The Egyptians used a limestone based mortar or cement, but did not use concrete per se..
IIRC, while there was some use of the egyptian cement in casting, such castings were decorative, not structural..
Roman concrete is also not the same as our concrete. I studied concrete in college. I remember reading somewhere that no one knows how the romans made concrete. THat technology was lost. Modern concrete was discovered/invented in England or Scotland during the industrial revolution if I remember correctly, and it is different than roman concrete.
I've never heard of egyptian concrete untill reading this thread. I'm concluding that it isn't really concrete at all but more like a high strength plaster that can be ground up and re-used over and over again just like plaster of paris. You can't do that with concrete. It is an irreversable chemical reaction with H2O. ONce its hard, adding water wont soften it up, and grinding it up and mixing with water will only give you wet rocks and sand.