Monday, 13 December 2010

Geopolymerisation and the pyramids

One of the themes of May’s SRCR ’11 conference is “Developments in geopolymers as alternatives to conventional cements”. Geopolymer is a term covering a class of synthetic aluminosilicate materials with potential use in a number of areas, essentially as a replacement for Portland cement and for advanced high-tech composites, ceramic applications or as a form of cast stone.

Minerals Engineering has published a number of papers on geopolymerisation over the years, and, far from being a mundane subject, it is a field of great scientific potential, with some fascinating implications, which bring together two of my interests, science and history.

I am fairly sure that the first paper on this topic published in Minerals Engineering was co-authored by my two old friends Jannie van Deventer and Leon Lorenzen, who were then at the University of Stellenbosch, but are now pursuing successful careers in Australia.

The paper, by Jannie, Leon and J.G.S. Van Jaarveld, entitled “The potential use of geopolymeric materials to immobilise toxic metals: Part I. Theory and applications” is an excellent review of the science of geolpolymeric materials, but what hit me between the eyes when I read it all those years ago was a couple of paragraphs describing the ideas of Davidovits, who postulated that the pyramids of Egypt were not built by the means previously thought, but were cast in place and allowed to set, creating an artificial zeolite rock. His ideas were published in a book (The Pyramids; An Enigma Solved, Hippocrene Books, Inc, New York, 1988). Unfortunately I did not follow this up, as at the time I thought it was just another crackpot idea, such as von Daniken’s 1968 book Chariot of the Gods, which proposed that the pyramids were built by aliens, or the later, and more believable, Fingerprints of the Gods by Graham Hancock, which proposed the building by a long-gone ancient civilisation, but which was also deeply flawed, being based on very selective “research”. I was then unaware that Joseph Davidovits was a respected materials scientist, who first applied the name geopolymer to these materials in the 1970s.

Barbara and me at Giza in 1995
Having visited the pyramids at Giza a couple of times, I am fascinated by not only their sheer size but also the precision in construction, by what was essentially a civilisation only just emerging from the stone age. There have been many hypotheses about the construction techniques, which seem to have developed over time, later pyramids not being built in the same way as earlier ones. Most of the construction hypotheses are based on the idea that huge stones were carved with copper chisels from stone quarries, and these blocks were then dragged and lifted into position. Disagreements chiefly concern the methods used to move and place the stones.

Davidovits claimed that the blocks of the pyramid are not carved stone, but mostly a form of limestone concrete and that they were "cast", as with modern concrete. According to this hypothesis, soft limestone with a high kaolinite content was quarried in the wadi on the south of the Giza Plateau. The limestone was then dissolved in large, Nile-fed pools until it became a watery slurry. Lime (found in the ash of cooking fires) and natron (also used by the Egyptians in mummification) was mixed in. The pools were then left to evaporate, leaving behind a moist, clay-like mixture. This wet "concrete" would be carried to the construction site where it would be packed into reusable wooden moulds and in a few days would undergo a chemical reaction similar to the "setting" of concrete. New blocks, he suggests, could be cast in place, on top of and pressed against the old blocks. 

In 1979, at the second International Congress of Egyptologists, Grenoble, France, Davidovits suggested that the pyramid blocks were cast as concrete, instead of carved. Such a theory was greatly disruptive to the orthodox theory and his research was fiercely opposed by some experts (geologists and Egyptologists).

My interest in this has been reawakened by a fairly recent peer-reviewed paper being drawn to my attention (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). The findings of Michel Barsoum and his colleagues at Drexel University, USA support Davidovits' hypothesis. They claim to have found particles and air cavities in pyramid limestone that do not occur in natural limestone. After extensive scanning electron microscope observations and other testing, they 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 or a calcium and magnesium-rich silicate mineral.

The stones also had a high water content, which is 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, their atoms not being arranged in a regular and periodic array. Sedimentary rocks such as limestone are seldom, if ever, amorphous.

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.

Egyptologists are consistently confronted by unanswered questions: How is it possible that some of the blocks are so perfectly matched that not even a human hair can be inserted between them? Why, despite the existence of millions of tons of stone, carved presumably with copper chisels, has not one copper chisel ever been found on the Giza Plateau? At the end of their most recent paper reporting these findings, the researchers reflect that it is “ironic, sublime and truly humbling” that this 4,500-year-old limestone is so true to the original that it has misled generations of Egyptologists and geologists and, “because the ancient Egyptians were the original-albeit unknowing-nanotechnologists.”

To counter this, Dipayan Jana, a petrographer, made a presentation to the ICMA (International Cement Microscopy Association) in 2007 and gave a paper in which he discusses Davidovits' and Barsoum's work and concludes "we are far from accepting even as a remote possibility of a “manmade” origin of pyramid stones."

So there is still much controversy, but what a fascinating subject this is. I would like to know what other researchers in the field of geopolymerisation have to add to this, and hopefully talking to a few of them at the conference in May.


  1. Very interesting indeed! There is a similar controversy with regard to some of the ancient Inca cities in South America. There are walls built with perfect fitting stones (walls were not even a needle enters between the stoneblocks). Some of the stones have a "vitrified" aspect. Others show a sort of a "blueprint" left on the lower laying stones, as if the weight of the upper stones gave the print in the once softer underlying stones. Some researchers suggest that a melted look is present and obvious, as if the "rocks" were subject to thermal disaggregation. Others say the "vitrified" aspect is natural and typical of volcanic rocks. Definitely a fascinating subject!
    Pedro Bottesi Neto, Ma'aden Saudi Arabian Mining Company, Saudi Arabia

  2. Thanks Pedro. Close to the Sphinx at Giza is the Valley Temple, which is built from close-fitting blocks of huge size, some weighing well over 100 tonnes. How were these lifted into place? Casting would have been a relatively easy option.

  3. Prof. Davidovits has been in touch with me, and recommends the following sites: and

  4. The problem of not existing a universally accepted theory to explain the construction of the pyramids is easy to clarify: - up to know civil engineers, which have the knowledge to explain and discuss the possible methods of construction, were not consulted or involved in the discussions. Egyptologists, like archeologists, are very aware of their science and nobody wants to invade their dominions, but what do they know about construction methods? The closest approach was involving architects, but as far as I know from 35 years of engineering practice (buildins, dams, walls and big infra and superstructures) they know very little about constructing simply because it is not within their academic background. Architects design, architects discuss the space, the color, the shadow, but they not build or define engineering methods for erecting a huge building or other type of constructions. What do they know about concrete technology, about concrete placing and cure, about formwork or scaffolding? I do not want to be rude neither to offend the very few architects that are familiar with construction methods.
    If you place the Davidovits theory to a group of Civil Engineers I would say that 99% of them would agree with it, because it is very simple, possible, repeatable with very easy tools and explains everything.
    Try for example to look at the pyramids from the apex, by a satellite image or simply by the Google Earth. You should note a very peculiar characteristic of all of them (not with the same intensity, anyway): - the entasis. This means that the sides of the pyramids are concave, which is consistent with the indications of Heron of Alexandria (10-70 BC that entasis had been invented by the Egyptians to disguise the optical illusion that gives curvature to large flat surfaces. What a surprise indeed….
    How is it possible to explain this construction feature? They had no surveying equipment, theodolites, total stations and levels. How were they able to carve and place a layer of stones in such a way to favor the entasis?
    Look at the pyramid steps, they are perfectly leveled? How?
    Look at the convergence of the four edges of each pyramid, they cross one another at the apex without deviation. They could only see 3 at a time, but not from above, only from below. They were not able by sight to detect any imperfection.
    How could they did it?
    The answer is very simple to civil engineers and very easy to do: The answer is very simple for civil engineers and very simple to put into practice: using a wire, as even today is used to score alignments or deploying curved surfaces (marking at regular spacements on the wire, distances to the final position of formwork).
    This can lead us to a very big discussion. To finalize: - In terms of Science nobody knows how the Pyramids were built. Davidovits theory anyhow is the closest, simplest and most supported theory to explain that mystery. It is supported by Egyptian documents and stelae. It is time for the Egyptologist to open their minds and try to translate from the old egyptian language the same documents he is presenting in his books. Is that so difficult? What is behind that apparent lack of interest? The well-known obstinacy of the Egyptian authorities, they do not want to counter? Or are they afraid to discover how wrong they are?
    Signed: A.Teixeira-Pinto, (ateixeirapinto@gmailcom)

  5. Pyramids - interesting post Barry. As I remember it inside Cheops there were massive blocks of granite with zero space between them. So 'in situ' casting of the limestone (theory) could not be similarly applied to the granite - unless I am missing something? As for the limestone/cement theory - I'm not convinced.

    1. Thanks Pete. The main structures of the pyramids are limestone (or geopolymer) blocks, and granite was used for the tunnels and chambers. And yes, zero space between the blocks, which is remarkable

  6. I have also been intrigued by the fact that so far (as far as I am aware), petrologists have not been able to clearly disqualify Davidovits hypotheses. We have so many microanalytical tools today. It should only take a good sampling protocol and some hours of work to definitely confirm or outrule the geopolymer hypothesis.

    Davidovits recently claimed (Materials Letters 235 (2019)) that man-made geopolymer blocks are also found in Tiwanaku (Bolivia)... I have strong doubts regarding this one. Nature is capable of (m)anything

    Eric Pirard, University of Li├Ęge, Belgium

    1. Yes I agree Eric. It would make a great project for a student


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