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    Pozzolan-Lime Mortar: Limitations of ASTM C593

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    Alone, neither a pozzolan nor hydrated lime is capable of setting under water. They are not hydraulic. When combined and mixed with water, however, the resulting reaction products are hydraulic. There is a renewed interest in pozzolan-lime binders, in particular for historic masonry. ASTM C593 provides a limited resource in defining suitable pozzolans to be used with lime for masonry mortars and exterior plasters. One of its limitations is that the specified pozzolan-lime weight ratio is not representative of a traditional volumetric ratio of one volume part binder to three volume parts sand. In addition, the standard requires accelerated curing, which is unrealistic for pozzolan-lime mortar.

    Preliminary results indicate that using specific ratios of pozzolan to lime and a vapor curing regime, as required by ASTM C593, does not necessarily promote the optimum pozzolanic reaction as tested by compressive strength. Results from ASTM C593 therefore do not represent the expected field behavior of pozzolan-lime mortars. The requirements of that standard should be modified with respect to pozzolan-lime ratios and curing conditions.


    pozzolan, lime, mortar, hydraulic lime

    Author Information:

    Thomson, ML
    Technical Manager, Chemical Lime Company, Henderson, Nevada

    Committee/Subcommittee: C07.07

    DOI: 10.1520/STP11035S