Three Gorges Dam in China
Concrete is one of humanity’s most useful materials as it starts in a semi-liquid form and hardens as it dries. Concrete is the most used man-made material in the world in terms of volume.
Concrete was developed by the ancient Romans and ancient concrete was not that different from the concrete that is used today. The Pantheon was built by the Romans out of concrete in 126 CE. It is still standing and its dome is still the largest un-reinforced concrete dome in the world!
The Pantheon
Concrete is made through a combination of aggregate (sand and gravel), water and cement. Thus, cement and concrete are not synonyms. Cement is a fine, powdery mixture that is the binder that holds the aggregate components of concrete together.
Cement is made by grinding together a mixture of limestone and clay, which is then heated at a temperature of 1,450°C. Cement usually makes up about 10-15% of concrete. Addition of water to cement causes a chemical reaction that produces calcium carbonate which hardens and acts like the glue that holds together the aggregate.
Unfortunately, production of cement is the cause of a lot of carbon emissions. According to Quartz, “The cement industry emits more than twice the amount of greenhouse gas as every airplane in the sky, combined.” Various companies are working to invent a low emissions cement.
Reinforced concrete (meaning that it has rebar in it) is the only building material that is highly resistant to both water and fire.
About 6 billion cubic meters of concrete is made each year.
China produces and consumes about 60% of the worlds cement. According to Vaclav Smil in his book Making the Modern World: Materials and Dematerialization, between 2011 and 2013, China consumed 6.6 gigatons of concrete – that’s more than the U.S. used in the entire 20th century. Think of what was built in the U.S. between 1901 and 2000: the Hoover dam (and lots of other dams, IFOD on Dams: Some Dam Facts), the interstate system and other roads, skyscrapers, stadiums, buildings. All those things used about 4.5 gigatons. The largest concrete structure in the world is the Three Gorges Dam in China (pictured at the top of the page, above).
What is really cool is we don’t have the strongest best recipe of concrete. With the Pantheon dome that recipe of concrete is different which is why it is stronger, but it got lost.