4.6 Article

Quantitative Correlation between the Degree of Reaction and Compressive Strength of Metakaolin-Based Geopolymers

Journal

MATERIALS
Volume 13, Issue 24, Pages -

Publisher

MDPI
DOI: 10.3390/ma13245784

Keywords

geopolymer; nuclear magnetic resonance; quantification; compressive strength

Funding

  1. National Science Foundation [DMR 10-08109]
  2. Department of Civil and Environmental Engineering at University of Illinois

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For geopolymers (usually composed of unreacted precursor and gel), the compressive strength is controlled by two factors. The first is the degree of reaction, or, equivalently, the amount of gel formed, including any calcium silicate hydrate gel in calcium-containing mixtures. The second factor is the gel composition, generally given by the Si/Al ratio. These two parameters are interrelated for typical silicate-activated metakaolin geopolymers. By separating out effects of Si/Al ratio and degree of reaction, this study quantitatively correlates the degree of reaction with the compressive strength of metakaolin-based geopolymers with and without calcium. Solid-state Si-29 nuclear magnetic resonance (NMR) aided with chemical extractions was used to determine gel amounts and composition for several geopolymer mixtures. The compressive strength was also measured for each mixture at 7 days. Both the increase of Na/Al ratio in mixtures without calcium and addition of external calcium increased the degree of reaction, and compressive strength correlated linearly (R-2 > 0.88) with the degree of reaction.

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