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Eggs in cement making?

  1. Sep 15, 2012 #1
    I was watching the film "Fetih 1453" (http://www.imdb.com/title/tt1783232/), and there is a scene when the Ottomans are building the walls of a fort that they use eggs (looked like Ostrich eggs, which is ok, because Ostrich used to inhabit Asia Minor) in the mixture of a cement paste. Do you know anything about this? What is the propose?
    Thank you
    Regards
     
  2. jcsd
  3. Sep 15, 2012 #2

    chemisttree

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    Eggs, blood, animal fat, cactus extract and so forth have been used as an air entrainer and water-reducer with varying success. Air in mortar should optimally be as much as 20% which increases the volume of the mortar, improves freeze thaw resistance, prevents bleeding and increases workability while water reducers increase strength. I've heard much about the bonding and compressive strength increase for mortar that incorporate eggs or other animal products but keep in mind that 'strong' modern mortar is a fairly weak product. Middle-age mortar was lime based and weaker still. It needed to resist cracking at the slightest deformation. Type N mortars (Normal) minimally achieves a compressive strength of 750 psi and Type S (Special) is 1800 psi. The rock and bricks used with mortar are typically 5000 to 10000 psi and ancient brick was even weaker than that. The mortar needs to both concentrate the stress and resist cracking. Anything useful at hand that would increase strength and entrain air would certainly have been tried.

    The Chinese used sticky rice as well.
     
  4. Sep 15, 2012 #3
    Thank you for your answer.
    By air entrainer you mean to trap hair in pores? How does that work?
    By water-reducer, you mean to increase waterproof?
    Regards
     
  5. Sep 16, 2012 #4

    chemisttree

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    You add a substance that stabilizes tiny air bubbles formed when concrete or mortar is mixed. The bubbles must be tiny and persist throughout the cure. There are theories regarding exactly how they work which I won't discuss here since there are numerous online sources you can find but the gist of the matter is that air entrainers behave very similarly to surfactants.
    No, what I mean are substances that act to maintain plasticity at lower water/cement ratios. The general trend is that lower w/c ratios increase strength. Lower w/c ratios generally mean tighter intergranular bonding which lowers porosity thereby increasing water resistance somewhat.
     
  6. Sep 16, 2012 #5
    There was a time when hair was incorporated into plaster mixes, as distinct from cementitious ones.
    This added substantial anticracking properties and flexural strength to unmodified plaster.
    This was (and still is) also carried out with dried mud construction materials.

    Since concrete is inherently a stronger material than plaster, hair is not strong enough but a modern version has been to incorporate stronger fibres such as steel, glass or carbon.

    go well
     
  7. Sep 18, 2012 #6
    They may have been using the eggshells as an additional source for Calcium for the cement paste.

    Eggshells are rich in CaCO3, and some modern research is into using egg shell ash as an additive to increase concrete strength, and as an accelerator to speed curing.

    One pdf file outlines some research into using it for roadbed construction:
    http://www.ipublishing.co.in/jcandsevol1no12010/EIJCSE2008.pdf

    The Ottoman-era masons and engineers wouldn't have had the insights we have now into the chemistry (and physics) of concrete, but local tradition may have provided a reason for using eggshells in the cement powder.

    They may also have been more inclined to use eggshell powder as part of a mortar for tile work.

    ***

    I also discovered that egg whites can be used as a foaming agent in concrete work. Here's one blog discussing the use of egg whites to help make a lightweight floating concrete (for insulation purposes.) Or so the story goes....
    http://sugarmtnfarm.com/2007/09/06/float-my-concrete-boat/

    Add: So the egg-whites-as-foaming agent would have been used for air entrapment in concrete.
    The purpose of air entrapment is to help prevent frost/ freezing damage to the concrete.

    If this does work, it wouldn't be cost-effective. Not at the price I pay for eggs....
     
  8. Sep 18, 2012 #7
    Thank you for your answer
    the eggshells were not used...
     
  9. Sep 20, 2012 #8
    I found my Conrete Technology text book and while the authors don't mention eggs or egg shells, they do state that animal fats and 'organic compounds' are added to cement in order to either retard the set rate (slow the cure time down) and lengthen the time the mortar can be worked, and as an air-entrainment agent. Air entrainment helps prevent frost/ freezing damage. A retarder slows down the 'rate of hydration'. These are used to increase the working time on a pour, and in the case of large concrete projects, reduce the amount of heat generated by the hydration. In this last case, hydro dams need these additives because there is so much heat generated inside a large mass of concrete, the heat itself can damage the process of 1: the curing of the concrete and 2: cause too much expansion/ contraction and damage the reinforcement.
    Slowing down the setting time can help prevent what are known as "cold joints"- where part of the mass has set before the next pour has time to bond physically and chemically with the first pour.
    Cold joints can, and does, lead to cracking if stresses are applied to the concrete. And leaks: something you don't want in either hydro dams or house foundations.

    I'm guessing that eggs could be considered as both 'organic matter' and animal fats.

    An added bonus might be that the addition of these agents also helps the mix spread out a little better when worked with a trowel. That's desirable if you're laying down tilework.

    Sugar is also a retarding agent: if you want an exposed aggregate finish to, say, your sidewalks, you pour the concrete and screed it, then dust the top with sugar (brown sugar, according to my former employer.)
    After the un-sugared concrete has set (the time varies depending on the weather), you hose off the top of the sidewalk and have exposed pebbles and a less slippery finish. :-)
     
  10. Sep 20, 2012 #9

    Borek

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    Organic matter - yes, animal fat - around 10%, so not that much.
     
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