Concrete as a carbon sink?

Enviro~C&CI concrete building - for sustainability.JPGAccording to Daniel van der Merwe, architect at the Cement & Concrete Institute (C&CI), although concrete is one of the most commonly used building materials in the world, some of the attributes it offers as a sustainable material are overlooked.

As global concern about the environment continues, Van der Merwe says, “Materials specification must play a critical role to reduce the embodied energy in a building.

Materials manufacture also needs to be factored in, in terms of measurable emissions, energy usage and the consumption of finite materials. Buildings now need to be constructed with a longer lifespan in mind, with the emphasis on durability and retrofitting rather than demolition.”

Van der Merwe adds that the cement and concrete industry has committed itself to responsible manufacturing. It has managed to boost production while decreasing the use of finite raw materials and the use of cement extenders has significantly reduced the clinker portion in certain cement products.

“The Department of Minerals and Energy has called for a 15% reduction in energy consumption by 2015 and cement producers have already reached 50% of this target. Through the use of alternative fuel sources – including hazardous waste and scrapped tyres – further reductions are possible.”

The fitting of bag house filters, or electrostatic precipitators, is further reducing particulate emissions and chemical admixtures are helping to reduce the cement and water content in concrete mixes. Through lightweight void form precast hollow-core slabs, the volume of in-situ concrete is also being substantially reduced.

“New permeable concrete pavers, soil erosion blocks and embankment stabilising blocks save water and prevent excessive storm water run-off, flooding and erosion. Self-compacting concrete in sustainable developments allows for architectural achievements previously regarded as impossible.

“Moreover,” says van der Merwe, “new research is producing exciting data on the re-absorption of carbon dioxide by hardened concrete. A Danish study has found that 50% of the volume of concrete will be ‘carbonated’ over 70 years of any building’s service life. This sponge effect makes concrete a more green choice than previously thought. And it indicates another way in which concrete can contribute to global sustainability.”

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