Stoichiometrically controlled C-(A)-S-H/N-A-S-H gel blends via alkali-activation of synthetic precursors

The extent to which the composition of the reaction mix affects the formation of a biphasic C-(A)-S-H/N-A-S-H geopolymer framework, and how the interaction of these phases affects geopolymer microstructure, can only be studied by strict stoichiometric control. Stoichiometrically controlled geopolymers containing both C-(A)-S-H and N-A-S-H gels are produced here by reaction of a sodium silicate solution with calcium aluminosilicate powders, which were synthesised via a novel solution-polymerisation method utilising polyethylene glycol as a polymer carrier to sterically inhibit movement of precursor cations. Increased Ca content in the reaction mix appears to promote greater formation of a C-(N)-(A)-S-H gel, while reduced Ca content and increased Al and Si content promote greater formation of an N-A-S-H gel in addition to the main C-(A)-S-H reaction product. The stoichiometrically controlled geopolymers constitute a chemically simplified model system through which the nature of the biphasic C-(A)-S-H/N-A-S-H gels present in alkali activated binders can be studied.