Alkali-activation of aluminosilicate solids using alkaline
hydroxide and/or silicate solutions can be used to synthesise
inorganic geopolymeric binders, or alkali-activated cements,
displaying excellent physical and chemical properties [1–4].
Experimental evidence suggests that the principal binding phase
within geopolymers, where low-Ca source materials are used, is
an X-ray amorphous aluminosilicate gel consisting of a threedimensional
framework of SiO4 and AlO4 tetrahedra linked by
corner-shared O atoms [1,3]. The negatively-charged tetrahedral
Al sites in the network are charge-balanced by alkali metal
cations such as Na+ and/or K+. This aluminosilicate gel can be
used to bind various mineral aggregates, such as sand, natural
rock and/or other mineral fragments to produce mortars and
concretes. On the other hand, if the raw material used is rich in
Ca, such as a blast furnace slag, there is growing evidence to
suggest that the binding phase formed is a mixture of calcium
silicate hydrate (CSH) and aluminosilicate gels, whose relative
proportions can be determined to a certain extent by the
abundance of Ca from the source materials and the stoichiometry
of the reaction(s)
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