Waste and Biomass Valorization

, Volume 9, Issue 6, pp 1047–1060 | Cite as

Comparative Studies of Alkali Activated South African Class F and Mongolian Class C Fly Ashes

  • J. Temuujin
  • J. Mapiravana
  • U. Bayarzul
  • G. Oyun-Erdene
  • Ts. Zolzaya
  • B. Darkhijav
  • M. Dlamini
  • C. H. Rüscher
Original Paper


The 7 days compressive strength of alkali activation of class C fly ash from Mongolia (Banganuur fly ash) and class F fly ashes from South Africa (Ash Resources, Ulala) were measured, depending on different waterglass (WG) to sodium hydroxide ratios in the activator. FTIR, XRD and SEM analyses were carried out. It is observed that Baganuur fly ash can be activated sufficiently using NaOH-solution only obtaining highest strength (33 MPa), whereas Ulala and Ash Resources almost fails (<10 MPa). The South Africa fly ash gains, however, around 28 MPa using 50:50% WG to NaOH ratios, where the class C-fly ash becomes a bit weaker (24 MPa). The different behavior is explained by formation of different geopolymer-types of network. In the case of class C fly ash alkali activation without the contribution waterglass is sufficient for the formation of amorphous C–S–H type phases due to the structure directing effect of the high amount of Ca-ions. This effect is lost with increasing the waterglass content. The waterglass effect—on the other hand—enforces the strength development for class F-fly ashes with high Al content instead of high Ca. Here network is formed mainly via preliminary chain formation due to condensation of the waterglass followed by cross-linking the chains via sialate linkages.


Class F-fly ash Class C-fly ash, alkaline solution Geopolymers Microstructure 



The present joint research was supported by the Council of Scientific and Industrial Research (CSIR) of the Republic of South Africa and the Mongolian Academy of Sciences. JT and CHR supported by Alexander von Humboldt Foundation, too, which is gratefully acknowledged.


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Copyright information

© Springer Science+Business Media Dordrecht 2017

Authors and Affiliations

  • J. Temuujin
    • 1
  • J. Mapiravana
    • 2
  • U. Bayarzul
    • 1
  • G. Oyun-Erdene
    • 1
  • Ts. Zolzaya
    • 1
  • B. Darkhijav
    • 1
  • M. Dlamini
    • 2
  • C. H. Rüscher
    • 3
  1. 1.Institute of Chemistry and Chemical Technology, Mongolian Academy of SciencesUlaanbaatarMongolia
  2. 2.Building Science and Technology, CSIR Built EnvironmentPretoriaSouth Africa
  3. 3.Institute of MineralogyLeibniz University of HannoverHannoverGermany

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