Effectiveness of Supplementary Cementing Materials in Controlling Chloride Penetration into Concrete

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Title: Effectiveness of Supplementary Cementing Materials in Controlling Chloride Penetration into Concrete

Author(s): R. N. Swamy and J. C. Laiw

Publication: Special Publication

Volume: 153

Issue:

Appears on pages(s): 657-674

Keywords: blast furnace slag; chlorides; compressive strength; drying; durability; fly ash; silica fume; slabs; tests; workability; Materials Research

Date: 6/1/1995

Abstract:
Presents the results of a study to investigate the effectiveness of ground granulated blast furnace slag, fly ash, and silica fume in controlling chloride penetration into concrete of high water-binder (w/b) ratio. To simulate field conditions, the tests were carried out on 1000 x 500 x 150 mm reinforced concrete slabs. to understand the basic roles of mineral admixtures in controlling chloride penetration, the cement was replaced, mass for mass, by 65 percent slag, 30 percent fly ash, and 10 percent silica fume without either modifying the water-binder ratio or using a water-reducer or superplasticizer. A constant and high water-binder ratio was deliberately used for all the concrete mixtures; the results are compared, where appropriate, with mixtures of lower w/b. the effects on workability, compressive strength, and chloride penetration were then evaluated, the latter two properties over a period of 18 months through cyclic exposure to four percent sodium chloride solution. Irrespective of their effects on workability and compressive strength, all the cement replacement materials reduced both the depth of penetration and the chloride concentration at a given depth from the concrete surface. Silica fume was the most effective and fly ash the least. Even at a very high w/b of 0.75, slag concrete showed a consistently lower chloride concentration for all exposure levels up to 50 cycles, and at all depths from the concrete surface compared to that of portland cement concrete. Both the type of supplementary cementing material and the period of exposure influenced chloride penetration, but the water-binder ratio also had a significant effect at all ages.