Pyramids: Cast Concrete?

http://www.livescience.com/history/070518_bts_barsoum_pyramids.html
More than two decades ago, Joseph Davidovits, Director of the Geopolymer Institute in St. Quentin, France, claimed that the stones of the pyramids were actually made of a very early form of concrete created using a mixture of limestone, clay, lime, and water.

Presentation by Michel Barsoum, Professor, Department of Materials Science and Engineering at Drexel University, Philadelphia, PA

Dr. Barsoum's web site is worth a look, too.

Interesting thoughts on the truth of the Great Pyramids and the implications for the future! Perhaps we have just about come full circle...