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Geopolymer is a term covering a class of synthetic aluminosilicate materials with potential use in a number of areas, but predominantly as a replacement for Portland cement. The name Geopolymer was first applied to these materials by Joseph Davidovits in the 1970s, although similar materials had been developed in the former Soviet Union since the 1950s under the name Soil cements  
Additional recommended knowledge
Much of the drive behind research is to investigate the development of geopolymers as a potential large-scale replacement for concrete produced from Portland cement. This is due to geopolymers’ lower carbon dioxide emissions, greater chemical and thermal resistance and better mechanical properties at both atmospheric and extreme conditions.
Geopolymers are generally formed by reaction of an aluminosilicate powder with an alkaline silicate solution at roughly ambient conditions. Metakaolin is a commonly used starting material for laboratory synthesis of geopolymers, and is generated by thermal activation of kaolinite clay. Geopolymers can also be made from natural sources of pozzolanic materials, such as lava or fly ash from coal. Most studies have been carried out using natural or industrial waste sources of metakaolin and other aluminosilicates.
The majority of the Earth’s crust is made up of Si-Al compounds. Davidovits proposed in 1978 that a single aluminium and silicon-containing compound, most likely geological in origin, could react in a polymerisation process with an alkaline solution. The binders created were termed "geopolymers" but, now, the majority of aluminosilicate sources are by-products from organic combustion, such as fly ash from coal burning. These inorganic polymers have a chemical composition somewhat similar to zeolitic materials but exist as amorphous solids, rather than having a crystalline microstructure.
The chemical reaction that takes place to form geopolymers follows a multi-step process:
|This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia article "Geopolymers". A list of authors is available in Wikipedia.|