May 26, 2011 at 12:12 am #1511
Ok, I understand why cement is the way to go as far as its durability, strength, ability to withstand salt water for extended periods of time…
But…what are the elements of cement that make it so durable against salt water?
Rock seems to be made up of many elements, could we narrow down the stuff that protects against corrosion and just coat something like plastic or steel?May 26, 2011 at 11:28 am #13564
Cement, concrete how ever you call it, is basically synthetic rock. It’s not really any ‘more’ durable than any other ‘rock’ in salt water but it is vastly more durable than wood or steel. One of the reasons that the structures built by the Romans and others have lasted literally thousands of years it because they didn’t use steel reinforcing. Water penetrates the concrete over time and rusts the steel which expands and causes ‘spalling’. If there is such a thing as plastic re-bar or carbon fiber reinforced concrete, that would be the answer. It would be almost indestructible! As for narrowing down or reducing the concrete itself, I think it IS the the lowest common denominator…May 26, 2011 at 11:47 am #13566
there is a stainless steel, and i think a carbon fiber. adduno. gotta do some research but there are alternatives that wont rust according to wikipedia page about reinforced concrete.
“Leadership and do-ership are not the same thing”May 26, 2011 at 2:27 pm #13572
There are actually a number of extremely interesting new constituent mixtures of concrete being experimented with, mostly in high-rise construction, with the aim of finding a mixture which will aid in the production of super-structure construction. A few here that I think you guys might find interesting…
In the field of Carbon Fibre, there are experiments being done with using carbon fiber threads, added to concrete mixture. The idea is that instead of using system which is based upon a substructure surrounded by cement, you would have strands of carbon fiber threading mixed throughout, and alligned along the designed stress avenues of the concrete structure. Thus, rather than two different yet co-dependent systems – substructure and superstructure – you have one single intermixed system. It is expected that this will do a great deal twoards preventing cracking throughout the entirety of a concrete structure, reduce seepage and eliminate spalling. This technique has been proven using other admixtures as well, but it is belived that carbon fiber would be a superior material.
A second experiment I was made aware of is the use of coiled steel in the substructure in addition to traditional rebar along the portions of a cement structure that would be exposed to tension stresses. This has yet to be tried on any kind of large scale successfully, but the idea is that you would stretch the coil substructure slightly before adding the cement superstructure. This would introduce an inherent compression into the system, which concrete is very good at handling, while giving the system greater resistence to tension stresses. Again, this concept is yet to be proven on a large scale, and the long term benefits are questionableMay 27, 2011 at 12:54 am #13580
The reason that Iron rusts is due to large amounts of carbon in the melting of ore with coal.
If we were to use a hydrogen, ammonia, or electric furnace then it would have none.
And thereby be rust-proof, much like the H1 nitrogen steel of some marine knives.
Also note that the iron pillar in Dellhi was made using wood fueled furnances,
and has low enough carbon to have minimal rust after centuries.
so methane or natural gas may potentially be clean enough.
So the answer I believe, is to either purify sources of iron by remelting and stirring,
or melt sources of iron ore and cast our own metal shapes.
calm aware desire choice love express intuit moveMay 27, 2011 at 6:45 am #13582
I’m quite sure you’ve got it mixed up there… Carbon has nothing to do with rust since the chemical formula for iron oxide(rust) is FeO3. Which has no carbon atoms in it.
Carbon is what turns iron into steel.
King Shannon of the Constitutional Monarchy of Logos.May 27, 2011 at 8:49 am #13583
I have to admit that I was not sold on the idea of concrete when I first started reading on these forums, but shredder and others me think, ask questions, and do research, and I am now quite on board.
Anyway, here are some more interesting additives…
This one, (not sure if this would be considered an admixture or an aggregate) called Elemix, is obtained by adding tiny polymeric spheres which contain a closed cell honeycomb inner structure. The mixture is advertised as being lighterweight and more crack resistant than normal concrete, preempting the requirement of a steel substructure in certain applications, but adaptations could be made so that the admixture were a complimentary structural component as well, making it more appropriate for our uses.
Another one, in the same strain as the carbon threading I referred to earlier, to give you an idea to its possibilities, is obtained using polymer fibers. They call it Concretum SuperFibers, and while the wording is exceedingly technical, you can google the terms you dont know or I can put together a paragraph or two breaking down the physics of it.June 1, 2011 at 4:32 pm #13685
I’m quite sure you’ve got it mixed up there… Carbon has nothing to do with rust since the chemical formula for iron oxide(rust) is FeO3. Which has no carbon atoms in it. Carbon is what turns iron into steel.
King Shannon of the Constitutional Monarchy of Logos.
“The carbon atoms in steel however, greatly decrease the ability of iron to resist corrosion.”
see so the carbon catylyze’s the OH- into being.
Also if Nitrogen was used instead of carbon can still get the same strengthening effects as steel.
Carbon is atomic number 6, and Nitrogen atomic number 7, so it should make a good fit.
Another thing is that nitrogen is fairly inert and thereby would be passive to presence of water.
Also phosphorous may be a good additive.
on Rust-proof-Iron from Wikipedia:
Ancient Indian smiths did not add lime to their furnaces; the absence of CaO in the slag, and the deliberate use of wood with high phosphorus content during the smelting, induces a higher P content (> 0.1%, average 0.25%) than in modern iron. There is more phosphorus as solid solution throughout the metal than in the slags (one analysis gives 0.10% in the slags for .18% in the iron itself, for a total P content of 0.28% in the metal). This high P content and particular repartition are essential factors in the formation of a passive protective film of “misawite” (d-FeOOH), an amorphous iron oxyhydroxide that forms a barrier by adhering next to the interface between metal and rust. From this technology recently rediscovered by metallurgists at IIT Kanpur through the study of the Iron Pillar of Delhi, rust-proof iron is at the last stages of being commercialized. This 1600 years-old rust-proof pillar is also of a remarkable strength, having withstood the impact of a cannon ball in the 18th century. Copper has a similar effect as phosphate regarding the formation of a passive protection film. Furthermore, the presence of phosphorus (without carbon) produces a ductile iron suitable for wire drawing, for piano wire.
Phosphorus is part of the nitrogen group on the periodic table.
calm aware desire choice love express intuit moveJune 4, 2011 at 7:55 pm #13705
If your question has not yet been answered, Elwar, let us know what specific questions you have, and we can get the conversation back on track for you.June 28, 2011 at 5:23 am #14001
Ductal is a fiber reinforced concrete which can also flex to reduce stress and cracking. I’m curious to see how it would work as a fiber reinforced foamed concrete for neutral bouyancy. This would allow forming it in floating molds in the water, removing the molds, joining the cast components into seasteads, then pumping out the water for a floating structure. http://www.ductal-lafarge.com/wps/portal/ductal/6_1-Ductal_overview
Oddly enough, plain carbon steel fiber performed better than stainless and glass fiber in Navy testing with samples submerged for 18 years in seawater, http://www.stormingmedia.us/38/3859/A385963.html .August 19, 2011 at 6:55 am #14799
This addresses something I was thinking about with all the concrete. What about spalling?
I mean, really, we’re in the water all the time, I’m sure there are a lot of (probably expensive, i’m woefully inexperienced in concrete working, just helped lay the slab for the little storage building/gym my parents built behind their house a while back, but as far as I understand spalling is a big problem especially if you want it to last as long as your house would (though I know if you count in house upkeep and land prices and taxes and all it probably comes out way on the side of concrete subs and such for sqftxyears) in a constant salt water environment.
But anyway researching inflatable concrete dome structures a while back (another possible solution to easier more perfectly rounded sub construction) I found one company that offered basalt rebar. Basically a lot of basalt fiber put together with some sort of epoxy, it’s way stronger and lighter than normal rebar, more or less completely corrosion and heat resistant, nonmagnetic, and I don’t think too expensive. It’s supposed to be the midground between glass and fiberglass rebar/rods (which have a lot of shortcomings, and which the basalt bar outperforms) and carbon fiber (which is super expensive and the basalt supposedly works as well as in some situations). I’ll look up the prices on it later (currently on another train of research) but from what I remember I think the company was charging twice as much for basalt reinforcement than steel, so it can’t be too expensive, and I don’t even think it’s too rare. I’ll also see where you can buy it.
But yeah, i thought of that stuff as soon as I started reading about ellmer’s designsAugust 19, 2011 at 2:08 pm #14801
To look for a fiber material that avoids rusting steel – is probably looking for imaginary solutions for a imaginary problem. The city block sized floating concrete structures that have been built in the 70 ties for the oil industy (Troll A, Ecofisk, Heidrun, Draupner, etc…) where expected to show some type of problem after 30 years of use – they proved to work 30 years perfectly without showing any problem of any kind. So they where declared ready for another 30 years of use in open ocean conditions in salt water ambient and with 1 million load cycles per year created by wave action.
In the meantime a whole new series of structures (nkossa, adriatic, monaco breakwater, glomar beaufort etc…) has been triggered by this experiences. Engineers now talk of 100 years maintenance free service life in open ocean conditions. Some studies even talk of 200 years.
The general consensus is : If you find ” supposed concrete spalling” or rebar rusting in a floating concrete structure, you are not looking at “real concrete “at all what you are looking at is the consequence of a faulty mix design from the very beginning.
Roman concrete structures like the Panteon in rome or the the harbor sturcture of Cesarea are in excellent shape after 2000 years of exposure to the elements. – So basicly there is no need to find a “better concrete” for building seasteads – present day concrete engineering has a material in hands that has anything what it takes to create seasteads that last centuries.
Key studies: here
You must be logged in to reply to this topic.
Posted on at
Written by Elwar