Quarrying & Mining Magazine

C02 improved concrete

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This article is a précis based on an article originally printed in Concrete Infocus – the official publication of the National Ready Mixed Concrete Association.

Carbon dioxide emissions and cement production are usually a source of attack among the manmade climate change faithful and the industry has responded with a number of ways to reduce ‘cement emissions’.

So it is ironic that a method has been explored to recycle ‘captured’ carbon dioxide into concrete products. This involves collecting CO2 byproduct from industrial operations and injecting it into fresh concrete where it becomes chemically sequestered within the concrete.

After the CO2 is purified and compressed, it is transported to ready mixed concrete production facilities where it is incorporated into concrete during mixing. The result is that the CO2 is permanently embedded within the concrete, thereby becoming “sequestered” within the concrete as a mineral.

The authors of this research say that, in addition to it ‘green market’ appeal the addition of CO2 can actually improve the concrete’s material properties such as compressive strength.

A company called CarbonCure Technologies is offering the technology that allows for the sequestration of CO2 to the concrete industry in North America, after initially launching it to the masonry industry.

The company says it is already installing its technology in several concrete plants across Canada and the US.

The technology is based on delivering CO2 to ready mixed concrete during production. A tank of liquid CO2 is connected to a gas control system and manifold and is then injected into the mixing drum where it reacts with the hydrating cement to produce a calcium carbonate product similar to limestone. Since the CO2 is converted into a solid, the CO2 sequestration is permanent.

To calculate the environmental benefits in a CO2 obsessed world, a project that uses 50,000 cubic yards (38227.743 cubic metres) of concrete could absorb the equivalent amount of CO2 that 25,000 trees or 460 acres of forest will absorb in a year.

As for the average compressive strength during two industrial trials of the CarbonCure Ready Mixed Concrete Technology at partner production facilities – results confirmed that the addition of CO2 resulted in a strength benefit exceeding 14 percent at all ages, including a 26 percent benefit at three days and 18 percent at 56 days.

More information: www.carboncure.com.

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