How rusty can rebar be?

[Andreas Lundgren]

Both rebar (8mm) in the picture were purchased new from two different hardware stores.

Now I'm going to order for a foundation and have it delivered, how rusty can I expect? How rusty is OK?

Best regards,
Andreas L

 

[Stefan N]

I wouldn't have used the lower one.

 

[ricebridge]

Both rebar (8mm) in the picture were bought new from two different construction stores.

Now I'm going to order for a foundation and have it delivered, how rusty can I expect it to be? How rusty is OK?

Best regards,
Andreas L

Well, that's how it usually looks. The upper one is actually unusually little rusty.

Rust is simply a chemical reaction between iron and oxygen (4Fe + 3O2 → 2Fe2O3, to put it chemically). Since there is quite a lack of oxygen inside the structure in which the reinforcement is embedded, the rusting does not continue—as long as no part of the reinforcement is exposed, of course.

 

[useless]

That the entire steel is covered with rust is not unusual. However, there seems to be a bit too much rust on the lower part for me to approve it. Surface rust is okay, but not loosely adhering rust on a larger part of the surface.

 

[Snigla]

I have probably never seen other islands "rusty" rebar items (neither mesh, posts, iron, etc.) thought they were all like that!

They're always outside (in all weather) so it's not really surprising if they rust...

I'll definitely check if I see something "shiny," on anything, next time I visit the building supplies store (now that I know they exist..)

 

[ricebridge]

That the entire steel is covered with rust is not unusual. However, it seems to be a bit too much rust on the lower part for me to have approved it. Surface rust is okay, but not loosely sitting rust on a larger part of the surface.

There is rust and there is rust in this world. Red rust (surface rust) does not affect strength. However, the dark brown pit rust does. In the picture, it doesn't look like there's any pit rust, except perhaps on the left side of the image. However, that could just as well be shadows from the grooves, so it's not possible to say for certain from the picture.

 

[sinclairhacker]

I've probably never seen other "rusty" reinforcement stuff (neither nets, posts, iron, etc.) I thought they were all like that!

They're always outside (in wind and weather) so it's not really surprising if they rust...

I'll definitely check if I see something "shiny," on something, next time I visit the hardware store (now that I know they exist..)

Surprised a friend when we were going to cast a smaller piece, with completely stainless reinforcement bars bought at Biltema.

Bought them there solely because they are indoors, and I wanted to surprise.

 

[Andreas Lundgren]

Since there is a rather lack of oxygen inside the structure in which the reinforcement is embedded, the rusting does not continue — as long as no part of the reinforcement is exposed, of course.

I'm mostly thinking that the concrete should adhere to the reinforcement. Even if it doesn't continue to rust, it should still hold, I think.

 

[Andreas Lundgren]

Gonna definitely check if I see anything "shiny" on anything next time I visit the hardware store (now that I know it exists..)

The upper one is one of 8 hand-picked I took at Byggmax. The lower one is a panic buy at PoG and it was the last they had left. Now I've polished it a bit with the angle grinder.

 

[Andreas Lundgren]

Thanks for all the answers!

I have now polished the lower one (a panic purchase, the last example). I'm casting a frame now, but will soon cast on a whole foundation and order materials for it.

 

[ricebridge]

I mostly think that the concrete should adhere to the reinforcement. Even if it doesn't continue to rust, it should still hold, I think.

THAT won't be a problem. If you've ever tried to knock old rebar off concrete, you know what I mean.

 

[C.Lundin]

I mainly think that the concrete should adhere to the rebar. Even if it doesn't continue to rust, it should still stick, I think.

Many designers, as well as inspectors, require the rebar to be rusty for better grip.
You can rest easy. (Edit: OK, not many. But it's also not uncommon)

As long as you don't see that the rusty iron is significantly larger than the others, there's no danger.

A little trivia is that some suppliers claim that their products should be stored dry, which is just pure nonsense.