Dec 5 2006
In partially solving a mystery that has baffled archeologists for centuries, a Drexel University professor has determined that the Great Pyramids of Giza are constructed with a combination of not only carved stones but the first blocks of limestone-based concrete cast by any civilization.
Michel Barsoum, professor of materials engineering, shows in a peer-reviewed paper published Dec. 1 in the Journal of the American Ceramic Society how the Egyptian builders of the nearly 5,000-year-old pyramids were exceptional civil and architectural engineers as well as superb chemists and material scientists. Barsoum wrote the paper with Adrish Ganguly, a an alumnus who received a doctoral degree in materials engineering from Drexel, and Gilles Hug of the National Center for Scientific Research in France.
Their conclusions could lead to a seismic shift in the kind of concrete used in construction and provide developing nations a way to build structures utilizing inexpensive and easily accessible materials.
The longstanding belief is that the pyramids were constructed with limestone blocks that were cut to shape in nearby quarries using copper tools, transported to the pyramid sites, hauled up ramps and hoisted in place with the help of wedges and levers. Barsoum argues that although indeed the majority of the stones were carved and hoisted into place, crucial parts were not. The ancient builders cast the blocks of the outer and inner casings and, most likely, the upper parts of the pyramids using a limestone concrete, called a geopolymer.
To arrive at his findings, Barsoum, an Egypt native, and co-workers analyzed more than 1,000 micrographs, chemical analyses and other materials over three years. Barsoum, whose interest in the pyramids and geopolymers was piqued five years ago when he heard theories about the construction of the pyramids, says that to construct them with only cast stone builders would have needed an unattainable amount of wood and fuel to heat lime to 900 degrees Celsius.
Barsoum’s findings provide long-sought answers to some of the questions about how the pyramids were constructed and with such precision. It puts to rest the question of how steep ramps could have extended to the summit of the pyramids; builders could cast blocks on site, without having to transport stones great distances. By using cast blocks, builders were able to level the pyramids’ bases to within an inch. Finally, builders were able to maintain precisely the angles of the pyramids so that the four planes of each arrived at a peak.
Although these findings answer some of the questions about the pyramids, Barsoum says the mystery of how they were built is far from solved. For example, he has been unable to determine how granite beams — spanning kings’ chambers and weighing as much as 70 tons each — were cut with nothing harder than copper and hauled in place.
The type of concrete pyramid builders used could reduce pollution and outlast Portland cement, the most common type of modern cement. Portland cement injects a large amount of the world’s carbon dioxide into the atmosphere and has a lifespan of about 150 years. If widely used, a geopolymer such as the one used in the construction of the pyramids can reduce that amount of pollution by 90 percent and last much longer. The raw materials used to produce the concrete used in the pyramids — lime, limestone and diatomaceous earth — can be found worldwide and is affordable enough to be an important construction material for developing countries, Barsoum said.