Look in PCA's "Design and Control of Concrete Mixtures" (I have found this
to be one the best reference books on my shelf). I don't believe there is a
quantitative definition of gap grading - - its basically just leaving out
certain particle sizes. One benefit is with exposed aggregate. Supposedly
it can be used for structural purposes, but I haven't seen that side of it.
From: Jim Todd [mailto:JIMT(--nospam--at)performainc.com]
Sent: March 22, 2001 6:51 AM
Subject: RE: Concrete: Shrinkage limit of .048?
Does anyone know a reference that defines "gap grading" vs. uniformly graded
aggregate? What would be the benefit to a mix by gap grading?
>>> SpragueHO(--nospam--at)bv.com 03/21/01 06:19PM >>>
Reducing water is the first step in reducing shrinkage. Getting a different
aggregate is obviously not an option. The aggregates in the Reno area are
volcanic in origin, and are pretty bad.
Consider a polycarbonate super plasticizer like Adva.
Use as large a maximum aggregate as possible.
Uniformly grade the aggregate. Don't allow gap grading.
Consider shrinkage a compensating admixture like Eclipse.
Cure, cure, cure.
You won't find much help in the ACI.
I would suggest that you contact Bud Werner at CTL Thompson in Denver
Another contact is Steve Parker in Reno. He works for a supplier, but I
don't know which one. Call the lab at Nevada Cement 775 575-2281. They
will know where he is.
Harold O. Sprague
> -----Original Message-----
> From: Joyce Fuss [SMTP:Joyce(--nospam--at)lbdg.com]
> Sent: Wednesday, March 21, 2001 5:39 PM
> To: 'seaint(--nospam--at)seaint.org'
> Subject: RE: Concrete: Shrinkage limit of .048?
> Harold, thank you for the reply. The location is at South Shore, Lake
> (on the California side). There are limited suppliers within a 90 minute
> range, and they have the same aggregate sources. To import aggregate is
> an option due to the tight budget (state job).
> We had another project at the same campus about 7 years ago and had the
> issue come up. With a similar mix we got shrinkage in the range of .06,
> had no problems with the walls, footings, beams or slabs. These results
> consistent with much of the construction of the casinos, bridges, and
> structures built there. We have the results of testing for 3000 psi
> 5000 psi mixes, all with shrinkage around .06% at 21 days. All these
> included plasticizer.
> I don't know why we have the .048 requirement in the spec, and I am
> for any type of reference as to when that would be appropriate, and what
> other limits would be recommended for various situations. I'm not
> it is necessary, but I don't see anything in the ACI manual of standard
> practice that gives a basis for evaluating shrinkage limits...
> > Joyce Fuss
> > Structural Engineer
> > Lionakis Beaumont Design Group
> > phone: (916)558-1900
> > fax: (916)558-1919
> > joyce(--nospam--at)lbdg.com