Geopolymerization is a geosynthesis (a reaction that chemically integrates minerals) that involves naturally occurring silico-aluminates. The silicon(Si) and aluminum (Al) atoms react to form molecules that are chemically and structurally comparable to those binding natural rock that allows for products to exhibit the most ideal properties of rock-forming elements, i.e., hardness, chemical stability and longevity that is equal to natural geologic longevity.
The geopolymers that are based on alumino-silicates are designated as poly(sialate), which is an abbreviation for poly(silico-oxo-aluminate) or (- Si-O-Al-O -)n (with n being the degree of polymerization). The chemical structure shown describes a poly(sialate-siloxo) Geopolymer resulting from the geosynthesis of poly(silisic) acid (SiO2)n and potassium alumino-silicate, in alkali medium (KOH, NaOH). In this structure the sialate (Si-O-Al-O-) is the cross-linking or networking element.
Examples of polycondensation into poly(sialate) and poly(sialate-siloxo):
The geo-chemical syntheses are carried out through oligomers (dimer, trimer, tetramer, pentamer) which provide the actual unit structures of the three dimensional macromolecular edifice. See in Davidovits’ book, GEOPOLYMER Chemistry & Applications, the Chapters 2, 5, 6, 7 and 8. In the figure displayed below, the traditional ionic, tetrahedral representation for silicates and alumino-silicates is displayed on the left; on the right the actual co-valent bonding formulation for geopolymers:
