I didn't know about the Egyptians, but it is certainly similar to that used by the Romans:
From my original link:

Professor Jannie van Deventer’s team at the University of Melbourne has found one. And surprisingly it’s chemically similar to a cement used by the ancient Romans.
Professor Janine van Deventer: The good properties of geopolymeric concrete are also present in the old Roman structures, so old roman concrete be made along similar lines in terms of the chemistry.
Narration: Over time the Roman knowledge was lost. The cement we know and use was invented in the 19th Century. The problem with it is its fundamental chemistry.

Or perhaps you are referring to Egypt under Roman rule?