STP99

    Effect of Calcination on Natural Pozzolans

    Published: Jan 1950


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    Abstract

    Calcination will improve the quality of some pozzolans, reduce the quality of others, and induce pozzolanic properties in some otherwise essentially non-reactive-substances. Natural pozzolans or natural materials in which pozzolanic properties can be induced by calcination at temperatures less than 2000 F. owe their activity to One or more of five kinds of substances. Consequently, natural pozzolans can be classified by their essential active ingredient as follows: Activity type Essential active constituent 1....................:...............Volcanic glass 2....................... Opal 3a...................................Kaolinite-type clay 3b...................................Montmorillonite-type clay 3c...................................Illite-type clay 3d...................................Mixed clay with vermiculite 4....................................Zeolites 5....................................Hydrated oxides of aluminum 6....................................Nonpozzolan

    Water requirement, setting time of lime-pozzolan paste, strength development of portland-pozzolan mortar, and control of alkali-aggregate reaction are affected significantly by calcination at temperatures up to 2000 F. Calcination of clayey materials, activity type 3, is essential to develop satisfactory pozzolanic activity. The quality of activity types 1, 2, and 4 frequently can be improved considerably by calcination. No materials of activity type 5 were included in the investigations.

    Pozzolans of activity types 1, 2, 3a, and 3b are the most promising from the standpoints of strength development and control of alkali-aggregate reaction in mortar and concrete, opaline cherts of activity type 2 being superior to all others. For these materials, calcination in the range from 1200 F. to 1600 F. will induce optimum activity.


    Author Information:

    Mielenz, RC
    Head, Petrographic Laboratory, Head, Durability Laboratory, and Head, Cement Laboratory, U. S. Bureau of Reclamation, Denver, Colo.

    Witte, LP
    Head, Petrographic Laboratory, Head, Durability Laboratory, and Head, Cement Laboratory, U. S. Bureau of Reclamation, Denver, Colo.

    Glantz, OJ
    Head, Petrographic Laboratory, Head, Durability Laboratory, and Head, Cement Laboratory, U. S. Bureau of Reclamation, Denver, Colo.


    Paper ID: STP39404S

    Committee/Subcommittee: C07.07

    DOI: 10.1520/STP39404S


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