Mitigating Effect of Pozzolans on Alkali-Silica Reactions

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Title: Mitigating Effect of Pozzolans on Alkali-Silica Reactions

Author(s): Mette Geiker and Niels Thaulow

Publication: Special Publication

Volume: 132

Issue:

Appears on pages(s): 533-548

Keywords: alkali-silica reactions; fly ash; pozzolans; silica fume; slags; sodium chloride; Materials Research

Date: 5/1/1992

Abstract:
Expansion of mortar bars with and without selected pozzolans exposed to saturated calcium hydroxide and sodium chloride solutions at 50 C has been measured up to 20 weeks of exposure. The mixes contained a Danish low-alkali sulfate-resistant cement or a French high-alkali cement, and inert quartz sand added 2 and 6 percent of synthetic cristobalite and varying amounts of pozzolans. Additions were 5, 15, and 25 percent fly ash; 3, 5, and 7 percent silica fume; 5 percent silica fume plus 15 percent fly ash; and 35 percent slag. Both fly ash and silica fume were found to prevent deleterious alkali-silica reactions. The amount of pozzolan necessary to prevent expansion increased with the amount of reactive aggregate and varied with the type of pozzolan. Additions of 5 percent fly ash or 3 percent silica fume were enough to suppress deleterious reactions in the mixes with 2 percent synthetic cristobalite during the period of testing. Twenty-five percent fly ash or 5 percent silica fume plus 15 percent fly ash were found to prevent deleterious reactions in the mixes with 6 percent synthetic cristobalite until 15 weeks of exposure.