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Slab Cracks

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Tony Luison wrote:
I am looking for a book or guidelines regarding cracks in
slabs-on-grade (mainly in residential construction). How else do
you explain to a lay person, after she or he removed the carpet and
finds cracks (hairline to 1/16") in the slabs (no vertical off-sets, no
signs of differential settlement or settlement) that these cracks
are shrinkage cracks (high water content ehen paced and/or little
or no curing) and that some may have gotten bigger due to the
earthquake and aftershocks. A (real estate) inspector friend of
mine is being taken to court because he should have seen these
cracks without removing the carperting!!!!!!
I wish I had a good answer to this problem because it happens
constantly.  There is no currently accepted standard for allowable
cracks or movement of a slab on grade.  Remember that ACI
defines a slab on grade as not being a structural slab, so ACI
guidelines for slabs do not apply.

There is currently an ASCE committee on designing residential
foundations on expansive soil.  The current draft that I just received
defines a "negligible" crack as 1.5 mm (about 1/16 inch).

ACI has several committees documents that also may have some
information.  ACI 360 is entitled "Design of Slabs on Ground" , ACI
302 is entitled Construction of Concrete Floors", ACI 332 is entitled
"Residential Concrete, and ACI 224 is entitled "Cracking in
Concrete".  An article from the February 1992 edition of Concrete
International entitled  "Cracking in Floor Slabs"  gives some help. 
There has been some research on acceptable movement of
residential slabs on grade.  I can't get my hands on any of the
references now, but I know there was a paper in the ASCE
Structures Journal regarding acceptable deflection of residential
slabs on grade.

I hope this helps.  Let me know if I can be of further assistance.
Brian Kehoe