Scientists explore whether Egyptians used concrete

[SF]

CAMBRIDGE - It's a theory that gives indigestion to mainstream archeologists. Namely, that some of the immense blocks of Egypt's Great Pyramids might have been cast from synthetic material - the world's first concrete - not just carved whole from quarries and lugged into place by armies of toilers.

Such an innovation would have saved millions of man-hours of grunting and heaving in construction of the enigmatic edifices on the Giza Plateau.

http://www.boston.com/news/science/articles/2008/04/22/a_new_angle_on_pyramids/

So what is it?:)