A great deal of internet web page space is devoted to the mistaken idea that the blocks used to construct the Egyptian pyramids were cast from concrete, and not quarried from stone. Wikipedia in particular is guilty of presenting this ridiculous assumption.
The cast theory apparently is based on believing that because the blocks fit tightly together they could not have been quarried. Nevertheless, ancient central American civilizations constructed walls and buildings with irregularly shaped stone blocks which fitted together with the same degree of precision. It is obvious that they were not cast in a variety of shapes, but rather that they were carefully fitted together.
While it is true that the Romans produced a type of concrete from fired limestone and volcanic ash, it was used as mortar and similar applications, not to construct building blocks. Furthermore, there was no supply of volcanic ash available to the Egyptians, and no record of its use.
Firing limestone at high temperatures produces "quicklime", a substance that when mixed with sand and water produces lime mortar suitable for use with brick construction. Lime mortar is not the same as concrete, and is not a suitable replacement.
Portland cement is the ingredient in concrete that transforms a mixture of sand, gravel, and water into concrete. It is made by firing clay and limestone at very high temperatures and then grinding the resulting clinker into a fine powder. The Egyptians clearly did not have the facilities for carrying out this process. They would have to construct a very high temperature wood fired rotary kiln and load broken up pieces of limestone and clay in a continuous stream. They would need large powerful grinding mills to convert the clinker to powder. Camel power would not suffice!
The proponents of the cast block theory ignore this problem by postulating a make believe process that spontaneously converts mud into concrete by mere drying. This is simply would not work to produce any kind of concrete.
However, even assuming that the Egyptians were able to construct and fire the enormous kilns and grinders necessary to manufacture the quantity of Portland cement needed, and that somehow this process was lost to the subsequent Greeks and Romans, there still remain other reasons to cast doubt on the "cast blocks" theory. Gravel had to be made and transported from limestone outcrops. Water had to be transported in buckets. How in the world would it be able, using simple manpower, for the Egyptians to hand mix the tons of sand, gravel, cement, and water necessary to fill each postulated mold? The necessary curing time would require hundreds of forms (molds) lined up in sequence. As the cured block is removed from a mold, fresh concrete is placed to cure for a period of at least 10 days. In order to supply the blocks for production line construction, a dozen forms would have to be filled, and a dozen forms would have to be stripped each day.
The whole concept is simply preposterous!
The concrete theory assumes that it would take less effort to manufacture cast concrete blocks than to quarry stone blocks. This assumption is totally lacking in credibility. In addition to the fact that the concrete block theory simply could not be carried out in ancient Egypt, the manpower per block that would be required for this process far exceeds that required for a simple quarrying operation.