Rusting Rebar is Dangerous!

Ran across the video a little earlier and thought I'd share it.

This sad article from the New York Times says that the search is coming to an end for survivors in the collapsed Condo in Miami. So far confirmed over 50 people dead. Probably over 80 still missing.

So what was the culprit? Many are looking to the problem of not attending to eroding rebar in the cement structure. Why and how this happens is explained in the simple video below:



It is said there were pumps that were draining seawater night and day from the foundation, as well as a leaky swimming pool causing corrosion. Rebar is made of steel and corrodes. The rust, or corrosion expands, causing the cement to crack. There are a number of ways rebar can corrode. A main cause is by chlorine that slowly seeps into the cement and reaches the steel. Here is a good explanation of how this happens and why with epoxy coated rebar is banned in many areas:




What a tragedy and leaving corroding rebar alone in old structures such as this condo complex and other buildings and bridges are more disasters waiting to happen.

Houses constructed with rebar in Scotland are classed as a defective construction and is difficult to get a mortgage lender to back a purchase of that type of construction never mind getting house insurance and for these very reasons shown in OP

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.

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

originally posted by: galadofwarthethird
a reply to: MidnightHawk
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.

Copper wouldn't work as non-ferrous metals don't stand up to strength testings. Furthermore, plastics actually gives you less structural integrity by increasing the load bearing on the slab itself.

You need to understand the point of rebar. To keep the slab intact if it is struck with a heavy object. A piece of plastic doesn't do anything integrity wise to the even harder and denser concrete it is encased in, it just increases the weight of the object more-so. Same goes for copper and any other non-ferrous metal, until they find a suitable candidate..

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

Precisely. Chloride rich cement will break down stainless steel faster than water will break down a ferrous metal.

What?!!?!? Really? What do you use then? 100% of house foundations and pretty much any concrete pour uses rebar in some way.
All this talk about cl2 is little on the bunk side. Cl2 reacts easily and with anything if there was cl2 in the concrete most of the reaction would take place simply during mixing and the cl2 would come from tap water and be in around 1-2mg/l. Not to mention the lye.

The lye in concrete reacts with cl2 very rapidly and it becomes NaCl or salt harmless salt....

I am thinking most of not all rebar corrosion is moister based not cl2.

a reply to: CthulhuMythos

if we are in a warming period in earths climate-this does not bode well as a warmer earth means a lot more rain and humidity across huge areas of the planet.

Aren't pretty much all tall buildings constructed with rebar/concrete?
Must be a crazy expensive and difficult job to try to project those buildings-if possible at all.

At some point in the future this could become a huge problem with skyscrapers and other huge buildings falling down all over the place.

If you notice the video is titled "Epoxy Coated Rebar". Rebar is actually allowed to rust before it is set in concrete. That lets the concrete adhere to the rebar. The epoxy coated rebar doesn't allow the concrete to adhere to the rebar, only the epoxy coating. If the coating is compromised in anyway the rebar will rust inside of the coating. This will detach the coating from the rebar, reducing the strength of the concrete member.

Personally I question the composition of the steel being used to make rebar. Much of the steel in the US comes from China and there have been issues with quality control for almost everything we get from there.

Buildings rarely fail because of one defect.
Usually it's a combination of factors.
Mostly human error

There are a number of ways that iron can corrode inside of concrete, not all require chlorine to be present. Electrolysis is one.
Here is a write-up on the subject: cement.org

I used to work for a major paint/coatings manufacturer in their facilities that housed the product development and testing. They had a specific lab just for rebar and their specific coatings.

I was not part of the lab groups so I can’t speak to what the composition of the coatings was but I know they spent big time and money running them through all kinds of corrosion testing and weather testing.

At some point everything fails and you can only do your due diligence. A major part of the coatings/products and if they fail or have a shorter life span is how they are applied or installed. My guess is that some of the companies that are coating some of this rebar are taking shortcuts which is helping premature failure as well as poor or improper installation methods a big example lots of people don’t think about is grounding or catholic protection like they use in pipelines and large fuel tanks

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.

a reply to: drewlander

Lose the "implode" bit. It just shows ignorance. The building collapsed.

a reply to: MidnightHawk

The building was also settling unevenly into Florida's notoriously porous limestone substrate.

a reply to: Silcone Synapse

Aren't pretty much all tall buildings constructed with rebar/concrete?

The foundations are, yes. However the superstructure of many buildings is constructed of structural steel, not reinforced concrete.

The relationship between steel and concrete's expansion and contraction is so close that these two work in tandem. Tension and compression are combined to complement each other, working as one.

It's tragic what happened. Something around the ground changing, and the resulting stress aggravating the structural integrity of the building. Reinforced concrete construction is generally very reliable, it's rare to hear about buildings having issues with these kind of failures. The way it looks to have sheared came to mind, thinking about the floors being typical.

I think there were probably deficiencies in the reinforcing, but have my doubts that were the primary factor. I get the impression cracks in the cover itself degrading the sections of the structure, as a result of dynamic forces at play in the surrounding areas. Once the concrete is too far gone, they stop working together as they were designed. With proper cover, I wonder if they would have even used epoxy bar at the time?

The galvanized rebar suggested in the video sounded like a practical solution to help resist these kinds of stresses.

originally posted by: AugustusMasonicus
a reply to: MidnightHawk

The building was also settling unevenly into Florida's notoriously porous limestone substrate.

I figured something like this, combined with the forces around the swimming pool...

Copper plating rebar would help, this is commonly used on electrical ground rods.

And there are a number of waterproofing admixtures for concrete and coating that also stop water.

Fresh water seldom causes problems with rusting rebar. salt is the killer.

originally posted by: ANNED
Copper plating rebar would help, this is commonly used on electrical ground rods.

Way too expensive.

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.