National Geographic Megastructures - Science of Concrete Documentary - BBC Documentary History
This article is about the construction material. For other uses, see Concrete (disambiguation).
Not to be confused with cement or mortar (masonry).
Concrete is a composite material composed of coarse aggregate bonded together with a fluid cement that hardens over time. Most concretes used are lime-based concretes such as Portland cement concrete or concretes made with other hydraulic cements, such as ciment fondu. However, asphalt concrete, which is frequently used for road surfaces, is also a type of concrete, where the cement material is bitumen, and polymer concretes are sometimes used where the cementing material is a polymer.
When aggregate is mixed together with dry Portland cement and water, the mixture forms a fluid mass that is easily molded into shape. The cement reacts chemically with the water and other ingredients to form a hard matrix that binds the materials together into a durable stone-like material that has many uses. Often, additives (such as pozzolans or superplasticizers) are included in the mixture to improve the physical properties of the wet mix or the finished material. Most concrete is poured with reinforcing materials (such as rebar) embedded to provide tensile strength, yielding reinforced concrete.
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. Today, large concrete structures (for example, dams and multi-storey car parks) are usually made with reinforced concrete.
After the Roman Empire collapsed, use of concrete became rare until the technology was redeveloped in the mid-18th century. Today, concrete is the most widely used man-made material (measured by tonnage).
Megastructures is a documentary television series appearing on the National Geographic Channel in the United States and the United Kingdom, Channel 5 in the United Kingdom, France 5 in France, and 7mate in Australia.
Each episode is an educational look of varying depth into the construction, operation, and staffing of various structures or construction projects, but not ordinary construction products.
Generally containing interviews with designers and project managers, it presents the problems of construction and the methodology or techniques used to overcome obstacles. In some cases (such as the Akashi-Kaikyo Bridge and Petronas Towers) this involved the development of new materials or products that are now in general use within the construction industry.
Megastructures focuses on constructions that are extreme; in the sense that they are the biggest, tallest, longest, or deepest in the world. Alternatively, a project may appear if it had an element of novelty or are a world first (such as Dubai's Palm Islands). This type of project is known as a Megaproject.
The series follows similar subjects as the History Channel's Modern Marvels and Discovery Channel's Extreme Engineering; covering areas of architecture, transport, construction and manufacturing.