Geopolymer Chemistry

What is geopolymerisation?  refer https://geopolymer.org

Si / Al =2/1 for cements and concretes

Avoid making very surface hard sample that is nothing more than soluble silicates that have migrated from inside the sample after de-moulding and air curing. (will not pass a water test). Moist curing essential.

Geopolymer mineral chemical compound or mixture of compounds.

eg silico-aluminate (-Si-O-Al-O-)

created by a process of geopolymerisation.

  • micro structures of geopolymers temperature dependent.
  • X-ray shows amorphous at room temperature
  • evolves to crystalline matrix at > 500 deg C

Geopolymerisation two synthesis routes

  • alkaline medium
  • acid medium

Is a process of combining many small molecules known as oligomers into covalently bonded network.

The geo-chemical synthesis are carries out through oligomers that provide the unit structures of the 3D macro molecule edifice.

Alumino-Silicate geopolymers Si:Al=2   -Si-O-Al-O-Si-O-  silate-siloxo (poly(silate-siloxo))

Polymerisation speed

  • slow siloxo ( -Si-O-Si-O-)
  • very fast  oligo-silate (-Si-O-Al-O-)

silate-siloxo

 How do we get silate and siloxo?

for example de-polymerisation (alkalination ) of alumino-silicate compounds

alkalination

alkalination

 

dehydroxylation

micelleGP-nano-micelle
OH
|
an oligomer  HO-Si-OH
|
OH

A geopolymetric micel
A siloxo
A silate
Chemically bonded water – a little shrinkage