Rebar in contact with soil - gotta go?

[Msradell]

I am aware there are nonmetal chairs, however, around here this is what is used

https://www.aftfasteners.com/produc...MJuWkWydn6WZ9nSRRIfi1BU3corYsXzxoCL4sQAvD_BwE

The only place I've seen those used around here are in highway construction. Just goes to shows it there different local standards in different parts of the country.

 

[BJN]

I know - old thread. I’m seeing some rebar chairs made of wire that is stuck in the ground - basically a three sided wire square stabbed into the ground that the rebar sits on, usually used for footings. They are not made of rust resistant material, or protected in any way. Does that cause the rebar to rust? Is it a violation? I can’t find anything specific in the Concrete Manual or ACI 318.

 

[Mark K]

As noted above metal chairs have been used for years

 

[SCBO1]

Would be concerned with mud on the rebar, which I'm seeing a lot more of lately.

 

[BJN]

It’s kind of a small to worry about, even if it did cause rust, it might take 50 - 100 years before it matters. I just saw some of those wire chairs rusting in the back of someone’s truck, so I wondered.

 

[ADAguy]

3" no?

 

[BJN]

Yes, the chairs do hold the reinforcement 3” off the ground as required in IRC R403.1.3.5.3. This 3” minimum is so we don’t allow rebar to contact the earth, which would allow rust to eat the ground contact rebar and anything attached to it.
Which was why I wondered how mild steel wires in contact with the ground didn’t cause the same problem (although, the answer is probably that they are much smaller in diameter than No. 4 rebar.)

 

[my250r11]

Yes, the chairs do hold the reinforcement 3” off the ground as required in IRC R403.1.3.5.3. This 3” minimum is so we don’t allow rebar to contact the earth, which would allow rust to eat the ground contact rebar and anything attached to it.
Which was why I wondered how mild steel wires in contact with the ground didn’t cause the same problem (although, the answer is probably that they are much smaller in diameter than No. 4 rebar.)

Had an issue with an inspector many years ago on the metal chair in a 3' thick slab with 2 layers of rebar mats. He wanted us to remove the metal chairs and use the cmu rebar chairs. This slab was for a concrete tank an was 100' X 200'. This would require a lot of work to change and time & money. Called the structural engineer and he gave us a letter stating that the wire chair with or without sand plate will rust quickly which in turn causes the capillary break needed to stop the corrosion from continuing. That letter was given to the BO and was excepted. I have used that same mind set since. Just my 2 cents.

 

[BN4537]

Had an issue with an inspector many years ago on the metal chair in a 3' thick slab with 2 layers of rebar mats. He wanted us to remove the metal chairs and use the cmu rebar chairs. This slab was for a concrete tank an was 100' X 200'. This would require a lot of work to change and time & money. Called the structural engineer and he gave us a letter stating that the wire chair with or without sand plate will rust quickly which in turn causes the capillary break needed to stop the corrosion from continuing. That letter was given to the BO and was excepted. I have used that same mind set since. Just my 2 cents.

That is great information, thank you.

 

[BN4537]

Not a huge concrete expert, and I see a lot of creative ways of suspending the rebar - not always sure how to handle that. Just because it's ugly and lazy doesn't necessarily make it a code violation...