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New type of concrete protects the climate

COWI’s Concrete and Corrosion Network keeps up with the development of concrete. Shown is a new transparent form of concrete that uses embedded fibre optics to allow light to pass through, adding to its decorative potential.

Production of concrete accounts for five per cent of global CO2 emissions, but a new type of cement could help it improve its track record. What’s more, during its lifespan, it absorbs more CO2 than used when making it, says the head of COWI’s Concrete and Corrosion Network.

When it comes to climate change, concrete is a major culprit. The production process of one of the world’s most common building materials accounts for about 5 per cent of non-natural CO2 emissions. But before long a new type of concrete will be available that absorbs more CO2 than it releases.

“Concrete is composed of cement, water, sand and stone,” explains Berit Buhr Jensen, a chemical engineer and head of COWI’s Concrete and Corrosion network.

“Cement needs to be heated to about 1,400° C when it is produced, and that requires so much energy that for each ton you make, you release between half a tonne and a tonne of CO2. The new type of concrete contains a type of cement that is produced at about half the temperature.

CO2 absorption

“Then, once the concrete dries, it will be able to absorb more CO2 from the air than was emitted during its production, giving it a negative CO2 footprint.”

Jensen points out, however, that all forms of concrete absorb CO2. “So, in the long run, concrete isn’t the climate culprit it appears to be.”

Ready within a decade

Even though initial tests with the new type of concrete – produced by England’s Novacem – have returned promising results in pilot projects, its strength and durability have yet to be documented.

“So it’ll be a while before we go out and approve it to be used in major construction projects,” Jensen said. “What’s more, we’d need to convince the construction industry, and they aren’t going to switch if it isn’t durable enough or costs too much.”

It will take at least five years before the new type of concrete can compete with traditional concrete on price, according to Jensen.

New tricks for old concrete

But even as consultants and builders wait for the new climate-friendly concrete, Jensen says there are number of things they could do to make today’s concrete greener. She suggests replacing cement with fly ash and slag from blast furnaces.

The concrete used in buildings, she adds, could also serve to reduce CO2 emissions indirectly.
“Concrete absorbs heat and releases it slowly.

There’s a lot of potential in using that heat to warm buildings at night. The only thing that is required is for the wall on the inside to be uncovered.”

By Kathrine Schmeichel, kats@cowi.dk
Published 17.09.2009

Crushed concrete – a CO2 vacuum

Concrete is made of sand, stone, water and cement. Making cement requires limestone to be roasted at extremely high temperatures. In addition to the CO2 released from burning the large amounts of fuel to heat it, the limestone itself releases CO2 when it gets that hot.

Concrete and cement production account for as much as five per cent of global CO2 emissions.

A 2006 Danish Technological Institute study showed that concrete absorbs CO2 from the air.

According to the institute’s findings, there are “significant benefits to be gained when the concrete has reached the end of its lifespan and buildings or other structures need to be demolished”. Their study found that when concrete is pulverised, it absorbs large quantities of CO2.

The climate gain is especially great when concrete is reused to build roads, since it means new materials do not need to be produced.

COWI materials lab

COWI is involved in a number of projects that involve concrete – and is responsible for tasks ranging from consultancy on new bridge, tunnel, port, building and road construction projects – to maintenance and repair of existing constructions.

Company specialists involved in these projects can make use of COWI’s materials laboratory to conduct advanced analyses to determine why materials behave the way they do, evaluate what consequences they could have and to come with ideas for how to deal them.