Substandard Construction and Accidents

[sunday]

Tomas told me they were exporting Pinatubo's ash from the 1991 eruption to Singapore to make cement.

[bojan]

Didn't Romans make cement out of it also?

[sunday]

On 11/8/2021 at 1:09 PM, bojan said:

Didn't Romans make cement out of it also?

Very much, and some buildings are still in fine shape, like Rome's Pantheon.

[bojan]

IIRC they also used wood ash based "concrete" also, especially in the parts of the world w/o enough limestone, like Panonia.

[rmgill]

8 hours ago, sunday said:

Very much, and some buildings are still in fine shape, like Rome's Pantheon.

Apparently irregular grain size is preferred for good concrete. River sand being good for this. Wind blown sand not as that is rounded. I suspect that volcanic sand tends on the VERY irregular. 

[rmgill]

Ahh. Yes. That's something I remember reading about. 2000 year old roman concrete is still solid in many cases. 

 

[bojan]

So solid that I have walked on it last summer.  There is also a reconstruction of the Roman villa built by using techniques available to Romans, including wood ash concrete mixed with ground volcanic rocks.

 

Edited November 11, 2021 by bojan

[Ivanhoe]

13 hours ago, rmgill said:

Ahh. Yes. That's something I remember reading about. 2000 year old roman concrete is still solid in many cases. 

 

There's a meme routinely posted to FB comparing a 2000 year old Roman road with a modern, pothole-ridden lowest-bidder asphalt road.

 

[Stuart Galbraith]

Roman concrete has been proven scientifically to be actually structurally stronger than concrete used in modern construction.

[DKTanker]

34 minutes ago, Stuart Galbraith said:

Roman concrete has been proven scientifically to be actually structurally stronger than concrete used in modern construction.

Which Roman concrete and which modern concrete, and stronger in what properties?  I ask because there is an almost infinite number of modern concrete formulations and probably nearly as many of Roman concrete.

[RETAC21]

43 minutes ago, Stuart Galbraith said:

Roman concrete has been proven scientifically to be actually structurally stronger than concrete used in modern construction.

And cheap Roman concrete wouldn't last 2000 years to compare...

[Stuart Galbraith]

12 minutes ago, DKTanker said:

Which Roman concrete and which modern concrete, and stronger in what properties?  I ask because there is an almost infinite number of modern concrete formulations and probably nearly as many of Roman concrete.

Well Sunday talks of Pozzolan, which I recall correctly was an ingredient popular with the Romans in making their concrete, and renowned for its hard wearing properties, as the continuing existence of the Pathenon or the Pont du Gard is used as evidence of quite how hard wearing it is.

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

How is it stronger than modern concrete? I dont know, im not a structural engineer, but Ive read that it gains strength more slowly than modern concretes, where due to size of construction, quickness of setting is a far more important consideration. You probably couldnt have built something like the World Trade Center with it.

 

I remember watching an interesting documentary on the reconstruction of Mostar Bridge, and they discovered when trawling the archives that part of the reason for the strength of the concrete may have been the use of animal blood in the mix, which gave a reaction which strengthened the concrete. As it stood for 429 years, it was clearly doing something right.

https://technologystudent.com/struct1/arch2.htm

 

[Stuart Galbraith]

7 minutes ago, RETAC21 said:

And cheap Roman concrete wouldn't last 2000 years to compare...

True...

There is apparently a single surviving tenement block, an insula, in Rome to this day, still in reasonable (if not exactly habitable) condition. But you kind of wonder if that was the one single builder that built one properly and went out of business, and all the others were throwing up slums and remained solvent.

https://www.quora.com/What-is-a-tenement-in-ancient-Rome

[DKTanker]

1 hour ago, Stuart Galbraith said:

How is it stronger than modern concrete?

I didn't ask how, I asked which.  For instance sidewalk concrete may have a compressive strength of 2500 psi and just enough wire reinforcement to prevent the spreading of cracks.  On the other hand precast structures such as culverts and bridge beams may have a compressive strength well over 10,000 psi and plastic and or glass fiber reinforcement to allow for some deflection.  The fiber reinforcement, part of the concrete formulation, can give tensile strength to modern concrete which Roman concrete could never imagined.  Moreover, not all Roman concretes are the same.  For instance, Roman concrete in areas easily accessible to Pozzolana, such as volcanic areas in Italy, are much different than Roman concrete formulated in Britain.

Edit to add:  Using fly ash in a modern concrete formulation can give it nearly the same properties as Pozzolanic concrete.  At my concrete plants we routinely used fly ash to replace as much as 25% of the Portland cement.  The compressive strength was increased as was the workability.  I said was, because since the Great Obama administration made coal fired power plants all but extinct in the US, there has been very little fly ash available.

 

Edited November 11, 2021 by DKTanker

[Stuart Galbraith]

18 minutes ago, DKTanker said:

I didn't ask how, I asked which.  For instance sidewalk concrete may have a compressive strength of 2500 psi and just enough wire reinforcement to prevent the spreading of cracks.  On the other hand precast structures such as culverts and bridge beams may have a compressive strength well over 10,000 psi and plastic and or glass fiber reinforcement to allow for some deflection.  The fiber reinforcement, part of the concrete formulation, can give tensile strength to modern concrete which Roman concrete could never imagined.  Moreover, not all Roman concretes are the same.  For instance, Roman concrete in areas easily accessible to Pozzolana, such as volcanic areas in Italy, are much different than Roman concrete formulated in Britain.

Well you are quite right, because hardly any Roman buildings stand taller than your knee in Britain. The sole exceptions are walls like Hadrians wall, or some gatehouses. It was presumably cost prohibitive to bring the best materials from Rome very often.

As Sunday says, they didn't seem to reinforce. But then they don't seem to have built structure s entirely out of concrete, but as a medium with masonry.

Chinese concrete as used in the Great wall is also reputedly very good. Like Mostar, they seemed to mix blood with it.

[DKTanker]

2 minutes ago, sunday said:

I think Romans did not use reinforced concrete. That is a big difference, as they had to use concrete in a way that minimizes tension stresses, like semicircular archs or domes.  But those are the same kind of structures that work with masonry or stonework, and the Antiquity had lots of practical experience with those. Concrete should have been cheaper and easier to work with - no more stone dressing by competent craftsmen.

Aside from the sidewalk example, I purposely didn't compare structural concrete strengths which included reinforcement not included in the concrete formulation (steel wire reinforcement).  When I reference bridge beams and culverts I was very careful not to include properties which can only be achieved through the use of reinforcement beyond that of the formulated concrete.  Using wire mesh or tensioned cables for instance. 

Romans could have included straw or obsidian fibers in their concrete formulations, to give them a bit of tensile strength, for whatever reason, they didn't.  

[bojan]

3 hours ago, sunday said:

I think Romans did not use reinforced concrete...

They did, through reinforcements were wicker, probably used so concrete would be able to better hold shape until it cures. This was just an update to a stone age old technique of using wicker base covered with clay, then letting clay bake in the sun.

Edited November 11, 2021 by bojan

[rmgill]

Some of the roman techniques like the brick work probably also contributes to the solidity. 

[rmgill]

Kinda reminds me of the Japanese Pagoda masts. The RF interference plan for that must be FUN!

[rmgill]

The structure may be simple, but I'm thinking of about how all the antenna may radiate and interfere with each other. 

 

[Stuart Galbraith]

20 hours ago, bojan said:

They did, through reinforcements were wicker, probably used so concrete would be able to better hold shape until it cures. This was just an update to a stone age old technique of using wicker base covered with clay, then letting clay bake in the sun.

Id not heard that, what structures did they use it in?

[lucklucky]

Pantheon  Dome interestingly  in not reinforced

Largest non reinforced.

[rmgill]

Lots of compressive fixes/balancing with the flying buttresses. 

[Stuart Galbraith]

14 hours ago, lucklucky said:

Pantheon  Dome interestingly  in not reinforced

Largest non reinforced.

Sure, I was just wondering what buildings they built reinforced in that manner.

[DB]

Apparently China uses treated bamboo as an alternative to rebar. This is presented as being criminal cost-cutting in some media presentations, but appears to have some legitimacy.