Roman concrete secret and cement-based marine structures

Discussion in 'Materials' started by Namu, Jul 23, 2017.

  1. Namu
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    Namu New Member

    Hello everyone, I'd love to hear your opinions on this recent discovery by Utah University researchers: How seawater strengthens ancient Roman concrete | UNews https://unews.utah.edu/roman-concrete/

    Basically, they think they figured out the secret of Ancient Roman concrete's durability in the face of thousands of years of exposure to sea water. It turns out that the use of specific volcanic ash in the cement mix allows for a porous structure that grows interlocking tobermorite (a very unusual mineral) crystals inside of its pores, from elements present in the sea water. Basically, Ancient Roman concrete accretes more and more minerals over time simply by being exposed to (alkaline) sea water, reinforcing it over time instead of corroding it away. Though it has a lower compressive strength that might have interesting uses in ferrocement builds ?
     
  2. Nick.K
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    Nick.K Senior Member

    Welcome. That's interesting, thanks.
    I don't know much about ferrocement but looking at older ferro boats, I think the useful life is probably more limited by build, maintenance and equipment issues than breakdown of the hull material. If it is well built, ferro seems to last a long time.
     
  3. Rumars
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    Rumars Senior Member

    No it won't work. Even if they rediscover the recipie in the near future (and it might take years) the steel armature would rust away from the salt. Even if you swich to textile armatures (glass or carbon fibre) the structure would still be permeable to salt water (not exactly what you want in a boat) and you would not be able to paint it (since paint would seal the water out and you don't have the desired effect).
    If you want a better ferro boat all you can do now is use textile armatures. But you can build a better boat using plastic resins with them.
     
  4. Nick.K
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    Nick.K Senior Member

    I've read about different types of fibres being added to cement to strengthen it but I have never heard of a textile armature. Is this an invention or can you point to a "better" boat built this way?
     
  5. Mr Efficiency
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    Mr Efficiency Senior Member

    I doubt there are too many good, cheap fibres to add to a concrete mix, when asbestos was banned, the best they came up with was celluose fibres, and that is no good exposed to water.
     
  6. Rumars
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    Rumars Senior Member

    This is a new developement, in Germany research begun 20 years ago, research is also ongoing in other countries. We are not talking here about adding shreded fibres to concrete, this has been done for a long time. The traditional steel mesh armature is replaced with a mesh made out of alkali resistant glass fibre or carbon fibre. This mesh is stiched on a machine like unidirectional glass, or stiched to a disolving substrate out of AR-glass or carbon tow. The mesh is engineered for the job, fiber orientation and quantity can be custom, 3D meshes are possible. The coatings applied to the tow impact the final product. This is paired with fine granulation concrete mixtures of different densities (usually light mixtures containing slag ashes and microspheres). Right now in Germany textile reinforced concrete has general aprovement for non load bearing applications. Load bearing applications are still subject to special approvement. Mainly they build bridges with it.
    Because glass and carbon don't rust there is no need to have the minimum thickness for corrosion resistance and the resulting structures can be engineered on strenght basis alone. This results in major weight reduction even with standard concrete mixtures.
    Boats are routinely buildt this way for the concrete canoes challanges. Remember the concrete submarine thread? Well is has been done nd it surfaced again.
    I only have links in german. Here a video about stiching the mesh, it is part of a series about textile reinforced concrete.

     
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  7. Nick.K
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    Nick.K Senior Member

    How is the cement applied to the textile? Presumably some type of mould is necessary since the textile is not rigid enough to stand alone or 'plaster' in the normal way. Have any boats larger than concrete canoes been built with this method?
    I agree, in most normal circumstances it seems to make little sense to build using cement but I have a friend now nearly 80 who spent his youth building ferro boats including several years building boats for communities in Africa where there was no access or budget for normal boat building materials. Cement and steel mesh were obtainable and with these basic materials they were able to create robust boats for fishing and trade. The mechanics were recycled vehicle engines.
     
  8. Rumars
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    Rumars Senior Member

    A mould is indeed needed. Application is manual, blasted or poured. I am not aware of any really big boats buildt or under developement with this technique. The sub was a small 2 person affair with pedal drive. The biggest boat I know of is a 12m one, it is buildt out of segments with carbon fibre armature. You can see it in this video
     
  9. Nick.K
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    Nick.K Senior Member

    Interesting developments. Unfortunately I don't speak German.
    What are the advantages? Is fibre-cement mechanically equivalent to fibre-resin (I doubt it!) I guess this is a material that could find uses in static floating structures (pontoon floats for example) or maybe some kinds of working boats where it may have advantages of fire resistance and economy of maintenance.
     
  10. Mr Efficiency
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    Mr Efficiency Senior Member

    What is the relative performance of galv steel mesh ?
     
  11. TANSL
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    TANSL Senior Member

    Interesting "material". I guess they will have to experiment to know their most effective applications and that, for now, there are some unresolved issues. It occurs to me to ask how it will be possible to repair a damaged hull to get the adequate resistance in the old zone/new zone interface.
     
  12. Rumars
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    Rumars Senior Member

    Textile concrete (not fibre-cement, that‘s the one with short fibers aded like in the old asbestos roofing plates, now chopped glass fibres or steel is used) is not a material developed for boats. The concrete canoe challange is just a technical demonstrator for students. The material is intended to replace normal concrete construction where lightness and corrosion resistance matters. Mainly bridges and tall buildings. The concrete mixtures used can go down to under the water density, basicly it floats. But any boat constructed like this would still have all the disadvantages of normal ferrocement construction. It would only be lighter and more expensive.

    Repairs would be done as is normal now, with epoxy primers at the interference.
     
  13. rwatson
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    rwatson Senior Member


    It has ??? Cant find it on Google. Can you post the links ?
     
  14. Rumars
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    Rumars Senior Member


  15. dinoa
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    dinoa Senior Member

    Thr volcanic ash the Romans used is called pozzolana or pumice. It is used in modern Portland cements up to 3% as an inexpensive filler in areas like Greece where pumice costs less than cement clinker. The pumice is mostly mined in Giali between Nisyros and Kos as well as Santorini. Southern Italy also has readily available pozzolana.
     
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