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. rwatson
    Joined: Aug 2007
    Posts: 5,852
    Likes: 290, Points: 83, Legacy Rep: 1749
    Location: Tasmania,Australia

    rwatson Senior Member

  2. Mr Efficiency
    Joined: Oct 2010
    Posts: 8,559
    Likes: 502, Points: 113, Legacy Rep: 702
    Location: Australia

    Mr Efficiency Senior Member

    This may, or may not, be irrelevant to discussion about concrete strength, but can anything pertinent to the matter, be learned from eggshells ? These are mainly composed of calcium carbonate, but also a protein matrix. We are all familiar with the strength of a typical hen's egg, but I was shocked when a keeper of laying hens demonstrated the much greater integrity of eggshells laid by hens fed a goodly amount of a small bait fish, (Atherinomorus lacunosus),as part of the diet. That demo consisted of him throwing some eggs down a bitumen road, where they just bounced along like golf balls, after attaining a height of at least 20 feet. Amazing. And the eggs, once you managed to break them, were superb eating! I never noticed the shells being excessively thick, but never measured them either. And I should add, the surface of that road was not smooth like asphalt, it was a rough surface that would be painful to bare feet.
     
  3. rwatson
    Joined: Aug 2007
    Posts: 5,852
    Likes: 290, Points: 83, Legacy Rep: 1749
    Location: Tasmania,Australia

    rwatson Senior Member

    Mr E, I think you have hit the nail on the head.
    Take it a bit further, and consider the performance of a seashell - even stronger.

    I picture this big stone Mold shaped as a boat hull, filled with an artificially bred mollusc body, that secretes a calcium shell over several months on the inside of the Mold.

    Now, THAT would be the ultimate concrete hull.
     
    Nate57 likes this.
  4. dsigned
    Joined: Aug 2017
    Posts: 179
    Likes: 12, Points: 18
    Location: United States

    dsigned O.R.C. Hunter

  5. dsigned
    Joined: Aug 2017
    Posts: 179
    Likes: 12, Points: 18
    Location: United States

    dsigned O.R.C. Hunter

    They use a fiberglass formulation that does not react with portland cement. As far as I can tell, one should not use regular fiberglass, but that which is specifically non-reactive.
     
  6. dsigned
    Joined: Aug 2017
    Posts: 179
    Likes: 12, Points: 18
    Location: United States

    dsigned O.R.C. Hunter

    There are a couple of different "types" of concrete, but generally speaking, concrete is different than the other materials you mentioned in that it has inherently high compressive strength, and low tensile and flexural strength. By adding rebar (in the case of "normal" concrete), we add tensile strength to the material, which is what allows for the large bridge spans that use concrete. In the case of UHPC, the rebar is replaced by steel fibers, and in GFRC, it is replaced by fiberglass (usually fiberglass bar or scrim). I would be interested to see what the actual forces experienced by boat hulls are, but I expect that in all but very round boats, there is a bit of flexural stress, which would require the tensile reinforcement. That being said, treating concrete as you say, with stringers, ribs, etc. is very possible, but the question is whether or not it would be lighter for the same strength. I think in theory, it would be, but the ribs, etc. would likely need to be spaced differently and be of different sizes (I'm guessing smaller).

    But that raises another question of what's the minimum thickness that one can control concrete quality? I know that professional pours have gotten really thin with UHPC, but I doubt that even a reasonably skilled homebuilder would be able to replicate it. Maybe a small manufacturer though. I think some of the more impressive structures have been accomplished by relatively small companies. I'd have to double check that though.
     
  7. upchurchmr
    Joined: Feb 2011
    Posts: 2,996
    Likes: 138, Points: 63, Legacy Rep: 579
    Location: Ft. Worth, Tx, USA

    upchurchmr Senior Member

    Build it. Lets see.
     
  8. dsigned
    Joined: Aug 2017
    Posts: 179
    Likes: 12, Points: 18
    Location: United States

    dsigned O.R.C. Hunter

    Lol. That's not too far off. But the data I can find indicates that UHPC concrete is actually stronger than seashells. I definitely like the idea of new kinds of bonds to add to concrete, as well as new application types (e.g. large scale 3-d printing).
     
  9. dsigned
    Joined: Aug 2017
    Posts: 179
    Likes: 12, Points: 18
    Location: United States

    dsigned O.R.C. Hunter

    I actually wasnt planning on building anything for a while, if ever. It was more just an interesting intellectual exercise. And I have several other projects, and the last thing I want is another half finished project, so if I start it, I'm going too have to do the rigging, etc. because I totally get not wanting a giant concrete anything sitting in your garage/backyard etc (garage for me).

    But I have the polystyrene, some super plasticizer, and I looked at the price of Portland cement the other day at Lowe's: super cheap. So so I need is some reactive powder, some basalt scrim, and chopped fiber, microspheres (maybe) and fly ash. It's a pretty cheap experiment, even if it fails miserably.
     
  10. rwatson
    Joined: Aug 2007
    Posts: 5,852
    Likes: 290, Points: 83, Legacy Rep: 1749
    Location: Tasmania,Australia

    rwatson Senior Member

    So, it IS another all talk, no result thread. No wonder anything with CONCRETE in the title is such a big letdown.
    I did predict this.
     
  11. rberrey
    Joined: Oct 2010
    Posts: 443
    Likes: 19, Points: 18, Legacy Rep: 112
    Location: AL gulf coast

    rberrey Senior Member

    If you're going to ply with it don't go to Lowes . Call a batch plant near you and see if they have some hign silica cement , tell them what you're doing , and how much portland you need, they might also give you some sample products to use in your test mixes. Get some small test cylinders, make three small batches of each mix design, make a cyclinder from each batch , and a 3/4 " flat slab , the batch plant will have access to a gun you can test them with on the cheap .
     
    dsigned likes this.
  12. dsigned
    Joined: Aug 2017
    Posts: 179
    Likes: 12, Points: 18
    Location: United States

    dsigned O.R.C. Hunter

    We'll see. Time is a limiting factor (oh, to be retired), so going to Lowe's may have to do for the dinghy, but for a bigger boat, I think you're right about sourcing the best stuff I can. That said, I think doing something that reproducible by the Everyman is also important: the more obscure ingredients the harder to replicate the (hopefully good) results.
     
  13. dsigned
    Joined: Aug 2017
    Posts: 179
    Likes: 12, Points: 18
    Location: United States

    dsigned O.R.C. Hunter

    Wow, you predicted the thing I said in the first post? You must be psychic.

    As for the lack of results: that can't have anything to do with the cacophony of *******s who provide no useful feedback and tons of seat of the pants (and factually erroneous) criticism?

    But you also seem to be seriously reading disabled: I'm saying that I'm changing my mind, as in I started the thread as an academic exercise, and have changed my mind and am thinking I'll actually build something.
     
  14. rwatson
    Joined: Aug 2007
    Posts: 5,852
    Likes: 290, Points: 83, Legacy Rep: 1749
    Location: Tasmania,Australia

    rwatson Senior Member

    No, I predicted it after a couple of pages of your telling us how good your ideas were, that nothing would happen. You said you might get a test panel done then.

    "cacaphony of ****s" ???? that's so funny. YOU are the promoter, the brains behind the project - now its "OUR" fault ??? :)
    I saw a whole lot of useful contributions myself, including contributions from an actual engineer or two, but you must have missed them


    Oh, NOW you are seriously thinking about building, I'm reading disabled ??
    Your first post
    "Ok, but in all seriousness, I'm considering doing a relatively small scale build (16 or 17 ft, because that's the length of my garage) catamaran. I'll try and do something resembling a fat Nacra 4.5, and stick an appropriately sized rig for the righting moment on it (or the rig I can find that's complete and cheap). It probably won't be before this summer (I have a half-finished basement and three little monkeys)"


    Now, lets see what my prediction was
    "Call me cynical, but appears that of all the "concrete revelation" threads that pop up over the years, the proposers spend a lot of time saying how great the idea, how easy, how cheap and argue the point with experienced boatbuilders ...... Then nothing happens."

    Yup, I think I picked it.
     

  15. Mr Efficiency
    Joined: Oct 2010
    Posts: 8,559
    Likes: 502, Points: 113, Legacy Rep: 702
    Location: Australia

    Mr Efficiency Senior Member

    Flat test panels would be a good start, before worrying about boat hulls.
     
Loading...
Forum posts represent the experience, opinion, and view of individual users. Boat Design Net does not necessarily endorse nor share the view of each individual post.
When making potentially dangerous or financial decisions, always employ and consult appropriate professionals. Your circumstances or experience may be different.