Anchoring steel for monoslab footing.

Posted by Robert Olin on September 7, 2009, 11:14 pm

Residencial code calles for one #5 bar in the center of a mono slab footing
or 2 #4 bars. Anyone know if it's ok to drive a verticle piece of rebar
into the ground to tie these horizontal bars to, or are they so anal
retentive that they think the steel will rust into the concrete?

Thanks,
Bob

--
Robert Olin
Bob's Water & Septic LLC
jolin@whidbey.net
http://soilsandseptic.com/bobs.html

Posted by jloomis on September 8, 2009, 8:56 am

Anal. (although since it is not a bridge, a high rise, or an overpass, I do
not see why not!)
Most of the times I just use a dobe - concrete block that ties to steel.
Or, make an angle out of a smaller rebar........right angle......say 2' x2'
and rest it on the concrete 3" x 3" dobe and tie the steel to it.

I cannot imagine the rust traveling from the ground........all the way up to
possibly compromise the steel horizontal piece.
john

> Residencial code calles for one #5 bar in the center of a mono slab
> footing or 2 #4 bars. Anyone know if it's ok to drive a verticle piece
> of rebar into the ground to tie these horizontal bars to, or are they so
> anal retentive that they think the steel will rust into the concrete?
> Thanks,
> Bob
> --
> Robert Olin
> Bob's Water & Septic LLC
> jolin@whidbey.net
> http://soilsandseptic.com/bobs.html
>

Posted by Tom Cular on September 8, 2009, 6:37 pm

Rebar should NOT touch the ground or be driven into the ground as a stake
to support other bars. There is a reason that most specs. call for a minimum
clearance of 2-3 in. from the surface of the concrete or earth contact. As
John stated earlier, use some concrete (NOT RED) bricks for chairs to
suspend the horiz. bars from the ground surface. The rust will travel to the
bars in the concrete over time and cause destruction of the footing or slab.
Surface rust or oxidation on reinforcing steel is harmless if contained,
however when the bars are subject to severe rusting they expand and will
ultimately cause the concrete to fail.

> Anal. (although since it is not a bridge, a high rise, or an overpass, I
> do not see why not!)
> Most of the times I just use a dobe - concrete block that ties to steel.
> Or, make an angle out of a smaller rebar........right angle......say 2'
> x2' and rest it on the concrete 3" x 3" dobe and tie the steel to it.
> I cannot imagine the rust traveling from the ground........all the way up
> to possibly compromise the steel horizontal piece.
> john

>> Residencial code calles for one #5 bar in the center of a mono slab
>> footing or 2 #4 bars. Anyone know if it's ok to drive a verticle piece
>> of rebar into the ground to tie these horizontal bars to, or are they so
>> anal retentive that they think the steel will rust into the concrete?
>> Thanks,
>> Bob
>> --
>> Robert Olin
>> Bob's Water & Septic LLC
>> jolin@whidbey.net
>> http://soilsandseptic.com/bobs.html

Posted by jloomis on September 8, 2009, 10:00 pm

Hi Tom.
I have always wondered about this, and we always do put steel on concrete
blocking. not red brick......either.
there is a maintained 3" from earth contact in most plans.
Is the steel like a electrical wire that would transmit rust?
I still have trouble visualizing rust following steel.
Anyway, I do use concrete dobies.....
john

> Rebar should NOT touch the ground or be driven into the ground as a stake
> to support other bars. There is a reason that most specs. call for a
> minimum clearance of 2-3 in. from the surface of the concrete or earth
> contact. As John stated earlier, use some concrete (NOT RED) bricks for
> chairs to suspend the horiz. bars from the ground surface. The rust will
> travel to the bars in the concrete over time and cause destruction of the
> footing or slab. Surface rust or oxidation on reinforcing steel is
> harmless if contained, however when the bars are subject to severe rusting
> they expand and will ultimately cause the concrete to fail.

>> Anal. (although since it is not a bridge, a high rise, or an overpass, I
>> do not see why not!)
>> Most of the times I just use a dobe - concrete block that ties to steel.
>> Or, make an angle out of a smaller rebar........right angle......say 2'
>> x2' and rest it on the concrete 3" x 3" dobe and tie the steel to it.
>> I cannot imagine the rust traveling from the ground........all the way up
>> to possibly compromise the steel horizontal piece.
>> john

>>> Residencial code calles for one #5 bar in the center of a mono slab
>>> footing or 2 #4 bars. Anyone know if it's ok to drive a verticle piece
>>> of rebar into the ground to tie these horizontal bars to, or are they so
>>> anal retentive that they think the steel will rust into the concrete?
>>> Thanks,
>>> Bob
>>> --
>>> Robert Olin
>>> Bob's Water & Septic LLC
>>> jolin@whidbey.net
>>> http://soilsandseptic.com/bobs.html

Posted by PeterD on September 9, 2009, 9:00 am

wrote:

>Hi Tom.
>I have always wondered about this, and we always do put steel on concrete
>blocking. not red brick......either.
>there is a maintained 3" from earth contact in most plans.
>Is the steel like a electrical wire that would transmit rust?

Absolutely, rust will travel along steel (such as rebar) under paint
and protective coatings. Because of the mechanics of how this rust
spreads, it is very difficult to prevent, hence we limit the ability
for water to contact steel.

>I still have trouble visualizing rust following steel.

Think of it this way. You get rust on the edge. Rust is very porous.
Water travels in the rust, to new virgin steel, and rusts it. It is a
continuous process, with the rust able to travel great distances by
water being drawn in by capillary action.

About the only thing that limits it (rust) is to use galvanized
coatings such as hot-coat zinc. (Electroplate zinc is usually not
thick enough to withstand long periods of time...) Not much rebar is
zinc coated however.

What makes things worse is some soils/sands are loaded with stuff that
promotes rust, such as salt! (even inland, you can have corrosive
sand, as the sand is often the result of ocean action over a long
period of pre-history...)

>Anyway, I do use concrete dobies.....
>john

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