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.
ACI does have some great info on techniques, detailing etc. Additionally,
the American Shotcrete Assoc (www.shotcrete.org) has a lot of info, and also
a Nozzleman Certification program, and has guides for core sampling,
testing, repair etc
an authority on shotcrete design and application is James Warner who is a
consultant in California. if you contact the International Concrete Repair
Institute (www.icri.org) they will put you in contact with Jim - he writes a
regular column in the Concrete Repair Digest. he has a lot of experience in
shotcrete applications (esp basement walls, seismic retrofit with large
rebar at close centers, and repairs). jim is an engineer, but has also been
a specialized contractor too.
Mark Geoghegan BE (Hons.-Structural)
S T R U C T U R A L T E C H - V S L
GUAM - HAWAII
DENNIS WISH WROTE:
I know I have asked a few of these questions before, but I need to get a
couple of opinions since I have had some conflicting responses. The
questions have to do with the installation of Gunnite and the standards
1. Does the Uniform Building Code (or 2000 IBC) make any specific reference
to the structural design of Gunnite Pools?
2. While it may be sound practice to follow a concrete building standard
for the clearance of reinforcing steel from earth and air, are there any
specific standards of practice or published codes that mandate the
placement and minimum clearance of steel in a swimming pool?
3. It is my understanding that the finish on most Gunnite Pools is
considered a structural plaster used to provide a smooth surface. It is
also my understanding that the plaster used is, essentially, concrete and
can obtain the same strength as the concrete wall below. Is this valid?
4. It is my belief that all concrete (including Gunnite) cracks. The crack
needs to be evaluated to prove if it is caused by defect or by normal
processes such as temperature cracking (hairline). I also understand that
most cracks will not cause sufficient leakage in a pool as the wetting of
the concrete surface would tend to swell the concrete and essentially seal
the crack. Is this a valid assumption for temperature and hairline cracks?
5. I've been told that the plaster finish on a pool is a waterproofing
finish. Is this considered a valid assumption by most of you?
6. There are a few contractors in the area who specialize in the repair of
Gunnite pools who rough up the surface of a pool considered to be a thin
wall shell and who add an additional 4-inch shell of Gunnite within. There
are alternatives that I believe are less costly - pool liners,
Epoxy-injection and new plaster finishes etc. What alternatives have you
used to repair minor cracks (no elevation changes and no cracks larger than
approximately 1/32" in width) in a Gunnite Pools
7. Final questions: Is the City Inspector required to inspect the placement
of the rebar cage before the Gunnite is shot on. If so, is the cage
generally set on chairs to hold it away from the earth to allow for
clearance between the earth and rebar (assuming that some standard or
minimum clearance was originally specified by the design engineer)?
If you prefer, please feel free to email me privately with your response.
If others want to know what the comments were, I'll be happy to post them
on the Structuralist.Net or if you prefer, leave them on the SEAINT list.
Thanks in advance for those of you who respond.
Dennis S. Wish, PE
Structural Engineering Consultant
760.564.0884 - Phone
208.361.5447 - Efax
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