CONF DAVIDOV

The research, by materials scientists from national institutions, adds fuel to a theory that the pharaohs' craftsmen had enough skill and materials at hand to cast the two-tonne limestone blocks that dress the Cheops and other Pyramids.

Despite mounting support from scientists, Egyptologists have rejected the concrete claim, first made in the late 1970s by Joseph Davidovits, a French chemist.

The stones, say the historians and archeologists, were all carved from nearby quarries, heaved up huge ramps and set in place by armies of workers. Some dissenters say that levers or pulleys were used, even though the wheel had not been invented at that time.

Until recently it was hard for geologists to distinguish between natural limestone and the kind that would have been made by reconstituting liquefied lime.

But according to Professor Gilles Hug, of the French National Aerospace Research Agency (Onera), and Professor Michel Barsoum, of Drexel University in Philadelphia, the covering of the great Pyramids at Giza consists of two types of stone: one from the quarries and one man-made.

"There's no way around it. The chemistry is well and truly different," Professor Hug told Science et Vie magazine. Their study is being published this month in the Journal of the American Ceramic Society.

The pair used X-rays, a plasma torch and electron microscopes to compare small fragments from pyramids with stone from the Toura and Maadi quarries.

They found "traces of a rapid chemical reaction which did not allow natural crystalisation . . . The reaction would be inexplicable if the stones were quarried, but perfectly comprehensible if one accepts that they were cast like concrete."

The pair believe that the concrete method was used only for the stones on the higher levels of the Pyramids. There are some 2.5 million stone blocks on the Cheops Pyramid. The 10-tonne granite blocks at their heart were also natural, they say. The professors agree with the "Davidovits theory" that soft limestone was quarried on the damp south side of the Giza Plateau. This was then dissolved in large, Nile-fed pools until it became a watery slurry.

Lime from fireplace ash and salt were mixed in with it. The water evaporated, leaving a moist, clay-like mixture. This wet "concrete" would have been carried to the site and packed into wooden moulds where it would set hard in a few days. Mr Davidovits and his team at the Geopolymer Institute at Saint-Quentin tested the method recently, producing a large block of concrete limestone in ten days.

New support for their case came from Guy Demortier, a materials scientist at Namur University in Belgium. Originally a sceptic, he told the French magazine that a decade of study had made him a convert: "The three majestic Pyramids of Cheops, Khephren and Mykerinos are well and truly made from concrete stones."

The concrete theorists also point out differences in density of the pyramid stones, which have a higher mass near the bottom and bubbles near the top, like old-style cement blocks.

Opponents of the theory dispute the scientific evidence. They also say that the diverse shapes of the stones show that moulds were not used. They add that a huge amount of limestone chalk and burnt wood would have been needed to make the concrete, while the Egyptians had the manpower to hoist all the natural stone they wanted

The concrete theorists say that they will be unable to prove their theory conclusively until the Egyptian authorities give them access to substantial samples.

Scientist Says Concrete Was Used in Pyramids

By JOHN NOBLE WILFORD
Published: November 30, 2006
In new research on the Great Pyramids of Giza, a scientist says he has found more to their construction than cut natural limestone. Some original parts of the massive structures appear to be made of concrete blocks.

If true, historians say, this would be the earliest known application of concrete technology, some 2,500 years before the Romans started using it widely in harbors, amphitheaters and other architecture.

Reporting the results of his study, Michel W. Barsoum, a professor of materials engineering at Drexel University, in Philadelphia, concluded that the use of limestone concrete could explain in part how the Egyptians were able to complete such massive monuments, beginning around 2550 B. C. They used concrete blocks, he said, on the outer and inner casings and probably on the upper levels, where it would have been difficult to hoist carved stone.

“The sophistication and endurance of this ancient concrete technology is simply astounding,” Dr. Barsoum wrote in a report in the December issue of The Journal of the American Ceramic Society.

Dr. Barsoum and his co-workers analyzed the mineralogy of samples from several parts of the Khufu pyramid, and said they found mineral ratios that do not exist in any of the known limestone sources. From the geochemical mix of lime, sand and clay, they concluded, “the simplest explanation” is that it was cast concrete.

Dr. Barsoum, a native of Egypt, said in an interview that he expected his interpretation to be controversial — and it already is.

Zahi Hawass, secretary-general of antiquities in Egypt and director of the Giza Pyramids excavations, said in an e-mail message, “The idea that concrete was used is unlikely and completely unproven.”

Noting that the pyramids have been restored and reinforced many times with the extensive use of concrete, Dr. Hawass said, “I would ask Dr. Barsoum the question: where did he get the samples he is working with, and how can he show that the samples are not taken from areas that have been restored in modern times?”

Most Egyptologists think the pyramids were built with limestone blocks that were cut to shape in nearby quarries using copper tools. The blocks were then hauled to the pyramid sites, lifted up ramps and hoisted into place with the help of wedges and levers.

But a geologist and another materials scientist, who were familiar with the research, said that Dr. Barsoum was a careful and reputable scientist and that his work should be seriously considered.

“I don’t know whether he’s right or wrong,” said Sheldon Wiederhorn, an engineer at the National Institute of Standards and Technology, in Rockville, Md., and associate editor of the ceramic society’s journal. “He makes a case that’s convincing, and I think his view should be heard.”

David Walker, a Columbia geologist who has read the report, said that the microscopic examination of the blocks “certainly revealed things you wouldn’t expect to find in normal limestone.”

In the journal report, Dr. Barsoum and his co-authors, Adrish Ganguly of Drexel and Gilles Hug of the National Center for Scientific Research in France, wrote: “We hereby acknowledge that nature is quite resourceful and could have — however unlikely — produced all the microstructures examined herein. We believe, however, that our work presents enough evidence to entertain the possibility that crucial parts of the Great Pyramids are indeed made of reconstituted limestone; only more research will tell.”

Pyramids were built with concrete rather than rocks, scientists claim

Charles Bremner, Paris ·

Method used only at higher levels

Blocks set using a limestone slurry

The Ancient Egyptians built their great Pyramids by pouring concrete into blocks high on the site rather than hauling up giant stones, according to a new Franco-American study.