What if a belching power plant could be used to create a green cement? Brent Constantz thinks he's got the trick—one that uses the pollution from a power plant or other factory. The inspiration for his process is, of all things, coral. Coral secretes calcium carbonate, which, when filtered through sea water, acts as a marine cement, creating the coral reefs over time.

Constantz studied earth sciences, geological sciences, and aquatic biology and previously developed a cement to repair bone fractures and for dental work. This background may have helped when he contacted venture capitalist and philanthropist Vinod Khosla, who has been investing in new technologies, especially green ones. With funding in hand, Constantz set out to green one of the most polluting building materials—the third largest source of greenhouse gas pollution in the United States, according to the Environmental Protection Agency.

Constantz's company, Calera, built a prototype plant in Moss Landing, Calif., where it is using the exhaust from a neighboring gas-fired power plant to create carbon-sequestering cement. The technique takes that exhaust and runs it through seawater from the Pacific. The carbon dioxide from the smokestacks bonds with magnesium and calcium in the water. The resulting sludge is heated and dried by the power plant's exhaust, which leaves behind cement that can be combined with other aggregates to form standard concrete—and, according to Constantz, every ton of his cement sequesters one-half ton of carbon dioxide into a useful material. It takes the plant's pollution and holds it in the concrete, where it stays out of the atmosphere. The process also avoids the huge amounts of fuel needed to heat cement, which is baked at 2,642 F and then needs to be pulverized. Calera is currently producing around 10 tons of cement a day at the plant. The company aims to have five more prototype plants up in the next year and its first commercial plant ready by 2010.

Constantz doesn't have the competitors running yet. He will have to achieve an economy of scale that makes the process affordable. Commercial use will also require testing and proof of compliance. Interest is building, though, and recent laws that limit carbon emissions, specifically in California, will likely drive people to Constantz's pollution-eating, cement-greening technology.