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RE: Concrete: Shrinkage limit of .048?

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Jim,

Gap grading is the practice of aggregate suppliers of removing a particular
size or sizes of aggregate from the designated C33 aggregate.  It is best to
look at the sieve grading contained in ASTM C33.  It becomes apparent that
for most of the standard aggregate sieve designations entire aggregate sizes
and ranges can be totally absent and still meet C33.  

In practice, the asphalt industry uses 3/8" aggregate, and 3/8" aggregate
will often not be present in aggregates for concrete production.  Back in
the 30's many concrete plants required by practice uniformly graded
aggregate.  The trend among some concrete mix gurus to minimize shrinkage
and increase workability is to determine the maximum nominal aggregate size
then require a minimum of 8% and a maximum of 18% from all the C33 sieves.  

The object uniformly graded aggregate is to occupy as much of the concrete
matrix with aggregate and minimize the amount of paste.  The paste shrinks
the most in the concrete matrix.  This is not a cure all for shrinkage, but
it is another consideration.

For more information, you can contact the concrete aggregate guru Jim
Shilstone http://www.shilstone.com/.

Regards,
Harold O. Sprague


> -----Original Message-----
> From:	Jim Todd [SMTP:JIMT(--nospam--at)performainc.com]
> Sent:	Thursday, March 22, 2001 8:51 AM
> To:	seaint(--nospam--at)seaint.org
> 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 >>>
> Joyce,
> 
> 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.
> 
> Other suggestions:
> 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
> 303-825-0777.
> 
> 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.
> 
> Regards,
> 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
> > Tahoe
> > (on the California side).  There are limited suppliers within a 90
> minute
> > range, and they have the same aggregate sources.  To import aggregate is
> > not
> > an option due to the tight budget (state job).
> > 
> > We had another project at the same campus about 7 years ago and had the
> > same
> > issue come up.  With a similar mix we got shrinkage in the range of .06,
> > and
> > had no problems with the walls, footings, beams or slabs.  These results
> > are
> > consistent with much of the construction of the casinos, bridges, and
> > other
> > structures built there.  We have the results of testing for 3000 psi
> > through
> > 5000 psi mixes, all with shrinkage around .06% at 21 days.  All these
> > mixes
> > included plasticizer.
> > 
> > I don't know why we have the .048 requirement in the spec, and I am
> > looking
> > 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
> > convinced
> > 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 
> > > 
> >