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Home > Publications > International Concrete Abstracts Portal
The International Concrete Abstracts Portal is an ACI led collaboration with leading technical organizations from within the international concrete industry and offers the most comprehensive collection of published concrete abstracts.
Title: Activation of Fly Ashes: A General View
Author(s): A. Fernandez-Jimenez and A. Palomo
Publication: Special Publication
Appears on pages(s): 351-366
Keywords: alkaline activation; BSEM; fly ash; MAS NMR
Abstract:Alkali activation of fly ashes is a chemical process through which the glassy structure of the material is transformed into a very well compacted cement. In general terms a variety of natural materials and industrial by-products rich in S'02 and Al2O3 may be activated with certain alkaline compounds to produce cementitious systems when cured under mild temperature conditions. The activation process may be considered as a set of destruction-condensation re-actions that initially lead to a series of unstable structure units and later produces the formation of tixotropic coagulation structures, which can condense to form the hydrated products. This paper describes a micro-structural study of a number of alkali activated fly ash matrices. MAS-NMR results has shown that the main reaction product in the activation of fly ashes is an amorphous aluminosilicate gel having a 3-dimensional structure in which the Si evolves in a variety of environments with a predominance of Q4(3Al) units when curing time is short, and Q4(2Al) units when curing time is long. Aluminium is essentially tetrahedrally co-ordinated. Microanalysis has provided additional information on the Si/AI ratio of the mentioned aluminosilicate gels too.
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