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Concrete curing time

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Frank,

In the example that you cite, I would not let the spancrete be installed until 
field cured test cylinders show that the concrete has reached 85 percent of 
its 28-day strength or until the lab cured cylinders have reached its 28-day 
strength.

First the spancrete is installed, then the tool boxes, then the reinforcing 
to form the next height of wall, then the compressor (whatever that may be 
used for) etc., etc.  Construction loads are frequently greater than the 
design LL.  (Estimate the weight of gyp board stacked 4-feet high.)

A. Roger Turk, P.E.(Structural)
Tucson, Arizona

Frank Glazewski wrote:

. > 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.

. > Thanks in advance.

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