Pozzolanic properties of reject fly ash in blended cement pastes

Chi Sun Poon, X. C. Qiao, Z. S. Lin

Research output: Journal article publicationJournal articleAcademic researchpeer-review

89 Citations (Scopus)


Low-grade fly ash (reject fly ash, r-FA), a significant portion of the pulverized fuel ash (PFA) produced from coal-fired power plants and rejected from the ash classifying process, has remained unused due to its high carbon content and large particle size. But it may be used in certain areas, such as in solidification and stabilization processes of hazardous waste and materials for road base or subbase construction, which require relatively lower strength and reactivity. It is therefore necessary to extend research on the properties of r-FA and explore its possible applications. This paper presents experimental results of a study on the mechanical and hydration properties of cementitious materials prepared by blending r-FA with ordinary Portland cement (OPC). Parallel mixes were also prepared with the good ash [i.e., classified fine fly ash (f-FA)] for comparison. Selective chemical activators were added to the mix to study the effects of the activators on the properties of the blend system. The results show that r-FA generally has a lower rate of hydration than f-FA particularly at the early stage of hydration. Adding Ca(OH)2alone almost had no effect on accelerating the hydration of r-FA. But adding a small quantity of Na2SO4or K2SO4together with Ca(OH)2significantly accelerated the hydration reaction. The results of the compressive strength measurement correlated nicely with the degree of hydration results. It was also found that water-to-binder ratio (w/b) was an important factor in affecting the strength development and the hydration degree of r-FA pastes.
Original languageEnglish
Pages (from-to)1857-1865
Number of pages9
JournalCement and Concrete Research
Issue number11
Publication statusPublished - 1 Nov 2003


  • Chemical activator
  • Hydration degree
  • PFA
  • R-FA
  • Reject fly ash
  • Strength development

ASJC Scopus subject areas

  • Industrial and Manufacturing Engineering
  • Ceramics and Composites


Dive into the research topics of 'Pozzolanic properties of reject fly ash in blended cement pastes'. Together they form a unique fingerprint.

Cite this