But it’s hard to modify a product whose chemistry is not well understood. “We have never actually known the exact chemistry of how this stuff gets hard,” said Hamlin Jennings, an expert on cement chemistry and head of MIT’s Concrete Sustainability Hub, one of several academic initiatives to forge “green” cement. “I don’t think there is any building material used in the world today that is more poorly understood than Portland cement.”
While the cement companies were tinkering with the original, Vlasopoulos took another tack. “You can only do so much to Portland cement to make it better,” he said. “It is what it is. It’s the material you start with. We had to come up with something else.” Vlasopoulos liked the idea of using magnesium oxide as a replacement for the limestone to form the cement, but it needed another material to make it hard. Mixing magnesium oxide alone with water wouldn’t do it—the mixture becomes slushy. And he needed to find a source of magnesium oxide that didn’t release so much carbon dioxide. The class of material he settled on was magnesium silicates, carbon-free compounds derived from talc, serpentine, olivine or other minerals. The world supply of these minerals is about 10,000 billion tons, an important factor because if one runs out of flour, no more cakes can be baked.
Vlasopoulos is not exactly keen to explain how his experimental compound works. His secret sauce is perhaps a very lucrative secret. Several patents have been filed. He will reveal this much: A few years ago, he began mixing magnesium oxide with other chemical compounds he created and water. The mixture hardened into a little ball. He brought it to Cheeseman’s office. “You could feel the heat coming off this little ball,” Cheeseman said. “Something was clearly happening.” Chemical reactions were firing; energy was being released. They did not get overly excited. “I mean, this is cement we are talking about here—it’s not exactly the sexiest stuff in the world,” Cheeseman said. “I wasn’t running up and down the halls doing cartwheels, but it was interesting.”
The chemicals Vlasopoulos mixes with magnesium oxide and water to make the cement harden are magnesium carbonates, which he makes by adding carbon dioxide to other raw materials. That means the cement, in some scenarios, is not just carbon neutral—it’s carbon negative. For every ton of Vlasopoulos’ cement produced, one-tenth of a ton of carbon dioxide could be absorbed.
Eventually Vlasopoulos, with Cheeseman’s help, started a company, Novacem, to develop a new cement. The firm, with more than a dozen employees and partnerships with some of the biggest cement companies in the world, is located in a business incubator for high-tech startup companies at Imperial College. While some other companies in the facility are life sciences startups, with microbiology labs full of gene-sequencing machines and collections of test tubes, Novacem’s lab is a spacious plant that produces loud noises, loads of dust and bucket after bucket of cement. It is the first cement works in central London since the days of the Romans.
Workers wearing hard hats, protective glasses, masks and white lab coats operate a miniaturized version of a cement plant not unlike the one Vlasopoulos worked in during summer breaks.
Though still refining its procedures, Novacem is racing with at least five other companies and university centers to come up with a greener cement. “Given all the attention to carbon these days, a lot of entrepreneurs have popped up,” said MIT’s Jennings. “They see the opportunity side.” With cement a $170 billion-a-year industry, investment money is pouring in.
A California company called Calera has perhaps the most unusual approach: It harnesses carbon dioxide emitted from a power plant and mixes it with seawater or brine to create carbonates that are used to make cement. They can be added to Portland cement to replace some or all of the limestone. Calera is backed by a $50 million investment from Vinod Khosla, a computer engineer who is perhaps Silicon Valley’s most respected and deep-pocketed investor in green technologies. “We are actually making our cement out of CO2,” said company founder Brent Constantz. “We are taking CO2 that would have gone into the atmosphere and turning it into cement.” The technology is still in development, with a demonstration plant in Moss Landing, California, and a partnership with a Chinese group to build a plant next to a coal mine in Inner Mongolia, where they plan to use carbon dioxide emissions to make cement.
Calix, an Australian company, makes cement using superheated steam, which modifies the cement particles and makes them purer and more chemically reactive. The process also separates out carbon dioxide, making it easier to capture the gas and keep it out of the atmosphere.
Louisiana Tech University, like Novacem and Calera, is doing away with limestone altogether; it’s using a paste called geopolymer, which is made of fly ash, sodium hydroxide and potassium hydroxide.