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Pour different slump concrete into the same foundation?

mikeso | Posted in General Questions on

I want to pour a monolithic concrete slab foundation. plan to pour less-slump concrete in the foot sections and in the slab, pour the high-slump concrete.

is this good? if yes, what are the recommended slump values.

many thanks.


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  1. User avatar GBA Editor
    Martin Holladay | | #1

    There shouldn't be any need for two types of concrete for this type of foundation. Either talk with the batch plant about your needs, or talk to an engineer.

    If you want a low-water mix of concrete (for strength), and are worried about workability, the usual solution is to add a plasticizer.

  2. mikeso | | #2

    hi, Martin,

    at the top, i want high-slump so i can level it easier. or i can use same high-slump for whole foundation.

    i am not sure if this make sense.

  3. User avatar GBA Editor
    Martin Holladay | | #3

    No, it doesn't make sense.

  4. mikeso | | #4

    so use same high slump?

  5. User avatar GBA Editor
    Martin Holladay | | #5

    The concrete needs to meet your engineering requirements -- no more, no less. These requirements are either set by the engineer, or established by a casual conversation with the dispatcher at the batch plant. You tell them what you want, and you trust them -- or you hire an engineer if you don't trust them.

    "Slump" refers to the slump test performed on concrete without plasticizers. Dry concrete is strong but harder to finish than wet concrete. Plasticizers replace some of the water in concrete without weakening it.

    If you are an experienced concrete finisher, you know what you want. If this is your first rodeo, hire a concrete contractor to advise and help you.

  6. mikeso | | #6

    but you didn't tell me why not make sense.

    i want the foot settle quick but easy to finish at the slab surface.

    i know what slump is.

  7. User avatar GBA Editor
    Martin Holladay | | #7

    If you know what you want, you don't need my advice.

    The main reason I'm recommending that you order a single type of concrete is to simplify your concrete order, delivery, and placement.

    But if you want to do it differently, go ahead.

    Maybe you are mixing your concrete in a wheelbarrow, or mixing it in a little on-site mixer. I don't know your plan.

    If you do it your way, my only advice is that you avoid a so-called cold joint. (You don't want to place the concrete on different days.) Your monolithic slab will be strongest if all the concrete is placed at the same time.

  8. mikeso | | #8

    same time but two trucks. total 17 yards. I planed to use same type but because i am still preparing so i want to hear some advice.

    most likely, I will rent a pump to same some labor.

  9. Malcolm Taylor | | #9

    Are you finishing this yourself? Have you done this before? Used a power trowel etc?

  10. mikeso | | #10

    yes, plan to.
    i don't need power trowel. 34x16 size

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