Fly Ash-Silica Fume-Cement Paste- Kinetics of Hydration

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Title: Fly Ash-Silica Fume-Cement Paste- Kinetics of Hydration

Author(s): W. Nocun-Wczelik

Publication: Special Publication

Volume: 242

Issue:

Appears on pages(s): 243-252

Keywords: calcium hydroxide; cement; conductivity; fluidized bed combustion ash; fly ash; heat of hydration; microstructure

Date: 4/1/2007

Abstract:
The mixtures of normal portland cement with fly ash from black coal combustion in classic installation and fly ash from brown coal combustion in fluidized bed were examined; the silica fume additive was used as a hydration process modifier. The hydration kinetics was followed by means of calorimetry. Then the calcium hydroxide content was determined by TG method and the electric conductivity of hydrating suspensions was measured. The course of so-called pozzolanic reaction between the additives and calcium ions was investigated and a selective consumption of calcium ions by silica fume was deduced from the data thus obtained. The use of silica fume as an additive brings about the acceleration of hydrolysis of cement components and acceleration of the formation of hydration products, usually by intensive consumption of Ca ions from the liquid phase. It has been found that silica fume, by quick consumption of calcium ions has a retarding effect in the beginning, but soon after, within a few hours, an intensive hydration, with the formation of dense C-S-H, takes place.