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Don't know if this will work or not. Works in my head anyway. I just know I had to get it out or it would just become another of those, (what was that train of thought again?) moments.
  [vote for,

When you wet porous concrete and then coat it with mortar the concrete acts as a sponge and pulls much of the lime from the bonded layer deep, <relatively speaking> into the latticework of hollows that make up the surface of unsealed concrete.
This bonded layer when it cures is WAY stronger than either the layer above or beneath.

So the idea is to build concrete structures using only the thinnest possible layer of concrete as the base template.
Subsequent layers would only be deposited by wetting the initial template and dusting with polymer modified mortar and allowing only what is absorbed to harden.

Once set excess mortar dust is blow away to be recollected for the next layers dusting.

I estimate, (based entirely on my gut feelings), that this calcification layering deposition will create concrete many-many times stronger than conventional concrete once cured, my brain on the other hand says; whoa your horses boy, ten times stronger should be a conservative enough estimate.
So ten times stronger it is.

Prove me wrong, I'll eat my shorts.

Despicable Dyslexic Me Despicable_20Dyslexic_20Me
Vile evil or vice versa [8th of 7, Nov 06 2020]

Vietnamese &#273;&#7891;ng https://en.wikipedi...e_%C4%91%E1%BB%93ng
Ding, dong, kerching ! [8th of 7, Nov 06 2020]

Employment in agriculture https://ourworldind...e-vs-gdp-per-capita
[kdf, Nov 06 2020]

(?) UAE sand import. https://www.bbc.com...for%20construction.
[bs0u0155, Nov 06 2020]

What makes sand soft? https://www.nytimes...akes-sand-soft.html
A complicated question [kdf, Nov 09 2020]

3D Printing with concrete https://www.google....lALgQ4dUDCAc&uact=5
It's everywhere! (OK, just a few places, but getting pretty much figured out...) [neutrinos_shadow, Nov 09 2020]


       You need to be clearer about the difference between cement, mortar, and concrete.   

       Most of the strength of concrete comes not from the (portland) cement, but from the aggregate.   

       Mortar is mostly sand, again "glued" together with either lime or cement.   

       And cement is, well, just that.   

       The thickness of layer you can pour is going to depend entirely on the mesh size of the aggregate. Mortar can be applied in thin layers because the sand grains are small.   

       But the limiting factor is the quality and consistency of the bond between successive layers, which is difficult to control.   

       We consider it likely that the final structure may have a tendency to spall or delaminate when stressed or exposed to freezing conditions unless it's very carefully poured.   

       Some layered structures, like Japanese swords, are indeed both strong and flexible, but it probably doesn't work like that with brittle silicate materials such as concrete.
8th of 7, Nov 06 2020

       I thought this would involve invading Turkey or something.
pocmloc, Nov 06 2020

       It could possibly be an evil scheme of Gru and his Minoans ... <link>
8th of 7, Nov 06 2020

       I went to Crete for the first time this year and, as this idea suggests, it was super, so [+]
hippo, Nov 06 2020

       What [8th] said. It's called a cold joint, and is mostly considered a bad thing.   

       It's certainly possible to surface-harden fully cured concrete using cement, lime, epoxies, drying oils etc. - anything that fills the air spaces and then hardens. I've done so myself. I've also built up concrete in layers somewhat as you describe (using cement-water slurry as a bonding agent), but only for small home projects. For anything mission-critical you would really need to know what you are dong.
spidermother, Nov 06 2020

       //what you are dong// - indeed, yes...
hippo, Nov 06 2020

       Would that be the Vietnamese Dong <link> ?   

       It's always about the money, isn't it ?   

       Of course, if [spidey] had written "For anything mission-critical you would really need to know what you are doing." then that could be [marked-for-tagline] ...
8th of 7, Nov 06 2020

       By the way, concrete structures used to be built in layers; my old copy of "The Complete Handyman" suggests doing so, and the result can be seen in the floors of old sheds and the like. The idea was to use successively less, and finer, aggregate. It was a cost-saving exercise; the bulk of the slab was a cheaper mix (mostly rubble) while the top layer had fine aggregate (allowing it to be screeded and trowelled smooth) and enough cement to make it durable.
spidermother, Nov 06 2020

       Whoops! Indeed, I didn't knob what I was doing.
spidermother, Nov 06 2020

       //then that could be [marked-for-tagline]// - Funnily enough, I was just about to add a [marked-for-tagline] for that phrase when I noticed the typo and thought that, rather than celebrating [spidermother]'s contribution to the accumulated wisdom of mankind, a bit of petty, annoying pedantry was the response more in keeping with the ethos of this site.
hippo, Nov 06 2020

       Indeed it is, and we thoroughly approve. Well done; have a notional croissant in reward for your efforts.   

       // concrete structures used to be built in layers //   

       That's fine if you have the time - the layers need to be poured at carefully chosen intervals since (as you have so presciently pointed out) bonding between layers needs to be efficient. Thus the next layer must be added after the previous layer has set, but before it's fully cured. Control of the moisture content of both layers is also vital for success.   

       Sometimes it's considered necessary to scabble or scarify the parent layer prior to the next pour.   

       And the thicker the slab, the more heat is evolved, which needs to be allowed for. Just as an example, the way the Hoover Dam was constructed - in blocks - is highly instructive. If it had been poured as a single unit, the heat evolved in the massive thickness of material would have cracked and weakened it.
8th of 7, Nov 06 2020

       I haven't found the book, but from memory the instructions were to wait until the previous layer is perfectly hard and dry, sweep it clean, sprinkle it with a paste of neat cement in water, then immediately pour the next layer   

       I mentioned the layers thing to a concreter about a year ago; he gave the fairly obvious answer to why it's not done, which is that concrete is cheaper than it used to be, so it's not worth the small saving on materials to spend the extra time.   

       (I think // ... know what you are dong// still works as a tagline.)
spidermother, Nov 06 2020

       // wait until the previous layer is perfectly hard and dry, sweep it clean, sprinkle it with a paste of neat cement in water, then immediately pour the next layer //   

       That sounds about right, although there are a lot of variables - whether the original pour had retarder in it, what the mix was, temperature ... it needs expertise/experience.   

       Certainly, de-dusting/cleaning and then wetting the surface is the very minimum needed; and the amount of water needed is surprisingly large.   

       Layering is still used when specific mechanical properties are needed, but it's a massive subject. Modern buildings with reinforced, or pretensioned, or posttensioned cast-in-place slabs are very sophisticated, and the modifiers that go into the mix (to aid pumping, or control curing speed) are numerous. It's not just the old aggregate, sand and cement either - modern mixes can contain polymer fibres (of very specific thickness, length and density), metal wire or flakes ...   

       There are degree courses that just teach about concrete; there are chemists and materials scientists who spend their professional lives working on concrete. HUGE subject ...
8th of 7, Nov 06 2020

       (Q. Why is a concreter like a cartoon mouse? A. Underlay! Underlay! Rebar!)
spidermother, Nov 06 2020

       //there are chemists and materials scientists who spend their professional lives working on concrete// For most workers it makes little difference what the floor of their workplace is made from.
pocmloc, Nov 06 2020

       We disagree; ice skaters, farmers, footballers ... all would find concrete an uncongenial surface for the relevant part of their professional activity.
8th of 7, Nov 06 2020

       I did say "most". Do you have any statistical breakdown of the workforce (of any country of your chosing) to show the percentage of the workforce who are employed as //ice skaters, farmers, footballers//?
pocmloc, Nov 06 2020

8th of 7, Nov 06 2020

       Links coming up shortly...
Agricultural employment numbers were easy to find; footballers and ice skaters, not so much. 8th, what have you got on that?
kdf, Nov 06 2020

       You need to break down the agriculture numbers, to exclude people working in indoor / enclosed places e.g. mushroom farms, milking parlours, illegal cannabis houses, etc.
pocmloc, Nov 06 2020

       I don't think so. If someone is primarily employed in anywhere in agriculture, concrete is just as important to them. When I get to the ice-skater numbers I''ll probably have to include not just figure skaters but also hockey players, sport team owners, Zamboni drivers, etc...
kdf, Nov 06 2020

       The specification was //working on// so I disagree.
pocmloc, Nov 06 2020

       We have a comprehensive list of halfbakers broken down by age and sex, but it's sad rather than interesting ...
8th of 7, Nov 06 2020

       Well [8th] I'm sorry to hear that age and sex have broken you down. There are support groups for both I believe.
pocmloc, Nov 06 2020

       //ten times stronger should be a conservative enough estimate. So ten times stronger it is.//   

       I initially thought "pfft. there's not the potential in a material like concrete for that kind of range". But, my brother is professionally motivated to be a concrete* nerd. Turns out that 25 MPa is a good ball park for garden variety concrete. But, the top, top stuff is ~250 MPa, so bang on.   

       //Most of the strength of concrete comes not from the (portland) cement, but from the aggregate.//   

       Not at the top end. The fancy stuff is aggregate free, they go instead with fumed silica and steel. It's not far off mild steel in terms of compressive strength, but then the cost isn't far off either.   

       //For anything mission-critical you would really need to know what you are dong.//   

       This is true. There's a dizzying amount of variables that go into it. Concrete can be 1/2 the strength on day 1 vs day 10, so it's possible to build a structure to the fully cured specs that can't support itself initially. As a huge pile of chemistry, the environmental conditions factor in enormously. You have to stay on top of suppliers too, construction and criminality have a big Venn diagram overlap and pile of aggregate A Vs B can change your concrete 50% on top of your curing variation, so on day 1, your structure might be 1/4 the spec strength. Then there's people sneaking in desert sand, which is a big no- no.   

       *used to be tree nerd, but the middle east is much more enthusiastic about concrete than trees for some reason.
bs0u0155, Nov 06 2020

       The best feature film about concrete pouring is “Locke”, starring Tom Hardy
hippo, Nov 06 2020

       Does concrete not have a few categories in the Oscars? It's not just about the supporting roles you know...
bs0u0155, Nov 06 2020

       <Reads anno/>   


       <Re-reads anno/>   

       <Considers further/>   

       <Long silence/>   

       <Very slow handclap/>
8th of 7, Nov 06 2020

       //desert sand//
Is that because it's too dry, and soaks up the water that should be bonding with the cement? (I'm designing a house, & need to know more about concrete...)
neutrinos_shadow, Nov 06 2020

       //Is that because it's too dry, //   

       I think it's because it's been blown around for a few millennia and subsequently is smaller and rounded off. A lot of it may be just certification/testing but at the moment this leads to the hilarious situation in which the UAE is a major sand importer <link>.
bs0u0155, Nov 06 2020

       Wow. I think I just learned more about concrete reading these annos than I did in thirty years of working with the stuff.   

       You guys are awesome.
Don't let anyone tell you different.

       We only listen to The Voices In Our Heads.   

       Since that's us, it's not a problem.   

       //Is that because it's too dry, //   

       No, professionally manufactured concrete involves taking moisture measurements of all the components - aggregate, sand, cement, additives - and then adding carefully calculated amounts of water to get the exact required characteristics both during the fluid phase and the setting and curing phases.   

       The "sharpness" of both the sand and aggregate is critical. In the same way that railway ballast uses broken (sharp) granite to form a resilient water-permeable bed for the sleepers (ties), rounded river gravel or shingle is unsuitable because the individual stones don't "lock" together. It's much easier to "pour" spheres than cubes; try it with dried peas, and then again with sugar lumps.   

       Particle size is also very important. A concrete made with sharp sand, small sharp gravel aggregate and larger rounded stones will have a very different set of properties, both when liquid and set, to one made with round sand, small round gravel and larger sharp crushed stones. Things like interstitial voids may or many not develop; the amount of air entrained in the mixing process is important. Vibrating pikes are used to dislodge bubbles from freshly poured mix, and there are chemicals to try and reduce trapped air too.   

       It's very complicated ...
8th of 7, Nov 07 2020

       I get that.
Concrete is brittle and without aggregate or steel reinforcement crumbles under lateral stress.

       I was thinking that this may make for a concrete more like stalagmites or calcium deposits where there are very few negative spaces in the porosity compared with conventional concrete.   

       Deposition with underlying layers wicking lime from subsequent layers would seem to be the way to go.   

       That's all I had in mind.
If it hasn't been tried before it bears looking into is all.

       These things just pop into my head.
Whether they are wild gooses remains the chase of others.
I have neither the knowledge, time or wherewithal to pursue them.
I share my brain-farts with you guys because...
...because I've always been the dipshit in any given situation and I'm used to it. I try to surround myself people smarter than me so I can learn from them and I've never not been in over my head, so...


       You guys are it!   

       <begins running in a random zig-zag pattern>   

       {Assumes Brownian Motion. Starts trying to calculate the mass, velocity and/or spatial distribution of the invisible objects [2 fries] is bouncing off.}
pertinax, Nov 09 2020

       Brownian Motion is a chaotic system; you'll need to know the EXACT initial conditions, and any varying environmental conditions.
neutrinos_shadow, Nov 09 2020

       ... or then again, you could just follow the trail of the 11.3 metre length of green twine we tied round his left ear while he was busy staring pensively at a heap of gravel ...   

       // I try to surround myself people smarter than me //   

       Well, that's hardly difficult, is it ? Now, "dumber than you", yes, we can see you might struggle with that ...
8th of 7, Nov 09 2020

       Is that what that was ? I thought his brain was leaking.   

       [2f] thoughts of 3d printing a wall ?
FlyingToaster, Nov 09 2020

       // you'll need to know the EXACT initial conditions//   

       That is quite impossible, as you well know. Do you want vector or position?
Voice, Nov 09 2020


       // 3d printing a wall ? //   

       It's a nascent technology; lots of problems to be overcome, but it's being worked on.   

       If it's possible to 3D-print a full size ship's propeller, then walls should be manageable too, if the money's there to do the development. There are already sophisticated semi-automatic metal formwork systems for CIP concrete pillars. If it can be made, then eventually it can be automated - if the cost -benefit is there.
8th of 7, Nov 09 2020

       "...sand (and lots of other stuff) ... is very complicated ..."
—8th of 7, Nov 07 2020

       Quite. And coincidentally, Randall Monroe's piece in this morning's NY Times (linked) tries to explain what makes sand soft.
kdf, Nov 09 2020

       Relatively soft ... again, you have to factor in impact velocity, grain size and geometry, moisture content ...   

       It's complicated ...
8th of 7, Nov 09 2020


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