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RE: accelerating curing of concrete slab

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Ken,

This is a recurring problem.  You have diametrically opposing issues.  In
order to minimize shrinkage and curling, you want a wet cure.  In order to
get the membrane on ASAP, you want the water out of the slab.

First, design the slab concrete mix with a uniformly graded aggregate (as
large as possible on max. aggregate size) to minimize the cement which
minimizes the amount of water required for hydration.  Use a good
superplasticizer to make the concrete workable, and again to minimize water.
Use a sheet of poly over the concrete slab to contain the moisture for the
curing period.  Use rebar in the slab to control curling.  You will be
taking the moisture out in a hurry, which has a tendency to curl concrete
slabs.  The rebar helps to mitigate the curling.

Now to get the moisture out.

One method (high road and high price) is to place the vapor barrier, then
spaced perforated drain pipes in a 4" bed of 3/8" crushed rock.  Place a
layer of geotech fabric over the crushed rock, then place the steel
reinforced slab on grade on the geotech fabric.  The geotech fabric allows
free passing of water vapor while providing a slip plane.  After 7 days of
curing, you can place some blowers and dehumidifiers to dry out the concrete
from above and below the concrete slab.  Contact Munters at
http://www.munters.com/.  Munters has developed methodology to predict
humidity in slabs on grade.

Re: "Drying Concrete", by Lew Harriman, The Construction Specifier, March
1995.  Munters will happily send you a copy.  Munters can also give you
guidance on proper testing of moisture in the slab.

Another method is the cheaper way, but has results that are more variable.
Contact the membrane manufacturer, ask for their recommendation for a
topically applied water insensitive bonding agent epoxy.  Apply the bonding
agent in 2 applications placed 90 degrees to one another to achieve the
total required mil thickness.  This will minimize holidays.  The cheaper
solution may cost more, if it does not work well.  If an isolated
delamination is acceptable and repairable, go for it.

Regards,
Harold Sprague

> > -----Original Message-----
> > From: Ken Peoples [mailto:lvtakp(--nospam--at)yahoo.com]
> > Sent: Friday, August 11, 2000 8:49 AM
> > To: seaint(--nospam--at)seaint.org
> > Subject: accelerating curing of concrete slab
> >
> >
> > We have a project that is in an extreme hurry to be
> > constructed (even more than usual)and my dilema is
> > this:  The Owner needs to place a membrane over a new
> > concrete slab as soon as possible after the concrete
> > is placed - to keep the project on schedule.  The
> > manufacturer of the membrane wants to be sure that all
> > of the moisture is out of the slab before installing
> > the membrane.  What can I do to accelerate this?
> > Would a high-early mix help?
> > Thanks for your help,
> > Ken Peoples, P. E.
> > lvta(--nospam--at)fast.net


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