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RE:Mat Foundation

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Abe, We have placed huge mats (like you read about in ENR) and out of the
12+  in the last 5 years we have have seen only one where the designer
required the slab to be split into pours. However, those pours  were neither
square-ish in shape nor were they as small as W&K suggest. The reason was
anticipated shrinkage and the resulting stresses that would be passed on to
the waterproofing membrane beneath the mat. At 86 x 75 ft, 2 feet thick, you
are looking at 478 CY neat; that is just a long morning for a single pump
(in good condition) and an adequate concrete plant with maybe 8 trucks
dedicated to the pour. It is not quite thick enough to be a "mass concrete"
case (IMHO) so if you have adequate reinforcing, why not let it go at one
pour? The cost of forming and stripping joints, pump mobilizations (two day
break between pours?), etc will be dear. And at 86 ft x 75 ft, that is not
really a  huge single placement. Consider these measures:
	-Use a mix with fly ash or GGBFS as a cementitious material (less
cement=less shrinkage)
	-Go at as low a 28 day strength as you can (less cement=less
shrinkage)
	-Why not look at 56 day strength
	-Try bigger aggregate (whoops---that is hard to pump)
	-Specify a nice compactible, granular layer under the mat, and place
2 layers of kinda heavy poly sheet as a two part slip sheet, so any
shrinkage that does occur is not restrained
	-look at what your expected shrinkage strains and stresses will be
and reinforce accordingly--reinforcing is cheap compared to
forming/stripping joints and mobilizing pumps/cranes on 3 day intervals (1
time vs. at least 3 times)
	-watch concrete and ambient temperatures, too big a differential may
cause problems (a nod toward mass concrete)
	-if a finish is required on top, consider a second pour to "top" the
slab to get the finish and floor profile you want.

If it must go in 30 ft or so squares, other suggestions are nice. Consider
making the first one (in the middle-middle) as big as you can stand, let
them use "sta-form" mesh sheet as the form (It stays in place!) and then let
this sequence go:


					3   2   3
					2   1   2
					3   2   3
That yields 3 pours, only one of which really needs to be pumped or
crne/bucket because the outer ones are all fairly shallow so the material
can be "chuted" into place. I guess that will cool down the dollar issue.

Since the top and bottom steel is continuous through all joints, dowels
should not be necessary and the sta-form product gives a real rough
interlock surface. You may want to consider a bentonite strip in the joints
at the bottom under the bottom-bottom steel. Splices for top steel should be
near to the piers, columns, or load points; bottom steel should splice in
between those nodes.

Good luck!
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From: "Abe Knapp" <AKNAPP(--nospam--at)state.wy.us>
To: seaint(--nospam--at)seaint.org
Subject: Mat Foundation

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--=__PartCBE8C934.0__=
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Fellow Engineers,
=20
I am looking for some guidance on a Mat Footing.
It is 2 feet thick and 86'x75'.  Winterkorn and Fang recommend placing the =
concrete in approximately 30 foot square sections and letting each pour =
set for two days before placing the next adjacent area.  I am looking for =
some guideance on how to specify the joints.
Thanks in advance.
=20
Abe Knapp
Wyoming


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>
<META content=3D"MSHTML 6.00.2900.2604" name=3DGENERATOR></HEAD>
<BODY style=3D"MARGIN: 4px 4px 1px; FONT: 10pt Tahoma">
<DIV>Fellow Engineers,</DIV>
<DIV>&nbsp;</DIV>
<DIV>I am looking for some guidance on a Mat Footing.</DIV>
<DIV>It is 2 feet thick and 86'x75'.&nbsp; Winterkorn and Fang recommend =
placing the concrete in approximately 30 foot square sections and letting =
each pour set for two days before placing the next adjacent area.&nbsp; I =
am looking for some guideance on how to specify the joints.</DIV>
<DIV>Thanks in advance.</DIV>
<DIV>&nbsp;</DIV>
<DIV>Abe Knapp</DIV>
<DIV>Wyoming</DIV></BODY></HTML>

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