What Happened to Green Concrete?
Concrete that absorbs carbon dioxide has made slow progress but is finally hitting the market.
In 2010, this publication cited more environmentally friendly concrete as one of its 10 Breakthrough Technologies of the year (see TR10: Green Concrete). Given that the world’s appetite for concrete contributes around 5 percent of global carbon dioxide emissions, the impact could be huge. But has the idea gone anywhere?
Five years ago Novacem, a company spun out of Imperial College London, was at the forefront of green cement. The company’s chief scientist, Nikolaos Vlasopoulos, had discovered a way to replace Portland cement—the binding material in concrete—with a magnesium oxide material. This material captured carbon dioxide in its structure when mixed with water, and the carbon dioxide and magnesium formed carbonates that strengthened the cement. The material didn’t require limestone, which releases carbon when it is heated during the cement-making process.
Despite the material’s promise, Novacem could not raise enough funds. Vlasopoulos says the financial crisis that began in 2008 made it hard to attract investors. The company sold its intellectual property to Australia’s Calix and was liquidated in September 2012. Vlasopoulos now works at the cement giant Lafarge.
A green-concrete company called Calera is still active, but it is no longer pursuing its idea of mixing carbon into Portland cement. Calera demonstrated this technology in sidewalks a few years ago, but it found more value in using the material to make fiber cement boards used in bathroom tile backing or exterior siding, says the company’s chief operating officer and president, Martin Devenney. Calera is running a pilot plant that produces up to two tons of cement from carbon dioxide and industrial waste per day, sequestering about four-tenths of a ton of carbon dioxide in each ton of the material. The company plans to start producing the boards commercially this year but expects that scaling up the technology will take several years.
CarbonCure is selling a technology that injects carbon dioxide captured from industrial processes into Portland cement along with water. The solids formed in this process can improve the material’s strength by 10 to 20 percent, says the company’s CTO, Kevin Cail. About 20 building installations have used blocks made with CarbonCure’s process since it was commercialized in 2013, says Cail. Two recent projects in Miami have saved more than 2,700 tons of carbon dioxide, as much as 125,000 trees absorb in a year, says Jennifer Wagner, the company’s vice president of sustainability.
However, the carbon footprint of each block is typically reduced by only 5 percent. If a cement plant doesn’t sequester its own carbon dioxide (and most do not), the gas must be brought in from other sources. The process is also not mobile yet, so it can’t be used for on-demand applications like filling in driveways. A version that can be used at construction sites is coming within the next few months, says Cail.
Solidia Technologies, founded in 2008, is still developing its technology to sequester carbon dioxide in concrete, but it has support from big companies such as Lafarge and from the U.S. Department of Transportation’s Federal Highway Administration. The technology, first developed at Rutgers University, involves mixing a cement powder with sand and then filling in open spaces with water and carbon dioxide. The cement reacts with the carbon dioxide to make calcium carbonate and silica, which harden the material into concrete. The concrete could be 10 to 25 percent stronger than today’s materials, says Solidia’s CEO, Tom Schuler, and it will be more resistant to cracking in environments where freezing and thawing are common.
More with less
Storing carbon dioxide in cement is not the only way to improve the material’s environmental footprint.
MIT’s Concrete Sustainability Hub has shown how nanoengineering can make concrete twice as resistant to fracturing without significantly changing the weight or chemical composition, says the lab’s director, Franz-Josef Ulm. This would allow manufacturers to use less concrete in the overall building process without sacrificing strength. The finding appeared in Nature Communications last year.
Another approach is to change the properties of concrete by adding materials like fly ash, a by-product of burning coal. That material has been added to concrete in small amounts for decades, but CeraTech, a company based outside Washington, D.C., is making concrete that is 95 percent fly ash. It uses half as much water as the Portland cement it replaces and lasts up to three times longer, says Mark Wasilko, the company’s executive vice president. The material is made through a chemical reaction instead of being baked in a kiln. CeraTech is aiming the product at oil and gas companies that need materials with thermal and corrosion resistance. The Sefa Group, meanwhile, has developed a process for making concrete with fly ash taken from the ground in addition to what can be captured from coal-fired power plants. This technique can help clean up landfills and ponds filled with ash that has been sitting for years.
Concrete that is better for the environment is being used today at small scales. But overall, the recipe for concrete hasn’t changed too much. Although the Portland Cement Association, a trade group, points out that upgraded factories and processes have helped the industry improve its energy efficiency by 40 percent since the 1970s, new technologies will be required to move the needle significantly more.
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