I'm curious what most people do to prevent rebar from sinking into the dirt as pressure is applied during the pour (especially with workers stomping over it during the pour). I know about the TieBrick product, and interested how many use that, but also about what most do to insure that the rebar remains at the depth in the concrete as intended.
Use rebar chairs
Flat workers pull the rebar up into the pour as they go.
Flat workers *are supposed* pull the rebar up into the pour as they go. [g]
rebar up into the pour as they go.
we use concrete bricks ("dobies)
What's a "flat worker" and where is that expression used?
"flat workers" those are the drunks after the pour
Someone who does flatwork. The expression is used whenever discussing flatwork or flatworkers.
That may be true for welded wire mesh, but not for actual bars. Bars are supposed to supported on chairs or masonry blocks made for the purpose, commonly called "dobies" as "marson" posted in his message.
Don't ever depend on finishers to pull up rebar, it is impossible once the concrete is on it, and architecturally supervised pours will not allow it. Sand chairs are difficult to keep in position, most everyone uses concrete brick.
Even if wire mesh gets pulled up by the flat worker he will only step on it and push it back down when screeding.
Not if they have X-ray vision and 4"x4" feet...
There's an amazing 'spit' here in Toronto made mainly of construction detritus, and it's a 'little sop of horrors' if you like to see reinforcing steel where the drawings say it should be. Chunk after chunk have the steel substantially out of place. Even the easy parts like columns.
I've never seen the brick used. Is it for work on grade only? Are they typical 'concrete bricks' or a special, smaller product?
You're going in circles. Is 'flatwork' slab work, as opposed to columns or walls?
yes
Michael:
Here's a link to a fancy style "dobie". Note that it has tie wires to hold the rebar in place. Most times the block is just plain.
I've seen those! Thanks, Bob.
Bob, I've seen these used before and always wondered how much they weaken the slab. Do they bond pretty well to the concrete? I suppose if the slab is well supported the lose in bending strength shouldn't be a big deal, but it does seem as though the dobies would cause a fair loss in the ability of the slab to resist a positive bending moment in that area.
Matt
Not really. The blocks are only a few inches long. The rebar in the area is anchored on either end of the block by embedment in the slab.
Think of it this way: the rebar works even if there is no concrete at the middle of a beam as long as it is anchored on the ends. The sections are assumed to be cracked (no concrete) at ultimate design strength. In elevated beams the main reason for the bottom concrete is aesthetics and to protect the rebar from corrosion. A similar thing is true for slabs on grade.
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