Concrete is the second most consumed material after water and is the basis for the urban environment. It can be roughly estimated that in 2006 between 21 and 31 billion tonnes of concrete (containing 2.54 billion tonnes of cement)3 were consumed globally compared to less than 2 to 2.5 billion tonnes of concrete in 1950 (200 million tonnes of cement).4
Concrete is made from coarse aggregate (stone and gravel), fi ne aggregate (sand), cement and water.5 Primary materials can be replaced by aggregates made from recycled concrete. Fly ash, slag and silica fume can be used as cementious materials reducing the cement content. These materials can be added as a last step in cement production or when the concrete is made.