Dec. 8, 2006 — Concrete was poured to build the Great Pyramids about 5,000 years ago, according to controversial research, which suggests the ancient Egyptans predated the Romans by thousands of years as the inventors of concrete.
Michel Barsoum, professor of materials engineering at Drexel University in Philadelphia, and colleagues report in the current issue of the Journal of the American Ceramic Society that the pyramids were constructed with a combination of carved stones and blocks of limestone-based concrete.
The study, drawn on a research made in the mid-1980s by the French materials scientist, Joseph Davidovits, consists of a detailed examination of samples taken from the pyramids and their vicinity.
The aim was to determine whether the pyramid materials are natural or synthetic.
"Davidovits proposed that the pyramid blocks were cast in situ, with a wet mix of limestone particles and a binder, tamped into molds," wrote the researchers.
In time, the French scientist claimed, the wet mix hardened into a concrete that featured the appearance and properties of native limestone.
But Davidovits’ theory lacked hard evidence and was widely rejected by the Egyptologist community.
The longstanding belief is that the pyramids were built with blocks of limestone carved from nearby quarries. The blocks were cut to shape using copper tools, transported to the pyramid site and then hauled up huge ramps and set in place using wedges and levers.
Using scanning and transmission electron microscopy, Barsoum and his co-workers, Gilles Hug of the French National Aerospace Research Agency, and Adrish Ganguly of Drexel University, analyzed and compared the mineralogy of a number of pyramid samples with six different limestone samples from their vicinity.
They found that pyramid samples featured mineral ratios that did not exist in any known limestone sources.
"The most convincing argument is the presence of amorphous SiO2 (silica)," Barsoum told Discovery News. "In sedimentary rocks, the SiO2 is almost always crystalline."
He also noted that some samples of calcite and dolomite taken from pyramid samples featured water molecules trapped inside — again, he said, this is not a phenomenon found in nature.
The researchers believe that a limestone concrete, called a geopolymer, was used for, at most, 20 percent of the blocks — in the outer and inner casings and in the upper parts of the pyramids.
Davidovits, himself, tested a limestone-based concrete recipe at the Geopolymer Institute at Saint-Quentin.
He concluded that diatomaceous earth (a soil formed by the decay of tiny organisms called diatoms), dolomite and lime were mixed in water to produce a clay-like mixture. This was what the ancient Egyptians would have poured into wooden moulds at Giza to obtain concrete blocks in a few days.
Indeed, with this recipe, Davidovits produced a large concrete limestone block in ten days.
