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

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drew,

thank you for your comments re shotcrete/gunite. there was no typo re gunite
etc.

whilst the original trade name "Gunite" was been around since 1910, ACI in
the 1950's, and most recently the American Shotcrete Association (ASA was
formed in 1998) have adopted the term "shotcrete", to define ALL
pneumatically applied concrete, and then distinguish the application methods
namely, "dry-process" or "wet-process".

dry-process shotcrete has and continues to be used in structural
applications. recent developments in materials and techniques have seen
successful structural project applications in Canada, Australia, Europe and
the USA. set control admixtures have advanced shotcrete materials
significantly in recent years. dry process techniques have be used, for
example, in structural applications in rising tide conditions for marina's
etc - very complicated applications!

some prepackaged material manufacturers interchange the same identical
products, that can be used successfully for either wet or dry process
shotcreting. the prepackaged material we have most experience with does have
coarse aggregate, and work equally well for dry or wet process work. even
rebound and dust levels can be matched between the wet and dry processes.

THE most important aspect of shotcreting (dry or wet) is the material
selection and the nozzleman's ability. a suitably experienced dry-process
nozzleman and assistant are able to undertake structural applications with
results that meet or exceed conventional concrete placement. mock-up tests
(prior to real application) are important to ensure suitability of
materials, application, and nozzleman etc.

maybe it is time that your firm updated its "standard general notes for
pneumatic concrete", most especially its definitions, to be more consistent
with ACI and ASA. one thing that the construction industry and engineering
communities do not do too well is consistent nomenclature and definitions.

gunite sometimes get a bad rap because it has been often associated with
some real bad contractors doing bad work. the ASA Nozzleman Certification
program (commenced in 1999/2000) is becoming a requirement in many project
specifications and this is good for the construction industry and the
engineering community. it runs certification for nozzleman in wet or dry,
vert or overhead.


mark

ps -	for the record - whilst i did state that the design of shotcrete
concrete is similar to conventional concrete (which it is), i also DID state
that the DETAILING AND MIX DESIGN (specifications) were very important for
successful shotcreting".





>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 ...


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