My name is Prof. Mario Collepardi and I am a professor of “Materials Science and Technology” at the Politecnico of Milan, Italy. Yesterday I have seen your interview by Mr. Giacobbo at the “Stargate” program on “La 7” Italian TV channel. I am very interested to your theory about the building technique used by Egyptians for the Pyramids, even because my research work is in the area of cement chemistry and concrete technology (www.encosrl.it ). I am sure that this technique, according to your theory, can explain how the Egyptians could erect the Pyramids without using sophisticated techniques of cutting, transporting and rising heavy blocks of natural stones, which were not available at that time.
I have three questions:
A) As far as I know, the Egyptians at the time of the Pyramids were able to produce gypsum (in form of calcium sulphate hemy-hydrate) as binder, but they were not still able to manufacture lime due to the higher burning temperature (900 °C instead of 150°C) with respect to that required for the gypsum manufacturing process. Am I correct? If so, how can you justify that the Egyptians were able to use lime as one of the ingredients for the concrete mixture used in the Pyramids? Were the “engineers” of the Pyramids at a more advanced progress with respect to their colleagues in the other areas of Egypt?
B) I understand, from your interview, that the limestone aggregate available in the area of the Pyramids was relatively rich in the clay content (a sort of a marl rock), so that the concrete mixture in the fresh state was cohesive and relatively easy to compact up to a dense and hard cementitious material. If so, the lime manufactured by treating at high temperature the limestone available in that area was really a sort of mixture of calcium oxide and metakaolin (belonging to the family of pozzolanic materials) and this could explain the hydraulic behaviour of that Egyptian concrete even in the absence of carbonation. In other words, not necessarily the Egyptians had to use natron (sodium carbonate) to transform the lime into calcite. Isn’t it?
C) Have you found natron in the area of the Pyramids? If so, how could the Egyptians, at that time recognize and individuate this mineral without any chemical background?
A) Lime versus gypsum: you are not correct. This is part of the granted ideas introduced by Egyptologist A. Lucas in 1924. Yet, calcining limestone into lime requires temperatures far lower than the temperatures needed for smelting copper. A. Lucas postulated that lime was not calcined in Ancient Egypt until the Ptolomaic time, i.e. 2000 years after the pyramids were built because of the scarcity of wood as fuel. But the Egyptians had several trees at their disposal: the acacia, the carob, two species of palm, etc. The truth is that it was difficult to detect lime in the mortars, for several reasons. Yet, owing to new sophisticated techniques, modern science has shown that lime has been found in mortars from the III, IV and V. dynasties, not in the VI and later. (Analysis by D.D. Klemm, 1990).
B) But lime CaO is not produced by calcining limestone. It is the result of the making of bread. The ashes of Palm wood and reeds they used for bread cooking contain a very high amount of CaO. This explains why we do not find kilns for lime, but very important bakeries (for bread) with great quantities of ashes. In my new book , recently published in Paris, titled: Ils ont bati les Pyramides (They have built the pyramids), I have dedicated several pages to this issue. They had sufficient ashes from bread cooking to make all the pyramids they wanted. The only problem was to collect them and to transport them to the site.
C) They were intelligent and smart; it is very easy for a non chemist to recognize between NaCl (common salt) and Na2CO3 (natron, sodium carbonate), just by the taste.
Prof. Dr. Joseph Davidovits