Geopolymers - The Need For Standardization: What Is A Geopolymer?

The Need For Standardization: What Is A Geopolymer?

In the 1950s, Viktor Glukovsky, Kiev, Ukraine, in the former Soviet Union, has developed concrete materials originally known under the names "soil silicate concretes" and "soil cements". . Yet, since the introduction of the geopolymer concept by Joseph Davidovits, each scientist involved in different fields of applications has his own terminology and definition of what is a geopolymer. The six examples below were taken from recent scientific publications (2011), written by scientists with different backgrounds.

Six different definitions of the term geopolymer

For chemists

'...It is known that alkali-activated aluminosilicates are able to produce alumino-silicate geopolymers. The hardening mechanism involves the chemical reaction of geopolymeric precursors, such as alumino-silicate oxides, with alkali polysilicates yielding polymeric Si–O–Al bonds.'

For geopolymer chemists

'...Geopolymers consist of a polymeric Si–O–Al framework, similar to zeolites. The main difference to zeolite is geopolymers are amorphous instead of crystalline. The microstructure of geopolymers on a nanometer scale observed by TEM comprises small aluminosilicate clusters with pores dispersed within a highly porous network. The clusters sizes are between 5 and 10 nanometers.'

For geopolymer material chemists

'...The reaction produces SiO₄ and AlO₄, tetrahedral frameworks linked by shared oxygens as poly(sialates) or poly(sialate–siloxo) or poly(sialate–disiloxo) depending on the SiO₂/Al₂O₃ ratio in the system. The connection of the tetrahedral frameworks is occurred via long-range covalent bonds. Thus, geopolymer structure is perceived as dense amorphous phase consisting of semi-crystalline 3-D alumino-silicate microstructure.'

For geopolymer ceramic chemists

'...Although geopolymer is generally X-ray amorphous if cured at standard pressures and temperatures, it will convert into crystalline ceramic phases like leucite or pollucite upon heating.'

For alkali-cement scientists

'... Geopolymers are framework structures produced by condensation of tetrahedral aluminosilicate units, with alkali metal ions balancing the charge associated with tetrahedral Al. Conventionally, geopolymers are synthesized from a two-part mix, consisting of an alkaline solution (often soluble silicate) and solid aluminosilicate materials. Geopolymerization occurs at ambient or slightly elevated temperature, where the leaching of solid aluminosilicate raw materials in alkaline solutions leads to the transfer of leached species from the solid surfaces into a growing gel phase, followed by nucleation and condensation of the gel phase to form a solid binder.'

For ceramic scientists

'...Geopolymers are a class of totally inorganic, alumino-silicate based ceramics that are charge balanced by group I oxides. They are rigid gels, which are made under relatively ambient conditions of temperature and pressure into near-net dimension bodies, and which can subsequently be converted to crystalline or glass-ceramic materials.'