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Any recommendations on maximum permitted areas of slab pour?

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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