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When can they start setting precast

When can they start setting precast

When can they start setting precast

(OP)
Situation: Concrete foundation walls poured today. Type 1 cement (no accelerating admix).

The contractor is wondering when he will be able to start setting precast wall panels (single story, 33' high) on the foundation wall. My first response was after 7 days of curing. Is that too early?

RE: When can they start setting precast

Just run some quick numbers on punching shear, beam shear, flexure etc as appropriate for your geometry based on an assumed concrete strength. Break some cylinders at 7 days to confirm concrete strength and you're golden.

I suspect it would be fine given that there won't be any live loads, snow loads, etc in place.

Peer reviewing precast structures, we usually insist on cast in place reaching it's 28 day strength prior to erecting precast or a letter from the EOR stating that early erection is ok.
 

RE: When can they start setting precast

I have designed many buildings soundig similar to yours and this question always comes from the contractor.  I have always allowed erection to start after a break shows 2000psi (for a 3000 foundation) but at least 48 hours after the pour.  As long as they are onyl erecting panels and not fully loading the structure it should not be an issue.

RE: When can they start setting precast

(OP)
SrVaro,

Thanks for the input. Considering that conc under normal circumstances would gain 70% of its strength in 24 hrs (correct me if I am wrong), your 48 hrs response makes sense. May be I'll tack at least a couple more days on just to feel better, so 4 days with a break showing min 2000 psi.

RE: When can they start setting precast

70% should be at seven days.  I would expect maybe 30% at 24 hours.  However, with all the admixtures, this can vary wildly.

RE: When can they start setting precast

WWT...jgailla is correct.  70% in 7 days, assuming no admixtures. If using flyash or slag cement, figure 45 to 50% in 7 days.

RE: When can they start setting precast

If the concrete is lightly loaded, I typically let them start at 3 days... The concrete likely has enough strength to not fail.

Dik

RE: When can they start setting precast

Why not spec a High Early?

Mike McCann
MMC Engineering

 

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