Rusting Rebar is Dangerous!

a reply to: AugustusMasonicus

It can also lead to galvanic corrosion.

a reply to: JIMC5499

Normally it wont cause a galvanic reaction but if chlorides are present it will from what I can recall.

a reply to: AugustusMasonicus

NaCl

a reply to: CthulhuMythos

Do they then demolish them?

originally posted by: JIMC5499
NaCl

Yeah, which was the case this time.

originally posted by: galadofwarthethird
a reply to: MidnightHawk

Ya. Over time, the rust will effect the cement. And it does not take all that long. Its why they demolish all these building every generation or two. Concrete is porous, iron oxidizes like crazy. Its bound to lead to problems as the rust forms and expands.

They could use stainless steel, or copper bars, or other material, like and even hard plastic bars or carbon fiber. But? rebar is so much more cheaper. Im not sure rebar would be considered as steel. But then again I dont consider anything that has anything under .60% carbon content as steel.

More or less rebar is iron. And things like stainless steel, would be much more expensive. So ya. Demolished every generation or few generation. Or just wait, in time it demolishes itself.

Correct. The majority of reinforcing bars are made of steel.

originally posted by: drewlander
a reply to: Athetos

Yeah, i dont get it. This is literally how every parking garage everywhere in the country is built and im not seeing them fall over every day. Not to mention this should be a problem in three dozen other nearby buildings in Miami alone. Im doubtful that corroding rebar caused the 30 years old building to implode.

From article:

CBSNews
June 29, 2021·2 min read

Newly-emerged photos could possibly hold more information about what may have caused the catastrophic building collapse in Surfside, Florida.

An anonymous contractor shared the pictures with the Miami Herald, taken just two days before the collapse. They show a wet floor, cracked concrete and severely corroded rebar in the building's pool equipment room.

The contractor also reported deep standing water in the building's parking garage, just below the pool deck.

Photos taken two days before condo collapse show corrosion

From another article :

"The salt water slowly corroded the concrete and rebar (the steel bars used to reinforce the concrete) and load-bearing members (the concrete pillars holding up the likes of the parking garage), reducing the thickness of these critical support structures over years."

originally posted by: ArMaP
a reply to: drewlander

In Portugal, almost all the buildings are made with a reinforced concrete structure. I am writing this on a building with that type of construction and is some 60 or 70 years old. It's only a 4 stories building, but it doesn't show any signs of breaking and it has witnessed a few small earthquakes and a 7.9 Richter scale earthquake.

The environment always plays a factor. I'm guessing that these buildings are also probably given maintenance. It is possible there are cracks you are never aware of because they are taken care of before you notice them.

I have a friend that spent the spring treating cracks in the concrete behind his house (on the beach.) I now know why it was cracking.

FRP sounds like a great alternative for making concrete boats with.

Good eyes Hawk!
a reply to: MidnightHawk

a reply to: MidnightHawk

Rebar won't corrode enough to crack the cement its placed in. Other factors may affect the cement but expanding rebar corrosion isn't one of them.

Rust doesn't expand much if at all. It only extends as far as the base metal on which it occurs. In most cases the base metal appears to erode away getting smaller rather than larger in the presence of rust. That is how metal rusts completely away over time. Oxide jacking, suspect expansion of corrosion, is overstated and does not typically cause structural damage. When rust appears to expand it is typically due to flaking caused by leaching at the grain boundaries.

You are correct that chlorides can cause significant corrosion. But the amount of corrosion depends greatly on the type of metal and the concentration of the chlorides as well as the presence of other contributing or mitigating factors. There is far too little information available to the general public at this time to make any conclusive statements regarding the building collapse.

originally posted by: Vroomfondel
a reply to: MidnightHawk

Rebar won't corrode enough to crack the cement its placed in. Other factors may affect the cement but expanding rebar corrosion isn't one of them.

Rust doesn't expand much if at all. It only extends as far as the base metal on which it occurs. In most cases the base metal appears to erode away getting smaller rather than larger in the presence of rust. That is how metal rusts completely away over time. Oxide jacking, suspect expansion of corrosion, is overstated and does not typically cause structural damage. When rust appears to expand it is typically due to flaking caused by leaching at the grain boundaries.

You are correct that chlorides can cause significant corrosion. But the amount of corrosion depends greatly on the type of metal and the concentration of the chlorides as well as the presence of other contributing or mitigating factors. There is far too little information available to the general public at this time to make any conclusive statements regarding the building collapse.

Corrosion of reinforcing steel and other embedded metals is the leading cause of deterioration in concrete. When steel corrodes, the resulting rust occupies a greater volume than the steel. This expansion creates tensile stresses in the concrete, which can eventually cause cracking, delamination, and spalling

Source

a reply to: MidnightHawk

Yes that is a neat article. As I said, its overstated. Water itself damages cement over time. Ask anyone who ever had a cracked foundation if you don't believe me. If there is enough water seeping through interstices in the cement to cause such significant oxidation in the rebar, that water alone can do enough damage to the cement to cause problems. As I stated above, other factors are likely present that affect the cement.

I am not saying the article is wrong, just overstated. It places too much emphasis on the effect of expanding oxidation and too little on the additional contributing elements in the root cause mode of failure. In other words, the same conditions that caused the corrosion of the rebar caused damage to the surrounding cement.

a reply to: MidnightHawk

Nice. How convenient they took photos two days prior.

Also the pillars would not lose thickness from expanding rebar. They should gain it, which is the problem they are claiming. The part I dont get is how they can point the finger at the rebar in this building. Every adjacent concrete building was likely built the same way. Buildings across the country are built the same way. Only this one is collapsing after 30 or something years. Taking photos two days prior and popping them on the news only makes me more suspicious.

a reply to: Vroomfondel

In other words, the same conditions that caused the corrosion of the rebar caused damage to the surrounding cement.

It's called concrete, actually. Learn the difference.
Water is not bad for concrete. There is plenty of concrete under water. But it is bad for steel, especially when it is salty water.

originally posted by: markovian
a reply to: galadofwarthethird
A protective coating might be better

I'm no expert but wouldent the rigidity of ss make it bad when used in concrete

Not really? There are literally hundreds of different types of Stainless Steels out there. The most cheapest and wildly available? Would work for use in reebar.

But it would be more costly then rebar. Chromium? The element in Stainless Steel, which give it its stainless factor. That is, just like iron it rusts. Chromium when exposed to oxygen oxydises and forms a layer on the steel at a microscopic level.

Basically Stainless Steel does not rust orange and dusty is because the chromium in the stell is rusting on contact with oxygen, forming a protective chromium oxide layer of rust on the metal.

Also? Its is because its not as cheap and wildly available as Iron is. Even the cheapest Stainless Steel is still more expensive then the mild steel that rebar is made of.

But ya! Coating the rebar is a easy and cheap fix. Even spray painting them before encasing in concrete would help in expanding its oxidation life. Even encased in concrete which is pours material, that means can not only water molecules enter, but so to can oxygen. So even in concrete? Its gona rust.

Leading to cavities in the concrete around the rusting rebar, and leading to it being rubble in the not to distant future.

However even that would just add up to cost while building. And so? What do you think people and companies do when there pocket books are on the check?

Yup! The go the easiest and cheapest method. To save a few bucks? And why? Because people like money.

And also everything is made to be broken.

a reply to: JimmyNeutr0n

An interesting theory guy. I mean, it does not seem to last in practice.

But an interesting theory none the less. You do know that the rebar is not holding the weight? The concrete is. The metal is only there to keep the slab of concrete from fracturing and crumbling for the most part. To which giant slabs of concrete any concrete is prone to? So unless your pouring on the ground?

Then pouring over metal encased in the concrete, is only there as a structural mechanism, to make sure its does not split or crack. Because once a crack happens in concrete? Its spreads and eventually leading to fracture of the whole pour.

And once its vertical, and not just floor?

Holding weight? Tons? You don't want a crumbly floor do you? So why would you want a crumbly wall holding a lot of weight?

So what exactly are you talking about when you say? Metal rebar increases its strength? If your talking about tonnage only? Then your talking about only one aspect of the meaning of the word strength in that equation.

a reply to: Phage
Well ya Phage? Who would put iron metal in concrete they know is going to be underwater? Its gonna rust. Saltwater does some damage to steel fast, even stainless steel begins rusting after mostly a month or so, at most, held in saltwater.

Which means? Its gonna rust, and its gonna rust like crazy. And so? The Romans didn't put rebar metal in the concrete they know was going to be submerged under water for long periods of time. Obviously they were more advanced then us back then. They had the advantage of common sense.

And there common sense barely even lasted a 1000 years. Most of it rubble now.

a reply to: galadofwarthethird

Did the Romans use reinforced concrete anywhere? Or did they use mortar to hold stonework together?

Yeah. Reinforced concrete can be a problem. Spalling is a good indication of those problems.

originally posted by: drewlander
a reply to: Athetos

Yeah, i dont get it. This is literally how every parking garage everywhere in the country is built and im not seeing them fall over every day. Not to mention this should be a problem in three dozen other nearby buildings in Miami alone. Im doubtful that corroding rebar caused the 30 years old building to implode.

in the last ten years or so i have seen a lot of concern over those parking structures. and i have seen many that have had to be pretty much rebuilt, due to this problem with rust in reinforced concrete. generally due to the salt usage on roads in winter. one reason why so many places have been looking for a replacement for salt used on roads.

a reply to: Phage
What a silly question phage guy?

You know how much iron that would take? The Romans were running out of wood just using it for the nails required for yearly crucifixions.

To think that they had that kind and amount of tonnage on iron, or even know of steel. Would be silly. They were in the bronze age. To the average roman citizen. Iron was a mythical metal, one which 99% of them had yet to even hear of.

So no. They did not use reinforced concrete, ie put rebar in concrete. Simply because? They had none. Copper and bronze were all the rage back then. Its why its called the bronze age. They had yet to reach the iron age. In fact not that far out of the stone age.