The cement industry produces about 2.6 billion tonnes of cement annually. The most important use of cement is in the production of concrete, twice the amount of which is used than the total of all other building materials, to construct our homes, schools, hospitals, sewage systems, pavements and more. Concrete is the most used used man-made material in the world, a fact not widely known. Concrete has a cement content of between 10-15%.
Cement is made by heating limestone with small quantities of other materials (such as clay) to about 1450 ˚C in a kiln. The resulting hard substance, called "clinker", is then ground with a small amount of gypsum into a powder to make ˜Ordinary Portland Cement", the most commonly used type of cement (often referred to as OPC).
With modern and innovative technologies, the cement production process has become more eco-efficient over time. Increased usage of alternative waste fuels (providing a novel and key waste management option), clinker substitutes (such as slag and fly-ash), and energy efficiency improvements have all reduced the industry's CO2 emissions. Half of all CO2 emissions from cement production originate from the basic calcination process the heating of limestone to form lime. 40% comes from usage of fuel, and the remaining 10% from electricity usage and transportation.