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RE: Air entrainment vs hardener

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The use of AE in smooth finish floors is not "recommended", but it is
allowed.  The difference is the level of effort it takes to finish the
concrete.  It tends to blister if you get on it too soon.  AE is often used
in pumped concrete on regular trowelled office floors to aid the pumping
guy.  It won't be in as high a dose as required for freeze thaw protection.
It can play hell with the finishers especially in winter when they need to
get on the concrete to get a finish in a hurry, and the ambient winter
temperature retards the set.  Anything to reduce the initial set time
without creating a flash set problem is beneficial.

I would suggest a test pour with the finishers to see what works.  I have
found that polycarbonate super P works well to reduce the set time, and
reduce the water required.  A reduced set time will allow the finishers on
the slab sooner without blistering the concrete finish.  It is also more
predictable than accelerators.  I would also recommend magnesium trowels.
They stick less than steel trowels, and is what is commonly used in concrete
with silica fume.

Consult with the finishers in the area where the concrete is to be placed.
Figure out the properties you need.  If you need the AE, use it where you
need to use it.  Then get with the finishers to add what they need.  A slab
on grade will probably be tail gated or slick lined (horizontal line pump).
Either of these methods will not draw off the air like a boom pump will.

I like to have a preconstruction meeting with the concrete supplier,
finisher, and pumper.  Tell them what you need, and they will figure out how
to place it, and get whatever finish you specify.  Everyone needs to
coordinate what they need.

You are in Colorado.  Contact Dale Marrou of Marrou Concrete in Fort Collins
or Carl Ytterberg at Kalman Floors in Evergreen.  They know how to finish
concrete.  LaFarge is also a good resource.  

Harold O. Sprague

> ----- Original Message -----
> From: "Sherman, William" <ShermanWC(--nospam--at)>
> To: "SeaInt Listserver (E-mail)" <seaint(--nospam--at)>
> Sent: Wednesday, November 06, 2002 4:18 PM
> Subject: Air entrainment vs hardener
> > I'm curious how others solve the following problem: I have a floor slab
> at
> > grade for which a concrete surface hardener is desired in an industrial
> > equipment area. The outside edges of the floor slab will be exposed to
> the
> > weather in a freeze-thaw environment (northeast US), but it is otherwise
> in
> > an enclosed area. The building interior is industrial and the interior
> > temperature will be kept above 50 or 60 degrees F.
> >
> > 1. Should the slab be air entrained due to freeze-thaw exposure at the
> > edges? It seems that this is the worst freeze-thaw exposure, right at
> > finished grade where moisture and temperature will vary the most. On the
> > other hand, will the limited surface exposure and heat from the interior
> > reduce the effects of freeze-thaw on the exposed concrete edges?
> >
> > 2. Air entrainment creates finishing difficulties and is not recommended
> for
> > trowelled finishes with shake hardeners. (Possible blistering and
> > delaminations if not finished properly.) A separate surface applied
> epoxy
> > topping could be applied after the concrete cures, but this would add
> > considerable cost relative to a shake hardener.
> >
> > So what solutions have others used?
> >
> >
> > William C. Sherman, PE
> > CDM, Denver, CO
> > Phone: 303-298-1311
> > Fax: 303-293-8236
> > email: shermanwc(--nospam--at)
> >

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