It’s being called Geopolymer.
The claim is that it explains how the Egyptians made the pyramids. While I’m “not so sure” about that (it would take a closer look at the stones of the pyramids; plus we have this eye witness report from Solon that they were assembled using ‘machines’ of some sort, no mention of buckets of slop…) But in any case, we have that as the impetus, and someone then figured out an interesting new technology.
It is not just Portland Cement / concrete…
This has sent me off for a couple of weeks (at odd times of day) learning more about silicate chemistry. The basic effect looks to be that in strong alkali, the silicate monomer tends to become a silicate polymer and that SiO2 – SiO4 range ions come off of various minerals and react.
We typically make Portland Cement with one of these silicates and a particular alkali.
( Lime, Calcium Silicate)
From the wiki on Portland Cement:
Portland cement clinker is a hydraulic material which shall consist of at least two-thirds by mass of calcium silicates (3 CaO·SiO2 and 2 CaO·SiO2), the remainder consisting of aluminium- and iron-containing clinker phases and other compounds. The ratio of CaO to SiO2 shall not be less than 2.0. The magnesium oxide content (MgO) shall not exceed 5.0% by mass.
It goes on to describe some of the other standards (that one is the European) and some of the other formulas.
Portland cement clinker is made by heating, in a kiln, a homogeneous mixture of raw materials to a sintering temperature, which is about 1450 °C for modern cements. The aluminium oxide and iron oxide are present as a flux and contribute little to the strength. For special cements, such as Low Heat (LH) and Sulfate Resistant (SR) types, it is necessary to limit the amount of tricalcium aluminate (3 CaO·Al2O3) formed. The major raw material for the clinker-making is usually limestone (CaCO3) mixed with a second material containing clay as source of alumino-silicate. Normally, an impure limestone which contains clay or SiO2 is used. The CaCO3 content of these limestones can be as low as 80%. Second raw materials (materials in the rawmix other than limestone) depend on the purity of the limestone. Some of the second raw materials used are clay, shale, sand, iron ore, bauxite, fly ash and slag. When a cement kiln is fired by coal, the ash of the coal acts as a secondary raw material.
That last line about “acts as a secondary raw material” has a bit of hint in it. There are two common reactions in cement. One that makes the basic cement, the other that is a reaction with various kinds of embedded silicate materials. The Romans used a cement that was mostly based on this reaction and used volcanic ash for their silicate source. Who’s to say other similar paths are not available?
The Pozzolanic reaction is the chemical reaction that occurs in hydraulic cement, a mixture of slaked lime (calcium hydroxide) with amorphous siliceous materials (namely, pozzolan or pozzolana, a finely divided volcanic ash, rich in obsidian, a mineral glass commonly found in lava), forming non-water-soluble calcium silicate hydrates. It is the main reaction involved in the Roman concrete invented in Ancient Rome and used to build, for example, the Pantheon.
At the basis of the Pozzolanic reaction stands a simple acid-base reaction between calcium hydroxide, also known as Portlandite, or (Ca(OH)2), and silicic acid (H4SiO4, or Si(OH)4). Simply, this reaction can be schematically represented as follows:
Ca(OH)2 + H4SiO4 → Ca2+ + H2SiO42- + 2 H2O → CaH2SiO4 · 2 H2O
The “question” is this: Are there OTHER potential reactions that can also give us ‘liquid stone’? The answer looks to be ‘yes’…
First, some links to the Geopolymer site:
The general thesis is presented here, in brief:
The abstract reads: “A comparison was made of the solid-state 29Si, 27Al and 43Ca MAS NMR spectra of the outer casing stone from Snefru’s Bent Pyramid in Dahshour, Egypt, with two quarry limestones from the area. The NMR results suggest that the casing stones consist of limestone grains from the Tura quarry, cemented with an amorphous calcium-silicate gel formed by human intervention, by the addition of extra silica, possibly diatomaceous earth, from the Fayium area.”
That “amorphous calcium-silicate gel” is another way of saying ‘Portland cement’ of a very particular form.
The site also sells a book about it, with the first chapter available as a download pdf here:
In it, just a little ways down, is a very striking photograph of several Egyptian style busts, all moulded out of different colors of ‘geopolymer’ or liquid stone.
kaolin, natron salt and chalk, could be poured out and compacted into moulds just as concrete is, directly on the site of the pyramids.
Natron is an alkaline sodium salt, rather than an alkaline calcium salt, but the effect ought to be the same. Silicate from the clay reacting with calcium from the chalk, forming a Calcium Silicate cement (either in a crystalline form or the amorphous form called a ‘gel’ – but it is still a hard stone…)
This causes me to wonder how many OTHER alkaline catalyzed or alkaline facilitated silicate forming chemistries might exist that we have not explored? Feldspars, for example, are a silicate (but containing other metal ions – Potassium, Sodium, Aluminum, etc). Might it be possible to make ‘liquid stone’ using feldspars? Diorite, for example, is very hard but still just another silicate. In Peru are giant stones with ‘interior carving’ made of diorite that folks frequently say “We don’t know how to carve these even today!” (usually followed by pronouncements about extraterrestrial visitation…) Yet the local legends talk about liquid stone and folks making the stone liquid. Rather than some alien rock softening ray gun, might it just be possible to make an alkali catalyzed feldspar that makes a ‘diorite like’ stone on hardening?
The stones do look like various shapes we see in cast concrete. We cast very large objects in concrete, too. Is it THAT far a leap to think we might not have found all ‘liquid stone’ methods? Have we even looked, once we found Portland Cement?
The wiki says some folks are looking:
Geopolymer binders and geopolymer cements are generally formed by reaction of an aluminosilicate powder with an alkaline silicate solution at roughly ambient conditions. Metakaolin is a commonly used starting material for laboratory synthesis of geopolymers, and is generated by thermal activation of kaolinite clay. Geopolymer cements can also be made from sources of pozzolanic materials, such as lava or fly ash from coal. Most studies on geopolymer cements have been carried out using natural or industrial waste sources of metakaolin and other aluminosilicates. Industrial and high-tech applications rely on more expensive and sophisticated siliceous raw materials.
Notice this reaction proceeds at ambient conditions. That “alkaline silicate” is a bit vague, but could be something as simple as water glass. Simple sodium silicate. I first ran into this stuff when my Dad needed to fix a cover over the floor furnace. It had a kind of ‘window’ about 2 inches in diameter that you would vaguely see flickers of fire through… nice to know when it was running. Pour some water glass on, heat, viola! Fresh “glass”…
So mix water glass with clay. Got it ;-)
How do you make it? Mix sodium carbonate with silicon dioxide and heat. That’s natron with quartz sand.
Kaolin is a clay mineral:
Kaolinite is a clay mineral, part of the group of industrial minerals, with the chemical composition Al2Si2O5(OH)4. It is a layered silicate mineral, with one tetrahedral sheet linked through oxygen atoms to one octahedral sheet of alumina octahedra. Rocks that are rich in kaolinite are known as kaolin or china clay.
The name is derived from Kao-ling (Chinese: 高岭/高嶺; pinyin: Gaoling), a village near Jingdezhen, Jiangxi province, China. The name entered English in 1727 from the French version of the word: “kaolin”, following Francois Xavier d’Entrecolles’s reports from Jingdezhen.
Kaolinite has a low shrink-swell capacity and a low cation exchange capacity (1-15 meq/100g). It is a soft, earthy, usually white mineral (dioctahedral phyllosilicate clay), produced by the chemical weathering of aluminium silicate minerals like feldspar. In many parts of the world, it is colored pink-orange-red by iron oxide, giving it a distinct rust hue. Lighter concentrations yield white, yellow or light orange colors. Alternating layers are sometimes found, as at Providence Canyon State Park in Georgia, USA.
So, aluminum silicate instead of calcium silicate. Made by weathering feldspar.
When mixed with natron, a sodium carbonate salt, might we not get some kind of mixed silicate ‘cement’ formed between grains of feldspar? Making something that looks enough like Diorite to be accepted as it?
In this link:
There is an interesting video about some of the chemistry involved, along with a discussion in print of a trademarked cement, named Pyrament, made using some of these geopolymer ideas.
In 1991, the world was impressed on how fast the US Air Force managed to build and equip temporary military airports in the wilderness of Saudi Arabia during the Gulf War. One of the reasons for this efficiency might result from the application by the US Air Force Engineering of a very new rapid high strength and high performance cement, the Pyrament®. Sources: US Air Force Command report and Pyrament brochure.
The American Cement Company, Lone Star Industries, introduced this exceptional cement in 1988. It was the result of an unique collaboration that started in 1983 between the Lone Star Industries Research Center in Houston, Texas, and the Geopolymer Institute. Geopolymer chemistry, in particular the Poly(sialate-siloxo) based system, improves the properties of Portland cement and regular concrete. In the recently updated book Geopolymer Chemistry & Applications several chapters are dedicated to geopolymer , metakaolin-based, rock-based and fly ash-based cements and concretes, see in Chapters 8, 9, 10, 11, 12, 24 and 25. You may also go to the Geopolymer Library and download several papers.
The Pyrament® blended-cement is the ideal material for repairing runways made of concrete, industrial pavements, and highway roads. In the case of a runway, a 4-6 hours hardening is enough to allow the landing of an Airbus or a Boeing. The geopolymeric cement reaches a compression strength of 20 Mpa after 4 hours, whereas plain concrete gets to this strength after several days.
Yeah, 4 to 6 hours to ‘hard as rock’…
There are other interesting products being made as well, though likely not at ‘ambient temperatures’:
Has Calcium Silicate (anhydrous) forms being used to replace asbestos in various heat demanding applications. They also sell an intriguing “silicate based glue” for installing it:
The Russians also made a cement similar to Pyrament, but have generally only sold finished product and not talked much about the formula, as near as I can tell, other than calling it ‘soil cement’.
So, about that ‘secondary reaction’ in cement. Is it the same thing or similar? Yup.
Back To Egypt
There is an interesting bit of testament to some kind of Egyptian “liquid stone”, plus a couple of other hints that they worked in this general area of chemical technology.
First we have a “stele” or stone marker enscrptions:
The “Irtysen Stele”:
The Louvre gallery in Paris is where the Irtysen Stele is preserved. This ancient stone inscription does not go back quite as far as the era when the Great Pyramid was built. But it is very old. Some four thousand years old…
It is the autobiographical funerary stele of Irtysen a master craftsman of the priestly caste, who lived 2.000 years BC. In this text Irtysen says he possesses a “secret knowledge” to fabricate stone statues, not by carving them but by casting them in molds.
Irtysen affirms he used a material mixture that hardened when cast inside molds to reproduce any kind of object or figure – a material that fire could not consume, nor water dilute. This suggests that Irtysen worked with a chemically-produced binding matter that could be mixed with certain minerals and poured into a mold, to produce statues.
Sure sounds like ‘liquid stone’ to me. There are a variety of old Egyptian “stone” artifacts that would just be hell to carve, but straight forward to cast or mould. There are some stone dishes that look like fine china, with smooth nearly liquid folding to the ‘petals’.
Then we have two ‘chemically related’ materials. Faience and Egyptian Blue.
Faience has been defined as the first high technology ceramic, to emphasize its status as an artificial medium, rendering it effectively a precious stone. Egyptian faience is a non-clay based ceramic composed of crushed quartz or sand, with small amounts of calcite lime and a mixture of alkalis, displaying surface vitrification due to the soda lime silica glaze often composed of copper pigments to create a bright blue-green luster. While in most instances domestic ores seem to have provided the bulk of the mineral pigments, evidence suggests that during periods of prosperity raw materials also available locally, such as lead and copper, were imported. Plant ash, from halophitic plants typical of dry and sea areas, was the major source of alkali until the Ptolemaic Period, when natron based alkalis almost completely replaced the previous source. Although the chemical composition of faience materials varies over time and according to the status of the workshop, also as a cause of change of accessibility of raw materials, the material constitution of the glaze is at all times consistent with the generally accepted version of faience glazing.
Do we REALLY know if Egyptian faience was fired, other than for glazing? It has about the right chemical composition for a geopolymer, and we have a stele telling us of the maker claiming to cast similar objects…
Another iconic Egyptian technology was “Egyptian Blue”. Widely used, and traded, as a semi-precious material and used as a very blue permanent pigment (the Egyptians really liked blue!)
What is the chemical formula for Egyptian Blue?
Egyptian blue is chemically known as calcium copper silicate (CaCuSi4O10 or CaO·CuO·4SiO2). It is a pigment used by Egyptians for thousands of years. It is considered to be the first synthetic pigment. The pigment was known to the Romans by the name caeruleum. Vitruvius describes in his work ‘”De architectura” how it was produced by grinding sand, copper and natron and heating the mixture, shaped into small balls, in a furnace. Lime is necessary for the production as well, but probably lime-rich sand was used. After the Roman era, Egyptian Blue fell from usage and the manner of its creation forgotten.
The ancient Egyptian word wedjet signifies blue, blue-green and green, and the same word is used for the human eye, and the protective Eye of Ra.
Couple of things here. Clearly they are working with silicates. They have furnace formed Egyptian Blue, and wet formed (then fired) faience that may or might not need firing. In the case of Egyptian Blue, the product is a Calcium Silicate (not hydrated) but with Copper substituted to some extent to give a nice color. These folks knew something about silicate chemistry…
What was “the mix”?
Silicate sand, copper, natron salt. Heated and formed. With a bit of lime.
Is there any reason to think that mixing lime with silicate could cause it to harden? To form ‘stone like’ materials? Perhaps even if NOT fired? Well, yes. Dumping lime on soft clay soils is a common technique in building and road building to stabilize and harden the soil…
Lime Stabilized Soils and Related
This is a fascinating old PDF about lime stabilized clay. I’ll leave the common construction uses for folks to key word search on their own.
Calcium hydroxide was allowed to react with various clays, other silicates, and quartz at slightly elevated temperatures for several months. The reaction products were examined by X-ray diffraction, DTA, and electron microscopy, and were shown to be poorly crystallized calcium silicate hydrates of the tobermorite family, and calcium aluminate hydrates. Quaternary phases were not detected, but some isomorphous substitution probably occurred. The extent of reaction was shown to be such that under appropriate conditions almost all of the clay mineral was decomposed. Electron micrographs of the reacted materials indicated that attack occurred from the edges of the particles, and in general the remaining unattacked portion of the clay did not suffer appreciable loss of crystallinity. It was postulated that the reaction involved progressive dissolution of the mineral at the edges of the particles in the strongly basic environment maintained by calcium hydroxide solution, followed by separate precipation of the reaction products. In these experiments the calcium silicate hydrate generated by the reaction between lime and quartz was uniformly calcium silicate hydrate gel (CSH (gel)); reaction with kaolinite mid montmorillonite produced either CSH (gel) or calcium silicate hydrate (I) (CSH (I)) depending on the conditions of the reaction. At 60 degrees C the alumina-bearing phase was tricalcium aluminate hexahydrate; at lower temperature the phase produced was a hexagonal material closely resembling 4CaO.Al2O3.13H20 (C4AH13) but retaining a constant 7.6 Angstrom basal spacing regardless of its state of wetness or dryness. It was found that under appropriate conditions the formation of CSH(I) resulted in as effective a cementation as did the formation of CSH (gel).
Gee, mixing lime with silicate sand forms hard materials… Same thing with clay.
This other paper is mostly looking at using minerals to clean water. But it does talk a lot about silicate chemistry. Of particular importance is that it shows the degree of longer chains of silicate increases with more alkaline pH.
It basically finds that many metal ions (in particular things like iron, aluminum, and arsenic) can be bound to silicate and that the tendency for this to happen increases at more alkaline pH. (Plus a whole lot more…)
So lets put some of this together…
We have reasonably well demonstrated silicate chemistry involving many different metal ions, with or without water and / or heat, making a variety of stone like materials. We have the Egyptians making at least two demonstrable products using these materials. We have a demonstration that with increasing alkalinity the silicate polymer is longer and the reaction rates are faster (sometimes much faster). We have the Egyptians making various ‘burned alkali’ materials.
Is it really THAT far a leap to think that there might be a ‘liquid stone’ formula that used more potassium and ended up with a silicate that was a CaK (silicate) or feldspar like material? Perhaps even just by using potassium hydroxide (as used in soap making…) as the alkaline agent? Or perhaps that the Peruvians knew something of similar technologies?
My instinct tells me ‘this fits’. That this is just Yet Another Ancient Technology we are rediscovering. I doubt if much work has been done on mixes of natron, lime, lye (even potassium lye), quartz sand, clay, and feldspars. With just that list and an “in / out” you have 2^7 combinations to try (minus a couple of obvious non-starters like ‘only one, others out’) and if you add in various proportions and various treatments of heating, drying, wetting… Rather rapidly there is a huge area to search. (I would suggest starting with micro crystalline structure of the ‘rocks’ in Peru and Egypt and looking at what the ‘cementing part’ is, and how it relates to the ‘stone grain’ parts).
We know that K, potassium, participates in such reactions and makes kinds of stones. Are we, perhaps, “going there” and don’t even realize it?
MATERIALS OF CONSTRUCTION
The Amazing Acid Resistance of Potassium Silicate Concrete
You may not even notice potassium silicate concrete’s most amazing performance feat. Properly mixed and applied, you won’t notice any sign of weakening after it is exposed to some of the strongest acids for days, weeks, or months on end. Unlike Portland Cement based concrete, potassium silicate based polymer concrete is resistant to immersion in all concentrations of nitric, hydrochloric, phosphoric acids, and sulfuric acids, including oleum. And with compressive strengths hovering around 4,000 psi, with appropriate design, it can be used for structural applications such as footings and foundations in acid-contaminated “brownfield” sites.
What makes potassium silicate concrete resistant to acid? Let’s first examine why Portland Cement based concrete is not resistant to acid. Portland Cement, the binder that holds the aggregate in concrete together is an alkaline material that reacts with acid. This reaction between the Portland Cement and acid conveniently neutralizes the dangerous acid, but at a considerable expense to the concrete’s structural integrity. Once weakened, the products of this neutralization reaction are susceptible to erosion, often leaving only the larger aggregate behind, remnants of the mighty concrete that once was.
Potassium silicate concrete is a polymer concrete, meaning it contains no Portland Cement binder. It relies on inorganic potassium silicate binder technology. Once cured, potassium silicate polymer concrete does not react with acid in a way that leaves the material weaker. Under certain conditions, potassium silicate concrete gains strength in the presence of acid.
Gee… “potassium silicate binder”… that sounds familiar… Now if we just make it Potassium Calcium Silicate, that is different from feldspar how?
One of the hardest stones around that, supposedly, needs diamond to cut it (though you can pound of bits) carved into a fine vase. Or, perhaps, cast? Might it even be possible that with alkali treatments the Egyptians made the surfaces of some stones softer and easier to carve, only hardening back to full strength after acid neutralizing?
Diorite has a lot of feldspar in it. What does that formula look like?
Well, there are several kinds:
“Feldspars (KAlSi3O8 – NaAlSi3O8 – CaAl2Si2O8) are a group of rock-forming tectosilicate minerals which make up as much as 60% of the Earth’s crust.”
The ‘key bits’ being soduium / potassium / or Calcium mixed with Aluminum in a silicate. So mix clay and quartz then add alkali? Just saying… if a thin layer of such a material were binding together larger bits of natural stone, would we even notice without microscopic examination?
No, I don’t know “the magic formula”. But it is pretty clear from all the kinds of ‘cements’ we are making today, that we are slowly expanding into the non-Portland Cement silicates. We’ve done this in just a few hundred years. The Egyptian Empires lasted 4,000+. I think they had time to work it out; and they were ‘working in that area’…