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

    What difference does the color make? I think the smaller the fibers the better, you'll get a better cross link.
     
  2. dsigned
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    dsigned O.R.C. Hunter

    Second test panel, and update on the first:

    First test panel had quite a bit of cracking, albeit mostly due to my wife picking it up before it had cured (a few hours).

    To answer a few of the questions:
    The purpose of the white pozzolan is mostly for aesthetics, and because I think I can. Based on the research I've done recently, it looks like VCAS is just crushed glass, and of all the possible pozzolans, I think has the lowest impact on the color. There is another purpose though: permeability. The other side benefit of building reactive powder is reduced permeability to ions. In other words, if seawater can't penetrate, then you can use (non-stainless) steel fiber, and not worry about corrosion. Similarly, you don't have to worry about coatings: the concrete is its own coating, which would make for a really really low maintenance boat.

    Anyhoo, things I didn't like about test panel #1:
    Too thick. Aggregate size was as large as 1 cm, I was hoping for nothing bigger than 2mm.

    Too heavy. No lightweight aggregate.

    Still too brittle.

    Too many voids

    I did a bad job troweling.

    Sanding revealed aggregate, which was a pain.

    I likely used too much water, and didn't use any water reducer (albeit the mix contained quite a bit already).

    Things I did like:
    White. Took a water-based stain really well (a nice deep blue).

    Sanding gave a really smooth finish

    Ultimate strength for the mix is 9000psi, which is pretty good, and it is supposed to contain quite a bit of polymer. It may be worth meshing out the aggregate.

    Chopped fiberglass was pretty easy to add.

    For MK II, I bought an open bag of mortar (55 lb.) for $8 and a bag of vermiculite for $4 (8 qt).

    Vermiculite seems to be a cheap and locally available lightweight aggregate that has some pretty neat advantages:
    Either improves (or at the very least, doesn't hurt) strength.
    Provides some pozzolonic activity
    Makes heat a non issue (is used to make refractory concrete)
    Makes the concrete insulating.

    EDIT: Also, it's crazy light. Apparently you can add up to a 7:1 vermiculite to Portland cement ratio, which results in something on the order of 15% the weight.

    Disadvantages include that it turns the concrete gray again (which may be due to the pozzolonic activity, but I'm not sure).
    No word on other properties yet, but the concrete hasn't cracked.

    This mix was a 2:1 (or maybe 2:1.5) mix of mortar and vermiculite, with a ton of glass fiber. Still no water reducer (esp. in the form of acrylic liquid) or other pozzolon. Also, still no source for decent microspheres ordering locally. The local precast place hasn't returned my calls (yet?).

    I may crush some of my own glass, as it will allow me to get really clean stuff, as well as controlling particle size (powder).

    I also may reduce the number of glass fibers, and try and increase the ratio of vermiculite, to get the mix as light as possible.

    I actually want to switch to PVA fibers. They bond better than anything else, and as far as I can tell from reading, give the most impact resilient and crack resistant concrete. I don't know if I can find any locally and I'm trying to avoid paying shipping.

    Finally, in speaking with a fellow teacher (who is a former civil engineer) and in reading some more of the canoe design papers, I may experiment with post-stressed concrete. The idea here being that pre and post-stressed stuff can be made way lighter (and the best and fastest concrete sailboat I'm aware of to date, Helsal I, was prestressed). Post stressed would have the advantage of being able to have its cables inspected. I think I would only want to do pre-stressed if I could a) get the permeability down to zero and b) get a cable I knew could tolerate some exposure to sea water. I'm not sure whether the fiberglass and basalt rods can be used this way.
     

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    Last edited: Feb 2, 2018
  3. dsigned
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    dsigned O.R.C. Hunter

    Also here's a super cool motorboat build by a German built from concrete. Can't tell if it's carbon or basalt mesh, but it's definitely not steel. Wish I could find more info....

     
  4. dsigned
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    dsigned O.R.C. Hunter

    Further update. I resent my previous email to my old concrete prof, and she emailed back this time:

    HI,

    I am sorry I didn't respond last semester. Things were hectic and a lot of emails slipped through the cracks. There is a retired engineer who helps the canoe team out with their materials and worked in the concrete industry for his whole career. I am going to forward your message to him, because I think it is the kind of interesting topic that would get him excited. His name is [redacted]. Let me know if you don't hear from him in a week or two.

    Dr. [redacted]

    (I'm not posting their names because I haven't asked them if it's ok).
     
  5. dsigned
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    dsigned O.R.C. Hunter

    Here's an interesting blurb about a 1973 concrete canoe:
    Christened the Floating Irish, her construction began with fabrication of an expanded polystyrene form. A #2 smooth steel bar was installed in each gunwale and a layer of nylon mesh was placed on the form. To these surface was applied a neat cement paste and then a three-sixteenth inch layer of vermiculite concrete (using presoaked aggregate) made at a water cement ratio of .40 and a cement aggregate ratio of 2:1 by weight. Another layer of nylon mesh, a final coat of neat cement paste and an epoxy-based paint brought her final weight to 130 pounds.

    http://www.concreteconstruction.net/how-to/materials/consider-the-concrete-canoe_o
     
  6. rberrey
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    rberrey Senior Member

    Let,s add xypex to our wish mix
     
  7. Rumars
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    Rumars Senior Member

    I just finished reading this thread and it makes me wonder. Ferrocement or acually textile reinforced concrete (since that is what is discussed here) can be good for boatbuilding (in its limitations of course), but there are a lot of misconceptions.
    The biggest one is that it's cheap. Sorry to say but it's not. Yes the cement part is cheap, even with all the modern fillers and admixtures. But it's only part of the equation. The reinforcement is not cheap by any means, and it will stay so for a while. Even for ferrocement the money was in the steel armature and not in the cement. Basicly you have three non-steel options: basalt, glassfibers and carbon. Then this fibers need to be wowen to a specially designed mesh fabric that takes the loads into engineered paths, and coated with adhesion enhancers. Square mesh from the roll is passe. Then you need to do find an appropiate concrete mixture and do a shitload of actual testing for panel strenght, and afterwards someone needs to engineer the hull to the materials numbers. Sorry to say but if you want the benefits of textile reinforced concrete you have to do this. The material is not yet so far along that one can benefit from mass-market savings neither in price nor in engineering. This kind of building needs a mold and you have to factor in the cost. In the end you have to have a large workforce doing the actual plastering, or be capable to build a mold for a pour in system, wich means a complete female and male mold capable of supporting the finished weight, plus a system to hold them precisely apart. So you are basicly stuck with the large workforce doing hand plastering over a male mold, since the other alternative is to expensive for a one of.
    The only savings to be had between this and a conventional fiberglass build is the lower price of cement versus epoxy or vinylester resin. But any saving you make in materials will be eradicated by the price of work. To come out ahead you need free work, and lots of it.
    Then I read here that modern concrete is light. Yes modern mixtures can be made with a specific gravity under 1, so they float by themselves. The problem is that this mixtures don't have good properties for structural building. So all you can do (as far as I am aware of course) is come into the region of solid fiberglass when it comes to weight/physical properties ratios. No way to come into wood, plywood, or cored advanced composites territory when it comes to small objects like recreational boats.

    All of the above does not mean don't build with concrete, it only means that the time has not yet come for the concrete renessaince.
     
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  8. dsigned
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    dsigned O.R.C. Hunter

    You've got some interesting points, but then make some specious claims in support of them, which are claims that would be especially odd for someone who had experience with concrete (in the past 20-30 years)

    I'm not sure how it is in Germany, but rebar is cheap in the US, as is fiberglass.

    You forgot one of the most important fibers: PVA.

    Third, your statement that the rebar needs to be woven into "engineered paths" and "coated with adhesion enhancers" is unsupported, esp since most of the stuff you buy for masonry is designed for masonry. Also, what on earth do you mean that mesh from the roll is "passe"? We're not talking about fashion, we're talking about making a cement hull that outperforms any previous hulls, and (hopefully) also plywood.

    Fourth, I can't fathom how you would come into a discussion about concrete and seem to have no concept of pre-stressed concrete.





    Do you have any support for any of these statements? As far as fiber reinforced cement not being "far along": this is quite possibly the most absurd statement you made in your whole post and demonstrates a really baffling level of ignorance about a topic you seem to be trying to be taken seriously discussing. Cementitious composites have quite possibly more money thrown at them than any other building material other than steel.

    Again, what? It takes very little time to lay a 1 inch layer of plaster.


    Yeah, this is all "old man yells at cloud" kind of stuff.
     
  9. Rumars
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    Rumars Senior Member

    Well I know for a fact that textile reinforced concrete is only recently (a few years) been aproved for general use in non-loadbearing applications, and loadbearing applications still require special permits. Wich tells me clearly that the technology is not yet as far along as to benefit from the economy of scale, like classic ferrocement does.
    Just to clarify some terms so we are sure to talk about the same things, in my book fiber reinforced concrete is concrete where a mixture of small chopped up fibers is aded to improve the tensile strenght. This has long been used, with different fibers from steel to fiberglass and plastic. It has nothing to do with the armatures material.
    Textile reinforced concrete is concrete where all the armature is made out of something else then steel. The armature is also not a composite in itself, so no fiberglass/epoxy rebar.
    So what type of construction do you envision: pure textile reinforced concrete or composite rebar with non ferrous mesh? Fiber reinforced concrete can be used with either, as can be used with normal steel armatures.

    If composite rebar and fiberglass are cheap in the US, good for you. All the stuff designed for masonry is coated with adhesion enhancers from the factory. You can not use normal fiberglass or carbon (the kind used with polyester or epoxy) for cement work. I don't know if this is also the case for basalt reinforcement.

    When I say that square mesh from the roll is passe I mean it. If you want to use the advantages an all textile reinforcement offers then you use a stiching machine from the textile industries to create a mesh where individual fiber bundles of different weight are stiched togheter in complex patterns according to the expected load paths. This is not different to using unidirectional and biaxial fabrics of different weights in other composites. Yes you can still use square mesh like other composite technologies still use plain weave fiberglass, but if you really want the benefits you have to do it.

    Let's talk about plastering. In order to lay a smooth layer of plaster at a constant thickness over curved surfaces you need highly skilled workers. That is why in many of the concrete canoes building videos you see the students plastering sheets of concrete in a form on a table then putting that sheet on the mold and pressing the textile armature over it. It is the only way for them to assure specified thickness an by that respecting the design weight. And as we know from ferrocement boat experience meeting design weight and doing a good fairing job is the biggest problem for amateurs and professionals alike.

    One of the benefits of non ferrous armatures is that you do not need a minimum coating thickness over it in order to protect from corrosion. That is where weight reduction comes primarly. One inch layers of plaster would be needed only for very big boats. Think more like 1/4 to 3/8 inches for your normal mom and pop boat.
    The other weight saving is from using lightweight mixtures, but as I said they need to be carefully tested because strenght decreases.

    So if you want to make the best possible ferro boat you need to do all the normal work for composite boat design. Wich is expensive no matter how you take it.
    The other option is to mimic classic ferrocement construction substituting composite rebar and non ferrous square mesh for steel rebar and welded steel mesh. Add some fiber reinforcement to the cement mixture and plaster a boat. That is after someone designes it for the material.
     
  10. alan craig
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    alan craig Senior Member

    Here are the details from the video description:
    Verwendete Materialien: Bewehrung: Carbon mit SBR-Tränkung Größtkorn Feinbeton: 1 mm Zementgehalt Feinbeton: ca. 600 kg/m³ Wassergehalt Feinbeton: ca. 280 kg/m³ Technische Daten: Länge: 5 m Breite: 2 m Masse Betonrumpf: ca. 750 kg Gesamtmasse inkl. Motor: ca. 1200 kg Leistung Aussenborder YAMAHA 2-Takt: 90 PS Höchstgeschwindigkeit: ca. 50 km/h
    I think that means carbon.
     
  11. Rumars
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    Rumars Senior Member

    I'll translate the above and add some comments:
    Reinforcement: SBR coated carbon [SBR is Styrene Butadiene Rubber aka common synthetic rubber. The one producer I know about is Solidian, here is the link: Flat Reinforcement https://www.solidian.com/en/products/flat-reinforcement/ ]
    Maximum aggregate size of the fine concrete: 1mm
    Cement content of the fine concrete: 600 kg/m³
    Water content of the fine concrete: 280 kg/m³

    Boat stats:
    LOA: 5m, BOA: 2m, concrete hull weight: 750kg, total weight including motor: 1200kg, powerplant Yamaha 2-stroke outboard, Vmax: 50km/h
     
  12. dsigned
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    dsigned O.R.C. Hunter

    "Textile" reinforcement implies some sort of woven fabric. I've never heard of textile not including composites, and if you're including "woven" armatures, I think you're defining yourself into a bit of a corner. But, that said, the nomenclature in concrete sucks (high performance concrete, ultra high performance concrete, etc.), so who are we to change things?

    As far as it goes, I can't imagine getting a custom woven armature would be worth the cost for a homebuilder. One of the issues I have with many of the people who post around here is that vague terms like "cheap" and "lots" get tossed around without much reference, or support. So in this case, what would the comparitive strength of a woven armature versus one with "square" weave? And is that a glass to glass comparison? Glass to carbon? It seems like the cost would be such that you'd be doubling the cost of the hull.

    As for the cost: maybe we're taking about different things? Yeah, clearly custom woven stuff isn't benefitting from economies of scale. But the water reducing admixtures, the super plasticizers, the pozzolons, the fiberglass and pva fibers: those are all things that are common in current contract that I'm not aware of any ferro boats making use of. Furthermore, and again, pre stressed concrete has been around for a long time, and it hasn't been used beyond the original helsal and the concrete canoes.

    As far as plastering goes, how good does it need to be? As far as it goes though, a lot of the canoe guys have been using masonry sprayers to get a really consistent thin coat. It seems that this would also make the process go faster (potentially). For my test panels, I'm at about +- 1/8 inch, albeit that's with a really dry mix with a crap ton of fiberglass.

    My understanding of the hull thickness was that it was related to the necessity for flexural and impact strength.
     
  13. Rumars
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    Rumars Senior Member

    The terminology is what it is, I didn't invent it. The people doing research into it since the 90's here in Germany (Aachen and Dresden university) refer to it as such, so I follow suit. Textile concrete is the official name.
    The fibers are not woven, they are stiched togheter with a separate thread. The coatings are applied out of necesity. The individual fiber strands are very fine and when bundled togheter into rovings you have the problem that no concrete mixture, no matter how fine, can penetrate to the centre of the roving. Concrete is only coating the outside of the bundles fibers, so something is needed to keep the whole stack togheter. Epoxy and other resins are used in special formulations. Another popular coating is SBR. The resulting material is different from the glass fibre rods used as rebar, and are not refered to as "composite" or "fibre reinforced plastic". The coating also improves adhesion properties since the cement will not go into chemical bonding with the reinforcement, so there is a need for better mechanical adherence.

    Any structure can be designed for square mesh and have comparable strenght. It's the job of the NA who is doing the scantlings. He will probably need to use more material (armature not cement). He will have to specify what kind of armature, how much of it, where to place it, what cement mixture, etc. I am not aware of any design outside canoes where this is currently done.
    Think of it as engineering a bridge. The guy doing the numbers first determines the forces acting in the structure, adds the required safety factors, considers any other requirements there my be, and then looks at the available materials and tries to combine everything to meet the design goals of stability, weight, cost and life expectance.

    Plastering consistency is crucial. Like bridges, boats are weight sensitive structures. It's not only the added weight, but also the weight distribution. After all the boat must float level and on the designed lines. If it's not one must correct it with compensating weights. Let's asume your 3mm variation. At concrete standard weight of 2400 kg/m³ that is +/- 7.2 kg/sqm. May not seem much to you but that ads up quickly. In fact it's equivalent to 14mm of okoume plywood. And it's dead weight doing nothing at best, and compromising the engineering at worst. In a small boat with just 10 sqm of total surface you just shaved a passenger of the list, or compromised the ability to plane with the designed horsepower. Or if the 3mm are missing, your hull has weak spots and will crack when it hits a wave at speed.
    So if that's the best you can do, the NA has to be aware of it and design the boat so that it can handle the potentially added weight or missing strength. Not to mention the fairness issue. So either you plaster in a perfectly fair female mould so that any inconsistency is on the inside, or you fair the structure afterwards with filler. If you use filler you must then paint, so bye bye no maintenance concrete boat. Plastering is the most crucial step of the whole process, no way around it. It's why ferro has it's bad reputation today and why you don't see new commercial ferro designes. Plus of course the fact that design has moved to shapes and weights that are difficult to impossible to engineer in ferrocement or even textile concrete.

    With steel armatures hull thickness is determined by corosion. You must have a minimum thickness coating of concrete over the steel in order for it not to rust. This amounts to much more then actually needed for strenght or flex. That is actually the huge benefit of non ferrous armatures. It's not only about the weight saving by eliminating the surplus coating. Ferrocement behaves just like FRP. There is an optimum ratio of concrete to reinforcement. If there is to much concrete the composite becomes brittle just like FRP with to much resin.

    A comment about costs: if the home builder has to phone the manufacturer of the reinforcement just to get a price or ask who the hell sells this stuff it's still expensive. Carbon is about 16 times more expensive per pound than steel (more or less, the price fluctuates every year). AR glass and basalt are cheaper but still over the price of steel. Textile concrete is usually viable because of the total project cost reduction, not by itself. A bridge may need smaller foundations because it's so light, even if the actual spanning element is extremely expensive in material and labour. You can build it off site and just drop it in place with a only one truck and one crane.
    It's just like everybody keeps saying here, the hull is only a part of the finished boat, and not the most conductive to reducing costs. If the boat has no interior and no systems then hull costs become significant (rowboats and canoes for example, where hull costs can be 90% of the total cost).

    As for prestressed or poststressed or not stressed that is a choice the NA makes if he determines it brings some benefits to the project. For example one of the carbon concrete bridges in Germany is not stressed at all. Why? It either was not necessary at all, or it was deemed a complication, I don't really know. But the bridge is just fine without it.
    I don't really want to be the NA specifying pre- or poststressing a structure that will be buildt by someone I have no control over. That is probably the reason you don't see it done. Amateur boat construction is not supervised, that's why they have so little market value. You sell the plans and are available for questions and support but you have no ideea if the guy building has any ideea of what he is doing. You just hope for the best because your name will still be atached to the finished product.
     
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  14. dsigned
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    dsigned O.R.C. Hunter

    MK II pic:

    Still haven't used any water reducer or pozzolans (although I think the vermiculite is supposed to have a mildly pozzolanic effect, I think this is offset by the need to use more water).
     

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  15. dsigned
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    dsigned O.R.C. Hunter

    Another update:
    Spoke with the guy from "Loveland Precast", who can get me silica fume, steel fibers and various water reducers, etc. Unfortunately, some of my big ticket items, VCAS (ground glass), microspheres, expanded glass and PVA fibers are still elusive.

    More good news though:
    Waste glass powder as partial replacement of cement for sustainable concrete practice - ScienceDirect https://www.sciencedirect.com/science/article/pii/S2212609016301157

    Looks like VCAS is pretty similar to crushed glass. Just crushed a glass jar today (pasta sauce) for a test panel. I used another large soup can In theory, if my test boat is going to weigh 150 lbs, let's say I might need 15-30lb of crushed glass.

    This guy was easily the most entertaining guide to glass frit:


    This is the method I actually used (so far).


    Finally, test panel #2 has lost some water weight and is down to 900g from 980g.
     
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