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  1. #1
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    Concrete Mixture Test

    We always hear about substandard concrete in Thailand.
    Is there a simple test for mixture ratio, a test that could be done prior to each load being discharge to the building site.

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    not sure about here in uk if you request one they got to do it .FYI the wetter the concrete the weaker it is

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    Concrete Mixture Test

    Quote Originally Posted by Mozzbie47 View Post
    We always hear about substandard concrete in Thailand.
    Is there a simple test for mixture ratio, a test that could be done prior to each load being discharge to the building site.
    Look up 'slump test'.... It is a mandatory procedure by law in the USA. Once before it leaves the plant and once more before the pour. Woolyback has it 50% correct. It also has to do with the cement/aggregate ratio...ie. sand, gravel, pea stone, etc. Good luck with that here...asking for that is like making a 90 year old dog jump through a hoop on fire...

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    Quote Originally Posted by Mozzbie47 View Post
    We always hear about substandard concrete in Thailand.
    Is this concrete mixed on site by local workers or concrete delivered in a ready-mix truck?
    The drying may also be a factor here. I believe concrete has to be dampened after initial setting.

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    Each truck load has a mix ticket or should have. This certifies the mix type, ingredients, and pour time. ticket will indicate how many bags of cement, rock, additives, superplasty, and type. You can get a lab to come to the site and pour cubes or cylinders for break tests. this will cost you but if you're serious then its easy to arrange through your concrete provider.

    All this will not guarantee that you have a good pour, but will guarantee that the mix is what it should be and you've paid for what you've received.

    Quality of the mix is just one aspect of a good pour. Important, but no certainty of its labor once poured. Make sure no additives after arrival is seriously considered. Thai's and for that matter most labor always want to water down their mix so it pours and spreads more easily. Don't do it.

    Concrete heats up while curing. Keep it cool using burlap bags for covering and water the bags to keep the curing process even with no excessive heat cracking, or shrinkage. curing is really important and here in Thailand relatively few do this with any consistency. Mostly I've seen them using spray on curing agents with out any water curing whatsoever.

    There are lots of on-line technical articles on concrete pours and methods. I hated civil engineering a one time, but as I was forced to sub for them on numerous occasions I became a very interested party to concrete and its use. 500 cu. meter pours were common and many times we had three different batch plants operating to keep up with the daily pours. We actually used "ice," as a additive to keep the temps down during travel.

    Enjoy!

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    Thailand Expat superman's Avatar
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    Quote Originally Posted by flyfisher davis
    Look up 'slump test'.... It is a mandatory procedure by law in the USA. Once before it leaves the plant and once more before the pour. Woolyback has it 50% correct. It also has to do with the cement/aggregate ratio...ie. sand, gravel, pea stone, etc. Good luck with that here...asking for that is like making a 90 year old dog jump through a hoop on fire...
    This is correct. It's also law in the UK with regards construction. The firm I worked for always did random 'Slump Tests' and would refuse delivery of substandard mixes. Which would cost the supplier. So it was very rare for a batch not to come up to standard.
    Last edited by superman; 31-01-2013 at 10:57 AM.

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    Thailand Expat superman's Avatar
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    Quote Originally Posted by ltnt
    You can get a lab to come to the site and pour cubes or cylinders for break tests.
    I don't know about this. What my firm always did, even after having a 'Slum Test' done prior to pour, was to take a core drill sample in the cured concrete which was then taken away for testing.

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    Batch box measure.
    Eg 4:2:1 Mix
    Sand: Gravel: Cement

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    There is a reason why you have to wet concrete while waiting for it to solidify... if the water evaporates too quickly you can say goodbye to your floor/wall.

    It also takes up to 40 days to completely solidify, sure after 1 day you can walk on it but it's strength might only be 50% yet.

    p.s. it's not just simply gravel, portland cement and water nowadays. Take for example Sodium Aluminate, this speeds up the solidification of concrete.

    //edit: In the Netherlands you must test your concrete, they always take 1 small cube per truck and test the concrete. Without this test you are not even allowed to live in there.

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    If this is for a house being built here. Then I would say the quality of the rebar and the curing method, the water content in the mix and the distance from the ready mix plant will be more important than the actual "quality" of the mix.

    If the ready mix plant is close, you could visit and ask.

    If this is for an industrial project and a big pour , hire a structural engineering firm to recheck the rebar design and get them to test and supervise during the pour.
    Better to think inside the pub, than outside the box?
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    Quote Originally Posted by superman
    Slum Test' done prior to pour, was to take a core drill sample
    Slump test is for mix ratio,ie: to much water. Core drilling is a possibility, but easier if you take cylinders or cubes during the pours. Cubes/cylinders are to be left in situ on site for the required durations for break tests, 3days, 7 days, 14 days and 21 days normally.

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    I just always look at at what is coming out of the chute, to determine if it was good concrete or not. Experience I guess.

    Trust me, I have told them to stop as it was crappy concrete.

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    ^Not perfect, but it works.

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    Guest Member S Landreth's Avatar
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    Quote Originally Posted by Mozzbie47 View Post
    We always hear about substandard concrete in Thailand.
    Is there a simple test for mixture ratio, a test that could be done prior to each load being discharge to the building site.
    No

    You could ask for a batch ticket with each load delivered (I donít know if they do it here), but youíre in Thailand and would you really trust any quantities that they wrote on that ticket?

    You have to trust your supplier or maybe talk to a contractor in your area that pours concrete and ask them who they use.
    Keep your friends close and your enemies closer.

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    concrete mix

    Quote Originally Posted by Mozzbie47 View Post
    We always hear about substandard concrete in Thailand.
    Is there a simple test for mixture ratio, a test that could be done prior to each load being discharge to the building site.
    if your in a big city you can control what you get but if your out in the sticks a bit,be careful not to upset the concrete company too much,if you refuse to pay you just wont get any concrete from them,best thing is if its not too far is go to the plant when your expecting the order,if they see your serious about the mix being correct they wont mess you about and you will get what you ask for,usually if you order it in the morning you can get it in a few hours so you dont have to panic,the only thing is like someone else said the workers like to have it self level so not too much work,if its a slab your pouring bring the plastic up with a course of bricks round and once its looking matt finish you could flood the slab quietly or sheet it down with plastic to keep the moisture in,if its pillars,once the shuttering is off wrap it in cling film or thin plastic for a few more days just to let it fully cure.
    hope it helps a bit

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    Concrete QC

    we just had a test done on ready mix concrete delivered from CPAC

    Costs 110 baht for the metal cast which CPAC delivered - our engineer studies at CMU so we didn't pay for the actual test itself - not sure how much it would cost.He did say that although the concrete passed - it wasn't the best - lucky we ordered 350kg/cm3 as its only 90 baht more expensive per m3.

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    '' Rebar '' too someone mentioned quality! We found 3 different prices for the same Bar, 3 different quality's
    some Bar is not pressed as it should be so the strenght is compromised , OK for making a cheap garden wall! not a 3 story Shop House..

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    Curing impacts every single attribute of concrete and I would follow ltnt's advice very carefully. Curing costs virtually no money and if you don't cure it right your concrete may never reach even half of its design strength and crack badly. If you are serious about getting it right then read the knowledge accumulated on curing packed into ACI 308.

    Just because concrete appears dry, which is the test I see done in Thailand, does not mean it is ready to support weight. In places like the US it is illegal to put weight on a foundation within 30 days of the pour. Even 30 days in concrete has only achieved 80% of its strength though that is deemed just sufficient enough due to over design.

    Finally can't resist mentioning the worst of all mistakes I see in Thailand on a typical basis. Never lay rebar on the ground. In contact with wet earth it simply turns into a pile of rust. Support rebar using rebar chairs so it is completely encased in concrete.

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    I have seen it laid on the ground, but then I have seen them lift it after the pour so it is not on the ground

    crude but better than nothing!

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    Typical specs where concrete is in contact with dirt require the rebar to be minimum 3" inside the concrete. Pulling at them is not a reliable way to accomplish this for many reasons including concrete is opaque so you can't see if it was done correctly or not. You only get one chance to get it right. That's why rebar chairs are used.

    Back to the main question, as others said you want a slump test. I have observed concrete in Thailand is mixed with the perfect amount of water in the truck and arrives just the way you want it. Then before the pouring starts your guys doing the work will ask the driver to water it down to make the concrete easier to spread so that their job is easier. This is a huge mistake. Wet concrete is weak and porous and when dry will wick up water like a sponge in all the pores where the excess water was taking up space. Unless you really understand the ramifications, you need to tell your people you don't want a single drop of water added by the driver.

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