Strength and microstructure of class-C fly ash and GGBS blend geopolymer activated in NaOH & NaOH + Na2SiO3

Sasui Sasui, Gyuyong Kim, Jeongsoo Nam, Tomoyuki Koyama, Sant Chansomsak

Research output: Contribution to journalArticlepeer-review

49 Citations (Scopus)


In this paper, class-C fly ash (FA) and ground granulated blast-furnace slag (GGBS)-based geopolymer activated inNaOHandNaOH+ Na2SiO3 was studied regarding setting time, compressive strength, porosity, microstructure, and formation of crystalline phases. When comparing the effects of alkali type on the FA and GGBS geopolymer composites, results revealed that NaOH has a lesser effect in developing strength and denser microstructure than does NaOH + Na2SiO3, since the addition of Na2SiO3 provides the silica source to develop more compact structure. Incorporation of Na2SiO3 reduced the crystallinity and the paste was more amorphous compared to NaOH activated pastes. The class-C FA and GGBS blends resulted in prolonged setting time, reduced strength, and loose matrix with the increase in fly ash content. The un-reactivity of calcium in blends was observed with increasing fly ash content, leading to strength loss. It is evident from XRD patterns that calcium in fly ash did not contribute in forming C-S-H bond, but formation of crystalline calcite was observed. Furthermore, XRD analyses revealed that the reduction in fly ash leads to the reduction in crystallinity, and SEM micrographs showed the unreactive fly ash particles, which hinder the formation of a denser matrix.

Original languageEnglish
Article number59
Issue number1
Publication statusPublished - Jan 1 2020

All Science Journal Classification (ASJC) codes

  • Condensed Matter Physics
  • General Materials Science


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