Volume 7, Issue 2 (January 1985)

    Mechanism of Pozzolanic Reactions and Control of Alkali-Aggregate Expansion

    CODEN: CCAOAD

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    Abstract

    The mechanism of pozzolanic reactions and their control of expansion caused by alkali-aggregate reaction was investigated. Mixtures of tricalcium silicate, opal, sodium hydroxide, and water having calcium oxide to silica mole ratios from 1.07 to 3.0 were prepared and reacted from seven days to four years before filtering. The solids (precipitates) were studied by X-ray diffraction to determine the phases present, and the alkali content of filtrates was obtained by chemical analysis.

    Results suggest that pozzolans reduce or eliminate alkali-aggregate expansion by producing additional calcium silicate hydrate and low lime calcium silicate hydrate. These hydrates can retain additional alkali, thus reducing the amount of alkali available for reaction with reactive aggregate. In order to control alkali-aggregate expansion by the addition of pozzolan, such as fly ash, results indicate that about 30% low lime fly ash is required. However, this amount could be reduced considerably, to a level as low as 20% (cement basis), if the concrete contains reactive siliceous aggregate.


    Author Information:

    Bhatty, MSY
    Principal research chemist, Portland Cement Association, Skokie, IL


    Stock #: CCA10372J

    ISSN: 0149-6123

    DOI: 10.1520/CCA10372J

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    Author
    Title Mechanism of Pozzolanic Reactions and Control of Alkali-Aggregate Expansion
    Symposium , 0000-00-00
    Committee C09