Influence of Silica Fume on Permeability of Concrete to Oxygen for Temperatures up to 500 C

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Title: Influence of Silica Fume on Permeability of Concrete to Oxygen for Temperatures up to 500 C

Author(s): M. S. Zadeh, G. Debicki, P. Clastres and Y. Billard

Publication: Special Publication

Volume: 178

Issue:

Appears on pages(s): 975-996

Keywords: cracking; high performance concrete; oxygen; permeability; porosity; silica fume; temperature; water.

Date: 6/1/1998

Abstract:
Progressive utilisation of silica fume in concrete reactor containment walls that are susceptible to accident conditions, requires the study of leak tightness and the integrity of such structures, when exposing them to high temperatures. This paper deals with the influence of the silica fume dosage rate on the permeability coefficient for temperatures ranging from room temperature to 500°C. The use of silica fume reduces the oxygen permeability of concrete by 2 to 3.6 times at room temperature. When concrete, with or without silica fume, is exposed to heating up to 500°C free and bound water are released progressively; most hydrates are decomposed, the porous structure is modified and finally heating cracks are created, leading to concrete damage and an increase in the permeability coeffkient. However, the advantage of silica fume addition to decrease the loss of leak tightness integrity, depends strongly on the use of the optimum dosage rate of silica fume (i.e. 6-7% in these tests). The optimum dosage rate of silica fume can be estimated from 28 days compressive strength tests using silica fume dosage rates between 5 and 15%. A higher silica fume dosage rate leads to higher evaporable water content at T=lO5“C and for temperatures above 105’C leads to higher decomposing CSH, which causes the loss of more weight at any given temperature.