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Title: Effect of Element Distribution on Strength in Fly Ash Geopolymers

Author(s): Chamila Gunasekara, David W. Law, Sujeeva Setunge, Iko Burgar, and Robert Brkljaca

Publication: Materials Journal

Volume: 114

Issue: 5

Appears on pages(s): 795-808

Keywords: compressive strength; element distribution; fly ash; geopolymer; porosity

Date: 9/1/2017

Abstract:
This study evaluates the influence of the elemental distribution in the fly ash particles and their impact on phase formation and compressive strength of five low-calcium fly ash geopolymers. The degree of geopolymerization in each geopolymer system was assessed by FT-IR and solid state 27Al MAS-NMR analysis. The corresponding pore volume changes were investigated by mercury intrusion porosimetry (MIP). The uniformity of the distribution of SiO2 and Al2O3 in the fly ash was observed to directly influence the dissolution of the amorphous surface layer in the initial geopolymerization process and control aluminosilicate gel precipitation and gel-phase creation. The results showed that the higher the uniformity of distribution (coupled with the stable conversion of aluminium from octahedral to tetrahedral coordination), the higher the aluminium amalgamation with silicates. The result of this is the production of a three-dimensional (3-D) polysialatesiloxo (Si-O-Al-O-Si) polymeric gel structure with high rigidity and stability, which in turn results in higher compressive strength. It was also observed that an increase of meso-porosity in geopolymer phase formation coupled with a cumulative pore volume below 1000 nm (3.937 × 10–5 in.) is a good indicator of the degree of geopolymerization.




  

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