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Re: Concrete curing time

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Depends what the "construction loads" are.  If testing is being done, then the increase in strength over time may be obvious, even @ 7 days, otherwise the increase is, I believe about 70% at 14 days (?), so if your concrete strength ends up, at 28 days, well over the spec'd strength, then you may even begin loading to full construction loads earlier than 14 days.  The construction loads are also "real" loads and one shouldn't rely on the safety factors in the design!  The material behaviours under "full" loading for the different strength levels may also have to be considered.  In this case I would guess that 7 days is probably enough to start loading since the deck pour load will probably be done at 10 days, 2 which time you probably have a reliable 60% of full strength available.

Thor A Tandy P.Eng
Victoria BC
Canada
e-mail: vicpeng(--nospam--at)sprint.ca
 
----- Original Message -----
Sent: Thursday, July 12, 2001 8:33 PM
Subject: Concrete curing time

Hello,

Over the years, I have been asked the same question on numerous jobs.
After concrete is placed, how long until it is ok to apply construction
loads to a concrete element? In this specific case, the contractor wants
to set spancrete decking on the top of a concrete wall. The concrete
wall is constructed with reinforced 2500psi concrete.

Typically, it has been my understanding that seven days is adequate to
allow sufficient curing to begin applying construction loads.

I would appreciate opinions on this subject, maybe even relating to;

a.    Backfilling concrete retaining walls (28 days?)
b.    Erecting structural steel.