Two-Stage Processing to Promote the Use of the Reject Coarse Fraction of Fly Ash into Blended Cement

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Title: Two-Stage Processing to Promote the Use of the Reject Coarse Fraction of Fly Ash into Blended Cement

Author(s): S.K. Antiohos, G. Tzouvalas, and S. Tsimas

Publication: Special Publication

Volume: 242

Issue:

Appears on pages(s): 403-418

Keywords: active silica; fractionation; k-value; processing; reject fly ash

Date: 4/1/2007

Abstract:
Reject fly ash (rFA) represents a significant portion of the fly ashes produced from coal or lignite-fired power plants. Due to the high carbon content and large mean particle diameter, rFA is not used in the construction sector (for example as a supplementary cementing material) and is currently dumped into landfills, thus representing an additional environmental burden. In order to maximize the use of solid wastes, there is a need to investigate potential applications for rFAs. The benefits, however, of the inclusion of recycled materials will only be realized if they result in improved performance and economic savings for the final product. In this work, critical mechanical and hydration properties of blended cements made by blending the coarse fraction (after grinding) of a lignite high-calcium fly ash with ordinary cement were measured and compared with the respective properties of a good quality fly ash-cement blend. The results reveal that a relatively cheap, two-step classification-grinding method is able to enhance the pozzolanic behaviour of the rFAs, so that the overall performance of rFA containing cement is significantly improved.