Ok everyone, it's that time of the year again: time to talk about concrete

Discussion in 'Materials' started by dsigned, Sep 21, 2017.

  1. PAR
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    PAR Yacht Designer/Builder

    Carbon and concrete, now there's an oxymoron . . .
     
  2. rwatson
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    rwatson Senior Member

    A bit of oversimplification here. What say you add in all the steel used in typical ferro builds, multiple layers of mesh with welded steel rod supports.

    Also, "potentially don't save is in time" is a real understatement too. As someone who has helped put all those twists that tie the layers of mesh together, after spending weeks rolling out the mesh on the steel armature, tightening it, making it fair etc. I can assure you that there is no comparison with epoxying and/or screwing plywood to frames. Also add the 12 hours of 6 man operation to do a continuous cement plaster to say a 40ft hull. Compare that to wetting out fibreglass on a 40ft wood hull, that can be done by one or two people over a week, for about 1/3 of the cost of those 6 man days.
     
  3. Wckoek
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    Wckoek Junior Member

    I suspect the rust free basalt armature which I would use if I were to build today would cost even more than steel rods in the past too.
    And I heard that ferrocement is a nightmare to drill, also low abrasion resistance and many got holed once hit on something (but there are claims that ferrocement are strong too, it all depends on the reinforcement from armature I believe)

    Nonetheless it have a reputation of easy maintenance, antifouling possible, round shapes possible, no corrosion (if steel armature wasn't used).
    I don't know of any yard who still know how to build in ferrocement.
     
  4. alan craig
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    alan craig Senior Member

  5. rberrey
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    rberrey Senior Member

    I am not sure why carbon and concrete would be an oxymoran , may be Par can explain . When a # 8 pc of rebar was left out of a footer beam , the Structural Engineer had a carbon tape added to the top of the footer to compensate for the #8 rebar . If carbon tape can replace a 50' long #8 rebar , then surely it could be used for a stringer . I think a Structural Engineer with a lot of concrete structural design experience , and a NA could sit down and come up with method and means for a concrete boat . I would like to understand why carbon fiber would not be a good fit for concrete boat construction when we combine them in buildings today .
     
  6. rberrey
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    rberrey Senior Member

    My question to the NA,s here is not would you build a boat from concrete , because I wouldn't . My question is if you had to build a boat using concrete today , what material,s would you use , and how could the boat be designed better than cement boats of the past ?
     
  7. Wckoek
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    Wckoek Junior Member

    Looking at a rusting large Buehler trawler on the market up for auction with no asking, think about it I would say I might if given there is available yard with experience and man power for reasonable cost (there is nothing cheap in boat building).
    It just strike me as the least maintainence needed compared to hull made of wood, steel, aluminum.
    They used to build alot of ferro boats in China, when the fuel crisis hits in the late 70's, it spell ends to the boom, some are still left and used by the homeless in Yancheng 40 years later, a testament to their longevity.

    You can insulate concrete effectively, affordably and easily today with insulating foils between layer of concrete, technology not available back then.
    No more rust on the steel reinforcement armature by replacing them with basalt rods.
    Also increase abrasion resistance with added basalt or steel fibers.

    Weight is still a problem regardless and I wouldn't consider a sailboat to be build out of cement but maybe for the heavy trawler or motorsailer type.
    Still is the noise and motion comfort.

    The argument by dsigned for a minimum viable product is compelling especially when upkeep and maintenance of boats became more expensive, and you are scrwd anyway when you have to sell your boat used regardless it is made of steel, aluminum or wood.
     
  8. Wckoek
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    Wckoek Junior Member

    Finding people who can build in ferrocement today is tough enough.
    I talk to the only one I knew in Jiangsu who build concrete boats for 3 generations, he was so jaded that he wasn't interested to listen to building an actual boat in cement.

    The building cost and labour is low enough 1,000 CNY or $150 per tonne in barge or platforms, but he keep remarked that cement boats are at its end, there is no future and future market, and he was the last of his generation of his trade, and wasn't interested in building one or even listening to it unless its a barge or platform regardless of price.
     
    Last edited: Oct 27, 2017
  9. rwatson
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    rwatson Senior Member

    This is worth checking out - thin concrete walls with Basalt reinforcing.

    I think this looks like a possible solution..
     
  10. Mr Efficiency
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    Mr Efficiency Senior Member

    The basalt mesh looked pretty stiff, which makes me wonder how easy to work with, is it ?
     
  11. rwatson
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    rwatson Senior Member

    So, use the cloth. Its used for roads, yachts, surfboards and wind turbines
     
  12. Mr Efficiency
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    Mr Efficiency Senior Member

    So there is hope for ferro boats ? Is basalt attractive price-wise ?
     
  13. rwatson
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    rwatson Senior Member

    The price depends on the type and size of weave. Its really hard to call up competitive quotes in Australia, but in Surfboard suppliers, it seems to be about double of S Glass in small quantities.
     
  14. dsigned
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    dsigned O.R.C. Hunter

    UPDATE: Materials for test panels "purchased."
    [Free] 1 bag of concrete countertop mix (ripped = free)
    [$11] bag fiberglass chopped fiber
    [Free] Azure water based stain

    Still needed, white pozzolon powder. Unfortunately, I don't think the place I got the other stuff from has white pozzolon powder, only gray.
    https://photos.app.goo.gl/4yyf9PocxHjgpO6S2
     

    Attached Files:


  15. rwatson
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    rwatson Senior Member

    Never heard of white Pozzolan.

    I would have used long strands of fiberglass. Chopped Fiber will be a bit haphazard not nearly as useful.

    Coarse mesh would be the best.
     
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