theoretically the strongest concrete

Look at an earlier post I made to this thread - If you need a spread sheet for the calculations I have one based on the Dinger-Funk distribution.
e-mail me - it really clunky - if it works you may want to buy Dinger's ad-in It works extremely well for large particle size distributions. I found that when the distribution was under 1/2 decade it didn't predict packing as well.
Gregg

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it may have to do with Kepler's problem, but a) using BBs will weaken it (too heavy), and b) "aerocrete" is actually stronger than that using sand: the aggregate has no tensional strength, between any two chunks. the thing about Portland Cement is that it's stronger, the longer it takes to dry -- so keep dousing it.

--Dec.2000 'WAND' Chairman Paul O'Neill, reelected to Board. Newsish? http://www.rand.org/publications/randreview/issues/rr.12.00 / http://members.tripod.com/~american_almanac
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Karl Hallowell wrote: (snipped)

In the optimal strength and durability of concrete, I am not sure whether sand alone is superior or less superior than a sand and gravel mix. Mortar has to be tough to hold together block and brick and it is sand only.

Well the problem originally was concrete mixes and sure I can find a whole different material stronger than a concrete block.

This is where experiment is needed. To find out if a 1 :: 1 mix of portlandcement to sand is better than a 1 :: 4 mix of 4 parts sand.

I need to find out how the Kepler Packing relates to the optimal mix of concrete and blacktop. Where the density of the Kepler Packing is that of pi/3sqrt2 or about 74% which yields a mix ratio of somewhere between 1 :: 3 to 1 :: 4
Archimedes Plutonium, a snipped-for-privacy@hotmail.com whole entire Universe is just one big atom where dots of the electron-dot-cloud are galaxies
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compressing concrete is quite common, and done with a vibrator, before it sets.
also, there are additives that help reduce viscosity or increase fluidity, while keeping initial water content low (but still enough water to react), similar to what is used in potter / ceramics.
E.V
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Erez Volach wrote:

I wonder if sand grains are mostly flat faced and not roundish? The Kepler Packing deals with spheres and it is the densest packing with 26% void gaps.
Does anyone know what the usual or average sand roundness or flatness is?
I suppose one can get gravel that is mostly roundish. I know the gravel of quartzite to make a concrete mix is mostly angular with alot of flatlike surfaces. Perhaps sand is much like this quartzite in having many flat surfaces. So that when one mixes a concrete mix of sand and aggregate gravel that many of the flat surfaces touch and leaving little if any room for portland cement to glue together those flat surfaces. And that the Kepler Packing of spheres with its density of 74% and 26% gaps for a glue. That in a sand and or gravel mix of concrete or asphalt that the 26% gaps need not have a glue because they are mostly flat surfaces touching one another. So I suppose the 26% can be drastically reduced in these mixes because of "flatness"
E.V. , I am having trouble posting in that I suspect someone wrote a virus to prevent these posts of mine from appearing on all outside ISP, except for my own ISP of dtgnet. So am double posting.
Archimedes Plutonium, a snipped-for-privacy@hotmail.com whole entire Universe is just one big atom where dots of the electron-dot-cloud are galaxies
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If you use round sand the concrete will be weak. Sand like
http://www.couger.com/microscope/carl/sand.jpg makes lousy concrete.
Gordon

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for uniform-ball "aggregate," teh cement is the complement to the volume of the ball, inscribed within a rhombical dodecahedron; I think it's got pi and 18 in the ratio, as per Kepler's problem, about a fifth left-over. (congratulations on your proof via kissing; you've beat Hale, at last .-) I wasn't aware taht "sharp" sand is better, either. however, assigning a simple "1/3" ratio of various sizes will not be easy -- no easier than Kepler's problem.

--Dec.2000 'WAND' Chairman Paul O'Neill, reelected to Board. Newsish? http://www.rand.org/publications/randreview/issues/rr.12.00 / http://members.tripod.com/~american_almanac
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Our group in Grad school did quite a bit with particle packing. The computer algorithms were originally developed for a coal water slurry project (in the 70's). - size the coal - mix with water - pump and burn like oil. The short answer is - it worked - the DOE built built a large pilot facility in Fl and it was fully operational. (75 vol% coal with viscosities below 100cps and no dilatent behavior below 2000sec-1 shear rates) Why don't you see now? - 1. oil prices came down 2. railroads would not give right aways for the pipelines 3. you can see it in operation in china - they stole the technology.
The packing efficiencies can be calculated on a spread sheet from algorithms developed on a VAX (no super computers - just good imaginative science/ engineering) (Engineering is the key word because the model parameters and later confirmed by experiment - did not have any derived fundamental significance.) I know for years the group was trying to determine the fundamental significance of the parameter values with out much success. The procedures are given in detail in Predictive Process Control of Crowded particulate Suspensions by Funk and Dinger. ISBN 0-7923-9409-7
I know Dinger sells excel addins for $100.00 or so. I use my own spreadsheet - very clunky - but it works
Gregg
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I would imagine that civil engineers have studied topic this just about to death. The answer is probably dependent upon the sand particle size, salt, temperature history of the cement, amount of water available, etc.
Michael

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I can't imagine the answer being independent of the actual particle shapes. When studying the suitability of different sources of crumb rubber as an asphalt filler, for instance, it was found that rubber that was ground after cryogenic treatment resulted in a drastically less strong compound than rubber that was ground at room temperatures. This was determined to be because the cryogenically treated crumb had shear surfaces, like faceted gems, which provided less surface area to grip its binder than the more complex surfaces of the other crumb.
If different sources of sand produce significantly different particle surface textures, then I would think the strengths of compounds made of them would have different physical properties. I am no expert on sand, though, so I have no idea if particle surface texture varies or not.
Getting back to the original question, I think it would depend on exactly what kinds of "strength" was needed from the concrete compound. Adding different things to the mix (straw, dung, sawdust, rubber, steel rebar, hardware cloth, etc) can improve the strength/density ratio, or the resilience, or the total blunt trauma energy absorbed per unit mass of the compound, albeit possibly at the detriment of hardness or absolute flexural, shear, or tensile strength. Even if the concrete is only used to support a load which is static most of the time (eg, the foundation of a building), there may be other factors which complicate things, like occasional dynamic loading (Californian earthquakes), or water erosion (rain), etc. There is no single best formula for everything.
-- TTK
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Sharp sand and aggregate makes much stronger concrete than smooth sand and aggregate.
Gordon
message said:

to
salt,
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well, they have, but as any empirical science (sorry, I just had to write that) there is still a lot of room for improvement. Unfortunately i don't know the right english words for the coming remarks; i hope it is still understandable. Often highest strength is not the aim, but early strength to allow quick formwork removal, or low porosity (high density) to make a barriers for ground water protection etc. Concretes are optimized to set under suboptimal circumstances like low/hi temperatures, short times in formwork, low viscosity, very long/short pot life.
The posed 1:1 optimal concrete theory has no basis... a sand grain is a sand grain is a sand grain...silicon dioxide... a dead dog.. the "cement" however is more or less reactive depending on where it comes from, it is not a defined substance.. pure CaO has completely different setting behaviour than fly ash cements. Silica fume, plasticizers and thousands of other additives make this a real witchcraft system. So no 1:1 ratio, neither m:m, nor v:v or mol:mol have the slightest chance of being a general rule, let alone specify some concrete mixture. The quality of the concrete widely varies even with the same cement/sand ratio (and using the exact same materials in different experiments) with different water/cement ratios. Depending on water content of the sand, its specific surface, the quality of the cement etc., the "brickie" on the building site has to slightly modify the recipe every day to just get the ideal, same consistence.
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snipped-for-privacy@web.de wrote:

Well yes, there is a direct link with theory and with analysis. We have the Kepler Packing to be applied to concrete and to see if the Kepler Packing is a better concrete than the theory of 1 :: 1 mix of a 3-d chessboard mix.
I forgotten the 3-d Kepler Packing percent of voids. Was it somewhere around 23% voids? Let us say it was. So that a Kepler Packing Concrete mix would not be a 1 :: 1 mix but a 23% :: 77% mix or a 1 :: 3 mix.

Experiment: It should be easy to experiment as to whether a Kepler Packing concrete mix is superior to a 1 :: 1 chessboard mix. In that we get marble sized
balls and Kepler pack them in wet cement. We then pack some marbles in a configuration of a chessboard where the marbles and cement are in a 1 :: 1 ratio. We wait for the two samples to dry and harden. We then test them for superiority of one over the other.
Archimedes Plutonium, a snipped-for-privacy@hotmail.com whole entire Universe is just one big atom where dots of the electron-dot-cloud are galaxies
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I'm still betting that aircrete is stronger than those concretes taht use cement plus filler. but, what is your hypothesis on the "checkerboard" arrangment of the bubbles or rubble, compared to the closest-packing (Kepler) config.? even if you don't believe Hale's proof that it *is* the closest-packing (with the "hexagonal" closest-packing variants; there's another term for them), what possible "better" comes from the rectilinear stacking, which is definetly *not* closest-packed?

--les ducs d'Enron! http://larouchepub.com
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snipped-for-privacy@web.de wrote:

This is very true. Alcoa used to make its CA-14 and CA-25 calcium aluminate cements at a U.S. plant. These are high purity cements, used mainly in refractories (furnace linings) -- a very different breed from your standard Type III Portland cement. Anyway, a couple of years ago, Alcoa decided to shut down U.S. production and make the stuff in Europe (Netherlands, I think).
I was working for a refractories company at the time and we had a few products which used CA-25 as a binder. The European stuff turned out to be slightly different from the American stuff in terms of workability and set time. If I recall correctly, it took slightly more water to get the same workability and had a significantly longer set time. There were also some small differences in strength. The end result was that, even though it was supposedly the same cement, we couldn't get the properties we wanted anymore, and we wound up having to reformulate our products with another manufacturer's cement. Eventually we moved away from cements altogether and switched to a phosphate binder, but that's another story.
The moral of the story is that, not only are there many different types of cements (varying proportions of alumina, silica, calcia, and other stuff), but the same cement varies from manufacturer to manufacturer, and for the same manufacturer, from plant to plant. If that weren't enough, Portland cements often vary significantly from batch to batch. Obviously, depending on your application, these variations may not matter much. But Dave is absolutely right; you can't say that cement is cement is cement and leave it at that.
Then there are aggregates. Good luck finding a "uniform" grade of anything. At best, you can hope for 65-70% to be somewhere around the specified mesh size when you run a screen. Moisture content may vary from lot to lot, too; one week, we suddenly discovered that all of our test batches were taking a few percent less water than we expected. It turned out that one of the aggregates we were using came off of a barge which had been sitting uncovered during heavy rains.
Theory is great, but don't forget that it's always based on the rules which we've made up to help us conceptualize the real world, and that the "real" real world is often far more complicated.
Dave Palmer
(773) 955-2223 snipped-for-privacy@iit.edu
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I'd no more consult mathematicians about concrete than I'd consult a construction worker about mathematics.
Gib
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Even more real world.
Have you ever actually seen a cement truck?
They don't measure to the decimal point. Real construction workers throw in a bag of cement, a few shovelfulls of this and that, their lunch bag and soda or beer cans, etc. This is not a precision industry.
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On 18 Sep 2003 05:38:14 -0700, snipped-for-privacy@aol.com (TimR) wrote:

Now you've done it! You have opened up a can of worms. "Have you ever actually seen a cement truck?" Probably yes, but you wouldn't know it if you had. A real cement truck is a closed trailer that handles a bulk powder. A "concrete" mixer truck is the one that goes down the road with a rotating drum in back.
Also, we don't throw our beer cans into the concrete any more. We're afraid it might add strength to the concrete.
Pardon me while I take my tongue out of my cheek.
In reality there is a lot of high tech going into concrete these days. Materials science, computer simulation, advanced chemistry and other whiz-bang technologies are advancing concrete to the point that what you see in a modern high-rise building is not the same thing that went into your house slab.
Unfortunately, despite all the high tech efforts, the people who typically control the final placement and quality of the concrete are often minimum wage laborers and barely-trained technicians. Good contractors recognize the problem and have been taking steps to change it, but there is still a long way to go.
Jay Shilstone
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James Shilstone wrote:

May be concrete technology is still an empirical science, but its not a simple science !!
But ckeep in mind that in the industrial nations there will produce more concrete then steel (more then 2500 kg / person /a)!
The production of cement itself is about 400kg/person /a in the USA as well as in Germany (steel about 1200 kg)
Some remarks. Very simple said the comprehensive strength of concrete mainly depends on the water cement ratio ore better water / binder ratio and the finess of the material. So take a lot of cement, only a small amount of water, a lot of silica fume and fly ash , coarse aggregate smaller then 8mm and you will get a concrete with more then 100 MPa strength ..seems very simple.. but this is very expensive and the concrete is like a chewing gum so you need souperplastiziser and you will get a lot of shrinkage and so will get cracks...and so on. Not easy but, a real high strength concrete has nearly nothing to do with Mr. Kepler, as well as he is also a German guy like me ;-)
A second point: sand is very cheap, but the transport of sand is very expensive. So you __have__to__use__ the sand you will find near your bulding site. For example here in south Germany we have very smooth natural sand, in the northern part you have only very rough crushed sand.
So google for "high strength concrete" ore "very high strength concrete" ore "self compacting concrete"
for more infos.
Regards
Markus Greim
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