Concrete is one of the most commonly used building materials in the world.
Concrete is one of the most common materials used in construction today and has been used in construction since the days of the Roman Empire. Buildings, foundations, bridges, roads, sidewalks, dams and works of art are made from concrete. Concrete is a composite material made from cement, water and aggregates. Aggregates are rocks bound together by the reaction of the cement and water that give concrete its strength. Common aggregates found in concrete are sand, vermiculite, crushed limestone and shale.
Dehydration
Although cement and concrete are often erroneously thought to be the same thing, cement is actually a component of concrete. Cement begins with quarried limestone that is crushed and blasted into small pieces and mixed with clay, shale, sand and iron ore. The mixture is ground together to form a powder. The powder is then heated in kilns where it goes through dehydration as any free water in the powder evaporates.
Calcination
Continued heating from the kilns bring the cement to the next step in the processing called calcination. Calcination is a decomposition caused by the loss of bound water and carbon dioxide from the mixture while the mixture is heated to a temperature below its melting point, around 1300-degrees Celsius.
Clinkering
During the clinkering phase, the mixture is heated to temperatures between 1300- and 1450-degrees Celsius. At this stage calcium silicates are formed. The mixture is then cooled, forming aluminate phase, ferrite and a little belite. Finally, the resulting clinker is ground and mixed with gypsum to produce the Portland cement used in the production of concrete.
Hydration
Portland cement is mixed with aggregates to create the dry ingredients for concrete. When water is added to this mixture, the chemical reaction hydration begins. Concrete does not harden because of evaporation. It hardens because of hydration. The five major compounds in Portland cement are tricalcium silicate, dicalcium silicate, tricalcium aluminate, tetracalcium aluminoferrite and gypsum. During hydration, each of these compounds reacts with water to add either heat to the reaction or add strength to the final hardened concrete.
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