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From a young age I have been taught that the stones used to create the great pyramids were mined. Concrete and cements were largely invented by the Romans/Greeks especially for use as mortar. More recently, I've heard other explanations.

Prof. Joseph Davidovits has been making claims that the Egyptians used Geopolymer chemistry in order to create the stones used in the pyramids rather than mining them. This would explain alot about how the pyramids were constructed and about the developmental history of Cement, one of the most important man-made materials and chemical reactions. Researching this I also learned that gypsum was used by the Egyptians to make simple cements.

What do we currently know about the chemistry knowledge the ancient Egyptians had with regard to cementitious materials? Would they have had the ability to manufacture artificial stones on the scale needed to make the pyramids?

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    $\begingroup$ What is Davidovits background and do you have a reference? I would have thought natural rock would have been pretty easy to determine from the artificial kind (geology is my background). Also I seem to remember quarryman's marks being found on some stones (the "alien builders" crazies say these marks are in impossible places - now perhaps, but they were made before the stones were assembled!) $\endgroup$ – winwaed Oct 28 '14 at 23:26
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    $\begingroup$ I originally meant to link this website: geopolymer.org/archaeology His background is in material science. I don't think his idea is crazy but I also am not convinced of it yet and would like to see counter arguments. Note that this isn't Portland cement. His chemistry works; I've make similar "rocks". $\endgroup$ – kaine Oct 28 '14 at 23:31
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    $\begingroup$ Thanks. I note that the palaeomag paper referenced on that site identified some of the stones as being quarried from a local quarry. This would tally with with my recollection about the quarry marks (the marks identify things like way up and where the stones go in the corridor seals) - so at least some of the stones were quarried. $\endgroup$ – winwaed Oct 29 '14 at 0:27
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    $\begingroup$ The stones used in the great pyramids have been sourced most of it is from local quarries although some of the granite comes from as far aways as Aswan. This, of course, does not answer the question you asked but does shed some light on the techniques used in construction. Dr. Davidovits claims are very interesting but are not accepted by most experts and are not needed to explain the construction. Egyptians certainly knew how to make lime mortar which is part way to cement. They lacked a source of volcanic ash so I will have to say it is unlikely they cast the stones. $\endgroup$ – King-Ink Dec 27 '15 at 14:50
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Davidovits' theory appears to be moving slowly from fringe toward mainstream. Also the possibility of a mixed technique i.e. some carved stones along with cast blocks offers a compromise in the debate.

why were the pyramids not made wholly of these cast stones? After all it is easier to cast a stone than to cut and hoist it into place. The answer, embedded in our finding, is simple: making geopolymeric stone was an expensive proposition. For a primitive society, the fabrication of lime is non-trivial, especially the millions of tons that would have been required. Along the same lines, crushing tons of limestone is non-trivial either. Under these constraints, the ancient builders apparently compromised [1]

The quote goes along with a photograph (fig.6) showing distinctly the two types, the leading author, M. W. Barsoum, being a highky cited scientist (h=83) and the journal is a most academic one (J. Am. Ceram. Soc.). However there is an acknowledgement that some of the samples were provided by Davidovits. A more recent and no less academic work about Senefru's pyramid by Barsoum et al. [2] states

results suggest that the casing stones consist of limestone grains from the Tura quarry, cemented with an amorphous calcium-silicate gel formed by human intervention, by the addition of extra silica, possibly diatomaceous earth, from the Fayium area.

A 2015 Springer Handbook of Materials Structures, Properties, Processing and Performance [3] begins by mentioning the casting of blocks via ref[2].

Refs [1]M. W. Barsoum et al, (2006) Microstructural Evidence of Reconstituted Limestone Blocks in the Great Pyramids of Egypt, J. Am. Ceram. Soc., 89 [12] 3788–96 (pdf)

[2]M. W. Barsoum et al,Were the casing stones of Senefru's Bent Pyramid in Dahshour cast or carved?: Multinuclear NMR evidence, Mat. Lett.Vol. 65, Iss. 2, (2011),p 350-2

[3]L. E. Murr, (2015), Examples of Materials Science and Engineering in Antiquity, Handbook of Materials Structures...p.12

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I visited the American Museum of Natural History on Central Park in New York, which had on display a supposed small Egyptian sphinx. Some of the cladding had fallen off and It sure looked like cement was molded to me.

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