Concrete is a composite material composed of coarse granular material (the aggregate or filler) embedded in a hard matrix of material (the cement or binder) that fills the space among the aggregate particles and glues them together.[2]
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 was built largely of concrete and the concrete dome of the Pantheon is the world's largest.
After the Roman Empire collapsed, use of concrete became scarce until the technology was re-pioneered in the mid-18th century. Today, concrete is the most widely used man-made material (measured by tonnage) in the world.
Ancient additives[edit]
Concrete additives have been used since Roman and Egyptian times, when it was discovered that adding volcanic ash to the mix allowed it to set underwater. Similarly, the Romans knew that adding horse hair made concrete less liable to crack while it hardened, and adding blood made it more frost-resistant.[19]
Modern additives[edit]
In modern times, researchers have experimented with the addition of other materials to create concrete with improved properties, such as higher strength or electrical conductivity.[20]