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Re: Any recommendations on maximum permitted areas of slab pour?

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Cliff,

I am not aware of any restrictions on the size of concrete placements.  I
looked through both ACI 304 and ACI 301 and I did not find anything.

I do know that some engineers like to put limits on the placement size for
slabs-on-grade or slabs on metal deck to help "ensure" quality concrete.
Some times a contractors eyes get bigger than what they can follow up
with...that is they may try to place more concrete in one continuous
placement than they really can effectively handle.  The size of a flatwork
conrete placement is really a function of how well a particular contractor
can do the work...that is, is the placement small enough that they can get
it bullfloated out and finished in the appropriate amount of time as still
insure that the concrete is finished properly to supply a good quality
slab.  In addition, one must also factor in how quickly the batch plant
can supply the needed concrete.

HTH,

Scott
Ypsilanti, MI


On Mon, 18 Mar 2002, Cliff Schwinger wrote:

> Does anyone know of any published recommendations for restrictions on
> maximum areas of concrete slab pours?  I was told the other day by a
> contractor that he has been held (by the structural engineers) to a
> 6,000 square foot maximum pour restriction on several recent jobs. He
> asked me if I knew where the 6000 sq. ft. number came from.  I am
> assuming that the intent of the "maximum pour limit" is to reduce the
> chance of significant (visible) shrinkage cracks occurring - but isn't
> that what control joints (in slabs-on-grade) are for?  Our office also
> always specifies welded wire fabric in our slabs-on-grade. The WWF (if
> placed where it should be in the slab and if lap spliced properly should
> provide an additional margin of safety (in addition to the control
> joints) against the growth of large shrinkage cracks.
>
> As far as pouring slabs on metal deck, I always thought that the welded
> wire fabric would help keep the size of shrinkage cracks to a minimum
> and that the contractor could generally pour as much the floor they
> wanted in "one shot".
>
> With framed concrete slabs there is always plenty of rebar to keep
> shrinkage cracks from growing.
>
> So what is the reasoning behind the 6000 square foot pour restriction
> and where is this "magic number" published?  That's an area of about 77
> ft. x 77 ft.!  Seems kind of small to me. I wonder what the specifying
> engineer would say if a contractor said "OK, I'll pour the floor in your
> 1000 foot long building in 6 foot wide strips"?
>
> I've searched everywhere and can't find a thing - but I did learn some
> interesting facts along the way.  Did you know that the Romans built
> mile-long concrete aqueducts about 2000 years ago -with no control
> joints, and there were no shrinkage cracks!?  They used a concrete that
> had 1000 to 2000 psi compressive strength.
>
> Thanks in advance for any help anyone can provide.
>
> Cliff Schwinger
>
>
>


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