Thursday, December 21, 2006
Great Pyramids Of Giza - Building Blocks Made Of Concrete?
In partially solving a mystery that has baffled archeologists for centuries, a Drexel University professor has determined that the Great Pyramids of Giza were 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 to be published December 1 (2006) 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. His 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.
Barsoum will present his findings at a news conference November 30 at 5:30 p.m. (Central Europe standard time) at Le Palais de la decouverte, Avenue Franklin D. Roosevelt, in Paris, France.
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.
Source: Drexel University - Dateline Drexel (Keyword: Giza - November 30, 2007)
Based on the paper:
M. W. Barsoum, A. Ganguly, G. Hug (2006)
Microstructural Evidence of Reconstituted Limestone Blocks in the Great Pyramids of Egypt
Journal of the American Ceramic Society 89 (12), 3788–3796.
How the Great Pyramids of Giza were built has remained an enduring mystery. In the mid-1980s, Davidovits proposed that the pyramids were cast in situ using granular limestone aggregate and an alkali alumino-silicate-based binder. Hard evidence for this idea, however, remained elusive. Using primarily scanning and transmission electron microscopy, we compared a number of pyramid limestone samples with six different limestone samples from their vicinity. The pyramid samples contained microconstituents (micro-c's) with appreciable amounts of Si in combination with elements, such as Ca and Mg, in ratios that do not exist in any of the potential limestone sources. The intimate proximity of the µc's suggests that at some time these elements had been together in a solution. Furthermore, between the natural limestone aggregates, the µc's with chemistries reminiscent of calcite and dolomite - not known to hydrate in nature - were hydrated. The ubiquity of Si and the presence of submicron silica-based spheres in some of the micrographs strongly suggest that the solution was basic. Transmission electron microscope confirmed that some of these Si-containing micro-c's were either amorphous or nanocrystalline, which is consistent with a relatively rapid precipitation reaction. The sophistication and endurance of this ancient concrete technology is simply astounding.
*Info on current construction theories:
Many varied estimates have been made regarding the workforce needed to construct the Great Pyramid. Herodotus, the Greek historian in the 5th century BCE, estimated that construction may have required 20,000 workers for 20 years. Recent evidence has been found that suggests the workforce was in fact paid , which would require accounting and bureaucratic skills of a high order. Polish architect Wieslaw Kozinski believed that it took as many as 25 men to transport a 1.5-ton stone block. Based on this, he estimated the workforce to be 300,000 men on the construction site, with an enormous additional 60,000 off-site. [More]
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