Air Permeability of Concretes Mixed with Fly Ash and Condensed Silica Fume

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Title: Air Permeability of Concretes Mixed with Fly Ash and Condensed Silica Fume

Author(s): Shigeyoshi Nagataki and Isao Ujike

Publication: Special Publication

Volume: 91

Issue:

Appears on pages(s): 1049-1068

Keywords: air; concretes; Darcy's law; drying; fly ash; permeability; porosity; silica.

Date: 2/1/1986

Abstract:
The objective of this study was to investigate the behavior of air flow through concrete and to make clear the effects of use of fly ash and condensed silica fume on the air permeability of concrete. The air permeability of concrete was estimated by means of the coefficient of air permeability, and the difference of the coefficient of air permeability between concretes with and without fly ash and condensed silica fume was investigated. Furthermore the improvement of the airtightness of concretes with fly ash and condensed silica fume was discussed from the view point of the internal structure of concrete such as porosity. As the results of this study, it was confirmed that the flow of air through concrete obeyed Darcy's law. It is possible to apply the coefficient of air permeability as the index of air permeability of concrete. In the case of use of fly ash, the coefficient of air permeability of concrete cured in water for the period of 28 days hadalmost the same value as concrete without fly ash when compared at the same level of compressive strength. However, the concrete with fly ash cured in water for the period of 91 days is more airtight than concrete without fly ash. In case of use of condensed silica fume, the coefficient of air permeability decreased with the increase of replacement ratio of condensed silica fume, and did not depend on the period of the curing in water. These results can be quantitatively understood by means of the internal structure of concrete.