On Sun, 10 Dec 2000 07:52:26 -0500 George P Dausch IV <gpd4@juno.com>
writes:
>
>
> Elton, Clark, lotus, tony, et al
> Understanding that the ACI people have thousands of papers and
> hundreds of publications attempting to document why it did that,
> I'll give you my opinion of the real world for those of us who just
> want to roll our creepers. Based only upon real world experience,
> twenty years, million dollar annual payrolls, and trying to remain
> ahead of the curve.
>
> Concrete includes cement, sand, aggregate, and water. Mix it,
> place it, finish it. The optional vapor barrier underneath will
> minimize moisture and future chalking, particularly in a building
> heated only when in use. However, it also serves the purpose of
> keeping the water in the concrete while it is in the drying phase.
> If you ever touched drying concrete, the chemical reaction creates a
> lot of heat (and serious skin burns if left on your body while
> finishing). By keeping the water from draining out the bottom, the
> drying process is lengthened, which yields stronger concrete and
> minimizes shrinking..
>
> The other part of the preparatory process is the reinforcing. As
> the concrete dries, it will crack. This is a result of shrinkage
> cause by heat during the evaporation/curing /drying process. You
> make an educated guess on future uses, offset it against the dollar
> cost increase, and hope for the best.
>
> High end is a reinforcing bar mat, 5/8" or 3/4" bars 12" on center
> each way in the middle of the slab. Great for truck turnaround
> slabs.
>
> Next step down would be woven wire mesh, which most of us are
> probably familiar with. Old chain link fence works good too.
> Whatever you use, it has to be in the center of the depth. Lying on
> the ground does not help. Nor does poking up through the slab, or
> just under the surface where it rusts and ruins the finish.
> Both of the above serve to control primary cracking; i. e., hold the
> slab together after it cracks.
>
> Fiber reinforcing is just what it's name implies. Looks like
> chopped fiberglass matting, also available in bags of what can best
> be compared to chopped paper clips. Their purpose is to provide
> secondary reinforcement. While we all know the slab will crack, the
> fibers essentially turn the big cracks into billions of microscopic
> ones, or yield what appears to be a crack free slab. Generally
> around $10/12 a yard, put in the concrete by the ready mix producer,
> pissed and moaned about by professional finishers because it makes
> the final troweling tougher, but worth every penny.
>
> If start with a good subsurface, use a vapor barrier, consider the
> wire mesh optional (but cheap insurance), use fiber, trowel and
> finish properly, control the drying process (by keeping the surface
> wet/damp/cool), you can get a nice slab. However, once it's over
> 600 square feet or so, you still need a
> control/contraction/expansion joint, because the ambient temperature
> changes will still crack it in the future. In theory, you can get
> it to crack in the joint, which will be caulked at the top anyway.
> Commercial joints are available for purchase, and you just locate
> them prior to pouring.
>
> Little more than a paragraph, hope it helps somebody.
> GPD4
>
>
>
> > 8 Dec 2000 09:22:02 -0600 "Elton Clark" <lotus.tony@airmail.net>
> > writes:
> > > > 1. Sweep off the existing to remove loose crap, form the
> edges,
> >
> > > cover
> > > > with heavy mil visqueen, pour at least 4" new concrete with
> > fiber
> > > > reinforcing (wire is optional). This gives you a floating
> slab
> >
> > > on top
> > > > of the original.
> > > > 2. Sweep off the original, then water blast to remove all
> loose
> >
> > > stuff.
> > > > Allow to thoroughly dry and form the edges. Apply a coat of
> > > concrete
> > > > bonding agent according to directions. Pour somewhere arond
> > > 1.5"/2" of a
> > > > very high strength pea gravel mixture with fiber. This gives
> a
> > > bonded
> > > > slab, but counts on the integrity of the existing slab.
> Cracks
> > in
> > > the
> > > > original will migrate upward eventually, even if forced into
> > > preplanned
> > > > control joints.
> > >
> > >
> > > George, would you do us a paragraph on fiber reinforced
> concrete?
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