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Re: A few questions for those who design concrete pools.

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Peder,

Good background towards helping Dennis with the homework he needs to do if
he will be specifying pneumatic concrete.  I am sure that usage varies
regionally, and am aware that ACI uses the word "shotcrete" to cover both
the wet and dry mix methods.  My point in re Dennis' original inquiry was in
part that he needs to be careful to define his terms.  If a contractor is
talking to Dennis about making a pool out of, "gunite," he could be talking
about either wet or dry mix.  As you say, both have their own advantages and
disadvantages.  To put it another way, they are not the same thing, and the
engineer needs to be specific.

Drew

----- Original Message -----
From: "Peder Golberg" <peder(--nospam--at)jgpierson.com>
To: <seaint(--nospam--at)seaint.org>
Sent: Friday, September 07, 2001 2:43 PM
Subject: Re: A few questions for those who design concrete pools.


> I have a different definition.   Gunite is a copyrighted trade name from
the
> guy who invented the cement gun back in 1910.  Shotcrete term came in the
> 1930's from the AREA (railroad engineers) folks to describe the gunite
> process.   ACI has adopted the term "Shotcrete" (both wet or dry mixed)
for
> ALL pneumatically applied mortar or concrete back in 1966.   These
> definitions are from an ACI 506 seminar attended last year in Portland.
> Both wet and dry mix shotcrete has its own advantages and disadvantages.
>
> Peder Golberg, PE. SE
> Portland, Oregon
>
>
> ----- Original Message -----
> From: "Drew A. Norman, SE" <DNorman(--nospam--at)dnormanse.com>
> To: <seaint(--nospam--at)seaint.org>
> Sent: Friday, September 07, 2001 1:52 PM
> Subject: Re: A few questions for those who design concrete pools.
>
>
> > Dennis (and Mark),
> >
> > I fear that Mark Geoghegan's response to your post on gunite for
swimming
> > pools (see below) includes mis-statements that could get you (and he,
> unless
> > he just mis-typed) into trouble.  Specifically, gunite and shotcrete are
> NOT
> > the same thing, and NEITHER is the same as conventionally placed
concrete.
> >
> > The following language is excerpted from my firm's standard general
notes
> > for pneumatic concrete, which were developed based on relevant ACI
> > standards, including ACI 506 (Recommended Practice for Shotcreting) and
> the
> > City of Los Angeles Department of Building and Safety's Shotcrete and
> Gunite
> > rules:
> >
> > A. THE TERMS SHOTCRETE AND GUNITE IN THESE STRUCTURAL DRAWINGS REFER TO
> > CONCRETE WHICH IS PNEUMATICALLY APPLIED TO THE WORK BY A SUITABLE
> MECHANISM
> > DESIGNED FOR THAT PURPOSE.
> >
> >  1. SHOTCRETE IS MADE BY THE WET MIX METHOD, IN WHICH SUBSTANTIALLY ALL
OF
> > THE WATER IS ADDED BEFORE THE MATERIAL IS DELIVERED TO THE NOZZLE.
> > SHOTCRETE IS A MIXTURE OF CEMENT, WATER, AND FINE AGGREGATE WITH OR
> WITHOUT
> > COARSE AGGREGATE.
> >
> >  2. GUNITE IS MADE BY THE DRY MIX METHOD, IN WHICH SUBSTANTIALLY ALL OF
> THE
> > WATER IS ADDED AT THE NOZZLE.  GUNITE IS A MIXTURE OF FINE AGGREGATE AND
> > CEMENT TO WHICH WATER IS ADDED IMMEDIATELY PRIOR TO DISCHARGE.
> >
> >  3. GUNITE, SHOTCRETE AND CONVENTIONALLY PLACED CONCRETE ARE DIFFERENT
> > MATERIALS WHICH MAY HAVE SIGNIFICANTLY DIFFERENT STRUCTURAL PROPERTIES.
> THE
> > CONTRACTOR SHALL NOT SUBSTITUTE ANY ONE FOR ANOTHER WITHOUT THE WRITTEN
> > APPROVAL OF Owner, Architect, DANA AND Bldg Dept.
> >
> > While gunite (as opposed to shotcrete) has been used successfully in
> > structural applications, it is generally considered a non-structural
> > material, primarily because the water-cement ratio (and therefore the
> > strength of the material) is controlled by the nozzleman, who regulates
> the
> > amount of water added to the dry materials at the nozzle.  This allows
the
> > operator to alter the texture (slump) of the material as appropriate to
> > shooting conditions, and in the hands of a skilled nozzleperson will
> result
> > in a lower risk of such defects as sand pockets, voids or rebar
"shadows".
> > In addition, gunite does not typically contain coase aggregate, which
> means
> > among other things that it may be subject to much higher volumetric
> > shrinkage during hydration.
> >
> > Shotcrete is the variety of pneumatic concrete more commonly used for
> > structural applications.  While Mark may be right in principle to say
that
> > design is no different for shotcrete than for cast concrete, the same
can
> > certainly NOT be said for specification and detailing.  In addition to
> > significant restrictions on the minimum spacing and configuration of
rebar
> > (e.g., contact lap splices of large bars are not permitted), there are a
> > myriad of special quality control and quality assurance requirements,
> > including pre-qualification of each nozzleperson/helper team,
restrictions
> > on re-use of rebound material, and field sampling that the structural
> > designer needs to be aware of if he or she is going to specify or detail
> > shotcrete.
> >
> > My advice to you would be to do your homework before you try and specify
> > pneumatic concrete.
> >
> > Drew A. Norman, S.E.
> > Drew A. Norman and Associates
> > Pasadena, California
> >
> > 626-568-9322
> >
> > ----- Original Message -----
> > From: "Mark Geoghegan" <mgeoghegan(--nospam--at)structural-tech.com>
> > To: "Seaint" <seaint(--nospam--at)seaint.org>
> > Sent: Friday, September 07, 2001 1:05 PM
> > Subject: Re: A few questions for those who design concrete pools.
> >
> >
> > >
> > > dennis,
> > >
> > > i cannot assist you too much on the 7 question you have, however, the
> > > structural "design" of shotcrete (gunite) is really no different from
> any
> > > concrete design, BUT the detailing and mix design (specifications),
and
> > > EXPERIENCED applicators is very important for successful shotcrete ...
> >
> > <SNIP>
> >
> >
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