Expansion of Powerhouse Structures Due to Alkali-Aggregate Reaction and the Use of low Calcium Fly Ash to Ameliorate the Reaction in Future Construction

Alkali-aggregate reactivity, a reaction between the alkalies in the concrete pore fluid and certain siliceous aggregates was identified as a cause of disruptive expansion in concrete in Nova Scotia in 1962. Powerhouse structures, constructed with concrete containing meta-sediments and biotite schists, which are commonly used as concrete aggregate in Nova Scotia, caused expansion which created problems with the operation of the plants within 10 years after construction. Extensive studies in the mid 1960's and late 1980's of operating quarries and deteriorated structures, indicated that the reactive aggregates were widespread. Studies in the 1980's on the use of low calcium fly ash as a replacement or addition for portland cement showed conclusively that the reaction could be ameliorated with 15 to 30 percent fly ash replacement of the cement. Low calcium fly ash is now used systematically to lessen the potential for alkali-aggregate reaction.