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Keyway Details

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We do a fair amount of wastewater and water treatment work involving
concrete tanks.  We go round and round about the joint between the slab
and the bottom of the wall.  These joints need to resist shear and
moment.  Basically we have three options we keep arguing about.

1. Finish slab flat, with keyway.  Put waterstop in bottom of keyway.  1
1/2 inch key plus half a 6 inch waterstop makes 4 1/2 inches.  Thus,
either make the slab 3 inches thicker than needed and hold the top mat
down, or bend the bars down under the wall (reducing their depth just
where it's most needed).

2. Finish slab flat.  Roughen under wall, dispensing with keyway.  Use a
4 inch waterstop, touching the top mat; tie it to the inside vertical

3. Hang a 3 1/2 inch tall wall form, placing joint, key, and waterstop
up above the base slab.

I like option 2 myself; it's the simplest.  The wall will be rough there
anyhow because of the dowels sticking up in the way of the finisher.
Does anyone have any better ideas, or opinions on which of these options
is best?  Please weigh in with opinions and reasoning.


Mike Hemstad, P.E.
St. Paul, Minnesota

P.S.  I've tried to send this several times.  By coincidence I notice
that the Digest was very short yesterday.  Has anyone else had trouble
sending to the List?

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