[AT] another new shop

[Dave Ernst]

Cecil,
Charlies right. Concrete will crack and no amount of rebar or wire mesh will
stop it.
The control joints he's referring to should be no more than 20' apart, or no
more than 400 sf per floor panel (the square or rectangular sections created
by the joints).  After the concrete has cured a good joint sealant used to
fill the sawcuts will last a long time. I would use #4 rebar placed at 16"
on center held in the center section of the slab as reinforcement which will
give you all the flexural strength you will ever need and will control the
errant crack size. Other Engineers and myself have had varing opinions and
arguements on control joints through the years, but it is a known concensus
of opinion that if the substrate is questionable (possibility of
differential settlement) then it's a good idea to place smooth dowels at the
locations of the future control joints. The dowels will allow the slab
sections to move or slip horizontally while keeping the surface even in the
same plane.
Keep in mind concrete shrinks. The water used in mixing should not exceed
the water to cement ratio per the mix design and any additional water added
at the site will increase the shrinkage factor creating excessive shrinkage
and that leads to more cracking. Concrete will crack at any inside corner
and at any column or penetration more than 2X/d or if the debth is 4" holes
8" or greater are susceptible. Reentrant bars are necessary at these
locations.

Hey, email me off list and I'll assist you. I can go on with this
forever......

Dave