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Activation of fly ash and its effects on cement properties1

https://doi.org/10.1016/S0008-8846(98)00178-1Get rights and content

Abstract

A new method of fly ash activation with addition of Ca(OH)2 and a small quantity of Na2SiO3 is presented. Scanning electron microscopy, differential thermal analysis, x-ray diffraction analysis, alkali-absorption test, and strength measurement show that the activity of activated fly ash by this method is obviously increased, which can accelerate cement early hydration and promote setting and hardening.

Section snippets

Experimental materials and methods

FA for activation was obtained from Huang Pu Power Plant, Guangzhou, China. The ash was mixed with Ca(OH)2 in certain proportion by weight, Na2SiO3 addition = 3.91%, W/S = 3:1. After being homogeneously mixed, the mixture was held at a constant temperature of 55°C until Ca(OH)2 disappeared by optical microscopy observation [3], then kept at this temperature for another 8 hours. The sample was then wet ground for 40 min and dried at a temperature of 120°C; activated fly ash (AFA) was so

Activation of FA

The reasons for lower activity of FA arise from two factors. (1) The glassy surface layer of glass beads is dense and chemically stable. This layer protects the inside constituents, which were porous, spongy, amorphous, and therefore with higher activity [6]. (2) Its silica-alumina glassy chain of high Si, Al, and low Ca is firm; the chain must be disintegrated if activity is to take place. With Ca(OH)2 addition and higher basicity, the densified outer layer is corroded and the active core is

Conclusion

  • 1.

    A new method of AFA preparation is presented. With a small addition of Na2SiO3, the reaction between FA and Ca(OH)2 can be accelerated obviously because of the higher pH value in hydration liquid and circulating formation of NaOH.

  • 2.

    In early hydration the AFA surface is severely corroded, the amount of active groups is increased, more active cores are exposed, lower Ca/Si ratio calcium silicate hydrates as well as calcium aluminate hydrate are formed, and CaO absorption capability of AFA is

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There are more references available in the full text version of this article.

Cited by (127)

  • Mechanical and microstructural properties of lightweight CaO-activated fly ash composites in the presence of magnesium nitrate

    2023, Journal of Building Engineering
    Citation Excerpt :

    Thus, it is important to select optimal additives to stimulate the chemical reaction and to increase the strength of the lime-activated FA system. Many studies have been conducted to find additives for the lime-type activation of FA, such as CaCl2, Na2SO4 [6,7], Na2CO3 [8], silica fume, CaSO4 [9], Na2SiO3 [10], or NaCl [11]. However, in these earlier studies, the additives without chloride and sulfate (i.e., Na2CO3, silica fume, Na2SiO3) were invisibly beneficial in increasing strength, while the additives having chloride and sulfate (i.e., CaCl2, Na2SO4, CaSO4, NaCl) had the risk of causing durability problems, such as steel corrosion and sulfate attack, although these additives notably increased the strength [14].

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