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. dsigned
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    dsigned O.R.C. Hunter

    It doesn't seem to me that the concrete teams plaster their boats for the most part, and several of the teams actually sanded their boats. This of course presents its own challenges, but one of the advantages of the reactive concrete is that it's impermeable (which I take it is one of the primary purposes of plastering the hull: to seal it?). As for cost, again, I think we're talking in relative terms. Compared to just dumping concrete in a form, sure. But compared to making the whole tunnel or retaining wall out of marine plywood coated in glass and epoxy (much less foam core)? Still 10x cheaper.


    Hull design now has reached a point where a pretty fine line can be drawn, where performance and expectations can be accurately predicted. This wasn't always the case. Not but a few decades ago, it took quite a while (5 - 10 years) for a class to develop a design and move onto the next big breakthrough. Now, this is months of development, assuming the funds exist. No one does build a design that sucks out of the box. This isn't the old gun and run brigade stuff, where the old school master NA dreams up the newest design, pens it up and hopes for the best result for his client. This just isn't done any more, way too costly and problematic. Designs can be done, that actually float dead bang on the LWL the builder was told to paint on. This wasn't always the case. In fact, most old school designs required some "trimming ballast" which was typically about 10% of the actual ballast, just to get the boat to settle on her lines plumb and square. My last design floated dead bang where I said it would and this isn't unusual. This is because of accurate weight and volumetric studies.

    I think this is more true with iterations on proven designs than it is for completely novel designs though, and still, there's a lot of fear with actually implementing said novel designs that I think would be reduced with a lower cost material where if it doesn't work out, you're out a couple thousand dollars as opposed to a couple million (or whatever).

    As for insurance: you may be right. But if I need to insure it in France, so be it.

    Lol, I had an idea a while back (actually while I was in my last engineering class) for a polar coordinate based 3d printer for large scale prints (like prints measured in meters, not mm).
     
  2. dsigned
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    dsigned O.R.C. Hunter

    Technically I think that's a 100% gain, since you doubled the strength. Also UHPC varies between 150 and 250 MPa (21 to 32 ksi), so take your number and double it
     
  3. dsigned
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    dsigned O.R.C. Hunter

    More fun stuff:
    https://phys.org/news/2009-04-self-healing-concrete-safer-durable-infrastructure.html

    As far as I can gather from the paper, it seems as though they use a polymer as the reinforcement (as opposed to steel or fiberglass) which allows the concrete much more ductility and the ability to self heal. It's not clear to me what the mechanism of the self healing is, as they reference re-wetting the concrete as part of it.
     
  4. dsigned
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    dsigned O.R.C. Hunter

    Also, to be fair, I would bet that a significant portion of them never start because all the old guys tell them that their boat will sink and crack, and be uninsurable and slow and that they're dumb and never succeeded at anything and to listen to the wisdom of the combined thousand years of boatbuilding experience, etc. etc. Although I did see one telling a guy to build a smaller boat to test the material, which I think is fair, most of the responses I've seen are what I would consider unhelpful criticism, and essentially cause the OPs to conclude that since they don't have $100k cash in hand (or $30k for a used boat), that building a boat is impossible for them. I think this is an extremely unhealthy attitude for a pastime that is dwindling in very large part because of the high cost of entry. Sailing can't really afford to be scaring people away. So what if guys like PAR or gonzo are right, and the boat is slower than it would other wise be (or even doesn't get finished): there are tons of boats that never get finished: what's one more? However, I maintain that the weight issue is largely moot, as most monohull are ballasted to the moon, and the marginal difference in ballast or gross tonnage is going to be offset by having a potentially longer, slimmer hull than one would otherwise be able to afford (or nicer rigging, or what have you).
     
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  5. dsigned
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    dsigned O.R.C. Hunter

    Found the answers to the questions, if not the poster itself:

    1. What is your material/product? (What makes it unique/valuable/interesting?)
    “UHPC is a cementitious composite material composed of an optimized gradation of granular constituents, a water-to-cementitious materials ratio less than 0.25, and a high percentage of discontinuous internal fiber reinforcement. The mechanical properties of UHPC include compressive strength greater than 21.7 ksi (150 MPa) and sustained postcracking tensile strength greater than 0.72 ksi (5 MPa).[1] UHPC has a discontinuous pore structure that reduces liquid ingress, significantly enhancing durability as compared to conventional and high-performance concretes.”

    We are presenting reactive powder concrete, also known as ultra-high performance concrete. It is a niche form of concrete that has been developed in the past fifteen years or so, and has some unique properties with regards to its strength, durability, ductility, permeability, and more.
    Its basic composition is Portland Cement, fine aggregate (silica sand), silica fume, quartz flour, high range water reducer, steel fibers (or organic fibers) and water.
    To be frank, I fully expected “Ultra-High Performance Concrete” to be a hyperbolic title, and to have strength on the order of perhaps twice that of normal concrete, with some other resistance to sulfites or similarly singular advantage. Instead, it addresses nearly the entirety of the weaknesses of conventional concrete, turning many of them into strengths.
    2. What are some typical properties and uses of the material?
    The most striking property of RPC is its incredibly high strength. Roughly ten times stronger than standard concrete (120 - 200MPa) it approaches mild steel in terms of pound for pound strength, while retaining many of concretes favorable characteristics, in terms of being able to pour it into complex forms, its resistance to chemical and elemental processes.
    Because of its naturally high strength (both compressive and flexural), and its much greater ductility, RPC does not require rebar, as does normal concrete. This can greatly reduce the time needed to successfully pour the form.
    All of these improvements come at a much higher cost than typical concrete, however, so many of its uses are limited to artistic and decorative endeavors. However, it is increasingly being used in structural situations where its unique properties outweigh its high cost.
    Two of these situations include high performance bridges, and nuclear waste containment structures. In the case of Nuclear Containment, the high strength, durability, and especially its impermeability are all advantageous.
    Facades are another use of UHPC – where the wear resistance, strength and impermeability can serve to protect the structural concrete, thereby maintaining some of the advantages of UHPC, while making use of the economic advantages of traditional concrete.
    Freeze/thaw 100%
    (after 300 cycles)
    Salt-scaling < 60 g/m2 (< 0.013 lb/ft3)
    (loss of residue)
    Abrasion 1.7
    (relative volume loss index)
    Oxygen permeability <10-20 m2 (< 10-19 ft2)
    Cl- permeability < 10 C
    (total load)
    Carbonation depth < 0.5 mm (< 0.02 in.)

    3. What are the advantages of this material? (For this question you may need to consider a specific application, and the advantages relative to that application.)
    RPC is very similar in many respects to granite. Its strength and resistance to erosion being the two key features. Hence, working with RFP can allow for what amount to incredibly sophisticated forms to be cast “in stone.” These structures will last indefinitely, as they resist freeze thaw conditions extremely well (100% over 300 cycles, according to the PCA), and have excellence abrasion resistance, ductility and resistance to cracking.
    While it may be initially tempting to compare UHPC to traditional concrete, in many applications it is in fact competing with other applications where concrete would have traditionally been horribly impractical. For example, the specific compressive strength of steel is greatly superior to traditional concrete. What’s more, steel has much greater tensile strength as well. However, with UHPC, the advantages of concrete (formability, scalability, durability) can now be had in situations where weight, flexural and tensile strength are all factors.
    Stone is another area where UHPC has become competitive. Marble and granite, traditionally sought after for their extreme strength, durability and aesthetic appeal, can be mirrored in many respects by UHPC. In fact their performance characteristics are nearly identical, and UHPC has the advantage of being able to be colored according to the wishes of the client. In addition, whereas UHPC is expensive relative to traditional concrete, it is a bargain compared to marble!

    4. What are some potential drawbacks of this material? (Think about what arguments you might use against the material if you represented a competing product.)
    There are two main disadvantages to RPC. One has already been alluded to: it is extremely expensive in terms of its initial investment. The multiplier for strength also applies to cost – roughly ten times that of conventional concrete. If one considers steel to have an even lower initial cost, then this is magnified to an even greater extent. Therefore, if a low stress environment is being designed for, with a fairly small design life (10 years or less), then RPC makes little sense.
    The second disadvantage is that RPC does best with a very high curing temperature. It naturally releases quite a bit of heat, but it is about 30% stronger if heated while curing.
    Some of the same classical issues with concrete still apply, though much mitigated. Relative to steel, UHPC still falls behind in the areas of tensile strength and ductility. Though much improved over traditional concrete in these areas, it cannot escape what it is, and should not be understood to be synonymous with steel in all areas of performance.

    8. Where can an interested engineer go for more information? (Also you should include references on your poster.)
    Uses:
    Art (architechture, park benches)
    Nuclear Waste Containment
    High Performance Bridges
    Sherbrook Bridge
    Benefits:
    Strength between 120 and 200 MPA (like carving a building out of granite)
    Low Permeability
    Superior Ductility/ Tensile Stress, etc.
    Non-reactive (no rust)
    No Rebar required
    Freeze-Thaw resistance
    High abrasion resistance
    Claimed structural competition with steel


    References:
    http://www.durcrete.de/home-english/home-english.aspx
    Ductal® | Innovative UHPC Solution http://www.ductal-lafarge.com
    Concrete Technology Today August 2004 Vol 25 No. 2 (Portland Cement Association)
    Index - Ultra-High Performance Concrete, March 2011 - FHWA-HRT-11-038 http://www.fhwa.dot.gov/publications/research/infrastructure/structures/11038/
    http://www.dhs.gov/xlibrary/assets/uhpc-pathway-to-commercialization.pdf

    http://www.lafarge.com/05142008-research_innovation-liflet_Villa_Navarra-uk.pdf
     
  6. dsigned
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    dsigned O.R.C. Hunter

    I think I would be aiming for something in the neighborhood of 6 lb per sq ft (so a 1 inch hull) with a 20000 psi strength. Currently, I envision is something like the following (per 100lbs concrete):

    32 lbs Portland cement
    10 lbs Fishstone pozzolon
    42 lbs sand
    11 lbs water
    48 ml superplasticizer (water reducer)
    20 ml defoaming admixture
    5 lbs basalt fiber

    This is basically the fishcrete recipe, slightly modified (Basalt fiber being the big substitution, and omitting the liquid polymer). Use basalt or fiberglass rod for the armature. I'd finish with a stain (or possibly a dye) and a polyurethene coat (or three) on top, just to keep it from getting dinged. I might also do a few layers, with the face layer using PVA fibers to add impact resistance to the outer layer, so if someone runs into the boat, the leak is less likely to be severe. Build a few flotation cavities fore and aft to keep the boat from sinking in the event that the hull is breached.

    My first thought for building the forms is polystyrene foam insulation board, which will then be used to provide insulation for the hull and/or flotation. It's cheap, easy to work with (you can hot glue it together, bend it somewhat, sand it and cut it with a hot wire) and easily sourced. I'm guessing it won't hold up forever to salt water, but it doesn't need to.
     
  7. rberrey
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    rberrey Senior Member

    I cannot give you advice as a boat builder , but as someone who has formed and placed millions of sq ft of concrete I will tell you some of concerns and advice on a mix . First we know a concrete boat will float , so i take it we are looking at way,s to over come the short commings of a concrete boat . So we start with a one inch hull , one option would be to build a male form , have a stackable mix of a 3 or 4 inch slump and spread it on . But if the concrete is not vibrated yor will have honey combs ( void,s ) , and you will have the same issues you would have with non marine plywood . To get a mix that you don't need to vibrate you will have to have a flowable concrete mix ,or grout , one example would be what we call a LaFarge mix . If you look at these mixes you will find they are more plastic , more chemical,s used for hydration . To use a mix like this you would need a two sided form and pump the mix into it , sort of like vacume baging . Unless you were going to pop out a lot of hull,s the form would be cost inhibited for a one off . For your mix listed above I would add a stableizer such as the Delvo probuct , cut way back on water , and add in a product for crack mitagation , you might also need to add air depending on the climate of the area you intend to sail in . There is a new product for cracks that will add a hunderd years or so to a concrete structure , I think it is only sold in one country right now . I would also look at adding something like fine ground recycled plastic , a fill er is just that , a filler , I poured a mix with ground up tires once , not sure how it has held up . You need to expand your view on what you consider concrete to get the weight down and keep strength , also shoot for a more flexable design mix . If I were to build a concrete hull , which I wouldn't , I would view it as a core material only , glass it inside and out , adding what ever stringer,s needed using a closed sell foam or wood .
     
  8. dsigned
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    dsigned O.R.C. Hunter

    Voids: Vacuum bagging is an option. It's not that expensive to rig up a shop vac (I have a heavy duty one), but my concern is with the sweet spot between being able to force out voids and being able to retain shape. I'd be interested in reading some more about the various methods used to avoid them on ferrocement boats and in the concrete canoes, although I imagine the latter is likely not a huge concern as the boats are more or less disposable.

    Yeah, a male form created either from a fiberglass armature or polystyrene foam (pink insulation foam) is what I was thinking. I don't remember my concrete labs well enough to recall what a 3 inch slump equates to in terms of consistency, but I'm thinking something like cookie dough for spreading. What's a LaFarge mix? I'm familiar with the company (they had a trade name UHPC called Ductal), but not what you're referring to, and googling just brings up LaFarge's ready mix stuff. And you're right: I'd like to avoid building two forms if possible. It's not unimaginable to basically build the boat out of styrene first, then do a thin concrete cast of it, but then I'm left with molds that I would have to do something with, whereas a polystyrene mold can be repurposed fairly easily into insulation or flotation (or other projects).

    I considered doing a fiberglass outer layer, and it's not entirely off the table, but I'm leaning towards just doing a urethane or epoxy coating so I can show off the hull material. No point in having the world's fastest concrete boat if you can't show it off!

    stabilizer and crack inhibitors are both good points. I don't think air entraining is necessary for the UHPC mixes? It's been a while.

    The filler is another interesting point. It's actually what the U Florida guys did to keep their boat light while having a decent hull thickness. I'll go back and read: I think they used some microspheres intended for concrete after having tried perlite (unsuccessfully) the year before.

    Any preference for the kind of boat for the first round? I'm leaning towards making a planing skiff, but if I could find the right daysailing catamaran, I might attempt it just to have something more family friendly. If it works out, and I don't get bored and move on to something else, I'd eventually like to make a slim 40' cat along the lines of Bob Oram's 14R slim (but the 12R):
    Bob Oram Design | Queensland | Catamaran designs https://www.boboramdesign.com/14rslim
     
  9. rberrey
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    rberrey Senior Member

    The LaFarge mix is just one of many flowable mixes used in ICF construction , LaFarge was the first one around the Gulf Coast so we give them their due ,s . It is also a good example of a new mix design when the market demands . How much air in concrete depends on if your in South Fl where you need 0% or if your in Greenland and need 5% . Unless you can get the weight of your concrete mix way down , I don't see a catamaran . I would contact some rep,s from companies like Delvo and tell them what you want to do and ask them what products they have that might help you , I would also contact a student in structural engineering and see if they would design a mix for a student project , or kicks . Then I would try and find a NA student and do the same . Because of liability and cost , I don't think you will find a licensed professional who would design a mix for you . Keep in mind all cement is not he same , get a high silica type like is used in a suspended slab , make a number of test mixes . When you find a lite weight mix you like make 3 test clyinder,s , and after they set 58 day,s take them to a testing co. to break , then you will at least know the PSI you are working with . Not sure how you will come up with a good measure of Tensile Strength and Elongation .
     
  10. dsigned
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    dsigned O.R.C. Hunter

    I think the weight of the mix as is is probably close enough to plywood already to do a cat, the reason I wouldn't do one now is I haven't gotten the spousal permission units saved to do a big cat, so I'm thinking I'll do something smaller first to get a feel for working with concrete again. I did some mix design back in the day, but not as much working with the material outside of the theoretical to get a feel for laying it. But I definitely got an appreciation for people who do lay it professionally. It's almost like a really complicated large scale kind of baking: either it turns out or it doesn't.

    As for the mix design itself, I could probably do it myself if I dusted off the old textbooks. I have a professor (actually the professor who I did the UHPC project for) who's specialty is structural concrete. I'm not sure if she's the one who oversees the concrete canoe teams for the university, but either way, I could probably pick her brain.

    I honestly don't expect I'll do a whole lot of testing, especially for the smaller boat. If I sink in the middle of a small lake no biggie. For a bigger boat I'll probably worry about getting everything just so. It would be fun to do testing just for the hell of it though, just to get an idea of what the boat strength actually turned out to be.
     
  11. rberrey
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    rberrey Senior Member

    I would call the professor and try some team work if I were going to pump money even into a small boat . You will need to get your mix to the 40 pound per sq ft area to compete with ply and glass . I would look at a carbon products as reinforcement such as C-Grid from Chomarat for mesh , and carbon rebar for stingers . To form it I would go with a male form just like you would make for a foam build except I would strip it with masonite , and use proper size pvc pipe cut in half as battens where ever a stringer is located, proper size being what a NA design calls for . Your carbon rebar would located in these pipes prior to concrete placement as well as your mesh . I would present both data from my materials and my method and means to this forum and hope desighners would chime in . In the end whatever material you use has to meet the same strength as any other material used in boat construction . I would also go back on this forum and look at all the negatives listed , take each one and find a solution to correct the problem .
     
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  12. SamSam
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    SamSam Senior Member

    If I was to use this wondercrete, I would treat it like regular boat building methods and abandon the concrete procedure of embedded 'structure' (rebar). I would use it as a skin, like fiberglass, steel, wood and plywood are used in boats, with a separate internal structure of stringers, ribs, bulkheads etc. to support the skin.

    In it's raw state, being a non self supporting sludge like uncured fiberglass, fiberglass methods of boat building would probably be most applicable, with using a female mold generally being the best method.
     
  13. SamSam
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    SamSam Senior Member

    .
    I never understood this from the op. Silica is sand, fiberglass and concrete are both made from or including sand. How does that react with the cement?
     
  14. srimes
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    srimes Senior Member

    I'm interested in learning more. Eliminating steel reinforcement and greatly decreased permeability are great steps to improve longevity. Would be great for a houseboat.
     

  15. srimes
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    srimes Senior Member

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