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September 5th, 2008

Concrete solutions to pollution

Published on September 5th, 2008 | By: pwray@ceramics.org

Every year, concrete accounts for more than five percent of human-created, pollution-causing carbon dioxide emissions, reports Technology Review, an online news source published by MIT. Most of these emissions are created because cement – the active ingredient in concrete – requires limestone and clay powders to be baked at extremely high temperatures, usually generated by burning fossil fuels. Additional emissions also are generated if heat and steam are used to accelerate curing. Carbon Sense Solutions Inc. in Halifax, Nova Scotia , says it has developed a process that will enable manufacturers of precast-concrete products to collect and store their factories’ CO2 emissions in the products they manufacture.

CSS’ process does this by exposing concrete products to the CO2 flue gas created during a factory’s curing process. CSS’s president Robert Niven explains that his firm’s technology exposes freshly mixed concrete to a stream of CO2-rich flue gas, rapidly speeding up reactions between the gas and the calcium-containing minerals in cement. He estimates these minerals account for about 10 to 15 percent of the concrete’s volume and adds that his firm’s process also saves energy and reduces emissions by virtually eliminating any need for heat or steam during curing. If widely accepted, CSS’ still unproven technology has the potential to eliminate 20 percent of all cement-industry CO2 emissions, he claims. “Considering that concrete is the most abundant man-made material on earth and how fast the precast market is growing,” Niven says, “the estimated carbon dioxide storage potential is 500 megatons a year.” He says 60 tons of CO2 could be stored as solid limestone – or calcium carbonate – within every 1,000 tons of concrete produced and further claims that the end products produced will be less permeable to water, more durable and less likely to shrink or crack. Niven’s claims – and CSS’ new technology – will be tested in a pilot plant the firm expects to build in Nova Scotia later this year. Preliminary results are anticipated by the end of 2008.

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One Response to Concrete solutions to pollution

  1. Ellis Gartner says:

    This is more of the same old stuff in a new dressing! For many decades it has been known that you can cure (unreinforced) precast concrete items (blocks, etc.) with gases rich in CO2 and often end up with stronger and possibly also more durable products (and also with better dimensional stability since the shrinkage occurs in the factory!) A few precast companies already do it. I imagine that company is simply trying to sell a “bolt-on” module for precast concrete plants. The estimated potential for capture of 500Mt/yr is probably based on the assumption that the total world production of precast concrete would be treated. However, even then it is probably an overstimate because most concrete blocks have low cement contents to begin with and many of them are also quite porous and so actually carbonate quite rapidly in use without the need for any special manufacturing modifications. The sad thing about it is that the cement and concrere industries currently get no CO2-credit for the actual in-use uptake of CO2 by concrete.

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