Just curious to see if someone can shed light on the following: rebar cast into a footing, pier, or retaining wall, way down in the dirt, and it spends the rest of its life exposed to an environment that’s gotta be somewhat damp, permanently, especially in wet climates or high water tables. What’s happening inside there where the bar is? Is it rusting out? Lasting forever?
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It should be fine under most conditions assuming the minimum 3" clear cover for concrete cast directly against soil is used.
...that's not a mistake, it's rustic
David, 42 years ago I had the job of breaking up a concrete sidewalk at the Federal Reserve Bank in Philadelphia. The rebar was so old it was square, not deformed like we see today. It was in perfect condition, I do not no when it was placed. I imagine because it was square shaped it must of been in for many years.
mike
and I have torn a bldg down that had the bottom bar with no cocerage on one of the upper floor rusted in two #5 bar gone in 32 year old bldg.
The best employee you can have but you wouldn't want him as a neighbor " He the shifty type"
For iron to rust it needs oxygen as well as water -- providing it has the correct concrete cover it won't rust -- even in underwater conditions.
IanDG
Ditto to previous posts. With proper rebar placement and concrete cover, and proper mix design it should be fine. Where salts are involved (bridges, roadways) epoxy coated rebar is used. There was a building, the Miami International Trade Center iirc, that had to be torn down because of concrete spalling caused by the use of ocean beach sand in the concrete. The salts in the sand caused corrosion of the rebar which in turn caused the concrete spalling.
There's a lot of foundation work for contractors in San Francisco because of beach sand from Ocean Beach used in the early concrete. It turns into chalk. These days the mud is all made with river sand barged down from the delta.
As one of the other posters metioned, steel needs to be exposed to water and air to rust. In corrosive or underwater environments, one of the cheapest solutions is to increase the concrete cover to the rebar. There are more expensive solutions such as epoxy-coated or galvanized rebar.
FWIW: When I was doing footings & foundations, we could not let the rebar contact the ground, seems the theory was that the soil would rust the bar & eat all the way thru the bar. About the time I got out of concrete, plastic chairs came out, so the chairs would not wick the rust into the bar.
Oh yeah, you would not believe the effort we go thru to insure there is no debris underneath the rebar before we pour. Especialy bits of tie wire. Try real hard to keep 3" clear concrete around it.
SamT
Rebar is a slow motion bomb in concrete
Concrete particularly in colder climates will crack, air and water will find exposed iron and as it rusts it will expand and destroy the concrete it is encased in. Had the Roman Colliseum been made the way almost any mondern stadium is constructed, it would certainly not be here. There are other innovations in anchient concrete that contribute to its longevity, but iron rebar is the most consequential difference. I personally think it should be criminal to build municipal projects with uncoated Iron rebar.
so
read Concrete Planet did you?
I read it.
Scares the hell out of me.
Wow! Over 10 YEARS!"This has
Wow! Over 10 YEARS!"This has got to be the oldest thread resurrection I have ever seen. LOL
Ten years, meh :)
Built in 607, the Nara temple Hōryūji is the oldest extant wooden architecture in the world. I've always wondered what it'd be like to resurrect a forum of carpenters working on the temple just to see what technological, methodological, and economic conditions they were operating under (of course, the same could be said--and in spades--regarding the Khufu pyramid in Egypt).
Temple Hōryūji
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Now THERE'S some cantalevers!
Awesome buildings.
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