In a second year class I took the prof posed us the question: why don't we do this today? Why is this not part of an ASTM standard?
He ended up saying it's too tough to get a hold of proper pozzlanic ash, but I suspect its more a "this is the way we've always done it" difficulty. Does anyone know more to the story?
First, we only see the part of Roman architecture that lasted. There's an observer bias. The Romans also made plenty of ephemeral stuff, just like we are making plenty of ephemeral stuff.
Second, there's more to engineering than making stuff last long. There are different trade-offs. Cost being one of them, but also different material properties.
Eg re-inforced concrete is awesome for lots and lots of applications that the Romans couldn't even have dreamed of. Alas, it's not economical to make re-inforced concrete that lasts forever. (Not even sure if it's physically possible.)
Trade offs should be covered a lot more during engineering studies. I know that during my time at university, as an industrial engineer destined to work at the interface engineering and economics, that aspect wasn't covered nearly as extensive as it should have. The other question that usually get's ignored is maintenance. The Roman stuff we see lasted millennia without maintenance, we on the other hand can maintain the stuff we want to last a long time.
That we don't do it, e.g. infrastructure with the particularly bad maintained bridges in Germany, is not the materials fault, or the original designs fault.
Not to mention that concrete steel reinforcement is the main reason it doesn't last due to water eventually making its way and the rust taking expansion thus cracking the concrete.
Are you essentially saying that you don't think there are important material and chemical differences between Roman and modern concrete that might be responsible for orders-of-magnitude differences in durability, aside from the absence of rebar, and that it's basically a matter of building so many bridges, harbours, and aqueducts that some of them end up lasting for thousands of years despite being immersed in running rivers or salt water?
Something I'm curious about - there seems to be some sort of maintenance of reinforced concrete, where people periodically jackhammer a small patch and expose some rebar, and then cover it up again.
Anybody know what they are doing? I used to park in a garage where it seemed like they were always doing it.
A lot of the answer is that the types of structures you can build with concrete that isn't rebar reinforced is fairly limiting. You're pretty much stuck with arch bridges, dams, and domed buildings. Unfortunately, arch bridges don't scale that well (they take concrete proportional to length cubed), and people like buildings in shapes other than domes. As a result, you often have to have designs that hold together partially under tension, and the cost is it won't stay up for 2000 years (if you use rebar which rusts).
That said, in the past few decades there has started to be experiments with fiber reinforced concrete. This has the significant advantage of not corroding, but costs a good bit more than traditional rebar. That said, it might be the future for buildings where long life is desired.
There is an ASTM standard: "ASTM C618 Standard Specification for Coal Fly Ash and Raw or
Calcined Natural Pozzolan for Use in Concrete (AASHTO M 295)."[1]
Fly ash, like volcanic ash, is a pozzlanic ash. Both work in concrete. Fly ash is pulled out of the exhaust from a coal-fired power plant using electrostatic precipitators. Just like electrostatic air cleaners, but huge, they pull particles out of gases. So fly ash is cheap if there's a coal-fired power plant nearby. Convenient when there is no volcano handy.
There are downsides. The concrete takes longer to cure, which can hold up the next stage of construction. Curing in cold weather is difficult. The Romans didn't have that problem in their Mediterranean climate. Concrete curing requires some air in the mix, and fly ash, for some reason, tends to entrain less air than Portland cement.[2]
Yeah. incorporating unknown materials into million dollar projects is a really good way to lose millions of dollars. New materials can get added, but especially for big projects there is a long delay between tech invention and widespread use (think decades).
Because buildings change constantly.. notice how in the examples, you have building for which this requirement must not be fullfilled. Public show-off buildings, statues, temples and harbour walls, they do not change with every generation.
Now if you want to change it constantly, if a building is for living, durability is actually not that much of a value.
No. An industry does not make a plan 50+ years in advance to get more business.
They do, however, save on costs by delivering products that don't last as long because their customers also don't (as a general rule) care about 50+ year time horizons.
I think designing your buildings for more than a few hundred year counts as 'excessive' and more than 250 years should not allow for being disqualified under 'planned obsolescence'.
But surely some company would see it as an advantage over competitors and sell it if it was easily accessible. But we don’t see that so there has to be more to it. Maybe cost is too high for the average customer?
It depends on what you're building. Keep in mind that one way for politicians in office to control the number of jobs and money flowing through the economy is doing road work and other public projects.
Not really, especially jot for large contructions. Not everybody has a few thousand to million tons of sands of the right composition in their backyard, and cement comes from a factory.
I must be missing something. I’ve never used scihub before, and I can’t find the link to read the paper. All I see on this link is the name of the paper and the authors.
I am becoming partial to the ancient Egyptian concrete, that they might have used to mold the pyramid blocks in situ.
It takes just limestone crumble, clay (which was already in their limestone), natron, and water.
It is a fair bet the precursors to the Inka who built with the really big blocks had that, or a similar trick. Local observers report the big blocks do not show embedded marine shells at the surface, unlike native limestone. (I have not had opportunity to verify this.)
And while we're in the Sahara Desert with abundant sunshine, sand and carbon dioxide, let's build a silicon carbide brick factory. Sunlight to provide electrical power and, via focussed mirrors, heat. Sand to supply the silicon. Carbon from carbon dioxide to be extracted from the air at $100 per tonne (well, eventually).
Silicon carbide bricks, emerging gloriously from their tungsten moulds, would possess supreme corrosion resistance and almost double the crushing strength of engineering bricks. High thermal conductivity should reduce cracking and spalling, further increasing lifetime. A short railway journey to the nearest port and water desalination plant whence they can be distributed throughout the world.
We'll beat the Romans! Our public buildings will last for millennia!
It will take a very long time to beat the Romans, and more than twice that long to beat the Egyptians.
Corundum bricks would suffice. The Egyptians knew a way to cut corundum like butter; the method apparently was lost before the pyramids were built.
Solar panels have proven quite a lot cheaper than mirror-concentrated solar heat as a source of electrical power. Concentrated solar has not really been tried as a source of direct industrial heat, where it might yet excel. But choosing the bit of Sahara to site in has proven harder than expected. To make building materials economically useful, the site needs immediate sea access. Pisco, Peru might be a better choice, although Nouakchott, Mauritania is well sited. Broome, Australia might do.
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He ended up saying it's too tough to get a hold of proper pozzlanic ash, but I suspect its more a "this is the way we've always done it" difficulty. Does anyone know more to the story?
See also https://www.youtube.com/watch?v=qL0BB2PRY7k
Second, there's more to engineering than making stuff last long. There are different trade-offs. Cost being one of them, but also different material properties.
Eg re-inforced concrete is awesome for lots and lots of applications that the Romans couldn't even have dreamed of. Alas, it's not economical to make re-inforced concrete that lasts forever. (Not even sure if it's physically possible.)
That we don't do it, e.g. infrastructure with the particularly bad maintained bridges in Germany, is not the materials fault, or the original designs fault.
Anybody know what they are doing? I used to park in a garage where it seemed like they were always doing it.
Couldn’t it also possible that the romans had some techniques that they weren’t aware of that would last longer than others?
That said, in the past few decades there has started to be experiments with fiber reinforced concrete. This has the significant advantage of not corroding, but costs a good bit more than traditional rebar. That said, it might be the future for buildings where long life is desired.
Only of you go for one arch right?
Fly ash, like volcanic ash, is a pozzlanic ash. Both work in concrete. Fly ash is pulled out of the exhaust from a coal-fired power plant using electrostatic precipitators. Just like electrostatic air cleaners, but huge, they pull particles out of gases. So fly ash is cheap if there's a coal-fired power plant nearby. Convenient when there is no volcano handy.
There are downsides. The concrete takes longer to cure, which can hold up the next stage of construction. Curing in cold weather is difficult. The Romans didn't have that problem in their Mediterranean climate. Concrete curing requires some air in the mix, and fly ash, for some reason, tends to entrain less air than Portland cement.[2]
[1] https://www.cement.org/docs/default-source/fc_concrete_techn...
[2] https://www.fhwa.dot.gov/PAVEMENT/recycling/fach03.cfm
Is the construction industry really known for resisting the adoption of new materials like that?
Now if you want to change it constantly, if a building is for living, durability is actually not that much of a value.
They do, however, save on costs by delivering products that don't last as long because their customers also don't (as a general rule) care about 50+ year time horizons.
Not really, especially jot for large contructions. Not everybody has a few thousand to million tons of sands of the right composition in their backyard, and cement comes from a factory.
Also has a link to download the PDF for free.
It takes just limestone crumble, clay (which was already in their limestone), natron, and water.
It is a fair bet the precursors to the Inka who built with the really big blocks had that, or a similar trick. Local observers report the big blocks do not show embedded marine shells at the surface, unlike native limestone. (I have not had opportunity to verify this.)
Silicon carbide bricks, emerging gloriously from their tungsten moulds, would possess supreme corrosion resistance and almost double the crushing strength of engineering bricks. High thermal conductivity should reduce cracking and spalling, further increasing lifetime. A short railway journey to the nearest port and water desalination plant whence they can be distributed throughout the world.
We'll beat the Romans! Our public buildings will last for millennia!
Corundum bricks would suffice. The Egyptians knew a way to cut corundum like butter; the method apparently was lost before the pyramids were built.
Solar panels have proven quite a lot cheaper than mirror-concentrated solar heat as a source of electrical power. Concentrated solar has not really been tried as a source of direct industrial heat, where it might yet excel. But choosing the bit of Sahara to site in has proven harder than expected. To make building materials economically useful, the site needs immediate sea access. Pisco, Peru might be a better choice, although Nouakchott, Mauritania is well sited. Broome, Australia might do.
New title: Why Ancient Roman Concrete Outlasts Our Own (2017)