The best quality concrete bridges and structures etc suffer from carbonation (penetration of atmospheric carbon) No concrete exposed to air is immune to this. It gives todays concrete a life of about 40-50 years before maintenance required to exposed rusting reinforcing bar.
More atmospheric carbon - shorter concrete life!!

Understanding and controlling thermal mass - water!

Tom,

What happened to Steveleigh?

According to the test reports from Portsmouth University on the roofkrete website the depth of carbonation penetration for roofkrete material (asmet material) is 0.2mm in 50 years.

If a motorway bridge was this good it would have a life of about five thousand years before the carbon hits the reinforcing bar!

Thermal mass is an interesting subject, the more I learn the less I seem to know! I design with it quite conservatively and mainly as a base heat (target 18 degC) with capacity to absorb more, then use specific heat sources for specific activities like in bathrooms to top up.
Concrete has it's positives and as long as it's energy return on energy invested is good then I see as a useful material.
There are some structures built in 1870's of concrete here in NZ (thats very old for here).

Paul Johannsen has a point.
But, should the concrete industry try to regain market share when.
US scientists believe that 10% of man made greenhouse gas is created when making concrete? It has been the most popular form of building material for years, however, the UK industry is loosing out to more friendly materials

Some interseting discussions....

What people should be asking is where would we be without concrete? To comment on a few points...

In 2002, global cement production was responsible for around 3.63% of man-made CO2 emissions, not 10% as the one reader suggests (source: United Nation Environment Programme).
In 2004, the UK (and Crown dependencies) cement industry produced 1.74% of UK CO2 emissions (source: data from the British Cement Association and National Green House Gas Inventory).

In the UK, 2 tonnes of concrete are used per head of population per year - why - because it is a versatile, flexible, durable, inorganic, long lasting construction products that we could not function without in our modern world!

Proof of the excellent natural durability of concrete comes in the shape of Marine Crescent in Folkestone, an early concrete building that has stood just metres from the sea since 1870 and which, following renovation, looks set to celebrate its 200th anniversary with ease. Fourteen original dwellings converted into 91 contemporary styled apartments, fitting comfortably within the ODPM's minimum target for housing density. Acoustic and thermal values that conform with new Part E and L regulations respectively. And, above all, the re-conditioning and re-use of an existing building that has required comparatively minor remedial work, despite the harsh marine environment in which it is situated.

In spring 2004, the structural engineer's report on the by-then empty and largely derelict structure indicated that all the walls from a thickness of 150mm up to 450mm (the latter found in the basement) were in a satisfactory condition. Only some minor internal walls of 100mm thickness had in the end to be replaced.

The foundations, built straight onto the shingle, had shown very little movement over the course of 130 years, and despite the fact that the building had no design movement joints, it was felt that the structure's general robustness meant that none needed to be added.

Sea-facing balconies at first floor level had been made of concrete containing brick fragments, gravel and fine aggregate plus some small diameter steel bar reinforcement. These were found to be largely in good condition, although corrosion caused by wrought iron balustrades meant that some spalling had taken place towards their edge.

But the starkest contrast between different building materials emerged when it came to the condition of the bay windows. Bomb damage during the war destroyed the eastern-most section of the Crescent and it had been built again in solid brick. After 60 years, all the brick bay windows were found to have failed and needed to be completely rebuilt in concrete with a galvanised steel post and frame around the windows.

So what's it going to be like to live in one of the 1 or 2-bed apartments? Quiet for one thing, despite the relatively high density of the conversion. Acoustic tests performed by the contractors showed a performance of 57dB for airborne sound between partition walls, attained naturally by the mass of the concrete's construction. Lower energy bills should also be achieved by virtue of the same reason. The Victorian concrete's thermal capacity will keep the apartments cool in summer and warm in winter, with the highest energy efficiency to be seen in the semi-basements. The conversion of the basements into one-bed apartments ticks off another current sustainability requirement for optimum land-use a further advantage that concrete basement construction offers.

On visiting the Concrete Centres website they have some excellent infomation on thermal mass and climate change adaptation which is well worth a look - I am sure that the Olympic Delivery Authority were well advised by the Building Research Establishment (BRE) when they stated in their plans to minimise carbon emissions - "...The thermal mass and structure of the building will be utilised to minimise heating, cooling and electrical demand..."

Posted By: paul johannsenConcrete is great

Some folk say Allah is great. Doesn't convince me.

(concrete hating atheist)

Dennis
What about concrete carbonation and moisture penitration?

<blockquote><cite>Posted By: biffvernon</cite>>Fly ash is obviously a good idea, but hang on, where's this fly ash coming from? Oh, a coal fired powerstation. Now we'd be shutting them down if we took global warming seriously.</blockquote>

wel... come on, you can't have it both ways. Fly ash is a great example of recycling waste product and it doesn't just come from coal fired powerstations but as waste from other industrial processes. I'd like to know more about fly ash substitution. I have read that you can replace up to 60% of the cement content, does anyone have any more information on how to do this or suppliers who will provide a specfied mix? Is it widely done?

Ah, the iron industry. Now that's another one with a size thirteen carbon footprint. Who needs steel lintels anyway? If we want green and sustainable buildings we're going to have to use green and sustainable materials. Don't confuse not-quite-so-evil building with sustainable building.

Hi dennis. Kieran....
My knowledge of fly ash or GGBS in concrete is 15 years out of date, but those materials have their own properties which in the end mean more cement. It is cement in concrete that is the carbon wasting factor, you could make make concrete from lime mortar if you waited and eyed up your thickenesses.
Plus fly ash or GGBS may add unforseen contaniments, which are bad.

cheers

alex

In memory of Herman Kahn
See: http://en.wikipedia.org/wiki/Herman_Kahn

CONCRETING THE UNTHINKABLE

Climate change is worse than even the "expert" climate
modellers are predicting. We will soon discover
this to be true. That is my prediction.

So we must begin carbon sequestration and live in a
way that stores carbon rather than emits it --- and
in a big way. We must show the rest of the world how
this might be done, design lifestyles that they can
buy into. If we can't we might need to consider
military force.

First, getting our own house in order is imperative.
And talking of houses we must build them to store large
amounts of carbon, which has been extracted from the
atmosphere. It doesn't matter if this is short-term
(decades), without action there is no bearable
medium-term, let alone long term.

So let's set a target of building 70 tonnes of CO2e
into any dwelling during construction - rather than
emitting 70 tonnes during construction. That means
almost no products that have high embodied CO2
can be used. That means little or no concrete amongst
many other products. And, if that did mean no
structural elements capable of supporting buildings
much above the ground floor then so be it. We must
live on the ground floor.

We must also use non-fossil fuel energy (e.g. off-shore
renewable energy) so the heat storage ability of
concrete becomes irrelevant. Anyway, this is not
necessary if we believe the Hemp and Lime people.

I went to the Centre of Alternative Technology
recently for a "Hemp and Lime" conference. Several
of the speakers discussed the CO2 impact of Hemp
and Lime: basically it stores CO2 taken in during
its growth. One speaker estimated that 30 to 50
tonnes of CO2 can be sequestered in an average
house.

Of course there are many other things we must do
- or rather not do. Not fly, not drive etc.

But back to the military option: Say we were
concerned about forest destruction in the
Amazon basin. We would threaten to nuke a city
in Brazil, but to be equitable, (because we
have carbon-sinned more than they have) let
them nuke a city of ours with twice the population.
Before this we should, of course, offer the
Brazilians lots of money to be ecologically friendly.
And the Chinese ...

Herman Kahn would have insisted we must be
prepared to go ahead with military action if
we make the threat. But I remember James
Lovelock, who is an advocate of nuclear power,
recently saying that a nuclear war would not
kill as many as the coming climate change
catastrophe.

I will probably regret this tirade when I'm sober
and may wish I had not used my real name. But
I have friends who know about these sort of
things and they tell me that there really are
policy analysts paid to think these thoughts.

GIZZA JOB!!

Thanks Biff

It wasn't poetry. My poetry has more rhythm (not too much) and more
rhyme (not too much). The lines were a bit short but most lines on
discussion forums are too long ... I think newspapers have it about
right for readability.

But if you want some of my poetry:

ONE PERFORMANCE ONLY

We'll fly you over burning forests
We'll walk you through the starving hordes
We'll shoe you drowned and bloated corpses
At a price you can afford

You'll fly above the sky in comfort
You'll sleep your nights in quiet hotels
You'll sit and watch our views in comfort
Of mankind in a thousand hells.

(Correction: for thousand read billion)

Also see http://auntiejaynesolvesyourpoem.com

Posted By: paul.dixon27both concrete (OPC) and lime re-absorb the co2 that they give off during manufacture.

No. That just ain't true. The reaction calcium carbonate to cacium oxide to cacium hydroxide and back to cacium carbonate is exactly cabondioxide neatral (ignoring fuel used). The maunfacture and setting of OPC is much more complex but is not CO2 neutral. More is evolved that re-absorbed on setting.
And lime making uses less fuel than OPC making, mostly because temperatures are lower.

Gosh, no magnets!