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Re: CONC - Stripping of Deck Forms

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dennismc wrote:

> It has always been my understanding that
> strength may develop prior to
> the 28 days but the full elastic properties of
> the material will not
> develop until the full 28 days, that is why
> there is a 28 day
> requriement.

Under ideal conditions, concrete will continue to
gain in strength and elastic modulus almost
indefinitely (though at ever decreasing rates).
28 days just happens to be a convenient point to
take our measurement and so it has become a
standard.  Sort of a balance between time lost
waiting and strength gained.  Of course, different
measured properties, (such as compressive strength
and splitting tensile strength) do not develop at
the same rate.

Anyone looking for a good elementary guide to the
concrete side of concrete work should check out

Design and Control of Concrete Mixtures
Portland Cement Association

P.S.  My best guess is that the creep experienced
if you load at 7 days will be about twice as much
than if you load at 28 days.

Stan Johnson