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Concrete Freezing

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How cold did it get, and when?  Bear in mind that any
free water in the concrete isn't exactly potable-it's
got a lot of stuff dissolved in it.  This will lower
its freezing point considerably.  If the free water
actually does freeze, the matrix will be damaged, but
I don't know how to know if that has happened except
to test it.

Several years ago I had a project where the contractor
placed several thousand square feet of exposed slab on
grade during a blizzard just after Thanksgiving in
northern Minnesota.  He actually sent workers with
brooms and weed-burner torches ahead of the finishers
(his whirlybird power trowels were still frozen in the
slab the next April).  Temperatures that day were in
the teens with 30 mph winds; all insulation (straw)
and poly were gone literally before he left the
jobsite.  Needless to say, we summarily rejected the
slab.  But when he took cores and had them tested two
weeks later, the concrete was 4000 psi or close to it.
 We were shocked.  The result of his tests was a huge
argument and a lawsuit.

Don't take this to mean you should accept the
concrete.  And I'm not sure if the concrete may suffer
in durability even if it does make strength.  But it
did make me realize just how much can go wrong, and
the concrete still make strength.

Actually, if your wall was insulated or heated, and
then the insulation blew off, the concrete may have
sustained more damage from the rapid temperature drop
than from freezing.

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


>From: ADFPE(--nospam--at)aol.com
>Subject: Re: Concrete Freezing
>To: seaint(--nospam--at)seaint.org


>In a message dated 12/4/01 3:16:33 PM,
>dang(--nospam--at)karren.com >writes:

<< Anybody know of any good references that address

the effects of freezing on concrete?  I've got a
contractor

that placed a foundation wall, and didn't adequately
protect

it from the cold weather.


Dan Goodrich, P.E.

 >>

The issue is how much strength did the concrete have
when it froze.  Fully=20
cured concrete can easily sustain temperatures well
below freezing.  Concret=
e=20
is exothermic, so generates enough heat, when freshly
placed, to prevent=20
freezing at temperatures close to 32=B0 F.  I believe
that ACI 301 gives=20
guidance on this issue.  I have also heard about
research that the Army Corp=
s=20
of Engineers Cold Regions Lab in Hanover, NH is doing
that indicates that=20
concrete that cures at low temperatures (near
freezing) actually develops=20
better long term properties than concrete cured at
higher temperatures 80=
=B0 F.=20
=20

Regardless of the above, if it froze before it
achieved adequate initial=20
strength, it may  be just so much mush.

Alan Fisher, PE



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