Construct Canada session shows concrete eating CO2

The production of cement for concrete releases so much carbon dioxide that it is the second largest industrial producer of the greenhouse gas. As long as we continue to pave and construct using this ancient material, therefore, we badly need to find ways of reducing its environmental footprint.

At a session held on Thursday, December 5 at Construct Canada in Toronto last week, two speakers discussed promising technologies that involve directly sequestering carbon dioxide into building materials.

In “Innovative Concrete Technologies to Combat Carbon Emissions,” Christie Gamble of Halifax-based CarbonCure explained how her company has taken advantage of well-known chemistry to develop an innovative technology that sequesters carbon dioxide within masonry products such as blocks, pavers and retaining walls.

Gamble first pointed out the great need to find a means of reducing the carbon footprint of cement. She said producing 1 ton of cement production releases approximately 650 kilograms of carbon dioxide. Of that amount, 40% is produced during the combustion process to heat the limestone to fantastic temperatures of up to 1,500 C. The emissions from that combustion process can be managed to some degree, such as by using renewable fuels. But, Gamble said, the remaining 60% of the CO2 emissions are given off during the chemical transformation of the limestone into cement, so those emissions are an inherent byproduct of the process.

However, in 2007 CarbonCure Technologies began developing a way to reintroduce the CO2 into concrete masonry products at the manufacturing plant. CarbonCure’s equipment is installed on the assembly line to inject CO2 into the concrete as it is being mixed. As the CO2 is reintroduced it chemically converts into limestone that becomes embedded throughout the block. The CO2 acts as an accelerating curing agent, which improves the concrete’s strength by up to 20% and means it meets all CSA and ASTM standards.

The block manufacturer must purchase the CO2 from suppliers like Praxair or Air Liquide, which collect and refine the CO2 from large industrial emitters, Gamble said. But on the plus side, a building that uses the masonry products could gain valuable LEED points, especially as the rating program drives to become more holistic and is introducing tools such as environmental product declarations (EPDs) and health product declarations (HPDs). CarbonCure is leading the industry as they issued the first masonry EPD and first HPD for any concrete product.

With a few Canadian and American companies already producing the carbonated masonry products, they have been installed in the large Hullmark Centre at Yonge and Sheppard in north Toronto. Other installations are in Nova Scotia, New York, Chicago and San Francisco.

The company is also testing the process for the precast and ready-mix market. When members of the audience questioned the durability of the material over the long term, Gamble replied that the concrete absorbs and converts 100% of the CO2 so once the concrete comes into contact with rebar, the CO2 no longer exists, and so there is no problem with corroding the rebar.

Matt Novada, B.Eng. of St. Mary’s Cement in Ontario was the other speaker. He described a pilot project that involves a Toronto-area company known as Pond Biofuels. The company has installed a bioreactor at the St. Mary’s plant that incorporates light technology. Carbon dioxide emitted during the production of cement is piped into the reactor instead of being released into the atmosphere and the algae feed off the gas and then are transformed into a biofuel. Algae consume almost twice their weight in carbon dioxide. In a double benefit, the residual biomass from the transformation process can be used as a renewable fuel. (A demonstration biorefinery plant using the Pond Biofuels system is also being built at Canadian Natural Resources Canada’s oil sands site near Bonnyville, Alberta in partnership with the National Research Council of Canada.)

For more information on CarbonCure Technologies, click here.

For more information about Pond Biofuels, click here.