Did Pyramid Builders Use Cast-in-Place Concrete?

In a Boston Globe article titled “A New Angle on Pyramids,” Colin Nickerson describes the research conducted at the Massachusetts Institute of Technology by Linn W. Hobbs and his students. The professor of materials science suggests that the ancient Egyptians might have invented concrete. This would mean the technology was developed a couple of thousand years earlier than was previously thought. As Nickerson explains:

That’s a notion that would dramatically change engineering history. It’s long been believed that the Romans were the first to employ structural concrete in a big way, although the technology may have come from the Greeks. A handful of determined materials scientists are carrying out experiments with crushed limestone and natural binding chemicals – stuff that would have been readily available to ancient Egyptians – designed to show that blocks on the upper reaches of the pyramids may have been cast in place from a slurry poured into wooden molds.

If indeed the Nile denizens invented concrete, they would have made it from a mixture of crushed limestone, kaolinite clay, natron, and silica. Hobbs is one of a small circle of scientists trying to solve this inquiry into the origin of the most common building material used by humans. The concept of Egyptian invention is not new, but goes back to the theories of Joseph Davidovits, a chemical engineer, who posited sacks of wet cement being carried aloft by slaves in a kind of bucket brigade.

Another scientist believes that as many as 20 percent of the pyramids’ blocks may have been cast in place. In Philadelphia, Michel W. Barsoum announced in 2006 that the Khufu Pyramid had yielded stone samples that differ from limestone on a microstructural level. However, critics point out that although apparent concrete may have been found, it has been incorrectly interpreted, and will eventually prove to date not from the building of the pyramids, but from more recent repair work.

In “Concrete Pyramids“, Isabel R. Harris and Matthew W. A. Bruder V say the concrete pyramid theory has been around since the 18th century. They point to the process the ancient artisans used for making alabaster vases with plywood molds. Although wood for molds was very scarce in Egypt, it could, like many other commodities, be imported. There’s a whole lot of technical discussion about the precision cutting — or was it casting? — of the pyramids’ stone blocks, and the question of scrap is raised — where did it go? They do the math, and tell how many workers would have been needed, and how much time, to build pyramids of concrete.

Reading up on the subject in the cast-in-place concrete section of Architectural Graphic Standards, 11th Edition, we find that, in addition to portland cement, water and aggregates, concrete admixtures are of many types. An admixture might entrain air, reduce water, or control hydration. It might accelerate, retard, or superplasticize. Then there are “miscellaneous admixtures that aid workability, bonding, dampproffing, gas-forming, grouting (nonshrink), coloring, and admixtures that reduce permeability and inhibit corrosion.”

Given the evidence of their other accomplishments, is there any reason to believe the ancient Egyptians couldn’t have figured out concrete?

SOURCE: ” A new angle on pyramids” 04/22/08
photo courtesy of Ahmed Rabea , used under this Creative Commons license