Durability of Fly Ash Concrete

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Title: Durability of Fly Ash Concrete

Author(s): Val R. Sturrup, R. Doug Hooton, and T. Gerry Clendenning

Publication: Special Publication

Volume: 79

Issue:

Appears on pages(s): 71-86

Keywords: alkali-aggregate reactions; carbon; concrete durability fly ash; freeze-thaw durability; mass concrete; pozzolans.

Date: 5/1/1983

Abstract:
Since before the first utilization of imported fly ash by Ontario Hydro as a pozzolan in mass concrete in 1950, research programs on many aspects of its influence on durability were undertaken. Majo. areas addressed have been: 1. thermal crack resistance in mass concrete; 2. reduction of alkali reactivity; 3. freezing and thawing resistance, and 4. sulphate resistance (preliminary). When the first fly ash was produced by Ontario Hydro from thermal plants used for peak load power, the problems with utilizing variable and often high carbon content fly ash were also studied. This problem was overcome by selective storage along with provisior for fineness and carbon content checks for each tanker of ash leaving the plant. Major findings of the research include: 1. Fly ash has and is being used successfully in lieu of both CSA Types 20 and 40 (ASTM Types II and IV) moderate and low-heat cements to control temperature rise and thermally induced cracking in mass concrete. 2. The replacement of 25 percent of normal portland cement with fly ash has been found to be effective in reducing alkali silicate expansions. 3. As long as adequate air contents are obtained, carbon content does not adversely affect the freezing and thawing resistance of concrete at least within the 12 percent CSA and ASTM limits. As long as carbon contents are established for each delivery of fly ash, dosages of air entraining agents can be modified easily.