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Are Pyramids Made Out Of Concrete?

  1. Jan 11, 2008 #1
    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?
     
  2. jcsd
  3. Jan 11, 2008 #2

    russ_watters

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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.
     
  4. Jan 11, 2008 #3
    i think concrete cures by hydration which does not involve any CO2
     
  5. Jan 12, 2008 #4
    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 1450°C.
    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.
     
    Last edited: Jan 12, 2008
  6. Jan 15, 2008 #5

    chemisttree

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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.
     
  7. Jan 16, 2008 #6
    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 (1000°C instead of 1450°C).

    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?
     
    Last edited: Jan 16, 2008
  8. Jan 17, 2008 #7

    chemisttree

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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.

    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:
    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...
     
  9. Jan 17, 2008 #8
    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?
     
  10. Jan 17, 2008 #9

    chemisttree

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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.
     
    Last edited: Jan 17, 2008
  11. Jan 18, 2008 #10
    The question about the pyramid construction has been covered in this thread.
     
  12. Jan 18, 2008 #11

    chemisttree

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    I don't believe the chemistry and claims of Davidovits were well-covered in that thread.
     
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