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Are Pyramids Made Out Of Concrete?

by lalbatros
Tags: concrete, pyramids
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lalbatros
#1
Jan11-08, 06:25 AM
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Are Pyramids Made Out Of Concrete, as Joseph Davidovits claimed?

This page on wikipedia:

http://en.wikipedia.org/wiki/Joseph_Davidovits

presents a short bio of Davidovits and his theory about how pyramids were built.

According to this theory, the ancient Egyptians would have used a kind of concrete instead of carving huge blocks of stone.
For our modern times, this might still be an very attractive technology since the current cement industry generates huge quantities of CO2 in the athmosphere while it seems that the ancient Egyptians technology requires no fuels and needs no decarbonation of limestone.

But is this theory reliable?
And how would it be possible to produce such concrete on a large scale?
And what are the basic principles finally?
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russ_watters
#2
Jan11-08, 04:41 PM
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It's certainly possible from an engineering perspective, but I'm not an archeologist...

One thing though, I didn't see anything in the link to suggest that it wouldn't still produce CO2. It says in the link that it undergoes a curing process similar to that of concrete.
scupydog
#3
Jan11-08, 05:48 PM
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i think concrete cures by hydration which does not involve any CO2

lalbatros
#4
Jan12-08, 02:58 AM
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Are Pyramids Made Out Of Concrete?

scupydog ,

Concrete contains typically 200 kg of cement per cubic meter.
Cement is mainly made from decarbonated limestone that has reacted with some silica, a product named 'clinker' produced at 1450C.
Including the fuels for burning clinker and CO2 from decarbonation, the production of cement emits roughly speaking 1 ton of CO2 in the atmosphere per ton of cement. (actually something between 0.5 and 1.5 depending on alternative materials used and on the actual process used).

This explain why the cement industry is one of the largest CO2 producer.
I thing these days, the world cement production should be close to 3,000,000,000 tons per year.

That's the reason why measures to reduce CO2 emission for cement production is an interresting subject. Cement producers are doing a good job by using alternative raw materials (like blast furnace slag) and alternative fuels (increasingly biomass). They also improved their overall energy efficiency.

However, considering the total need of cement in the world, it is hard to believe that it could be replaced by something else.

A clearer view on Davidovits claims is my aim here.
chemisttree
#5
Jan15-08, 10:37 AM
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Yes, Davidovits' cement works. It works slower than standard concrete and usually requires some heating to achieve results. Standard concrete gives off heat when it cures but the geopolymer that Davidovits developed has a low exotherm. When GGBFS (Ground Granulated Blast Furnace Slag) is used, the early strength when cured at room temperature moves into the useful range, requiring only 15 hours for an ambient green cure and 1/2 hour at temperatures approaching 100C. Obviously, high temperature cure is only available for special processes and slow 15 hour cures have problems of their own related to drying shrinkage, mud cracking, delayed finishing time, etc...

Regarding the claims that no CO2 is produced.... You should understand that blast furnace slag is a byproduct of steel manufacture where limestone is added to the melt to complex with silicates and thereby purify the iron from that impurity. The limestone used in that process is no different than that used during the production of portland cement and does in fact produce substantial CO2 emissions. A fact conveniently overlooked by Davidovits and the Geopolymer Institute.
lalbatros
#6
Jan16-08, 12:57 AM
P: 1,235
chemisttree,

I know that GGBFS has produced CO2 in the blast furnace.
But using GGBFS reduces the CO2 emissions by subtitution of clinker.
If slag is used for other purpose, more CO2 is produced for clinker production.
The overall emissions from cement industry + steel industry is reduced by using slag in cements.

However GGBFS is not exactly the same as clinker since it contains mainly belite ((CaO)2.SiO2) as hydraulic component while clinker contains mainly alite ((CaO)3.SiO2). That's why it is best used in combination with clinker. Note however that one research track for reducing CO2 emissions from cement manufacturing is pushing on the belite side instead of alite. This is because belite contains less limestone than alite and can also be produced at lower temperatures (1000C instead of 1450C).

Concerning Davidovits concrete, I asked here about it because I was running out of patience when reading his web site and his litterature. It looks like kind of advertising and I could not find a clear summary that would allow me to make up my mind. In other words: I was frustrated by a mixture of show and hide of information.

For example, I would like to know how much of these geopolymers could reasonnably be produced on earth every year. Could they replace the traditional cements? What would be the production cost? What are the recipes and the raw materials and fuels consumptions? What would be their impact on the building industry. But first of all, is that even worth considering at all?
chemisttree
#7
Jan17-08, 12:01 PM
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Most GGBFS finds a use as an admixture in regular portland-based concretes. I don't know if any of it is being landfilled. I do understand the rationale regarding the differences between alite and belite. In my hands, the geopolymer based on 'calcined' clays cures only very slowly, but it does cure. It is almost useless for most concrete work but does find some specialty applications. He uses fairly large amounts of either sodium or potassium hydroxide (which produce CO2 emissions in their manufacture) to activate whatever pozzolan he is using. You might want to review his patent portfolio (as I have done) to get an idea of its usefulness.

Here is one example of one of his older formulations from Patent #4,349,386.

We prepared 317 grams of a reactant mixture containing 8.1 moles water, 0.47 moles sodium oxide, 1.65 moles of silicon dioxide, and 0.41 moles of aluminum trioxide. The source of aluminum trioxide is the alumino-silicate oxide prepared by dehydroxylating a natural polyhydoxy-alumino-silicate (Si.sub.2 O.sub.5,Al.sub.2 (OH).sub.4).sub.n. The source of silicon dioxide is this alumino-silicate oxide and an alkali silicate. The source of sodium oxide is sodium hydroxide. The oxide molar ratios in the reactant mixture are shown in Table D.

edit: Table removed by Chemisttree for clarity

The reactant mixture, which had the viscosity of a resin, was aged for a period of one hour at ambient temperature, then placed under vacuum to eliminate air and gas bubbles. The outgassed resin was poured into a urethane mold to reproduce the relief of a medal.

The surface of the resin in contact with the atmosphere was covered with a thin polyethylene film to prevent water evaporation during curing, which was effected at 85.degree. C., in an oven over a period of 1.5 hours.

The hardened mineral product was separated from the mold and dried at 85.degree. C. It reproduced the mold surface with all original details of the mold surface intact. The density of the product was 1.4 grams per milliliter, and its hardness was 3-4 (Mohs scale). The product was white and porous, and its external dimensions indicated that the polycondensation took place without any shrinkage or dilation of the material. Chemical analysis of the mineral product gave this molar composition:

which corresponds to the formula of (Na)PSS ##STR3## which has an x-ray diffraction pattern essentially that shown in Table A.

Materials from which the mold may be made include iron, paper, wood and plastics, indeed all materials except aluminum and copper. Even aluminum and copper molds can be used if they are covered with a thin layer of organic resin.
In this example he uses fume silica as the source of silicon dioxide and metakaolin (calcined or 'dehydroxylated' kaolin clay) as his source of reactive alumina. The synthesis is a solid phase version of a typical Zeolite A synthesis wherein kaolin green bodies are heated under strongly alkaline (NaOH) conditions to produce the zeolite with essentially 100% yields. His solid phase approach apparently avoids the recrystallization step (leading to crystalline zeolites) by producing high molecular weight polymers which are sterically disallowed to reorganize into their thermodynamically favorable crystalline cousins.

All that said, he uses very expensive ingredients like fume silica and strong bases to achieve reasonable reaction rates in this example, if 85C for 1.5 hours can be considered reasonable. His other patents use some form of reactive silica (slag or fly ash, for example) to achieve this reactivity. His latest patent using blast furnace slag uses the following in Example 1:
calcined kaolinitic clay 30 parts aluminosilicate oxide (Si.sub.2O.sub.5, Al.sub.2O.sub.2)
K silicate solution, 25 parts (by weight) K.sub.2O: 26%, SiO.sub.2: 21%, H.sub.2O: 53% blast furnace slag (calcium mellilite) 27 parts average grain size 8 microns water 31 parts
Potassium silicate solution at this high concentration is extremely expensive. It will never replace normal portland-based concrete and incurs a substantial amount of CO2 emission in its manufacture yet he claims that no CO2 is emitted. Of course he uses substantial amounts (30% by weight) of calcined kaolinite (metakaolin). This stuff is calcined at 650 to 950 C for several hours, no doubt with fuel that emits copious amounts of CO2. The curing schedule for this latest formula includes heating at 85 C for over an hour as well.

I don't think it will catch on as a replacement for portland-based concrete anytime soon...
lalbatros
#8
Jan17-08, 02:36 PM
P: 1,235
Thanks a lot Chemisttree for your analysis.
I found it difficult to evaluate the information made available on the web.

If you had comments about Pyrament I would also be quite interrested.
I would mostly like to understand why this product is advertised in the same context as geopolymer, and where is the innovation.

And more generally, about geopolymers: promise or hype?
chemisttree
#9
Jan17-08, 03:29 PM
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I believe that this patent describes the product known as Pyrament, but I'm not sure. The chemistries are all related of course. Alkali activation of slag is known (I believe there is an ASTM procedure for it) and in combination with the metakaolin would give you Davidovits' geopolymer.

The type of slag might be important to the product as well. The chemical analysis of the slag shows it contains a whopping 41.4% CaO content which is about 10% higher than high quality Class C Fly Ash. This is the reason for the fast set with this product. Fly ash could be substituted but would be less reactive unless formulated with citric acid.
Andre
#10
Jan18-08, 08:13 AM
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The question about the pyramid construction has been covered in this thread.
chemisttree
#11
Jan18-08, 03:29 PM
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I don't believe the chemistry and claims of Davidovits were well-covered in that thread.


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