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Thread: Question on shotcrete strength

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    ColdAirGuy's Avatar
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    Question on shotcrete strength

    So we are having our pool redone and I have a question with regards to the shotcrete process during a remodel or new build.
    So we had our shotcrete done yesterday (thursday) and the PB said he's planning to plaster on Tuesday.

    A city inspector showed up today while I was at work and told my wife no plaster until we perform a crush test on a sample of shotcrete (have some left in a bucket). I understand from calling a couple of places that will do this that typically 30 days is needed to fully cure.

    The city inspector didn't say that he wants us to wait 30 days but now i'm confused. Will my sample fail a compression test since it will only be 5 days old if I have it tested Monday morning?

    What is your experience in your area in regards to this type of testing? Do they make you wait a month to plaster your pool? Do you go forward and plaster your pool and then take your sample after a month for testing in order to get your final inspection done?
    Anthony 16,000 Gallon Oval, White plaster, 30' Long 15' Wide 5 1/2' Deep end 3 1/2' shallow end.
    Pentair Intelliflo, FNS Plus 60sf. DE, Pentair Intellibrite 5G
    TF100 Testkit

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    Re: Question on shotcrete strength

    Hi, how did you go?
    It'll be all done for you now, but typically concrete strength is rated at 28 days, so in Australia we use megapascals, or MPa ratings, and if concrete was rated as 32MPa, then it should reach 32 in 28 days. As such, a test in 5 days (early strength) will not achieve 32MPa, but should be around 60-70%, so around 20-22Mpa.
    In saying this, testing concrete that was "left in a bucket" is hardly scientific. The test is usually conducted on a standard sized and prepared sample, some of which are laboratory cured, some are site cured. Just putting a lump of concrete in a compression testing rig and crushing will tell you nothing at all. And to be honest, I don't see how it would affect your plastering.
    Since the plaster is also cement based, plastering in 5 days wouldn't be a problem.
    41k litre (11k gal) shotcrete in ground pool, Hayward super 2, Davey Monarch 28, zodiac SWCG
    - undergoing a transformation!
    2nd season Pool Owner. TF-100 testing
    Melbourne, Australia.

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    Re: Question on shotcrete strength

    You're PB should have been familiar with the codes and known whether he had to submit a sample or not. I would think it would have been included in the specs.

    Here's all I could find:

    http://www.poolspanews.com/mix-design/s ... ength.aspx

    It's a bit outdated but I couldn't find anything current.
    304K gal., IG, 75' x 82' (Shallow End 4', Deep End 9'-13'),Ceramic Tile/Grout, 2 Griswold 20 HP Pumps; SFHP 23, Flow rate on pump 2: 1,229 gpm, I'm currently collecting all the pertinent information when it comes to the pool.

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    ColdAirGuy's Avatar
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    Re: Question on shotcrete strength

    Quote Originally Posted by Kwikee
    Hi, how did you go?
    It'll be all done for you now, but typically concrete strength is rated at 28 days, so in Australia we use megapascals, or MPa ratings, and if concrete was rated as 32MPa, then it should reach 32 in 28 days. As such, a test in 5 days (early strength) will not achieve 32MPa, but should be around 60-70%, so around 20-22Mpa.
    In saying this, testing concrete that was "left in a bucket" is hardly scientific. The test is usually conducted on a standard sized and prepared sample, some of which are laboratory cured, some are site cured. Just putting a lump of concrete in a compression testing rig and crushing will tell you nothing at all. And to be honest, I don't see how it would affect your plastering.
    Since the plaster is also cement based, plastering in 5 days wouldn't be a problem.

    It went just fine actually. I took the bucket of shotcrete to a testing facility near my house and they cored 4 samples from it. The engineering spec'd that it had to meet or exceed the strength designated at 28 days. I convinced them to do it at 4 days on one sample and it easily passed. All the inspector wanted to know is that it met that minimum, so as soon as I got the results/report I called my contractor who came out and plastered the next day.

    I then called for an inspection once the water was in.....he said I never called with the results and I then handed them to him. By doing it this way, I technically did everything he required except I didn't have to lose a whole month in summer waiting for my shotcrete to cure.

    Sometimes it's easier to ask for forgiveness than permission.
    Anthony 16,000 Gallon Oval, White plaster, 30' Long 15' Wide 5 1/2' Deep end 3 1/2' shallow end.
    Pentair Intelliflo, FNS Plus 60sf. DE, Pentair Intellibrite 5G
    TF100 Testkit

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    ColdAirGuy's Avatar
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    Re: Question on shotcrete strength

    Quote Originally Posted by I Know Nothing
    You're PB should have been familiar with the codes and known whether he had to submit a sample or not. I would think it would have been included in the specs.

    Here's all I could find:

    http://www.poolspanews.com/mix-design/s ... ength.aspx

    It's a bit outdated but I couldn't find anything current.

    I asked my PB about this and said it's generally a waste of time and money to require a crush test with shotcrete and most inspectors in different cities never ask for a crush test. He left me a bucket's worth just in case.
    Anthony 16,000 Gallon Oval, White plaster, 30' Long 15' Wide 5 1/2' Deep end 3 1/2' shallow end.
    Pentair Intelliflo, FNS Plus 60sf. DE, Pentair Intellibrite 5G
    TF100 Testkit

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