The Activation of Class C-, Class F-Fly Ash and Blast Furnace Slag Using Geopolymerisation

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Title: The Activation of Class C-, Class F-Fly Ash and Blast Furnace Slag Using Geopolymerisation

Author(s): H. Xu, G. C. Lukey, and J. S. J. van Deventer

Publication: Special Publication

Volume: 221

Issue:

Appears on pages(s): 797-820

Keywords: activation; ASTM Class F and C fly ashes; blast-furnace slag; geopolymers

Date: 5/1/2004

Abstract:
An investigation of the activation of Class C and Class F fly ash as well as granulated blast furnace slag has established that the amount and nature of the calcium containing phases in these materials significantly affect the activation mechanism. The majority of calcium in blast furnace slag is associated with either Si or with S and it can be activated either by use of a highly alkaline solution or by an alkaline solution containing soluble silicate to produce a solid material having sufficient mechanical strength. Class C fly ash contains calcium that is partly structured with aluminium and silicon and it has been found that this class of fly ash can only be activated using a highly alkaline solution containing soluble silicate. It has been observed that Class F fly ash cannot be successfully activated by either a highly alkaline solution or an alkaline soluble silicate solution, but by a very highly alkaline soluble silicate solution. It is proposed that the poor activation of Class F fly ash is due to this material having significantly lower calcium content than either blast furnace slag or Class C fly ash and that the calcium is in an isolated form.