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Why Ancient Roman Concrete Outlasts Our Own (2017)

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Re: Why Ancient Roman Concrete Outlasts Our Own (2017)

#51

Post by pitspotter2 »

ncmncm wrote: post #47

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, unli…

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!

Re: Why Ancient Roman Concrete Outlasts Our Own (2017)

#53

Post by lstodd »

yourapostasy wrote: post #50
ithkuil wrote: post #39

Earlier quoted context omitted.

Would the use of stainless steel address this problem? What other problems would it create?

Stainless of the right grade to address the problem is project-killingly expensive. There is work on evaluating alternative kinds of reinforcement not subject to the same kinds of rust problems, but extremely few organizations today plan, build and maintain over the kinds of timescales where this comes into play. They'll give lip service to those timescales, but watch what they do with their budgets, not what they sa…

Well, fiberglass rebar is used more and more.

Its longevity has yet to be proven though.

Re: Why Ancient Roman Concrete Outlasts Our Own (2017)

#54

Post by ncmncm »

pitspotter2 wrote: post #51
ncmncm wrote: post #47

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, unli…

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 co…

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.

Re: Why Ancient Roman Concrete Outlasts Our Own (2017)

#55

Post by jaclaz »

Eelongate wrote: post #46
jaclaz wrote: post #43

Earlier quoted context omitted.

But beside that (whch surely is the main reason), there is also a great difference between pozzolanic and portland, nowadays (and since several years) pozzolanic cement (for whatever reasons[1]) came out of use and anything today (and since several years) is portland. I have worked with both in massive structures (mainly bridge foundations and tunnel lining) and the differences between the two is staggering, in pract…

What about non-volcanic pozzolans like fly ash? From what I understand, fly ash is sometimes substituted for some portion of the portland cement that might otherwise have been used, because works similar to volcanic ash to make the concrete stronger.

Fly ash is - generally speaking - an exceptionally good additive, its use is essentially due to the size of its particles, you can consider it as a very good filler with some added value (and it has some very useful side-effects, namely it makes concrete much easier to pump).

Besides the raw resistance, you have to imagine concrete as being a sort of artificial stone, the idea is to fit into a given volume as much material as you can, and you obtain this by mixing together gravel (usually one, two or even sometimes three sizes), crushed sand (rather big in size) and (where available) natural sand (or more finely crushed sand).

Then you add the cement, which is the finer "powder like" material, and water, BUT in many cases the "granulometric curve" remains "empty" in the lower part, and there are practical limits in the amount of cement you can put in the mix, so you need to add something (a filler) that is fine as or finer than cement, and this is often fly ash, which while not being as powerful as cement as a binder has anyway a pozzolanic effect, that helps in reducing the permeability of the set concrete, the matter is briefly explained in the second part of this:

https://en.wikipedia.org/wiki/Pozzolan

Re: Why Ancient Roman Concrete Outlasts Our Own (2017)

#56

Post by pitspotter2 »

ncmncm wrote: post #54
pitspotter2 wrote: post #51

Earlier quoted context omitted.

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 co…

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 sourc…

Corundum vs carborundum. It's a conundrum!

Re: Why Ancient Roman Concrete Outlasts Our Own (2017)

#57

Post by ncmncm »

pitspotter2 wrote: post #56
ncmncm wrote: post #54

Earlier quoted context omitted.

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 sourc…

Corundum vs carborundum. It's a conundrum!

Even the pre-dynastic Egyptians didn't turn dishes out of carborundum.

Corundum is aluminum oxide, the material of ruby and sapphire. Making dishes out of it was badassery we haven't matched.

Re: Why Ancient Roman Concrete Outlasts Our Own (2017)

#58

Post by jfletch25 »

Phithagoras wrote: post #2

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?

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.

Re: Why Ancient Roman Concrete Outlasts Our Own (2017)

#59

Post by adgjlsfhk1 »

rightbyte wrote: post #34
adgjlsfhk1 wrote: post #25

Earlier quoted context omitted.

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 par…

> Unfortunately, arch bridges don't scale that well (they take concrete proportional to length cubed), Only of you go for one arch right?

Multiple arches helps in some cases, but gets really expensive if you have to bridge a deep gap (especially over water where de-watering is needed) The massive advantage of a suspension bridge is that you get a really big span without anything in the middle.

Re: Why Ancient Roman Concrete Outlasts Our Own (2017)

#60

Post by eru »

markvdb wrote: post #42
hef19898 wrote: post #11

Earlier quoted context omitted.

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…

> 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. I have to respectfully disagree on this one. Humans in general have become spectacularly bad at maintaining physical infrastructure across longer timespans. Technological advances have ena…

> How much does this bridge benefit the local community where it is built?

Why does a bridge have to benefit the local community? Why not eg the wider community?

> Can we bring the design closer to the layman? Can we for example design a bridge so that it will visually degrade in step with safety degradation?

What's the benefit?

> I have to respectfully disagree on this one. Humans in general have become spectacularly bad at maintaining physical infrastructure across longer timespans. Technological advances have enabled a cheap/fast/overbuild culture. This very much includes the design phase.

You say this like it's a bad thing. If stuff becomes cheap enough to build that every generation can afford to build their own, that's much better, isn't it?

Your comment emphasis closeness in space a lot, with talks of local community etc. So why not emphasis closeness in time, too? Surely the people living at a particular point in time might be best place to judge what infrastructure they need; instead of having to forecast hundreds of years in advance?

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