Christian Science Monitor: Concrete, one of the most common building materials in the world, has an ugly secret: It's a major source of carbon dioxide (CO2) emissions, which contribute to global warming.

Roughly 5 to 10 percent of global CO2 emissions are related to the manufacture and transportation of cement, a major ingredient of concrete. "There is not one single cement company on this planet that is not thinking about how to [reduce emissions]," says Franz-Josef Ulm, a professor of civil engineering who researches concrete at the Massachusetts Institute of Technology in Cambridge, Mass.

Italy's Italcemente is the world's fifth-largest cement producer. It is looking beyond reducing CO2 emissions by creating a cement that actually breaks down airborne pollutants by adding titanium dioxide, which, in the presence of sunlight, acts as a photocatalyer, hastening the decomposition of such pollutants as nitrogen oxides, sulfur oxides, and ozone.

Ulm points out that the structure of human bones, at the molecular level, is similar to that of concrete. While cement must be heated to 1,200 degrees C (2,200 degrees F.) before it achieves strength and structure, bone is formed at 37 degrees C (98.6 degrees F.).

"That makes one think that nature can create at 37 Celsius a material that has similar properties as cement," Ulm says. "Can we mimic that?"