[GSBN] embodied energy and sequestration

Fri May 7 14:36:17 UTC 2010

This is indeed correct. Carbonation is the conversion of Calcium Hydroxide
to Calcium Carbonate. Calcium Hydroxide is lime, whereas in cement it is
also the product of the hydration process. none the less it absorbs
atmospheric carbon dioxide and should rightly be considered in any holistic
LCA analysis of above ground/water concrete. cement/concrete does generally
carbonate much more slowly than lime (due to its denser pore structure) and
whilst like lime carbonation is beneficial (for strength) carbonation of
concrete is seen as detrimental because of the pH reduction and subsequent
loss of passive protection for any embedded steel reinforcement. Carbonation
in plain (unreinforced concrete) is also beneficial for its strength
development. 

The embodied carbon of modern blended cements and efficient kilns  is
getting closer to that of hydraulic limes. We should specify lime because of
its favourable performance qualities (breathability, flexibility, aesthetics
etc) rather than because of the carbon argument. You can indeed achieve much
lower embodied materials of equivalent strength (if that's your criteria)
using blended cement binders compared to hydraulic lime (simply by using
less cement) because cement is a much stronger binder.

 For a really low embodied CO2 render use clay.

Pete

Prof. Pete Walker,
Director BRE Centre for Innovative Construction Materials,
Dept. Architecture & Civil Engineering,
University of Bath,
Bath BA2 7AY,
UK.
Tel: 01225 386646
Fax: 01225 386691
http://www.bath.ac.uk/bre

  _____  

From: GSBN-bounces at greenbuilder.com [mailto:GSBN-bounces at greenbuilder.com]
On Behalf Of John Straube
Sent: 07 May 2010 14:41
To: (private, with public archives) Global Straw Building Network
Subject: Re: [GSBN] embodied energy and sequestration

Concrete absolutely carbonates and consumes CO2. 
This is one of its problems: carbonation reduces the high initial pH of 13
and when it drops below 10 or so (some say 9, others 11!), steel within it
becomes much more susceptible to corrosion.
The industry has been working for years to produce very dense concrete, and
even produce CO2 blocking coatings, to reduce this problem. 
Porous lower strength concrete can carbonate several inches in a decade,
whereas high strength, low w/c ratio, high fly ash and silica fume concrete
carbonates much much slower (at least 10 times more slowly)

The CO2 released by the coal or nat gas during the firing of lime cant ever
be reabsorbed only the CO2 released by the chemical decomposition is.
Portland is likely the same.

On 2010-05-07, at 8:19 AM, Tom Woolley wrote:

Dear all

Maybe there is confusion here between cement and lime 

Lime can absorb C02 during carbonation and this can make a small
contribution to carbon sequestration over its life in a building

Cement however does not in most cases as cement works best if it does not
carbonate unlike lime. 

The argument that C02 is stored in concrete is a  bogus argument put about
by the cement and concrete industry to try and greenwash cement.
The carbonation argument seems to be based on the idea that concrete can be
crushed at the end of life and that this has some carbonation benefit
See
http://www.sustainableconcrete.org.uk/main.asp?page=85

The C02 is emitted during the manufacture of cement and is not recovered in
my opinion . It contributes to fossil fuel energy wastage and global warming
Even the use of recycled material like ash involves energy though the cement
industry have made great strides in reducing this

Cement manufacture remains one of the highest emitters of C02 in all human
activity as alternatives are not being used in many parts of the world

Pragmattically we probably all use a bit of cement from time to time but it
should be avoided if there are better alternatives like lime or earth
Here is an interesting paper which discusses these issues and compares
cement to alternatives

http://www.springerlink.com/content/56266t21424h4854/

Calculation of sequestration  in wood straw etc.

A paper on this is being prepared by David Robson of University of Cumbria
and initial findings have been presented to the UK Renewable Building Group
Several GSBN UK members are part of this group

This research will be made available when complete and will hopefully
provide some hard data on the sequestration contribution of renewable bio
based materials

Tom

On 7 May 2010, at 04:13, Mészáros Attila wrote:

Dear All,

I completely agree with Derek. Though the amount of the reabsorbed CO2
could be nearly 50 % of the portland cement's dry mass, the CO2 emission
during the production is higher than this amount.
The net CO2 production of portland cement production and curing is
positive. The whole process does not sink, but produces CO2. It is pure
chemistry and physics.

So I am really surprised on Martin's info on IPCC's perception.
I know personaly the hungarian member of IPCC, Diana Ürge-Vorsatz, she
is also a physisist.
So if we can have a bit more info, we can act. First informal ways, and
then even formaly...

Attila

Attila Mészáros
CEO, CereDom Ltd
email: meszaros.attila at ceredom.hu
tel: +36 20 9772258

2010.05.06. 23:22 keltezéssel, Derek Roff írta:

Thanks, Martin. Could you clarify a bit about this sentence? Do the

sources that you quoted give an explanation?

"cement-based products in contrary are accepted to reduce the PCF

(product-carbon-footprint) as the CO2 used for production is stored

for a long time."

What I find confusing, is that production of cement produces a lot of

CO2 from fossil fuels in mining, processing, calcining, and utilizing.

It produces/releases a fair amount of sequestered CO2 from the

limestone during the calcining chemical reaction. I'm not thinking of

any point at which "the CO2 used for production" is stored at all. A

small amount of CO2 is reabsorbed from the air by finished concrete,

but what I have read is that this is a tiny fraction, and needs to be

tiny, to maintain the integrity of the concrete.

So what CO2 storage are they talking about?

Derek

--On Thursday, May 6, 2010 9:24 PM +0200 martin oehlmann

<moehlmann at wanadoo.fr> wrote:

Dear all,

however not much response here on this issue... some possible

interesting observations in the meantime:

According the perception of IPCC and UN-FCC straw and wood are not

seen as CO2-sink, yet CO2 neutral, cause of the durability is

“difficult” to calculate. In contrary cement-based products in

contrary are accepted to reduce the PCF (product-carbon-footprint) as

the CO2 used for production is stored for a long time. (source:

Memorandum Product Carbon Footprint, German Ministry for Environment,

Nature Protection etc.)

Comment: compliments for the cement lobby, low cost cementbased

massproduction for housing with a lifespan 30-40 years.

If planted forests get cut after 30 years and seen as a CO2 sink, a

high quality building which lasts 100 years and longer built with

natural materials better should be perceived as storage, if the

intention from IPCC and UN-FCC is to support sustainable

constructions.

Nice day and all the very best,

Martin Oehlmann

Brittany

Derek Roff

Language Learning Center

Ortega Hall 129, MSC03-2100

University of New Mexico

Albuquerque, NM 87131-0001

505/277-7368, fax 505/277-3885

Internet: derek at unm.edu

_______________________________________________

GSBN mailing list

GSBN at greenbuilder.com

http://greenbuilder.com/mailman/listinfo/GSBN

_______________________________________________
GSBN mailing list
GSBN at greenbuilder.com
http://greenbuilder.com/mailman/listinfo/GSBN

Tom Woolley

Rachel Bevan Architects
80 Church Road
Crossgar
Downpatrick
BT30 9HR
tom.woolley at btconnect.com
028 44 830988

_______________________________________________
GSBN mailing list
GSBN at greenbuilder.com
http://greenbuilder.com/mailman/listinfo/GSBN

Dr John Straube, P.Eng.
Associate Professor
University of Waterloo
Dept of Civil Eng. & School of Architecture
www.buildingscience.com

-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.sustainablesources.com/pipermail/gsbn/attachments/20100507/7d826f07/attachment.htm>