Concrete is a composite material composed of aggregate bonded together with a fluid cement that cures to a solid over time. Concrete is the second-most-used substance in the world after water , [ 1 ] and is the most widely used building material. [ 2 ] Its usage worldwide, ton for ton, is twice that of steel, wood, plastics, and aluminium combined. [ 3 ]
When aggregate is mixed with dry Portland cement and water , the mixture forms a fluid slurry that is easily poured and molded into shape. The cement reacts with the water through a process called concrete hydration [ 4 ] that hardens it over several hours to form a hard matrix that binds the materials together into a durable stone-like material that has many uses. [ 5 ] This time allows concrete to not only be cast in forms, but also to have a variety of tooled processes performed. The hydration process is
In the past, lime -based cement binders, such as lime putty, were often used but sometimes with other hydraulic cements , (water resistant) such as a calcium aluminate cement or with Portland cement to form Portland cement concrete (named for its visual resemblance to Portland stone ). [ 6 ] [ 7 ] Many other non-cementitious types of concrete exist with other methods of binding aggregate together, including asphalt concrete with a bitumen binder, which is frequently used for road surfaces , and polymer conc