Geopolymers, first introduced by Davidovits in 1978 [1], are
inorganic aluminosilicate binders synthesized by the alkaliactivation
of materials containing Al2O3 and SiO2, i.e., kaolinite
clays or industrial byproducts (e.g., fly ash or slag) [2]. These
binders provide a better alternative to OPC due to their lower
environmental footprints and reduced CO2 emissions into the atmosphere,
compared to the cement industry [3e6]. A number of
studies have reported the effects of different parameters, i.e., the
raw materials, composition of the alkali-activator, or the alkaliactivator/
binder ratio, on the properties of geopolymers [7e11].
The mechanism of geopolymerization includes the following
steps: (1) the dissolution of Si and Al in an alkali medium (through
hydrolysis), (2) the condensation of the dissolved species into
monomers, and (3) polycondensation into polymeric structures,
which is similar with the mechanism of zeolite formation apart
from several differences in the synthesis conditions [12e14].