Forum Replies Created

Viewing 15 posts - 31 through 45 (of 244 total)
  • Author
    Posts
  • #23278
    Avatar of KatOnTri
    KatOnTri
    Participant

    Ellmer, floating-lagoon-house.jpg would look very pretty as Ocean’s shareware vacation houses behind the keys, but when a 5ft wave comes along all that carpet will get wet.
     
    I was using the forum search to try and locate the url for Home Depot fiber cement which i had mentioned. I was at the store yesterday to buy some of the fiber cement, but they don’t have it anymore. They have a fiber concrete, which i don’t see as a good idea for making floaties with walls under 2 inches thick. The gravel in concrete is great for compressive strength, but gravel will simply clog up the pour in such a narrow mold, and i am wanting tensile strength. Anyhow, this forum’s search didn’t find me mentioning the fiber cement at Home Depot. It did find someone else making floaties (round balls) of a particular cement from Home Depot, and the store quit carrying that cement. The search also found everything we have been saying the last 6 months has been said here 6 years earlier.
     
    So basically, what i have learned is: Adding portland makes the cement less porous, but it may shrink so much it cracks up in the mold (remove the mold asap?). Adding “mortar clay” will make the cement less porous, but no one sells it, and it may weaken the cement. Some cement advertised as “crack resistant” or “non-shrink” has reactive materials which create air bubbles, which is the same as saying “porous”. Glass fibers can be etched away by the alkalinity of the lime, so they must be coated the same as steel would be. Poly fibers stretch too much to be stable and permanent in salt water. If you can buy it today for a prototype, it will be unavailable after it has passed all tests you do on it. Marketting people will use different words for the same thing, or the same words for different things, and they will simply omit the important data, but they will say everything they sell is perfect for whatever you are doing.

    #23269
    Avatar of KatOnTri
    KatOnTri
    Participant

    You gave the url
    http://opensourceecology.org/wiki/Geopolymers
    which gives the url
    http://www.materials.drexel.edu/pyramids/GeopolymerWhitePaper-Barsoum.pdf
    which is 404. The correct url is:
    http://www.materials.drexel.edu/media/146620/geopolymerwhitepaper-barsoum.pdf
     
    This all reminds me of a silica solution i used once to repair a cracked windshield. Silica has a close index of refraction as glass, and the crack became invisible when the liquid set up.

    #23268
    Avatar of KatOnTri
    KatOnTri
    Participant

    Good stuff, Roger, thanks. I’d heard of manmade rock fibers (as in: not asbestos) used in various ways, but the energy input to make them seemed awefully high, is the situation different now? I had also heard of a liquid one could pour on sand that partially dissolved it, decades ago, before the internet, and when it “dried” could be used like a hard sandstone, and i had forgotten about it. I had heard someone had gone so far as set up a corporation to cast bricks from lava right at the volcano, but i have not heard of it in many years.

    #23258
    Avatar of KatOnTri
    KatOnTri
    Participant

    The SR520 highway floating bridge cross section drawing is at http://www.wsdot.wa.gov/NR/rdonlyres/993639C8-614E-4DD3-B8A1-B0926A8F9BF6/79646/PlannedBridge.jpg . Each pontoon is 360ft/110m long, 75ft/23m wide and 28ft/8.5m tall, and weigh 11,000 tons each. The standard anchor is 77 tons and deepest water under the bridge is 200ft/61m. And this bit of data: “Crews have repaired more than 30,000 linear feet of cracks since the 1993 Inaugural Day storm.”
     
    Any idea how they will attach the steel deck supports to the concrete pontoons?
     
    When i was pouring my house walls, i made a couple of stainless steel deck mounts, ~2 inches wide , 1/4 inch thick, and 7 inches long, with a hole drilled in each end. I set it in place as i was setting the rebar, with one stick of rebar thru one hole. The other end sticks out of the poured concrete for the deck to sit on and a bolt to pass thru the other hole. But i do not think this is the best way to attach to a cement boat hull, because wave motion will separate the steel from the cement where it enters the hull.

    #23255
    Avatar of KatOnTri
    KatOnTri
    Participant

    According to one report of stationary cement and concrete structures at the marine environment, the thickness of rebar cover wasn’t the problem with rust and subsequent spalling, it was the permeability of the material. It’s the same issue with paint. Apparently the porosity of cement mix is directly related to the portland content and type, and with paint it’s using a two-part epoxy type with zero outgassing (no outgassing = no bubbles and no pores). Since cement is a lot less flexable before the sand grains in it separate, it must be thicker over the rebar than paint, but the correct paint (and application) proves you need only fractions of a mm to protect the steel. For this reason, at least in the usa, coated rebar is required in some locations. To minimise movement in the concrete, rebar is often welded where it crosses over each other, and you cannot do that if it’s coated.
     
    What i mentioned yesterday about the cost of the cement used in making that boat on vimeo, the mix was very rich in portland (and they applied it pretty wet too, extra water = pores and voids), and portland isn’t cheap. The more portland in the mix, the less porous it is, the less cover needed over the rebar (and the vimeo boat used plain rod, not textured rebar!). But again, if the structure is stressed, especially if the rebar cannot be post tensioned, the cracks happen because the rebar will stretch and the cement won’t, and the cracks let in the salt. Adding glass or plastic fiber won’t help (much) because the portland will lose connection to those fibers as easily (or more easily) as to the steel. Sometimes things just simply do not work: after paving a portion of the interstate here with glass mixed in the concrete, they found the glass cut tiny bits from the car tires and made rubber marbles of it, causing accidents, so they had to grind up the road and re-pave it only a month later. A proper incubator for road innovations would have discovered this, and likewise we need one for seasteading.
     
    Another report was about the use of coated steel cables failing in a suspension bridge, the problem was two-fold: 1) the cables overlapping and cutting into the coating between them, and 2) the compression grippers used in post tensioning had teeth that cut thru the coating. Because of the #1 issue, the bridge was re-strung with the proper layup of tendons. For issue #2, the anchor block of steel with the grippers inside was flooded with 2-part as the tendons were tensioned, sealing each gripper and the puncture inside the added epoxy.

    #23253
    Avatar of KatOnTri
    KatOnTri
    Participant

    Kool, http://www.kgrawood.com/bb.htm is impressive. One of those first urls you gave looked rather sparse on the ferro part of the boat, not much rebar, and only chicken wire in lots of it. Maybe it was the lighting, but it looked fragile.
     
    Ellmer, i think that one boat had no fiber in it at all, i don’t have sound, but the print on the screen said sand and portland, didn’t say fiber, and the amount of portland it looks like they used, looks pricey. That boat needed better bracing under the seats, get two people to sit there next year after it’s rusted a bit, and the seat will collapse and pull the boat sides in. I’d have cast/plastered hollow cement seats, not those little tubes and a thin wood plank. Plus those tubes wriggling will let water into the chicken wire.
     
    Ocean, for my floaties, i hope to try deeper depths as life goes on. I will balance the floatie’s inside air pressure with the water pressure outside tho, so their depth is no concern. I am thinking of 2.5ft diameter and 5ft tall ferrocement cylinders, and standing upright. I figure they will support ~250lbs per foot they are displacing, use as many as needed. It may be a cheap way to make for a lot of floatation, and if it never cracks where it’s attached, will last forever. Ideally, they’d be horizontal like any other pontoon, but i cannot expect they’ll survive a lot of boat flexing if mounted in saddles like my steel pontoon boat, and i have not really solved that design problem.

    #23249
    Avatar of KatOnTri
    KatOnTri
    Participant

    Ocean, is chicken wire adequate to hold that size boat together if they beach it? It’s a nice looking lil boat in that video (steel prop tube!?), but shouldn’t there be heavier mesh, and some diagonal runs of real rebar too? That’s a work boat, it’s not a front porch for a houseboat, i expect much different stress levels there.
     
    Did you see http://www.youtube.com/watch?v=p0Ym1IkLTKM ? I need to get sound on a computer again. :-/
     
    I seem to remember an engineering paper on the ww2 cement boats, they used so much steel you couldn’t see thru it, before they put cement on it. Part of the reason for ocean-going cement boats at the time was to do with rebar being made of cheaper steel, rebar is easier to move around, wasn’t welded (welders were in short supply), and could be bent into the shape of a ship with no pricey tools. Remember, back then they were transitioning from rivetted boats to welding, it wasn’t real common. When ww2 opened, the usa was still using rivitted submarines even.

    #23245
    Avatar of KatOnTri
    KatOnTri
    Participant

    The deck, and it floating, and each piece of hull you add in not bouncing independantly like a seasnake.
     
    And i have my reasons for wanting a steel deck, at least on my first attempt at seasteading, and i already have the steel for a 16x30ft deck (and some of it is already welded together) and two 4x16ft all-steel freight barges, and i am not going to landfill the steel and it won’t sell for anything but scrap prices. The barges to haul building materials will look like people expect a boat to look, so less interference, but i want the seastead to be held up by cement floats. I have my design, my reasons, i am working on it, i plan to do it, and you can either keep telling me i am doing it all wrong, or you can be helpful.

    #23243
    Avatar of KatOnTri
    KatOnTri
    Participant

    I swear you get so dense sometimes, Ellmer. No one here can afford the first two pics, there’s no marina to launch or tie up anything like that anywhere in 100′s of miles, and i am not going to live on the the little 8x8ft bouncy thing in the 3rd picture. And i keep talking about launching small and growing, and to me the best way i can get a boat/barge built, carried to the ocean, and launched at the average marina with inteferrence is to make it look conventional in size and shape, and be easily growable after i push it to whereever the interferrence cannot see it. Frankly, i think it’s a fantastical that i am considering growing a personal seastead to 16x48ft/5x15m, but there is no way i can put anything that big in at one time, i cannot carry it, and there’s no place to launch it, or to park it. You want me to launch another Statfjord C base honeycomb, and you cannot launch a little submarine, or much of anything else? Hell, it would cost $millions just to build a new concrete plant where you want to build a new Statfjord C base honeycomb. You may as well show pictures of a base on Mars!
     
    And you changed the 2nd picture so it’s not a concrete honeycomb anymore. I’m not editing my reply about it.

    #23241
    Avatar of KatOnTri
    KatOnTri
    Participant

    There’s three of the longest floating concrete bridges in the world in the usa, one is being rebuilt now: http://www.wsdot.wa.gov/Projects/SR520Bridge/Gallery.htm . It’s not a one-piece construction.

    #23240
    Avatar of KatOnTri
    KatOnTri
    Participant

    Ellmer, by mentioning this link, i am not promoting it or advocating it, only saying it serves as illustration of a concept of a situation where i would be using cement instead of steel in the water:
     
    floating steel tubes
     
    In that company’s scheme, it’s all welded steel. A good way to attach the cement tubes to the steel platform is needed there, and i guess they have not discovered that way yet. This is also a situation it should be easy to add more beam or length to the steel deck, and “putting floaties like a barril under a deck”. Waiting until you can afford to build a single huge cast concrete honeycomb structure, or getting investors, will mean it never gets built. But someone can build a deck with a tube at each corner, and then grow the seastead as they build more floaties and more deck.
     
    I repeat, i am not planning on doing that plan, but it is a good showing of the reason to attach cement floaties to a deck or platform that someone is already living on.

    #23237
    Avatar of KatOnTri
    KatOnTri
    Participant

    Ellmer, i am not debating if it is ok to build floaties with cement. Over and over again i ask about how to attach the cement floaties i will make.

    #23235
    Avatar of KatOnTri
    KatOnTri
    Participant

    I did find where that photo was likely taken: http://phys.org/news3985.html or http://www.flexibleconcrete.co.nz/?page_id=127
     
    People familiar with it say it’s all about allowing microcracking, and hoping the polymer fibers pull the cracks closed again. The cement does not stretch at all, so the outer radius of a bend is full of microscopic cracks between the fibers and the cement. The greater the thickness of the material bent, the greater the damage to the outer radius. Typical uses are under 2in/6cm thick and placed on top of regular cement to keep it from flexing(!!), this is useless for trying to take advantage of the bendyness for a taller or thicker casting. I remember laughing about this stuff years before U-M (re)invented it, and now i know why there’s no mention of how to make it online. There’s no structural use for it, and latex mixes of cement last longer as coating material. It’s maybe possible to pour it around steel rebar, so the cement seems to stretch as much as steel does, but since it’s microcracking it’s only going to let the ocean salt in to the steel.
     
    Unless you have some contradictory information, Ellmer?

    #23234
    Avatar of KatOnTri
    KatOnTri
    Participant

    Ok, i do not see anywhere online how to mix cement to get that amount of bending.

    #23230
    Avatar of KatOnTri
    KatOnTri
    Participant

    I have asked several times about how to attach small cement bouyant structures (i call them “floaties”) to another structure. The floatie someone can bring to the water in their pickup truck, or lawnmower trailer, has a much higher chance of being used than a single piece 30ft anything. But even regardless of the vessel’s LOA, it’s going to flex in the water, and cement and concrete are known for being the least flexable material for building with, and having poor tensile strength. So if i wanted to replace a set of cylindrical steel pontoons with cement ones, to prove the cement is a better choice in that application, what is the best way to accomplish the replacement, such that the boat deck flexing (or not flexing) won’t stress the cement pontoons and crack them?
     
    The only way i can see to do this with one long hull is many self-leveling hydraulics like house movers use, to keep an apparent non-flexing interface spread out over the pontoon, but with a much larger range of motion. That will become an maintenance issue very soon.
     
    So has anyone actually done this?

Viewing 15 posts - 31 through 45 (of 244 total)