Imhotep’s formula to make limestone blocks
Imhotep had two different chemical formulas: a very simple one for the casting of the limestone core blocks, and another one to produce the high quality stones of the exterior layer. When all the blocks of the core were set in place, a layer of casing was applied. This meant preparing a more sophisticated type of mold to produce inclined limestone blocks following the slope of the pyramid, adding new ingredients to the mixture to yield a higher quality stone.
1. SOFT LIMESTONE
Pouring Natron salt to the reaction basin
To build the Step Pyramid, Imhotep located a quarry of soft limestone, just one kilometer from the construction site to provide the raw material he needed to cast millions of modular stones. Soft limestone can be easily disaggregated either under pressure or by diluting it in water.
Shallow canals were dug in the soft limestone along the Nile, forming ideal basins for producing large quantities of muddy limestone. Imhotep’s men began disaggregating the clayish soft rock with its water, until the lime and the clay separated, forming a mud with the fossil shells at the bottom.
2. NATRON SALT
The mixing of lime, Natron, limestone and water.
Next, a substance called Natron salt (sodium carbonate) was poured in. Salt is a very reactive substance that has a petrifying effect, which is why it is used to avoid the putrefaction of organic tissue (mummification).
Natron is found in very great quantities in the desert and in Wadi-El-Natron.
3. LIME
The limestone concrete paste.
More lime, the mineral which binds, was added. Lime is a powdery residue obtained by burning and reducing to ashes sedimentary rocks such as limestone and dolomite. The fire oxidizes and converts the rocks into a powdery residue, and that is lime. The ashes of plants are also rich in lime and the priests established the custom of receiving ashes from cooking fires from all over Egypt, to add them to the mixture.
4. CAUSTIC SODA
The first mold filled with limestone
Lime mixed with natron and water produced a third substance, a much more corrosive one, that sparks off a strong chemical reaction and transforms other materials. The water dissolved the Natron salt and put the lime in suspension, forming caustic soda.
Caustic Soda is the catalyst Imhotep needed to trigger off a powerful chemical reaction, one which would produce the fast integration of silica and alumina.
5. CEMENT
The leveling of the second mold.
Men mixed the ingredients in the canals until a homogeneous binder paste was obtained. Imhotep had invented a water-based cement. Now, he had only to convert that cement into concrete.
6. LIMESTONE CONCRETE
His workers added more fossil shells, limestone rubble and silt from the river Nile, producing a concrete paste, which they carried up to where hundreds of small wooden molds had been prepared. These molds had been smeared with rancid oil to facilitate the release of the concrete once hardened.
The mixture was rammed into the molds as in the making of the packed earth called pisé, becoming a dense re-agglomerated limestone, which was let to dry in the shade, to avoid its cracking under the glare of the hot sun.
7. LIMESTONE BLOCKS
The filling of the third mold.
The hardened blocks were released from their molds and easily carried up to the construction site, by means of small ramps over the tiers already set, until the men placed each block in its correct place.
The towering Step Pyramid was not only the first, but also the only one made entirely of small modular blocks weighing approximately 60 kilos apiece, easily carried by two men.
8. IMPROVING THE MANUFACTURE
The twelve-tonne limestone blocks.
This Step Pyramid was just the first one that simply took the crude brick techniques and, instead of using mud, Imhotep used a limestone paste. Then, the three Sneferu’s pyramids improved step by step the technology by increasing the size of the blocks and the height of the monuments. Whereas the pyramids at Giza showed how technical improvements helped to achieve one of the famous wonders of the world, only 60 years after the first pyramid at Saqqarah. In later times, by Sneferu’s Red Pyramid, at Dashour, much heavier blocks were molded and cast directly on the spot, which means they were not moved. This is how the Great Pyramids at Giza were built.
At the Geopolymer Institute, we tried to replicate this masterpiece by making life size blocks, that is to say from 1 to 4.5 tonnes. The next pages illustrate our experience.
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