I would roughen the
construction joints and extend the top and bottom mats of steel thru with a
lap splice to the adjacent placement. (No additional dowels required.) I
typically use up to a 40-ft spacing for construction joints, with at least #8(--nospam--at)12 rebar top each way to control shrinkage cracks
for this thickness slab.
Although I haven't
typically added extra steel at the joint as James Lutz suggested, I have often
seen the phenomenon he talked about at walls placed on a foundation. The
foundation slab restrains the base of the wall and causes periodic vertical
shrinkage cracks for a few feet above the base of the wall. I've sometimes
added additional steel near the base of wall to control such cracks, so the
same concept makes some sense in a mat foundation, if you are concerned with
having some minor cracking.
From: Abe Knapp [mailto:AKNAPP(--nospam--at)state.wy.us] Sent: Friday,
April 01, 2005 12:27 PM To: seaint(--nospam--at)seaint.org Subject:
RE: Mat Foundation
Thank you for your reply. I am in Casper (my home town is
Gillette) Both of the replies have been very helpful. The other
item I am wondering about is: do I need to put cold joint material in a slab
this thick and if so what The joints will be doweled together (two
mats of rebar top and bottom).
Cold joints between pours should be
dowelled together. Construction Joints are likely spaced 20 to 30
times the slab thickness. However, only having like 3 joints one way
and two the other isn't all that great. In a 16 inch slab, I have
joints between 20 and 32 feet O.C. That being said, with
your slab, maybe put the joints at 25' O.C. along the 75' length and 21.5'
O.C. along the 86' length. Is this what you're looking