Yep about two years ago the amusingly named Barsoum* made that claim, as of yet unsupported.
The main problem people have with this is that they fail to understand the nature of limestone. He has a nice theory but not the facts to back him up.
Davidouts tried this path too a few decades ago. It runs into the same major problem - the core stones are clearly individually cut and not from
molds.
What would the impact be of the Egyptians using concrete to make the pyramids? As they had a form of concrete already and used it for fill, not much.
It would be interesting thou but it also raises the question, if they invented concrete for structural use - why did they then abandon it?
The latest thing I could find on this theory is this.
Concrete
Ancient drawings and hieroglyphics are cryptic on the subject of pyramid construction. Theories as to how the Egyptians might have built the huge
monuments to dead pharaohs depend heavily on conjecture based on remnants of rubble ramps, as well as evidence that nearby limestone quarries
contained roughly as much stone as is present in the pyramids.
And good old Zahi offers up some uncompromising words
Zahi Hawass, head of Egypt's Supreme Council of Antiquities, minced no words in assailing the concrete idea. "It's highly stupid," he said via a
spokesman. "The pyramids are made from solid blocks of quarried limestone. To suggest otherwise is idiotic and insulting."
* A common Egyptian name but it always makes me think of John Carter
[edit on 15/7/08 by Hanslune]