This Behind the Scenes article was provided to LiveScience in partnership with the National Science Foundation.
“This is not my day job,” begins Michel Barsoum as he recounts his foray into the mysteries of the Great Pyramids of Egypt. As a well respected researcher in the field of ceramics, Barsoum never expected his career to take him down a path of history, archaeology, and “political” science, with materials research mixed in.
As a distinguished professor in the Department of Materials Science and Engineering at Drexel University, his daily routine consists mainly of teaching students about ceramics, or performing research on a new class of materials, the so-called MAX Phases, that he and his colleagues discovered in the 1990s. These modern ceramics are machinable, thermal-shock resistant, and are better conductors of heat and electricity than many metals — making them potential candidates for use in nuclear power plants, the automotive industry, jet engines, and a range of other high-demand systems.
Then Barsoum received an unexpected phone call from Michael Carrell, a friend of a retired colleague of Barsoum, who called to chat with the Egyptian-born Barsoum about how much he knew of the mysteries surrounding the building of the Great Pyramids of Giza, the only remaining of the seven wonders of the ancient world.
The widely accepted theory — that the pyramids were crafted of carved-out giant limestone blocks that workers carried up ramps — had not only not been embraced by everyone, but as important had quite a number of holes.
Burst out laughing
According to the caller, the mysteries had actually been solved by Joseph Davidovits, Director of the Geopolymer Institute in St. Quentin, France, more than two decades ago. Davidovits 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.
“It was at this point in the conversation that I burst out laughing,” Barsoum said. If the pyramids were indeed cast, he said, someone should have proven it beyond a doubt by now, in this day and age, with just a few hours of electron microscopy.
It turned out that nobody had completely proven the theory … yet.
“What started as a two-hour project turned into a five-year odyssey that I undertook with one of my graduate students, Adrish Ganguly, and a colleague in France, Gilles Hug,” Barsoum said.
A year and a half later, after extensive scanning electron microscope observations and other testing, Barsoum and his research group finally began to draw some conclusions about the pyramids. They found that the tiniest structures within the inner and outer casing stones were indeed consistent with a reconstituted limestone. The cement binding the limestone aggregate was either silicon dioxide (the building block of quartz) or a calcium and magnesium-rich silicate mineral.
The stones also had a high water content — unusual for the normally dry, natural limestone found on the Giza plateau — and the cementing phases, in both the inner and outer casing stones, were amorphous, in other words, their atoms were not arranged in a regular and periodic array. Sedimentary rocks such as limestone are seldom, if ever, amorphous.
The sample chemistries the researchers found do not exist anywhere in nature. “Therefore,” Barsoum said, “it’s very improbable that the outer and inner casing stones that we examined were chiseled from a natural limestone block.”
More startlingly, Barsoum and another of his graduate students, Aaron Sakulich, recently discovered the presence of silicon dioxide nanoscale spheres (with diameters only billionths of a meter across) in one of the samples. This discovery further confirms that these blocks are not natural limestone.