Locking Carbon Dioxide Into Concrete Is a Cool Idea

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The cement industry alone is responsible for about 8% of annual emissions of carbon dioxide. For every ton of cement that’s produced, a ton of greenhouse gases is released into the atmosphere. That’s obviously a threat to the planet, but it’s also an opportunity, because it means cement is a big, fat target for technological progress.

Global Cement magazine is all over this story. In April, London-based web editor David Perilli published an article featuring 15 concepts—some in the idea stage, some in use—for reducing the amount of carbon dioxide embodied in cement and concrete. This month, the magazine’s December issue features more ideas on the cutting edge, including solar-powered cement production.

Concrete, of course, is the synthetic rock that forms buildings, dams, bridges, and so on. It’s made from gravel, sand, air, water, and cement. Cement is the binder. The most common type of it, ordinary Portland cement, is made mainly from limestone and clay. The limestone is heated to break it down into lime (calcium oxide) and carbon dioxide, then the lime and clay are fused. There are traces of other materials in cement, including iron oxides. 

One of the coolest green ideas is to offset some of cement’s massive carbon dioxide emissions by putting carbon dioxide to good use in the production of concrete. It usually takes concrete a few weeks to reach maximum hardness, but injecting carbon dioxide speeds up the so-called curing process. The carbon dioxide becomes mineralized—and thus immobilized--by reacting with calcium ions in the cement.

“Because these building materials are used at enormous scale and have product lifetimes that span decades, mineral carbonation represents a significant opportunity for long-term carbon sequestration in addition to being an opportunity for carbon utilization,” a report from the National Academy of Sciences, Gaseous Carbon Waste Streams Utilization, said last year.

Bill Gates has invested in one of the companies in this space, CarbonCure Technologies Inc. of Dartmouth, N.S. Another player in carbon curing is Solidia Technologies Inc. of Piscataway, N.J. A venture between Korea Advanced Institute of Technology and Saudi Arabian Oil Co., known as Aramco, has also developed a method for locking carbon dioxide into concrete.

Another green idea is to replace some of the cement in concrete with other “cementitious” materials. Examples include fly ash, a byproduct of coal combustion, and slag, a byproduct of steel production. This isn’t exactly a new idea, but the urgency of reducing the environmental impact of cement and concrete is driving companies to invent ways to use these materials more.

A completely different approach to green cement featured in the December issue of Global Cement is being co-developed by Synhelion of Switzerland and Cemex of Mexico. The idea is to use mirrors to focus sunlight into a beam hot enough to sinter limestone and clay without any need for burning fuel. “It’s like an invisible flame!,” Synhelion Chief Executive Officer Gianluca Ambrosetti tells the magazine. The decarbonization of the limestone still emits carbon dioxide, but it’s pure, not mixed with combustion byproducts such as nitrogen oxides or sulfur dioxide, so it could potentially be used as a feedstock for synthetic fuels.

These are just a few of the ideas scientists and engineers are working on. Concrete is truly a building block of the modern world. It’s encouraging that there’s progress on making it less harmful to the environment.

©2020 Bloomberg L.P.

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