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Comment by ncmncm | Hacker News Reader

I see that we have known for more than a decade how the Egyptians could have used a form of concrete to make the blocks the pyramids were made out of, to mold them at the point of use. (It involves crushed limestone and clay.) But no one talks about that. Presumably, the (precursors to the) Incas could have done the same, explaining how they fit their odd-shaped stone blocks together so tightly.

Is there any reason not to use the same method for modern concrete, instead of the enormously polluting method used today?

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Egyptian pyramids might be more controversial, even though it makes a lot of sense that the clocks would have been molded in place from concrete. The large granite blocks inside the pyramid don't seem to be concrete based.

The South America sites with extremely precisely fitting, non-rectangular shaped blocks seem to have been very highly likely formed by using concrete and carved later. Cusco walls, Sacsayhuamán or bottom layers of Maccu-Picchu walls.

The site of Baalbek on the other hand suggests that ancients had the ability to lift up 1000 tons stone blocks. The nearby quarry with unfinished stone blocks shows that these were not formed using cement.

Perhaps the Eyptian pyramids were a mixture of methods. Perhaps some of the blocks were lifted up to position using an elevator like mechanism (the long pyramid side shafts without stairs), but then the regular blocks made with the concrete method. The "elevator" shafts don't go beyond half of the pyramid, so the idea of transporting large blocks all the way up is less compelling than using concrete.

It is clear that various ancient peoples also moved large rock objects wholesale. Egyptians and Ethiopians cut, lifted out, and transported 500-ton obelisks. If you can move the obelisks, 70-ton granite blocks for the king's chamber, or the 100-ton empty boxes in Saqqara, are smaller projects.

Whoever placed the 1000-ton trilithon blocks (before the Romans built temples on top) cut and moved them whole. The Baalbek temple entablature are, to my knowledge, the only example in the whole Roman Empire of handling rocks of more than 300 tons. Even when Rome looted Egyptian obelisks, they had to bust off the bottom third and leave it behind. So, I guess they had local help for Baalbek.

The pre-dynastic Egyptians were cutting rock as hard as corundum (ruby/sapphire aggregate) like butter to make dishware, tens of thousands of which ended up in graves. The method was apparently lost before the pharaohs. It's not hard to understand technology being lost; but how it came to be invented first is a mystery. And, what exactly it was they invented, because we don't know. Archaeologists seem to lack any interest in finding out.

Huh? I've never seen anyone seriously saying pyramids aren't made from natural stone. Seems like it would be very easy to check.

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

It's amusing to look into. Checking is not so easy - the concrete looks just like natural material. Finding an object embedded in the stone would prove it.

Or, failing to find expected objects embedded.

By report, the Peruvian block faces lack the embedded marine animal shells found in natural limestone. (I have not examined them myself.)

Couod we X-ray large sections of the pyramid?

X rays do not penetrate bone. Limestone, of whatever provenance, is denser than bone.

Examining a chip off a block under an electron microscope revealed differences from native stone.

X-rays do penetrate bone, just not very good. Otherwise one would not be able to make an X-ray of a human body.

It's easy to prove that ancients were unable to produce concrete. You just need to prove that they had no access to stone, fire, and water — the key ingredients required to make concrete.

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