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[SEAOC] Reactive Aggregate

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     Lynn wrote:

     "I would like to know if anyone has some information on how we
     determine if coarse or fine aggregate for concrete is reactive
or not."

     Most of the tests and limits for aggregate reactivity are shown
in the
     Appendix to ASTM C33, Standard Specification for Concrete
Aggregates.
     This includes the following:

     *  ASTM C295, Practice for Petrographic Examination of
Aggregates for
     Concrete.  This is a microscopic examination of the aggregate.
This
     is not an easy or quick test and not many laboratories can
perform
     this test.

     *  ASTM C289, Test Method for Potential Reactivity of Aggregates
     (Chemical Method).  This is a quick chemical test that only
takes 2 to
     3 days.  Test results are not entirely reliable but you can
specify
     that results should be in the "innocuous range".

     *  ASTM C227, Test Method for Potential Alkali Reactivity of
     Cement-Aggregate Combinations (Mortar-Bar Method).  This is
probably
     the best test but it takes 3 to 6 months for the results.
Expansion
     should be less than 0.05% at 3 months and less 0.10% at 6
months.

     Two other tests you can ask for are ASTM 1260, Test Method for
     Potential Alkali Reactivity of Aggregates (Mortar-Bar Method),
less
     than 0.10% expansion at 16 days, and ASTM C856, Practice for
     Petrographic Examination of Hardened Concrete, again this test
would
     reveal actual reactivity in the harden concrete but you must
find a
     laboratory that is very experienced in doing this test.

     Regards,

     Thomas Hunt, S.E.

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