Concrete Chairs

[lilranch2001]

I took one a little bit ago as well!

 

[RjCorazza]

Funny. There is a somewhat local (?) trucking company I have seen that the owner's name on the trailer (giant letters) is :
A. Duie Pyle
Sorry Mr Pyle, but I find that hilarious.

To stay on topic, I like concrete chairs.

 

[lilranch2001]

I’m starting to get the feeling that there’s a personal conflict between ole Moss and two bit……..

Come on guys get along. Have a good time!

 

[MossRoad]

I’m starting to get the feeling that there’s a personal conflict between ole Moss and two bit……..

Come on guys get along. Have a good time!

I'd love to. I've made it a point to not comment on his posts over the past year or so, yet he keeps commenting on me. Not my posts, me. So there you go. If he stopped commenting about me, you'd never hear a peep out of me about him.

Add to that, every time he tries to make a comment about me, my 2nd amendment, religious, family, political, social beliefs, etc., he's 100% wrong. Not sure what he's trying to accomplish other than stalking.

 

[two_bit_score]

Don't flatter yourself.

 

[KennyG]

Is there any evidence for the wire chairs, which are sitting either on dirt or visqueen, rusting out and lowing moisture to get to the rwbar and corrode them? The plastic chairs, typically used for wire wouldn't so that.
The reason I ask, is rebar should be, correct be if wrong, no less than 2.5x the diameter of the bar, from the closest edge of concrete. That wire rebar chair, the feet are touching the subgrade surface.

To get back on topic, the chairs are not a problem. You want to maintain coverage on the rebar because if it corrodes it will expand and potential accelerate cracking. The wire is so small that even if it rusts, it won't expand enough to cause a problem. As an interesting trivia point, the chemistry in concrete "passivates" the steel so it won't rust, even if there is moisture in the concrete. Rust only happens if the steel is exposed to air.

 

[two_bit_score]

To get back on topic, the chairs are not a problem. You want to maintain coverage on the rebar because if it corrodes it will expand and potential accelerate cracking. The wire is so small that even if it rusts, it won't expand enough to cause a problem. As an interesting trivia point, the chemistry in concrete "passivates" the steel so it won't rust, even if there is moisture in the concrete. Rust only happens if the steel is exposed to air.

It always concerned me that all the wire I saw going under the concrete was significantly rusty. Maybe it was just surface rust but it looked like more than that to me. I also saw a lot of wire in broken up concrete that had been pulled up which looked like it must have continued to rust after it was in the 'crete. So what you are saying sounds true because oxygen is needed for rust to continue but it goes against what I think I saw. I can accept the premise that the rust won't expand enough to accelerate cracking but if the rust could continue enough to corrode the wire that much it would also not have any ability to hold the concrete together and would become worthless at doing the job it was put there to do.

 

[lilranch2001]

And why is roadbed steel epoxied?

 

[jjeff]

Interesting thing I learned about putting poly or visqueen under concrete high density foam board does the same thing in terms of a vapor barrier and once the slab is heated by the structure it radiates to slab and maintains heat much better cuz it works like a thermal break I guess? I'm curious if the concrete experts on here use foam? Or recommend it's use? What are some of the problems using it besides added cost? it is much cheaper than doing in floor heating I'm sure of. I'm going on 10 yrs with two slabs I put foam under no cracks, no control joints, or apparent noticeable problems yet. Knocking on wood lol.

 

[ponytug]

Is there any evidence for the wire chairs, which are sitting either on dirt or visqueen, rusting out and lowing moisture to get to the rwbar and corrode them? The plastic chairs, typically used for wire wouldn't so that.
The reason I ask, is rebar should be, correct be if wrong, no less than 2.5x the diameter of the bar, from the closest edge of concrete. That wire rebar chair, the feet are touching the subgrade surface.

Both plastic chairs and concrete chairs ("dobies"?) are superior to plain wire supports, for corrosion and water leakage reasons. I believe that you can obtain epoxy coated wire versions, e.g. Meadow Burke, but I haven't used them or seen them used.

https://meadowburke.com/wp-content/uploads/2021/06/meadow-burke-technical-manual-reinforcing.pdf

The American Concrete Institute has numerous publications, but they get fairly technical...
https://www.concrete.org/topicsinconcrete/topicdetail/rebar Placement#webpages?search=rebar Placement ...

I like the concept of foam under concrete. In certain other countries, it is the norm, both for vapor barrier and insulation. Given the cost of a slab, it isn't pricey, at least from what I know.

All the best,

Peter

 

[paulsharvey]

And why is roadbed steel epoxied?

Maybe in areas where they brine/salt roads? It isn't here.

 

[paulsharvey]

Does the foam retain its shape/structure/insulating properties with that much weight on top of it? I've seen it used only in videos from eastern Europe, and typically with those radian heat floor tubes.

 

[jjeff]

Does the foam retain its shape/structure/insulating properties with that much weight on top of it? I've seen it used only in videos from eastern Europe, and typically with those radian heat floor tubes.

I used high density 1.5- 2" foam very minimal distortion, with wwf over it graded and compacted extensively before placing sheets even taped all joints. first time I used foam forgot to adjust for foam thickness lol needles to say I had a large pile of sand afterwords cuz of my f-up and should be in stupid thread. Btw I've had great results using compacted sand using a bit of water to help. I'll say I burn wood at my cabin the stoves on slab once that slab heats up it maintains heat for awhile. if I burn continuously for several days over 90% of the slab can be comfortably walked on barefoot and it's below zero outside.

 

[jfsawatzky]

My motto is use enough chairs that walking around on the rebar doesn't bend the rebar, or shift it.

What distance between chairs would accomplish that?

 

[ponytug]

What distance between chairs would accomplish that?

I think that depends on the size of rebar in use and the spacing of the grid, doesn't it? Small diameter (number) rebar needs more supports, and larger rebar needs less. I believe that there are tables, like this one; https://www.lotel.com/sites/default/files/user/Rebar-ups spacing chart B.jpg

However, I think the bottom line is "Is the rebar staying at the desired height off the base?", and "is it not deforming if the crew walks around on it?".

All the best,

Peter

 

[jjeff]

I'm stubborn and follow how I was taught commercially over 20,yrs ago pull wwf and or rebar as the concrete is placed. Only time I've used chairs is when a rotating laser retractable boom screed was used probably because they didn't want excessive crew members in between the rather large machine and screed board it was pulling so they gave me the job to put in chairs as the machine did its job. A machine that big moving around a grid will crush plastic chairs and deflect rebar no matter how well it's supported. Perhaps times have changed in over 20 years? From non commercial personal experiences I'd rather spend the money from not using chairs to put fibers plus wwf in the concrete so I'm for pulling as you place, and am far more concerned of wwf or rebar shifting to the edges of a form and being exposed, however I am not a concrete expert like a few on here, I also feel somewhat experienced building inspectors make the call if they want you to put in chairs based on getting a feel for your experience and or the reputation of the company. you hired, a rock bottom priced fly by night concrete contractor from previous problems the inspector might request they use chairs. Just my opinion.

 

[JJT]

My last large pour, (40 yards, 15+ years ago), I used chairs made from concrete with a built in wire tie. Very handy. I searched and cannot find them now. It seems like plastic or wire are the only choices. I used #4 rebar, 24" on center in a grid format. I have no cracks, I did not use fiber in the small aggregate 4000 psi concrete.

 

[MossRoad]

When I did my garage addition in 2020, I used these little plastic chairs. Pretty easy addition, cheap, and I know the rebar isn't laying on the bottom or 1/4" from the top. They are currently .29 each. Not sure what they were 4 years ago.

EDIT: They were .17 each in 2020.

Nice thing about Menards... they keep your receipts on-line for quite a while.

Plastic Rebar Chair

The 2-1/4in plastic rebar chair is a durable plastic rebar support system that is ideal for concrete applications. The chair is designed so that the rebar snaps securely into place allowing the rebar to sit above the ground while concrete is poured. The chairs are easy to work with and...

www.menards.com

(click to enlarge).

 

[jjeff]

Seen these concrete chairs at your overpriced big box store before, There are lots of companies making plastic chairs apparently it is the new requirement these days. Stubbornness with me prevails and I'll never use them lol.

 

[ponytug]

My last large pour, (40 yards, 15+ years ago), I used chairs made from concrete with a built in wire tie. Very handy. I searched and cannot find them now. It seems like plastic or wire are the only choices. I used #4 rebar, 24" on center in a grid format. I have no cracks, I did not use fiber in the small aggregate 4000 psi concrete.

You might try searching for "wire dobie" or just "rebar support", or "rebar concrete block".

FWIW: They are in my local Home Depots, but not the few I checked in Michigan. In the Michigan Lowe's that I checked, it was called a "rebar concrete block", but clearly had wires on it.

Search Results for Rebar block at The Home Depot

Search Results for Rebar block at The Home Depot

www.homedepot.com

https://www.lowes.com/pd/Common-3-in-x-3-in-x-3-in-Actual-3-125-in-x-3-125-in-x-3-125-in-Standard-Concrete-Block/3113953

All the best, Peter