Concrete is used for foundations and floors because of its stability, strength and durability. It is a very suitable base on which to erect buildings. The basic materials used to make concrete are cement, water and aggregate. Other ingredients are added to control the characteristics of the material.
Cement is a key constituent of concrete. It is a powder ranging from white to grey in colour. Portland is not a brand name, but the main type of cement used in building. Portland cement is made from calcium compounds, silica, alumina and iron oxide, according to the Portland Cement Association. Gypsum is also added to control the hardening rate of the cement. Another type of cement is High Alumina Cement (HAC), according to The Concrete Society. This may be present in concrete foundations and floors built from 1950 to 1970.
Aggregate makes up the main volume of concrete. Aggregates range in consistency from fine to coarse. Fine aggregates are principally sand. Coarse aggregate consists of larger particles of rock, including ballast. Different kinds of aggregate give concrete different qualities. A greater volume of aggregate makes the mix heavier. However, the correct ratio between aggregate and other components has to be used for the concrete to achieve the required strength.
Pigments are used to add colour to concrete, in accordance with customer demand. Some of the colours available include brick red, deep buff, nut brown, old York green, orange, strong yellow, strong white and terra cotta. They are added to the concrete at the mixing stage, usually in powder form. There is a wide range of coloured concretes available. Further, there are specialist companies who will mix precise shades of concrete for clients.
Other constituents include admixtures. An admixture refers to a mixture of chemicals added to give concrete additional characteristics. The most commonly used admixtures are plasticisers. Plasticisers improve the workability of concrete, making it easier to pour and mould. Polymers may also be added to concrete to create desirable chemical reactions. Steel fibres are added in some cases to give concrete more strength. Steel reinforcing bars -- called rebar -- are sometimes incorporated into concrete foundations and floors.
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