STP930: Alkali-Silica Reactivity: Effect of Alkali in Aggregate on Expansion

    Stark, D
    Manager, Concrete Materials Section, and Principal Research Chemist, Portland Cement Association, Skokie, IL

    Bhatty, MSY
    Manager, Concrete Materials Section, and Principal Research Chemist, Portland Cement Association, Skokie, IL

    Pages: 15    Published: Jan 1986


    Abstract

    Tests were performed on samples of alkali-bearing aggregates to determine amounts of alkali that could be removed by leaching in Ca(OH)2 solution and water at 38°C (100°F) and 80°C (176°F). Additional tests were made on one reactive aggregate which was first subjected to leaching and then used to make mortar bars for testing in accordance with ASTM C 227. Leach periods of 7, 28, 90, and 180 days were used.

    Results show that alkali present within concrete aggregate particles may participate in alkali-silica reactivity. Alkali levels much greater than those present in high-alkali cements can be leached from non-reactive as well as reactive aggregate materials. It is suggested that ion-exchange processes possibly augmented by partial dissolution of the aggregate, facilitate leaching of alkali.

    Removal of alkali from aggregates, prior to their use in mortar bars, was shown to reduce expansions. Expansions were progressively reduced as greater amounts of alkali were leached from aggregates prior to their use with low- as well as high-alkali cements.

    Applicability of these findings to concrete in service is discussed.

    Keywords:

    aggregates, alkali, alkali-silica reactivity, cement, concrete, durability, expansion, leaching, mortar bars


    Paper ID: STP18461S

    Committee/Subcommittee: C09.23

    DOI: 10.1520/STP18461S


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