Rusting Rebar is Dangerous!

a reply to: galadofwarthethird

So, this had nothing to do with it?

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.

originally posted by: Phage
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.

Wouldn't water, especially salty water be quite bad for concrete strength in cooler climates where it would freeze/thaw in winter? The expansion in freezing would cause microfractures and salinity would increase te rate of freeze/thaw cycles.

Not my subject at all and obviously doesn't apply to the building in Orlando but have a vague memory of my Dad teaching about the importance of inspecting/maintaining/resealing around the house prior to winter. Not sure if the damage was cosmetic, structural or to prevent damp, cold and mold coming in though.

originally posted by: Phage
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.

I know the difference, actually. Cement is an ingredient in concrete, about 15% by volume. It is what binds the coarse aggregates together. For conversational purposes the terms are pretty much interchangeable. But my statement is accurate and correct. The same conditions that caused the corrosion of the rebar caused damage to the surrounding cement. Water erodes the fines over time which weakens the concrete.

Water is harmful to concrete. Concrete meant to be under water is not the same as concrete meant to be on dry land. However, all concrete is porous and susceptible to damage from water. If rebar is rusting both water and air must be present. Rebar is fully contained within the concrete, usually as close to the center as possible. If enough water to cause significant oxidation is getting through it is damaging the concrete as well.

I am fully aware of the damage that can be caused by chlorides. Its not just the presence of chlorides, its also the concentration and temperature. It also depends on the type of steel. 304 will corrode faster than 316 for example. If the steel is passivated it is less likely to corrode at all. Passivated low carbon steel is better still.

I performed failure analysis of fluid system components for years as part of my job. Corrosion was the mode of failure in the majority of cases. I also wrote a white paper for my employer: Understanding Corrosion - Cause and Remediation. I didn't just google an answer - I lived it 8 hours a day 5 days a week for many years.

originally posted by: Vroomfondel
Concrete meant to be under water is not the same as concrete meant to be on dry land.

Roman concrete was universal in its use, they did not, unlike modern times, have differing formulas for specification applications. I find it odd that a similar style aggregate is not used now in salt water climes as Roman concrete is often considered one of the most durable building materials ever created.

originally posted by: galadofwarthethird
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.

Err, the Romans certainly were not in the 'Bronze Age' during their construction heyday, it was completely in the Iron Age by almost 1,000 years.

Also, they did reinforce structures with iron. The Colosseum, among other structures, shows evidence of iron reinforcement. Other structures, like Baths of Trajan, used iron clamps and tie bars.

a reply to: MidnightHawk

As long as air cannot get to the rebar it will not rust. However if the cement is cracked to much weight etc yes the rebar can start to corode. For the average house this is not a problem such as foundations. Where it becomes a broblem is things like bridges where loads are constantly applied.

There is alternatives that can be used now but for most jobs rebar will work just fine because there is a trade off. Rebar does expand and contract with the cement some alternatives do not. Currently the best is Glass fiber reinforced polymer, Its stronger than steele problem is its almost twice the cost so it should only be used when necessary. So i wouldnt recomend for a home or driveway for example. Because with a little care and maintanace they can last at least 50 years. If you allow pitting and cracks 20 or so.

I just had to do research recently when i had a driveway poured also go thicker and not just minimum.

a reply to: AugustusMasonicus

I am not familiar with roman concrete. Considering how long their structures have lasted its safe to say their practices were sound. I would think if it is better but not in use today it is most likely cost prohibitive.

"They don't make them like they used to" has real meaning.

originally posted by: Vroomfondel
I would think if it is better but not in use today it is most likely cost prohibitive.

I believe it's more the chemical composition not being fully known, the Romans did not write down the recipe anywhere.

Recent scientific breakthroughs examining Roman concrete have been gathering media and industry attention. Because of its unusual durability, longevity and lessened environmental footprint, corporations and municipalities are starting to explore the use of Roman-style concrete in North America, replacing the volcanic ash with coal fly ash that has similar properties. Proponents say that concrete made with flyash can cost up to 60% less because it requires less cement, and that it has a smaller environmental footprint due to its lower cooking temperature and much longer lifespan. Usable examples of Roman concrete exposed to harsh marine environments have been found to be 2000 years old with little or no wear. This stuff is harder than DB's head

a reply to: AugustusMasonicus

Were they? Its hard to keep track which ages they were in. They were all so primitive. I think its time to classify them all in one age. Anything from now, to the past 8000 years. Should be classified as one age.

a reply to: Phage
Ah? I dont even know what your talking about.

But plenty of submerged ports or cities even from Rome or ancient greek or phoecian. Go dig some of them up, break open the concrete you find under the sea ports. And see whats inside.

a reply to: AugustusMasonicus

It is known the secret ingrediant was volcanic ash. It helped dry the concrete The less water you use the stronger the concrete.

originally posted by: dragonridr
It is known the secret ingrediant was volcanic ash. It helped dry the concrete The less water you use the stronger the concrete.

It actually forms crystalline structures that prevent water permeation.

a reply to: Vroomfondel

Cement is porous. Air, oxygen, will get in cement easy peasy. Under water same thing, H2O water and the saltwater will corrode any rebar that's in the cement under water fast. Even if it was stainless steel? Under ocean water conditions? It will corrode it fast.

Roman concrete works not because water or oxygen cant get in there. Oxygen gets just about everywhere. I mean its on the magnitude of thousands of times smaller then something like a cell or even water molecules. If water can get in there? You best believe oxygen is.

I mean the only way to make sure that steel and stainless steels dont corode? Maybe if we bring the oxygen content of this planet down from 20% to maybe 5%.

But then that would cause other issues then the corrosion of steels. Oxygen? Literally bonds with anything. And the porous compositions and makeup of all cement? Is not going to keep oxygen from getting in there. Thats for sure.

But because of the mineral makeup, in salt water it will start corroding, but the mineral makeup of it will interact with the salt water and instead of cording its structure it will replace it with calcium carbonate.

So the reason why roman concrete works in the ocean and lasts this long. Is simply because its corroding and turning into a mixture of cement and coral reef, calcium. The volcanic ash and other ingrediants just react with the sea water. There is no iron rebar or anything in there. Its a simple chemical transaction over time the salt water is changing the chemical composition of the cement.

Roman cement that they found under the sea for those 2000 years? Is basically slowly turning into a form of coral reef. Its why its still there today.

And also? Probably to expensive to make now a days. Regular concrete will corrode under the ocean.


Stainless steel, is just not good for corrosion resistance under those conditions either. Any and all stainless steel will corrode, even things like Elmax or Vanax stainless steels. And price. There are some stainless steels that would work for underwater structure.

Things like Talonite an alloy of stainless steel. Will last in the ocean without showing signs of corroding for about 1000 years or more before it even begins to star showing signs of corroding. Gold and other metals off course, but they to are extensive. Talonite is harder then those metals, and would work as a construction material, or for hulls of ships, or building structures, and all that.

But for like a 2 inch by 5 inch piece 1/8 inch thick? Its like 100$ or more.

So may as well make it out of solid gold, it may be cheaper. Either way. its not going to last. I mean you make it out of cement and rebar? Its why they have insurance on these building or why they demolish them every so often. There not meant to last...period.