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Monday, 25 May 2009

Concrete Up-dates

This post follows naturally from my two previous posts on CO2 reduction in Concrete manufacturing and use throughout it's life-span. The figure opposite sums-up much of what has be written previously and is taken from a full well presented article in the NYT of 11 April 2009 entitled Concrete Is Remixed With Environment in Mind.

As often quoted in my pages (Napoleon) "A good drawing is worth more than a long discourse" the reader is cordially invited to consult the figure-click to enlarge.

The article is an excellent paper for public understanding of cement and concrete. All sort of careful chemistry is going on: Some add silica fume industrial waste which improves impermeability and gives reinforced steel bars corrosion protection from road salts. Some add titanium oxide to accelerate oxidation which breaks down organic airborne pollutants so producing a permanently attractive white surface.

NYT reporter Henry Fountain, goes much further than the scientists reported in my earlier post and introduces NYT readers to the much more heartening and ambitious aim of "reversing the manufacturing CO2 emissions equation" to achieve a negative carbon emissions, or overall absorption during the "concrete life-cycle", by both reducing the emissions during production and absorption of CO2 during it's useful life.

"Some researchers want to eventually eliminate Portland cement entirely and replace it with other cements to produce zero-carbon, or even carbon-negative, concrete."

Dr. Brent R. Constantz, company founder, of Calera does not describe Calera as a cement company:

“We’re primarily driven by the need to capture large amounts of CO2 and sequester it,”

NB. The high standard fall-out from Dr. Constantz, background in cements, having made specialty products for use in orthopedic surgery. But he

Back-ground from from NYT- cement manufacture basic process:

"Portland cement is at the heart of concrete’s environmental problems. About a ton of CO2 is emitted for every ton of cement produced. The basic manufacturing process involves burning limestone and other minerals at about 2,700 degrees Fahrenheit(about 1480°C) to create an intermediate product called clinker.

“Essentially, we’re trying to make the same minerals that they did in 1825,” said Mr. Stehly, who is head of a committee addressing sustainability issues at the American Concrete Institute.

The cement industry, particularly in the United States and Europe, has reduced CO2 emissions through the use of more efficient kilns and processes, and is now allowed to add some ground unburned limestone to the clinker, reducing the actual cement in the mix. But about half of the CO2 from cement cannot be eliminated — it is produced in the reaction, called calcination, that occurs as the limestone (which consists of calcium carbonate) is being burned."



NYT points to two innovative companies, strongly engaged in this adventure:

1. Calera Corporation, is developing a process to bubble gas-fired electric power plant flue gases through seawater or other brackish water, using the CO2 in the gases to precipitate carbonate minerals for use as cement or aggregates in concrete. The process mimics, to some extent, what corals and other calcifying marine organisms do.

2. Carbon Science associated with Novacem, a British start-up, is developing a cement that does not use carbonates and can make concrete that absorbs carbon dioxide.


1. Calera Corporation,

At a site adjacent to a gas-fired electricity generation plant in Moss Landing, Calif., the Calera Corporation is developing a process to bubble power plant flue gases through seawater or other brackish water, using the CO2 in the gases to precipitate carbonate minerals for use as cement or aggregates in concrete. The process mimics, to some extent, what corals and other calcifying marine organisms do.

Calera calculates that producing a ton of these minerals consumes half a ton of CO2, so the resulting concrete could potentially be carbon negative — sequestering carbon dioxide permanently.

Brent R. Constantz, the company’s founder, has a background in cements, having made specialty products for use in orthopedic surgery. But he does not describe Calera as a cement company. “We’re primarily driven by the need to capture large amounts of CO2 and sequester it,” he said.

The company probably will begin by making aggregate, because the barriers to making a commercially acceptable product are lower than with cement. Even with aggregate, any new product must meet standards and must be accepted by the concrete industry, which can be conservative. “Any time you introduce anything new,” Dr. Constantz said, “it’s a challenge.”

More about Calera in Scientific American[pdf].

2. Carbon Science associated with Novacem, a British start-up, is developing a cement that does not use carbonates and can make concrete that absorbs carbon dioxide.


"To reduce concrete’s carbon footprint to near zero or less, different approaches are needed. Novacem, a British start-up, is developing a cement that does not use carbonates and can make concrete that absorbs carbon dioxide. Carbon Sense Solutions, in Halifax, Nova Scotia, wants to bubble CO2 through wet cement, sequestering the gas through carbonation (a process that occurs naturally, though very slowly, under normal conditions)."

My professional house journal, Materials World, almost a year earlier (7 months ago) in their news report entitled Concrete carbonation,MW 01 Oct. 2008 described the above second highly innovative company(2) in a balance way.

The pros (a) and cons(b)
a)The pros:

Combustion flue gases will be redirected to the curing process. The resulting effluent is scrubbed of CO2 in under an hour. The gas is stored in the concrete as calcite with no further reactions occurring.

‘Calcite, otherwise known as limestone, is the process feedstock for cement. We are simply reverting it back to its natural and most stable state. You can call this cradle-to-cradle engineering,’ says Robert President of Carbon Sense Solutions. The material is said to store up to half the weight of cement as CO2.

Niven is guarded about revealing more about the process, but says, compared to previous efforts at concrete carbonation, this work involves ‘a new reactor design that achieves complete carbonation, faster processing and improved material properties [faster early strength development, lower permeability, reduced shrinkage cracking and efflorescence resistance]’.

b) The cons:

However, concrete and cement science expert Dr Charles Fentiman of Fentiman Consulting in Southwater, UK, is sceptical about the ability to achieve complete carbonation during curing. He reserves judgement until the work is taken out of the laboratory and shown to overcome the practical problems that have impeded academics and industry for decades.

He says, ‘This seems to be an idea of making concrete elements and giving a warm cure in CO2. [But] in my experience, as soon as cement hydration starts, the CO2 coats everything and blocks further hydration. It does accelerate hardening, but then ongoing strength development is low and the concrete remains porous because hydration is blocked’.

Fentiman explains that academics have previously tried to overcome this through super-critical carbonation after the concrete has cured and the cement hydrated. However, ‘this would greatly slow the manufacturing process and the extra cost would need to be covered by the end user’.

Prepare for the worst but hope for the Best.




Sunday, 24 May 2009

Link: Innovation_Two Commented Videos not to be Overlooked_Your Company (profit and loss) and even Country (Survival) bottom lines in Greatest Danger!

Link
Conversations-on-Innovations: Innovation_Two Commented Videos not to be Overlooked_Your Company (profit and loss) and even Country (Survival) bottom lines in Greatest Danger

Concrete Thinkers_Putting CO2 emissions into perspective_but how sucessful are they in this?

In my previous post, I recommended, from my scant readings of non-metallic materials, The Portland Cement Association ,Concrete Thinkers _ page and mentioned in my post, what I saw as short comings in several science news releases from the scientific community.

Specifically, I felt that the scientific teams mentioned lacked commitment and resolve in setting their sights and hence their objectives to the highest levels, ie. choosing near zero-carbon emissions and not categorically "zero-carbon emissions". [Either the scientists in question appeared to lack commitment and resolve in setting their objectives or having seen how difficult getting results from the lab. to full scale in industrial ( socio-economic) practice preferred to remain modest and prudent, I did not know. But we shall see in posts to follow that more ambitious approaches seek not only to achieve zero-emissions but carbon negative standards ie. CO2 absorption rather than emissions.]

Back to Concrete Thinkers site,while it does give a good summary of the state of the art, progress and approaches which now lead to 2% or less CO2 emissions with referenced white papers, the paragraph which caught my eye for future reference was as in the title of my current post title "Putting CO2 emissions into perspective". Upon a second reading with intent to blog I found the paragraph guilty of many of the faults over and above the use of non- International standard Organisation (ISO) units. The paragraph leads the reader to believe that one will gain a much more balance view of activities leading to specific and CO2 emissions based on units and comparable chores (daily,annual etc.) Meaningless comparisons, activities are not comparable between one another, no comparable standard activity is taken when common energy units are an obvious choice and these could be related to some common daily "global" activity cf. Prof David J.C. MacKay's approach referenced below:

Read Concret Thinkers page with some specific critical comments as follows:

"The manufacture of cement produces about 0.9 pounds of CO2 for every pound of cement. Since cement is only a fraction of the constituents in concrete, manufacturing a cubic yard of concrete (about 3900 lbs) is responsible for emitting about 400 lbs of CO2.[1] The release of 400 lbs of CO2 is about equivalent to[2]" [refs.1,2 refer to papers on their site]:

* The CO2 associated with using 16 gallons of gas in a vehicle (what sort of vehicle!!!)
(16x3.79 litres = 60.64 litres and if your Limousine gives you 100 kms per 5 litres then, => 60.64 /5)x100 = 1212.8kms and say at a speed of 100km/h Then you get 12.12h driving pleasure!)

* The CO2 associated with using a home computer for a year (24h a day connected?)
* The CO2 associated with using a microwave oven in a home for a year (a few minutes or 1 h, lets say per day?)
* The CO2 saved each year by replacing 9 light bulbs (N° of W (Watts and KWh?) in an average house with compact fluorescent light bulbs (Units please?)

Other sources responsible for CO2 emissions include: [I have given the conversion factors below to play with but....

* 28,400 lbs for an average U.S. house in a year
* 26,500 lbs for two family vehicles in the U.S. in a year
* 880,000 lbs for a 747 passenger jet traveling from New York to London

The reason concrete is responsible for 1.5 to 2% of the U.S. anthropogenic CO2 (that is, due to humans) is due to the vast quantities of concrete used in the world around us.

Metrics - Conversion
lbs, US: 1 pounds (lbs) (avoirdupois) is equal to 0.45 kilograms

Yards cu: 1 cubic yards is equal to 0.76 cubic meters
1 cu yd concrete 3900lbs ( kg) => 400lbs CO2 )

gallons US: 1 gallon (US) is equal to 3.79 liters
gallons GB: 1 gallon (British) is equal to 4.55 liters

miles 1 miles (statute) is equal to 1.61 kilometers.

Concrete
400lbs/3900lbs roughly, 1/10 =10% CO2
Therefore, For every unit weight of concrete produced the weight of CO2 emissions is 1/10 or 10% of the weight of concrete produced
Cement
For every unit weight of cement produced approximately the same weight of CO2 is emitted. (or 1 unit of cement produced roughly 0.9 or 90% of CO2 emissions is also produced)

Does anyone know of a better account?

Sources and References:

1. The Portland Cement Association ,Concrete Thinkers _ page

2. A much better approach is that of Cambridge,UK, Prof. David J.C. MacKay, in his freely available ebook Without Hot Air!

What a coincidence (serendipity) I came across David MacKay's Video on light bulbs!

3. CO2 and other greenhouse gases GHG's
Global Warming Potentials (GWP) and Atmospheric Lifetimes (Years)
LINK to US Environment Protection Agency (EPA).

NB. To be fair here are a couple of graphs from references on the Thinkers Site that are more informative than the written paragraph presented by the Thinkers. All and more are referenced on the Thinker site cf. in particular the Stewardship pages


High Purity Cr sources for Superalloys

Energy for th Future:Phil.Trans.A-Vol. 365, N° 1853 / April 15, 2007, curtesy The Royal Soc. London

Engineered foams and porous materials: Phil Trans A. Vol 364, N° 1838 / 06 curtesy_The R Soc. Lond