif. – 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.
Davis and his fellow researchers looked at the problem from a different angle. They investigated how much of the gas is removed from the environment over time by buildings, roads and other kinds of infrastructure. 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.
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From the following Science mag link, a missing phrase appears (4.5 gigatons carbon OR MORE THAN 16 GIGATONS OF CO2…).
http://www.sciencemag.org/news/2016/11/cement-soaks-greenhouse-gases
“The researchers estimate that between 1930 and 2013, cement has soaked up 4.5 gigatons of carbon or more than 16 gigatons of CO2, 43% of the total carbon emitted when limestone was converted to lime in cement kilns, they report online today in Nature Geoscience. That’s more than 20% of the carbon soaked up by forests in recent decades, they write.”
Since the limestone to lime contribution was about half the total, the rest being fossil fuels, the 43% number would be cut in half to about 20% of the total CO2 getting clawed back by the reabsorbtion.
I tried the link to the original paper in the Science mag but got a 404 notification.
I
4.5 Gtn out of 38.2 gigatons released hardly a game changer, is it?
“Cement has gotten a lot of attention for its sizable contribution to global climate change, …”
No, it may have made a sizeable contribution to human emissions, period.
Of about 1 degree C of warming which may have occurred since 1850, something like half is allegedly attrubutable to human influence, much of that is land use and other factors, not CO2. So lets say 0.3 , of which concrete is 5-8%.
That makes 0.015 to 0.024 or 15 to 24 MICROKELVIN of “global warming”.
Sizeable, not really.
The sinks in my house are porcelain, except for one that’s stainless steel.
Where do you go to buy one of these carbon sinks?
from a carbon trader , of course !
“The researchers estimate that between 1930 and 2013, cement has soaked up 4.5 gigatons of carbon or more than 16 gigatons of CO2, 43% of the total carbon emitted when limestone was converted to lime in cement kilns”
Yes, that sounds about right. As so often, the headline here is misleading. Concrete isn’t a net sink; 43% of the original emissions are eventually reabsorbed.
As many have mentioned, none of this is new. The idea of cement is that you heat limestone to drive of the acid part, CO₂, leaving the base CaO. This is then mixed with silica (acid) with the intent that it will over time form calcium silicate. But some recombines with CO₂ to reform carbonate.
Stokes,
Your chemistry lesson leaves something to be desired. If you pulverize limestone and wet it to determine the pH, it will be alkaline. If one adds acid, CO2 will be driven off. The CO2 only appears to be acidic when it reacts with water to form carbonic acid, and the CO2 plays the part of the anion. The acidic property is the result of hydrogen ions, supplied by the water, in excess of what is found in pure water. While silica-rich rocks are often called “acidic” by geologists, they are so insoluble that the concept of pH (i.e. “acidity’) is inapplicable. Hydrogen ions have a positive charge. in the calcium silicate, the calcium has a positive charge and the silica has a negative charge.
” The acidic property is the result of hydrogen ions, supplied by the water”
My chemistry isn’t weak. Yours is out of date. G.N. Lewis figured this out in 1923. An acid is an electron pair acceptor. CO₂ is an acid, CaO a base (donor), and
CaO + CO₂ → CaCO₃
is a simple acid-base reaction.
Nick,
“Although the Brønsted–Lowry concept of acids and bases as donors and acceptors of protons is still the most generally accepted one, other definitions are often encountered. Certain of these are adapted for special situations only,” i.e. your Lewis Theory.
“Numerous lengthy polemical exchanges have taken place regarding the relative merits of the Brønsted–Lowry and Lewis definitions. The difference is essentially one of nomenclature and has little scientific content. In the remainder of this article the term acid is used to denote a proton donor (following the Brønsted–Lowry terminology), whereas the term Lewis acid is employed exclusively to refer to electron-pair acceptors. This choice is based partly on the logical difficulties mentioned in the last paragraph and partly on the fact (see below Acid–base equilibria) that the quantitative description of acid–base reactions is much simpler when it is confined to proton acids. It also represents the commonest usage of the terms.”
You can take it up with Encyclopedia Britannica: https://www.britannica.com/science/acid-base-reaction/Alternative-definitions
In order for cement to be carbon-neutral, it must be made without burning carbon-based fuels and it must entirely convert back to carbonate. Good luck with it becoming carbonate while still being useful as cement. As the amount of concrete in use in the world grows, so does the amount of CO2 released from converting carbonate to oxide/hydroxide, plus the CO2 produced by burning fuel to produce cement.
The ancient Egyptians knew this – that’s why they mined and moved stone blocks by gangs of slaves instead of internal combustion vehicles. Maybe the pyramids were really carbon sequestration devices?
Here is the full abstract. The paper (actually a letter) is by Xi et al.
Calcination of carbonate rocks during the manufacture of cement produced 5% of global CO2 emissions from all industrial process and fossil-fuel combustion in 2013. Considerable attention has been paid to quantifying these industrial process emissions from cement production, but the natural reversal of the process—carbonation—has received little attention in carbon cycle studies. Here, we use new and existing data
on cement materials during cement service life, demolition, and secondary use of concrete waste to estimate regional and global CO2 uptake between 1930 and 2013 using an analytical model describing carbonation chemistry. We find that carbonation of cement materials over their life cycle represents a large and growing net sink of CO2, increasing from 0.10 GtC yr−1 in 1998 to 0.25 GtC yr−1 in 2013. In total,we estimate that a cumulative amount of 4.5 GtC has been sequestered in carbonating cement materials from 1930 to 2013, offsetting 43% of the CO2 emissions from production of cement over the same period, not including emissions associated with fossil use during cement production. We conclude that carbonation of cement products represents a substantial carbon sink that is not currently considered in emissions inventories.
Full paper here.
https://dl.dropboxusercontent.com/u/75831381/Xi%20Substantial%20global%20carbon%20uptake%20by%20cement%20carbonation.pdf
“Sheesh, I’ve known that for at least 20 years. And I’ve never bothered to actually study this subject.”
This explains why some are not very good at telling the truth. They read a headline that supports their agenda and do not bother with further study.
There are many environmental impacts besides the trivial climate change issue. While the science in the paper is interesting, it is just a small piece of the puzzle.
Concrete absorbs carbon dioxide and stores it in a process commonly called carbonation. This process gradually hardens up the concrete and is part of its curing process. Carbon dioxide may be absorbed by concrete in many forms such as buildings, bridges and pavements . Concrete does not have to be directly exposed to the atmosphere for this process to occur. Underground concrete piping, tunnels and foundations can absorb CO2 from the air in the soil, and from underground and underwater applications absorb dissolved carbon dioxide (carbonates) present in groundwater, freshwater, and saltwater. Concrete just keeps on giving, as the Romans knew.
But there is no real evidence that CO2 affects climate. There is no such evidence in the paleoclimate record. There is plenty of scientific rational that the climate sensivity of CO2 is really zero. It is all a mater of science.
When C02 and H20 combine they form HC03 Carbonic Acid
“Carbonation by Contact with Water
Natural waters usually have a pH of more than 7 and seldom less than 6. Even waters with a pH greater than 6.5 may be aggressive if they contain bicarbonates. Any water that contains bicarbonate ion also contains free carbon dioxide, which can dissolve calcium carbonate unless saturation already exists. Water with this aggressive carbon dioxide acts by acid reaction and can attack concrete and other portland cement products whether or not they are carbonated. A German specification, DIN 4030, includes both criteria and a test method for assessing the potential of damage from carbonic acid-bearing water. ”
http://www.cement.org/for-concrete-books-learning/concrete-technology/durability/acid-resistance
“Natural waters usually have a pH of more than 7 and seldom less than 6.”
This statement is correct for surface water. However it is often wrong for well water. PH levels for well water can be as low a 4. IF there is a volcanic source of CO2 PH can reach 3. This drop is mainly from CO2 absorbed by rain. If the rain water moves quickly down through the soil all the CO2 it picked up from the air makes it to the aquifer. This acidic water picks up a lot of minerals from the soil and rock forming hard water. When the water reached the surface the excess CO2 is quickly lost costing the PH to up. The water then becomes supper saturated with minerals which then deposits on faucets,sink and and other things
i thought it mattered how the cement was made. what ratios used, before there would be any carbon dioxide getting locked up in it over years. got enough lime? check. is this study saying there’s a net gain? more back than spent? how are they making their concrete? using an efficient process? they’re not using hempcrete are they? because that’s cheating. ;D sucks up carbon dioxide to grow the stuff, and sucks up more as it ages and hardens.
Concrete is calcium hydroxide and as long as it is “in use”, i.e. serves as structural element of buildings, most of it stays as calcium hydroxide with only few mm on the surface getting carbonated by atmospheric CO2. The depth of carbonation is proportional to square root of time, such as 1 mm in a year, 3 mm in nine years, 5 mm in 25 years. Given usual thickness of concrete walls and slabs, it’s negligible part of the volume in any reasonable timeframes.
http://www.understanding-cement.com/carbonation.html
Lime is also a key ingredient in many, many water treatment plants.
We add lime to water to change the calcium bicarbonate to calcium carbonate.
Calcium bicarbonate is very soluble in water and causes “hardness”. Calcium carbonate is not very soluble in water and settles out. (Making rock from water?8-)
We then add, you guessed it, CO2 back into the water to change the remaining, soluble calcium carbonate, back into the very soluble calcium bicarbonate so that it doesn’t settle out in the distribution system.
We currently get our CO2 from ethanol production.
I suppose we could get it from lime production if those older plants were set up to collect it, but then, what would the ethanol producers do with all their CO2? They are “saving the planet” after all.
I didn’t deep read the article, only skimmed the abstract, but the impression I got is previously studies under-estimate the CO2 reduction in the conversion from silicates to carbonates in both the cement and the concrete aggregate. This makes sense to me as concrete is much more porous than your typical silicate rock.
Well, duh! (What else can be said about something so obvious?)
Whoops indeed.
There’s a huge error in the article. CO2 can’t contribute any alteration to climate. There’s a law of thermodynamics written specifically for gases. CO2 can’t affect climate, and that’s why the thermo-billies who believe in it show such allergic reaction to the real science of atmospheric chemistry.
So something analogous to silicate weathering – the process by which newly exposed rock from tectonic activity absorbs CO2 – also happens in concrete? These weathering processes, if unopposed by processes like volcanic eruption and human burning of fossil fuel, will eventually kill off life on earth through CO2 starvation.
I put the blockquote wrong…
Question was: what about the remaining 57 %?
The folks at Biosphere II figured this out a long time ago…
It is not just cement that absorbs CO2. When alumni oxide is converted to metal, a waist byproduct called red mud is produced. This mud contains iron,, sodium, calcium, and magnesium that was originally trapped in the aluminum oxide ore. This sodium, calcium, and magnesium also absorbs CO2. Possibly much faster than in concrete. Also mining breaks up rock into fine particles And atoms in the mine tailing starts to react with air pulling more CO2 out of the air.
As far as I know no one has calculated how much CO2 is removed by these activities.
Strikes me that calculating the net sink or source of things like this is nearly impossible. The errors and feedbacks and unknowns dwarf the results.