For a structure as important and expensive as the GP, the Egyptians would only use material technologies in which the had an extremely high level of confidence, confidence in both the materials mechanical performance and in their ability to organize and execute such a massive project using that material. Concrete would only be used if it had a long history of success in previous large construction projects. Thus, if the GP blocks were really concrete, then concrete should be found in many and varied structures, including earlier and later pyramids, temples, mestabas, and engineering works such as canals, cisterns, etc. Since the GP was obviously successful structurally, one would expect its various technologies to continue to be used in many structures built after the GP. So, the issue is not just whether concrete was used for the GP blocks, but whether concrete was extensively used as a general building material at that time (in which case there would be so many examples of ruins using the technique that there wouldn't be any controversy). I am not aware that this is the case, but my knowledge is very limited in this area.
One objection I see to the theory of concrete use is that it is not clear what would have been gained. Concrete,
if properly and precisely constituted can be much stronger than many forms of limestone, but the limestone available to the Egyptians was quite adequate for the pyramid construction. If concrete is not properly proportioned, mixed, and cured it can become quite weak and subject to catastrophic failure. The Davidovits article (p.100) argues that the content of fossils in the blocks tapers off toward the top. If the blocks were concrete, this would indicate that the limestone cement had not been sufficiently ground and the concrete not properly mixed. If limestone is in short supply then concrete has the advantage that it only uses about 10% limestone, the rest being sand and gravel, so that you get ten tons of blocks for each one ton of limestone. However, limestone is not in short supply in Egypt or in areas close to Giza. And of course, it takes as much effort to haul 2.5 tons of concrete mix up a long ramp as it does a 2.5 tons limestone block. I don't see where there is any net energy saving in using cast concrete instead of cut limestone.
My biggest objection to this theory relates to the fact that concrete is made up of calcined limestone, sand gravel, and water, and that calcined limestone (or cement) is made by quarrying chunks of limestone, grinding the limestone to a fine powder, and 'calcining' it, i. e., baking it in ovens over a long period of time to dehydrate it - drive off the water that is chemically combined with the calcium carbonate. If this were common practice at that time, remains of the thousands of calcining ovens should be found. But my real objection is the huge quantities of wood that would have been required. Wood was a precious commodity in Egypt and usually had to be imported. This is what led the Egyptians to develop their awesome stone technologies for their edifices. Davidovits argues that the Egyptians use of mortar and plaster indicates that they would have been familiar with concrete. Avoid getting too close to any concrete structures that this guy designed. Mortar and plaster are fine for facings but are nothing like concrete and would totally fail structurally under stresses even a fraction of those felt by the GP's blocks. In fact, mortar and plaster technologies are really more akin to slapping some mud on the side of a building for environmental protection, a practice used since primitive times.
One thing I don't understand is that if you google on 'concrete pyramid blocks, you learn about all kinds of scientific tests using every scientific instrument ever devised to test this theory. From my understanding, all you have to do is wash the sample in some muriatic acid (weak hydrochloric acid - the stuff you use in swimming pools to balance Ph) which dissolves away some of the limestone, and then examine the etched sample under a low power microscope to see the various constituents of the material. I understand that well trained people can tell from this how the concrete was made or where the limestone originated. I would also think that if concrete casting was used that it would not have been in the form of all these blocks, but would have been in much larger contiguous sections cast in place. Since concrete contracts very slightly when it hardens, there would be a limit to the maximum size section that could be cast at one time, but it certainly would be much larger than the size of the pyramid blocks. If the sections are too large, there is a risk of cracks forming, but even this is not a problem since the whole structure is in compression and the cracks just relieve the stresses.
Finally, I think the Egyptian people and government would be tickled pink if it were proved that their ancestors had been clever enough to have developed such advanced concrete manufacturing, casting, and construction technology, and that that proof would greatly enhance the pyramids value as a tourist attraction. They would gladly fund and support any efforts to provide such proof and I'm sure would make sample chips available to qualified researchers.
I am not suggesting that anything I have brought up refutes the cast concrete contention. I'm really just one of those guys you all complain about who tries to appear like an expert on a topic after googling it for five minutes. I am just stating that there are sufficient reasonable arguments against the contention to make the cast concrete pyramid block theory an extraordinary claim that therefore requires extraordinary proof (and for us know-nothings, a good level of consensus amongst the experts).
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