Think of what our world would be without concrete. Look around and see how many homes, offices, schools, roads, bridges, dams, and other structures are made from this material. Did you realize that concrete is made from ordinary sand, gravel, water, and cement?
In concrete, the cement and water mix together and form a paste. This paste then coats pieces of sand or gravel or crushed stone, and when it hardens, it holds the pieces together to form a solid mass.
Concrete must be poured while it is still wet. Trucks that are used to deliver concrete have large drums to hold the concrete. The drum keeps turning while the concrete is being poured to prevent it from hardening in the drum. When wet, concrete can be poured into a mold of any shape. And when it hardens, it can’t be damaged by water, fire, or the weather.
Reinforced concrete contains steel rods or mesh that are set in the concrete when it’s poured. When the concrete hardens, the steel gives it extra strength. Most large concrete structures are made from reinforced concrete.
The largest concrete structure in the world, the Grand Coulee Dam in the state of Washington, contains more than 21 million tons of concrete!