STP597

    Use of Highly Active Pozzolans for Reducing Expansion in Concretes Containing Reactive Aggregates

    Published: Jan 1976


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    Abstract

    Since it takes only a small amount of reactive aggregate to cause deterioration of concrete due to the alkali-silicate reaction, vast deposits of aggregates throughout the world are in danger of being rejected as undesirable for use in concrete unless acceptable corrective measures are found. Although addition of commonly available pozzolans can effectively reduce the expansion associated with the alkali-silicate reaction, the quantity of pozzolan needed for this purpose is generally large enough to influence adversely the water demand and thereby the concrete quality.

    In this study the use of a highly active pozzolan, namely, rice hull ash, is compared with a normal pozzolan for reducing the alkali-silicate expansion. Whereas 25 percent of the latter by weight of the cementing material was required to reduce the expansion in the ASTM Test for Effectiveness of Mineral Admixtures in Preventing Excessive Expansion of Concrete Due to the Alkali-Aggregate Reaction (C 441-69) mortar by 90 percent, only 10 percent of the former was sufficient to obtain the same degree of effectiveness in reducing the expansion. Laboratory tests on concrete mixes containing the corresponding proportions of the pozzolans showed that, when compared with the control concrete, the mix containing the rice hull ash did not show strength loss at three and seven days whereas the mix containing the normal pozzolan showed severe strength loss at early ages.

    Keywords:

    aggregates, alkali-silicate reaction, pozzolans, mortar, expansions, concrete strengths, mortar pH, mortars (materials)


    Author Information:

    Mehta, PK
    Professor, Engineering Science, and professor, Civil Engineering, University of California, Berkeley, Calif.

    Polivka, M
    Professor, Engineering Science, and professor, Civil Engineering, University of California, Berkeley, Calif.


    Paper ID: STP32342S

    Committee/Subcommittee: C09.93

    DOI: 10.1520/STP32342S


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