Green Cement: Near Reality or Just a Dream?
Cement is everywhere. The foundations of our buildings, the driveways that lead beyond suburban garage doors, the walls of our schools, and the mortar joints between every brick we lay contain a binding substance we call Portland cement. Cement is the binding agent used to hold together the tough aggregate (rocky gravel) in the concrete we can use for just about everything in modern construction. It seems harmless enough. We don’t have to cut down trees to build with it. It isn’t particularly full of toxins, and is incredibly durable and long lasting, but the environmental cost of concrete is astronomical. The basic process for making cement heats limestone (calcium carbonate or CaCO3) in a kiln to well over 2550F. This process not only requires enormous amounts of fuel, but also releases literal tons of CO2 as it separates the limestone into its constituents, lime and carbon dioxide. The manufacture of cement releases a terrifying 9kg of CO2 for every 10kg of cement produced, but if building with wood is not as strong or durable and involves all the sticky business of cutting trees and building with concrete is nearly an environmental abomination. What is the world to do?
Our hope may lie with Brent Constantz and his California company Calera. Calera is creating cement that actually reduces the amount of CO2 put into the air by power plants. Their location, across the street from a major Californian power plant, siphons smoke stack emissions from the power plant, runs the gas through oil rig or brackish water, and the salts and minerals from the water bond with the carbon dioxide in the gas to precipitate out limestone in much the same way that mother nature does it. What he gets is cement, hard aggregate for making concrete, and water that is already a step toward being purified for drinking thus reducing the time and energy needed to return it to a potable state. The cement can be used just like Portland cement, for new buildings or even just patch jobs.
For further information: http://www.matternetwork.com/2011/7/green-cement-near-reality-just.cfm