Geopolymer is a term coined by Joseph Davidovits in the 1980s to designate inorganic synthetic polymers of aluminosilicates that come from the chemical reaction known as geopolymerization. However, these compounds had already been developed in the 1950s in the Soviet Union under the name Soil cements. Geopolymers are also known as inorganic aluminosilicates.

Geopolymers have a high potential to be used in numerous fields, but their use as substitutes for Portland cement predominates, a field towards which most of the research has been directed. Geopolymers have the advantage of having low CO emissions in their production, great chemical and thermal resistance, and good mechanical properties, both at room temperature and at extreme temperatures.

The geopolymerization reaction occurs under highly alkaline conditions "Base (chemistry)") between an aluminosilocate powder and an activator solution (based on a molar mixture of sodium hydroxide and an alkaline silicate, for example sodium or potassium) at ambient conditions. At the laboratory level, metakaolin is usually used as a starting material for the synthesis of geopolymers, this being generated by the thermal activation of kaolinite. Numerous studies have been carried out using industrial waste (Methakaolin) and other aluminosilicates.

The polymerization process is carried out by putting the pozzolanic material in contact with the alkaline activator solution, which results in the formation of polymer chains after the ions in solution have been reoriented. These polymer chains can be considered hypothetically as the result of the polycondensation of orthosialate ions. Since the exact reaction mechanism has not yet been completely determined, it is usually assumed that the synthesis is carried out by means of oligomers, which provide the unitary structures of the three-dimensional macromolecular network.

Geopolymers that are based on aluminosilicates are called polysialates. This term is an abbreviation of poly-(silico-oxo-aluminate) or (-Si-O-Al-O-), with n being the degree of polymerization. The sialate network consists of SiO and AlO tetrahedra linked by shared oxygen atoms. Within the lattice cavities, positive ions (Na, K, Li, Ca, Ba, NH, HO) must be present to counteract the negative charges of Al so that aluminum can be bonded to three oxygens, like silicon. The empirical formula of polysialates is as follows:.

Where M is any of the cations mentioned above, n is the degree of polymerization, z, which can be 1, 2 or 3, determines the type of resulting geopolymer, which means that if z is equal to 1 the network will be of the polysialate type, if z is 2, the network will be poly(sialate-siloxo) and if Z is 3, the network will be poly(sialate-disiloxo), and w is the number of water molecules. associated.