Replies

1. 
   Guest_ | Apr 05, 2000 10:06pm | #1

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   Hi L.

   Depends on what you want it to do, what you will put on it, what kind of soil you have, what size the slab is, etc.

   Typically, a standard basement slab is not re-enforced with steel whereas a standard garage slab is.

   A structural SOG is re-enforced with re-bar and a sidewalk poured in place has none.

   No one application suits all.

   Chat later

1. 
   Guest_ | Apr 06, 2000 10:09am | #2

   *Consder specifying fiber in your mix. It will not prevent big cracks but it is good insurance for the small ones.

2. 
   Rich_Lange | Apr 09, 2000 03:36pm | #3

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   I will be replacing my old black top driveway with concrete. I have been investigating the material for beneath the slab. Some sources say to use crushed rock, others say to use sand so the curing concrete can slide on the sand as it shrinks, this is supposed to reduce the possibility of cracks. Does anyone have any opinion about which is better to use?

1. 
   Gene_Leger. | Apr 09, 2000 06:48pm | #4

   *L. Olson. If you are "reinforcing"the slab because you want a stronger floor, just increase the thickness of the slab. Instead of a 4-inch slab use a 6-inch slab which is 125% stronger than a 4-inch slab.See pages 27, 28, and 29 in my book, Complete Building Construction 4th Edition published by Macmillan Publsihing Company.Rich Lange. Sand is not a good base for a slab. The sand can shift as the concrete is poured and results in a slab with varying thickness.Use 4-inches of crushed stone, and "choke"it off with stone screenings or fine sand. The screenings or sand will fill the voids in the crushed stone and reduce the subgrade drag: the concrete will more more readily. The crushed stone is not a permeable as the sand base but it wwill readily absorb the excess water from the bottom of theslab.NOTE: Tell slab finnisher not to add any water to the mix. If he claims it is too stiff to work, tell him to have a mid range water reducer added.The advantage of the stone base is that is will not shift during the pour, and provides better support of the slab and guarantees a slab with uniform thickness.GeneL.

3. 
   Guest_ | Apr 09, 2000 07:03pm | #5

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   Hi Gene,

   WHAT!

   Sorry buddy, but what a pile of rubbish.

   Most varieties of sand can be compacted to 100% and whether you install sand or stone, both should be compacted to prevent voids from developing under your slab.

   Increasing the strenght of the slab by increasing the volume and cost by 50% is a waste of money. Strenght can be increased by changing the concrete mix from 2000psi to 3000psi for example.

   Having said that, NOTHING makes a slab like consistency and a good base.

   Gabe

4. 
   Harley_Parkes | Apr 29, 2000 03:43am | #6

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   Not a great many great ideas here. The MOST important things are the strength of the concrete mix and the cure time of the concrete. A vapor barrier under the concrete is there, not to keep water out later, but to keep moisture in the concrete during the curing process. Pouring concrete on dry sand is one of the worst things you can do to concrete. A good compacted sub base goes without saying.

1. 
   Jeff_Lynne | May 09, 2000 01:50am | #7

   *I'm looking for info on where the re-bar should be placed within a foundation slab...should it be suspended within the upper portion of the concrete pour or just laid along the bottom just above the gravel. The slab is to be poured tomorrow and I need help as soon as possible. Thanks.

5. 
   Guest_ | May 10, 2000 04:23am | #8

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   Jeff,

   You might want to do a search. This has been talked about quite a bit. I have no expertise in this area, but since you're in a hurry, you will find that laying the rebar "along the bottom just above the gravel" is not good. Search.

   Rich Beckman

1. 
   Guest_ | May 11, 2000 09:19pm | #10

   *Jeff, Might be too late but check out ACI (American Concrete Institute).....they have a research database and publications with specs for placement, hook length, concrete cover, etc.

6. 
   L._Olson | May 11, 2000 09:19pm | #9

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   I am planning an addition that includes a basement and slab-on-grade play area. My question is this: Do I need to reinforce the concrete in the basement floor and/or slab-on-grade?

   Why or why not?

   Thank you in advance for your help.