By volume, Portland cement is the most common manmade product on Earth; it's a component of concrete, mortar, stucco and grout. In the year 2000, the manufacture of Portland cement also added 829 million metric tons of carbon dioxide (CO2) into the atmosphere. That's 1.25 tons of CO2 for every ton of cement produced [source: Hanle et al].
However, the manufacture of Air Krete releases only 20 to 40 percent of the CO2 of traditional cement, mostly due to the source of Air Krete's primary component being as plentiful as the waters of the ocean rather than mined as limestone from mountain hillsides. Not that Air Krete is a substitute for structural cement, but the name "cement" that tends to scare off the environmentally conscious deserves a second look in this case.