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re: concrete cure time

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Richard,

 

So they are in a big hurry to get the house built so it can sit on the market for a year? I don’t get why anyone in Florida is building anything, there is so much on the market and complete neighborhoods full of pads with plumbing stubs and empty cul de sacs full of weeds….

 

But, the key thing you said is residential clients, so we are talking one story CMU most likely. Like Harold said, it all depends on the project. I cannot remember the last time I ran a foundation concrete design calc on a single or two-story CMU house…. Usually just design it for 2000psf soil bearing capacity or 1.5-2ft wide. I can’t remember concrete strength ever controlling much of anything in this application, but if I dug into it I believe I could come up with a comfortable number in PSI terms to give to the GC for the break tests as Harold said. Keep in mind the loading sequence would be 1 or more days of hollow block loading on the footing depending on how big of a mason crew they have, then grouting, and the trusses probably don’t get set for several more days. So the full load will not be in place for 7-10 days or much longer. The GC can give you that schedule if you really want. I would think with residential, monolithic foundations, the main concern is cracking at the footing-to-slab transition due to settlement….

 

I am not sure where everyone got the three days from but for some reason that sounds good! Probably what the older engineers at all of our offices just taught us. But that is for low rise stuff. Wood framing I probably would let them start as soon as they could walk on the concrete. But I try not to tell GCs anything that is close to means and methods for legal reasons, but maybe give them an off the record opinion with a read between the lines type answer.

 

Andrew Kester, PE

Orlando, FL