> What does 28 -day strength mean?
>
> Concrete hardens and gains strength as it hydrates. The hydration process
> continues over a long period of time. It happens rapidly at first and slows
> down as time goes by. To measure the ultimate strength of concrete would
> require a wait of several years. This would be impractical, so a time
> period of 28 days was selected by specification writing authorities as the
> age that all concrete should be tested. At this age, a substantial
> percentage of the hydration has taken place.
It also can be months before surface cracks appear,
and that may be impacted on the consistency of early
daily hydration, weather conditions, and later environmental
changes.
I am guessing that different psi's allow behave differently.
Our new home slab was 3500psi. It was well hydrated during
early curing and showed no cracks for 8 months. Because we
only treated it with three layers of white epoxy and because
it is in an air conditioned home kept at 78 degrees (meaning
it is fairly dry) it now shows cracks.
Fall in Iowa presents temperature and moisture changes,
daily and seasonable. Not sure what they will mean to
your particular slab but imagine there are folks here
who can help you to calculate that.
--
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Thanks! & 73, doc kd4e
Echoes of Eden Blog: http://bibleseven.com/blog1/blog.html
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