Concrete is an artificial conglomerate consisting of a mixture of binder, water and aggregates (sand and gravel) and with the addition, as needed, additives and / or added minerals that influence the physical or chemical characteristics of the conglomerate both fresh and hardened.
The fresh concrete is thrown into the formwork and compacted with vibrators, but there are modern formulations of concrete, called self-compacting concrete, fundamental in contemporary architecture because they ensure a homogeneous and uniform result, which doesn’t require vibration but it is compacted exploiting the force of gravity.
Famous concrete structures include the Hoover Dam, the Panama Canal and the Roman Pantheon. The earliest large-scale users of concrete technology were the ancient Romans, and concrete was widely used in the Roman Empire. The Colosseum in Rome was built largely of concrete, and the concrete dome of the Pantheon is the world’s largest unreinforced concrete dome.
After the Roman Empire collapsed, use of concrete became rare until the technology was re-pioneered in the mid-18th century. Today, concrete is the most widely used man-made material (measured by tonnage).