As the title suggests. If roman concrete supposedly has the capabilities to mend tiny cracks via chemical reaction, why isn’t it used with modern reinforcements to seal the pathways to the steel beams to protect it from oxygen and elements and prevent corrosion? Are there any major downsides to hot-mixed concrete, is it not as good as the studies make it out to be, or is it simply not viable due to cost and manufacturing process/storage requirements?
In: Engineering
Its more expensive.
All the supposed benefits of Roman concrete are well known today, and we can make concrete significantly better in every way than they did. So why dont we?
Cost. Thats it. It costs more, and building today is all about controlling costs.
We could make glass fiber reinforced concrete with self healing properties and whatever else. The building would last 1000 years. But the client is paying for a building that lasts 100 years, not 1000. So we build it for what is being paid for.
Up until they had trucks to deliver concrete the process of pouring walls was completely different than what they do today. If you even tear into a concrete wall from 100 years ago what you find is concrete around all the big rocks they could throw in. It was cheaper and easier to use the concrete as a medium to hold stones than to entirely make up the wall. If you have ever mixed concrete by hand in a wheelbarrow you would understand.
The idea that Romans built concrete or roads better than we do is a complete falsehood. It’s perpetuated by people who have no idea what they’re talking about. This “self healing” concrete is far weaker than concrete wet use for construction. It’s brittle and the parts that “heal” are even more brittle. As for roads, sure there are still Roman roads that appear to have more longevity than our roads. But people seem to forget that Roman roads had to carry people and horses. Our roads have to carry millions of cars and trucks weighing 80 tonnes moving at 100kmh every single day
the truth is, it doesn’t. Some Roman concrete had imperfections with the mix that created little pockets of lime that would mix with water leaking in and reharden the cracks, but when people talk about this stuff they are forgetting the vast majority of roman concrete throughout Europe that didn’t have this and didn’t survive until today.
They likely didn’t know of this quality as a feature at the time they poured those castings, it’s only been revealed to us after some 2000 years.
The big issue is simply that it’s horrid to use. The volcanic ash / calcium oxide was processed to produce highly caustic material. This will burn off your skin and is much, much worse than modern cement. Also volcanic ash isn’t uniform so it isn’t consistent, leading to varying strength and curing times.
We only recently figured out the method for making it, but more than that, it’s just not as strong as modern concrete. It can’t bear nearly the same load.
The thing that gives it the self-healing properties also makes it inconsistent and creates weaknesses in the material.
I’m also unsure of how rebar would react to it. The self-healing is triggered by water getting into cracks, but that would cause the rear to rust and swell.
As others have mentioned roman concrete isn’t as great as many people like to pretend. It is good, but we have long since surpassed it.
Also, rebar reinforced concrete ultimately has a life span because of corrosion of the rebar, which while you can reduce the corrosion, you will never eliminate it. The only concrete you will see standing 500 years from now is unreinforced concrete in favorable conditions which isn’t nearly as strong as reinforced and requires specific designs like archs to use and requires more concrete overall which is more expensive.
Most reinforced concrete is expected to be compromised after 50 years without annual inspections to verify its integrity, and after 100 years it will almost all be trash. But it was built with the engineers knowing that from the start.
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