Floating Concrete Shell and Honeycomb Structures
March 26, 2014 at 5:56 pm #23246
You are doing it all wrong Just messing w/you You can build your floaties in ferrocement.March 26, 2014 at 6:14 pm #23247March 26, 2014 at 6:27 pm #23248
I like the last one. Heavy duty, no thrills, no rocket science, will last “forever”. Don’t even have to paint it… Just hop on and goMarch 26, 2014 at 6:45 pm #23249
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.March 26, 2014 at 8:26 pm #23250
I would be a bit concerned about voids, rebar rusting and adequate steel embedding in that process…honestly i have seen smarter ways to build shells, especially to “introduce the fiber component” into the build. Would consider this close to “worst case scenario” for producing a rusting rebar desaster in a marine splash zone ambient.
http://vimeo.com/50990903March 26, 2014 at 8:35 pm #23251
I guess for that size boat is good enough. For ocean going boats the armature is much stronger and they use multiple layers of chicken wire.
What different stress levels?…LOL, aren’t we talking about “floaties”? I mean, where (or how far) offshore are you gonna take them? How big are they anyway, if I might ask?March 26, 2014 at 9:03 pm #23252
Yes, the ferrocements boats got a bad rap because of some really lousy “backyard” built ones. But 2 companies got it right in the 70′s and their boats quality is outstanding, most of them still cruising as we speak. Samson Marine of Costa Mesa CA, and Hartley of Auckland New Zealand.March 26, 2014 at 9:40 pm #23253
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.March 27, 2014 at 8:40 am #23254
The rebar i see in those videos is supposed (and designed) to be the “fiber component” of a 20cm strong structural concrete wall and have a concrete cover of at least 3cm (according to european concrete engineering norms) to “avoid its rusting” – so to make it part of a 2cm wall and leave it under merely 1mm concrete cover and complicate the proper embedding of the steel by “littering the place” with chicken wire that hinders as proper void free embedding of the fiber component into the cement matrik additionaly, is a “clumpsy and unwise use of the fiber component” at best. In fact it is “utmost surprising” that there are shells that where built with that kind of method that do NOT rust and fall apart in a decade. That talks good of the “craftiness” of their builders in the sense that they got relative good embedding in spite of the chicken wire hindering them. If i would have the task to figure out a method to produce “short lasting shells” i would really choose something like that…a good shell will last 200 years for sure and probably 2000 years (as the Panteon) without showing minor signs of decay – so the fact that a few “ferrocement shells” last a couple of decades does not say a lot either. When talking about seasteading we need foundations that last centuries or millenia in marine ambient – i doubt that methods like shown in the videos and pictures are up to that task.
I would suggest to look into the following:
1) do not use steel rebar if you can not assure a proper embedding depth of 3cm.
2) forget the clumpsy chicken wire.
3) find a better method to hold the wet matrix material in place while curing than chicken wire.
4) explore non rusting fiber components where the required cover of 3cm can not be achived.
5) keep steel reinforcements out of the “spashzone” where corrosion is expected to be worst.
Basicly ferrocement is only on the table because it was the “first idea” of Joseph Monier to introduce some kind of fiber into a cement matrix and get a composite material out of it.
Like always the “first idea” almost never is the “best idea” the better ideas come if you give it a second third, and fifth tought – that include feasible solutions to the above list of issues. Just forget “ferrocement” and think about smarter fiber components and smarter fillers and smarter aplication methods, do a series of tests find the better way. With space age fiber components and understanding of shell structures at hand we can really do a better job than the “ferrocement” invention of Monier…March 27, 2014 at 2:05 pm #23255
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.March 27, 2014 at 5:22 pm #23257
No doubt you can “mess up a composite material from every direction” and on base of each of its components and you can find studies that document cases of each of those cases in practice. Therefore it is so important to become crafty with each of the components have a clear picture what are the problems you really need to look after, what are the imaginary problems, what is the range of each issue, how you stay in the center of the “workable zone” and avoid setups where only a “extremly crafty fellow” can produce a product that works. What you look after is a setup where the material still has a certain level of “forgivness for small production irregularities” and still comes out good. “Extra water at will of the craftsman” is definitly one of the “don’t ever do it setups”. Low cement quantity and quality also. Fibers that do not connect, misdesigns that open cracks, trough the protective layer, etc., etc,.etc, counting on paint to cover up fundamental composite design errors is problematic and fails almost certainly. The risk is that steping into that witout testing and personal experience you end up looking after “imaginary problems” and create real problems by trying to solve the imaginary ones. The good thing is there is no hidden failure mode – if you mess a concrete shell in marine ambient up the failure will be at plain sight in a few months (concrete spalling) and no paint can cover it up. So the good way is to use each component in a series of well documented tests and look after what happens a couple of months (years) later to the material produced this way.March 27, 2014 at 10:18 pm #23258
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.March 27, 2014 at 10:55 pm #23259
Dahhh,…what’s cheap nowadays?? The mix is 2 to 1 portland to sand. If anybody’s gonna “mess” that one up they belong to a Zoo…
Guys,…I owned a 40′ Samson ferrocement sailboat in the 90′s. “Medusa” was beautiful… She was custom built in 1975, all teak interior, circumnavigated twice and spend most of her life in the South Pacific. Her hull was bulletproof,..literally and everything on her was built to far better than Lloyd’s specs, stainless steel and bronze everywhere. Heavy displacement ocean cruiser, 20 tons. I have and will always regret selling her…
There are no better boats than ferrocement boats (of course, when built right) and they will outlast any boat out there,…for decades.March 28, 2014 at 6:13 am #23263
Concrete Honeycomb Shell engineering modern design.
The data kat it bringing up here sounds like “zoo” messing up the basic mix design to me (30,000 linear feet of cracks sounds like somebody wanted to turn that into a “liftime repair job”), i have data of dozends of floating concrete structures where not a single one has shown any kind of problem in 30 years at sea. http://concretesubmarine.activeboard.com/f541915/outstanding-floating-concrete-structures-news/
I think that paints the picture – the question “does it last for ever” or “is it desaster bound” depends basicly on “who is in charge” of the build. Its the builder – not the material.April 4, 2014 at 4:13 pm #23292
I was just looking around for data on concrete/cement drydocks, use and construction methods, and found the following concerning drydocks in the early 1940′s in the usa:
ARDC Construction. — Eight of these docks were built on the East Coast, at Wilmington, N.C., and five of the West Coast, at San Pedro, Calif., in dry basins excavated for the purpose. Pile-supported platforms were constructed on which the hulls were built. Forms were of wood and masonite, and were held to close tolerances to avoid wide inaccuracies in fin displacement. Concrete was composed of stone or gravel aggregate, with about 8.4 bags of cement per yard and a water-cement ratio of five gallons per bag of cement to secure maximum density and a 28-day strength of more than 4,000 pounds per square inch. A total of 3,300 cubic yards of concrete was required for each dock.
ARDC Service. — Five of the self-contained docks of this class were towed to advance bases in the Pacific or to Pearl Harbor, where they were utilized with great success in the repair of many combat-damaged vessels. In service, these drydocks proved unexpectedly popular, because of their relatively great mass compared with their lifting capacity. This characteristic lowered the center of gravity and also made the dock exceptionally stable. It was not necessary to admit water into the wing walls to sink the docks, and additional space for machinery and quarters was thus made available. These docks also proved exceptionally watertight and required practically no hull maintenance.
The ARD docks, in particular, were fine freight carriers and seldom left for their overseas bases with an empty center chamber. On the contrary, they usually carried their own work barges, small boats, dredges, cranes, locomotives, piling, and other supplies too numerous to mention.
Near as i can tell, the basic concrete floating drydocks were more successful than the concrete ships, as no drydock was damaged in towing or in contact with other ships.
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