The exact mechanism of setting and hardening of the geopolymer material is not clear.
However, most proposed mechanism consists the chemical reaction may comprise the
following steps:
(1) Dissolution of Si and Al atoms from the source material through the action of
hydroxide ions.
(2) Transportation or orientation or condensation of precursor ions into monomers.
(3) Setting or polycondensation/polymerisation of monomers into polymeric structures
[15].
Such frameworks are called polysialates, where sialate stands for the silicon-oxoaluminate
building unit. The sialate network consists of SiO4 and AlO4 tetrahedra linked
by sharing all oxygen atoms. Positive ions (Na+
, K+
, Ca2+, etc) must be present to balance
the negative charge of Al in 4-fold coordination. Chains and rings may be formed and
cross-linked together, always through a sialate Si-O-Al bridge. Polysialates are chain and
ring polymers with Si4+ and Al3+ in 4-fold coordination with oxygen and range from
amorphous to semi-crystalline. The amorphous to semi-crystalline thre