Influence and role of feedstock Si and Al content in Geopolymer synthesis

Abstract

This study evaluates the role and relationship between SiO₂ and Al₂O₃ contents of aluminosilicate material on the properties of Si-rich geopolymer systems using Australian fly ashes and existing published data. The selected fly ashes, with varying amounts of amorphous and total SiO₂ and Al₂O₃ were assessed for their overall reactivity. XRD analyses yielded traces of sodalite in addition to conventional amorphous geopolymer phase for the fly ash mixtures with amorphous SiO₂/Al₂O₃ = 3.31. The other two fly ashes with higher amorphous SiO₂/Al₂O₃ ratio tended to produce sodium aluminosilicate zeolitic phases comprising mainly of Na-P1 zeolite and faujasite. These latter phases originate from Na₂O–Al₂O₃–SiO₂–H₂O gel assemblages but the pathway appears to be governed by the available reactive SiO₂ and Al₂O₃ in the reaction environment. However, indices based on the amorphous content or more precisely amorphous SiO₂/Al₂O₃ ratio provided a relatively good correlation with the compressive strength of the final product.

Keywords:

• Geopolymer
• aluminosilicate source
• compressive strength
• amorphous phases
• SiO₂/Al₂O₃ ratio
• zeolite

Additional information

Funding

Funding. The research was partly supported by the Australian Research Council grant (ARC grant number LP120200774), awarded to the Swinburne University of Technology, Australia.