Green Undressed: Green Cement

Greening the concrete jungle just came a step closer with an eco-friendly alternative to traditional concrete.

Concrete is the second most widely used material on earth, after water. It is also the third-largest manmade source of carbon dioxide, responsible for over 5 percent of global emissions each year–more than 2.5 billion tonnes. Its footprint is growing rapidly thanks to the construction boom around the world, but now there is a greener alternative.

Reuse, reduce, recycle

Sixty percent of cement’s CO2 emissions come from the chemical reaction that breaks down limestone (calcium carbonate) into calcium oxide and its by-product CO2. But green cement, or geopolymeric concrete, to give it its proper name, uses fly ash, which is a waste product from burning coal, and slag which is a waste product from iron making.

By mixing in some sand and an alkaline compound known as an activator aluminium and silicon are dissolved out of the slag and fly ash and bind together into incredibly strong geopolymers. No carbon dioxide is produced, it has low embodied energy and the end product looks and feels like concrete.

In some cases is even better, according to Tom Glasby, project manager Earth Friendly Concrete (EFC) at Wagners in Queensland.

“Our EFC has been shown to have lower shrinkage rates, higher flexural tensile strength, produces less heat when it is mixed resulting in no thermal cracking, and increased fire resistance. It is also very durable,” he explains. “It can be used for all the same purposes as general structural grade cement, such as house slabs, paths, driveways and precast panels.” EFC recently won the 2011 Premier’s ClimateSmart Sustainability Award, and may have the potential to revolutionize the construction industry.

Back to the future

While green concrete may be a new concept the technology behind it has stood the test of time–more than 2000 years in fact. Old Roman concrete used similar chemistry in its production, with many structures still standing today.

A similar type of cement was also developed in the communist Soviet Union in the 1950s and 1960s.

According to the University of Melbourne’s Professor Jannie van Deventer who developed E-crete, another geopolymer concrete, the Ukrainians developed a concrete using the same chemistry–alkali activation–although they used only slag, not fly ash. Speaking on ABC TV’s Catalyst program, he said their structures have now been standing for almost 50 years and are still strong.