3 Citations (Scopus)

Abstract

Using alkali activation, un-calcined soils have potential as precursors for low carbon, low cost, geopolymer-stabilised construction materials. This technology has been recently promoted as a lower impact alternative to cement stabilisation for walling materials in construction around the world. There is a lack of fundamental understanding around the alkali activation of un-calcined montmorillonite and illite, which, along with kaolinite, are clay minerals commonly found in soils. Kaolinite, as a 1:1 clay mineral, has been shown to form crystalline hydrosodalite when alkali-activated, but 2:1 montmorillonite and illite could form stronger geopolymer structures due to the higher Si:Al ratio in the precursor mineral. The lack of understanding of the underlying mechanisms at work with 2:1 clay minerals is a barrier to knowing how viable un-calcined geopolymer stabilised soil materials are for the range of soil types found in nature. In this study, montmorillonite and illite precursors were activated with a range of sodium hydroxide concentrations, compacted, and then cured at 80 °C for 24 h. The cured samples were characterised using a variety of advanced analytical techniques, including powder XRD, SEM, TGA, 27Al and 29Si-MAS-NMR, and FTIR. For the first time it was confirmed that alkali activation of uncalcined montmorillonite forms a NASH or (N,C)ASH geopolymer as the major product phase, which increases in quantity with increasing Na:Al molar ratio of the system. Although it has a similar Si:Al ratio, alkali activation of illite seems to result in structural alteration and increased porosity for Na:Al ≥ 0.5. The behaviour of these individual clay minerals suggests that the alkali activation of un-calcined 2:1 clay minerals is complex. Although alkali activation of montmorillonite can form a geopolymer, alkali activation of soils containing illite may lead to poor quality materials. This research has shown that the focus of future development work should be around montmorillonite-based clays.
Original languageEnglish
Pages (from-to)250-261
Number of pages12
JournalApplied Clay Science
Volume166
Early online date4 Oct 2018
DOIs
Publication statusPublished - 15 Dec 2018

Fingerprint

Bentonite
Alkalies
Clay minerals
montmorillonite
illite
clay mineral
Geopolymers
Chemical activation
Soils
Kaolin
kaolinite
soil
Kaolinite
MAS
Sodium Hydroxide
hydroxide
nuclear magnetic resonance
soil type
analytical method
stabilization

Keywords

  • Alkali activation
  • Clay
  • Geopolymer
  • Illite
  • Montmorillonite

ASJC Scopus subject areas

  • Geology
  • Geochemistry and Petrology

Cite this

Alkali activation behaviour of un-calcined montmorillonite and illite clay minerals. / Marsh, Alastair; Heath, Andrew; Patureau, Pascaline; Evernden, Mark; Walker, Peter.

In: Applied Clay Science, Vol. 166, 15.12.2018, p. 250-261.

Research output: Contribution to journalArticle

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abstract = "Using alkali activation, un-calcined soils have potential as precursors for low carbon, low cost, geopolymer-stabilised construction materials. This technology has been recently promoted as a lower impact alternative to cement stabilisation for walling materials in construction around the world. There is a lack of fundamental understanding around the alkali activation of un-calcined montmorillonite and illite, which, along with kaolinite, are clay minerals commonly found in soils. Kaolinite, as a 1:1 clay mineral, has been shown to form crystalline hydrosodalite when alkali-activated, but 2:1 montmorillonite and illite could form stronger geopolymer structures due to the higher Si:Al ratio in the precursor mineral. The lack of understanding of the underlying mechanisms at work with 2:1 clay minerals is a barrier to knowing how viable un-calcined geopolymer stabilised soil materials are for the range of soil types found in nature. In this study, montmorillonite and illite precursors were activated with a range of sodium hydroxide concentrations, compacted, and then cured at 80 °C for 24 h. The cured samples were characterised using a variety of advanced analytical techniques, including powder XRD, SEM, TGA, 27Al and 29Si-MAS-NMR, and FTIR. For the first time it was confirmed that alkali activation of uncalcined montmorillonite forms a NASH or (N,C)ASH geopolymer as the major product phase, which increases in quantity with increasing Na:Al molar ratio of the system. Although it has a similar Si:Al ratio, alkali activation of illite seems to result in structural alteration and increased porosity for Na:Al ≥ 0.5. The behaviour of these individual clay minerals suggests that the alkali activation of un-calcined 2:1 clay minerals is complex. Although alkali activation of montmorillonite can form a geopolymer, alkali activation of soils containing illite may lead to poor quality materials. This research has shown that the focus of future development work should be around montmorillonite-based clays.",
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