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RE:Mat Foundation

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Rick has the right idea.  To control shrinkage reduce
water and cement.

The idea of waiting two days between pours is a waste
of time and moneyfr nb .  So little shrinkage occurs
in those two days that there is no benefit.  This is
the reason that ACI has stated that pouring slabs in a
checkerboard pattern was not recommended.  I wonder
how long it will take for this missconception to die.

Note that a 2 foot mat will shrink less than will a 8"
slab given the same mix.  This is because it is harder
for the water to leave the thicker mat.

The bigger aggregate could be placed in those part of
the pour that can be reached with chutes or conveyors.

If the concern has to do with the impact of the
shrinkage on the membrane then consider a slip sheet
as Rick suggested.  In any case the waterproofing must
be capable of accomodating the cracks that are normal
to concrete.

I am still not clear on the use of the "sta-form" mesh
sheet due to a concern that the concrete on the
perimeter may not be properly consolidated and thus be
weaker in shear.  I would be interested in tests on
the sear capacity capacity of these joints.

Mark Gilligan

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