I read a very interesting article by Patrick Rapa in Philadelphia citypaper, a local weekly newspaper explaining the proposal of a Drexel professor about how pyramids were built. As I understand the article, Professor Barsoum published a paper indicating the pyramids were built with two components: “rough stone quarried and hauled into place” constituting 80% of the material used and concrete for the “smooth uniform arrangement of the outer blocks” and possibly the inner walls for the remaining 20%.
This concrete material was made on site from materials locally available: “water, lime (by heating limestone), diatomaceous earth (a crumply, porous rock made of fossilized algae) and limestone rubble and limestone rubble (ground to powder).” Professor Barsoum does not claim to be the first to propose a concrete solution. His proposal explains how the Egyptians could have made concrete from materials locally available that would have be stronger than Portland Cement.
Obviously I need to think about this.