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  1. #1261
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    Quote Originally Posted by kustomizer View Post
    That'll do.............

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    I think that laying on the ground might produce at least as strong of a pour as with that blocking things up.

    ???


    ----------------------

    Think Snow Eh!
    Ox

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    It's actually code that rebar be supported like that Ox - it was explained to me that one way rebar fails is that water reaches it, rusts it, it expands when it rusts, and that expansion breaks the concrete. (Opposite of the intent of the rebar.) An extreme case of this is the Champlain tower that fell down in Miami. As I recall when my slabs were poured I was told that code required the rebar to be 2" off the bottom of the pour (and I think 2" below the top - the slab has a double matt.)

    And my collegues on the ground in Africa report that oh yes people can screw it up - current effort has gotten help from various experts in how to supervise the pour of a foundation. Slump tests and break tests exist for a reason...

    Hopefully the blizzards, earthquakes, and cow misadventures can hold off long enough for Kustomizer and Wonder Woman to get a good slab.
    Last edited by bryan_machine; 10-15-2021 at 02:16 PM. Reason: spelling

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  5. #1264
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    Not saying that laying on the floor is good, but from my Monday morning chair here, that tower appears that it would not allow "filling" inside it's cone, and even what part was filled would have a lot of surface not in contact with the rest of the pour. Essentially it looks like a conical black hole to me, lined right up with the rebar, seemingly negating any benefit of the rebar to begin with.

    I would rather see it warred up to short rods pushed into the ground.

    * I am not a concrete engineer.


    -------------------

    Think Snow Eh!
    Ox

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    Yeah now that I look at those supports, they are hollow................may make a void? I have seen other supports that were an upside down "T"...no voids...............but I like my 80¢ paver method...........chunks of crete imbedded in crete..............and I'm a tight wad

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  8. #1266
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    The rebar is fiberglass under the slab other than the 2 in the footings, the little cone things are supposed to fill up with concrete, so I am told, they have five 2" holes in them, one on top and 4 around the outside, they look like they would fill.

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    Quote Originally Posted by Ox View Post
    I would rather see it warred up to short rods pushed into the ground.

    * I am not a concrete engineer.
    Can't argue that.

    Moisture and rust from the soil yah pushed those into - or used moisture-carrying, then also rotting - wooden supports - follows Iron-bearing re-bar INTO the 'crete.

    Iron rust expands to as much as 14:1 vs pure Iron and has essentially zero strength in shear, tension, or cohesion.

    Ergo.. "crete done that way ultimately fails.... starting right along the line of the re-bar or wooden "pegs".

    Not complicated.

    Just inexorable.

    More thought went into those plastic gadgets than first appears.

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    Quote Originally Posted by thermite View Post
    Can't argue that.

    Moisture and rust from the soil yah pushed those into - or used moisture-carrying, then also rotting - wooden supports - follows Iron-bearing re-bar INTO the 'crete.

    Iron rust expands to as much as 14:1 vs pure Iron and has essentially zero strength in shear, tension, or cohesion.

    Ergo.. "crete done that way ultimately fails.... starting right along the line of the re-bar or wooden "pegs".

    Not complicated.

    Just inexorable.

    More thought went into those plastic gadgets than first appears.
    Don't discount the fiberglass rebar

    ain't the world we started our training in is it?

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    Quote Originally Posted by kustomizer View Post
    Don't discount the fiberglass rebar

    ain't the world we started our training in is it?
    Yes, it largely IS the "same world". The properties of natural minerals and process-derived materials are still what they always were - Persian, Greek, Roman engineers to present-day.

    So I do discount it.

    As if not even there. Horse hair has a better, longer track-record.

    Neither glass nor plastics bond as well to Portland cement as "clean" Iron - simply Phosphatized - does. Basic Chemistry thing. Low-level. Very. Look it up.

    Thankfully, it's just a passive slab.

    It could do the job well-enough with nowt but expertly graded and compacted waterbound macadam, Gypsum stabilized, not even requiring Portland cement.

    Lots of stuff in "our modern world" like that.

    It doesn't get paid for because it is optimal.

    It gets paid for because ... it was not expected to do anything especially challenging in the first place but .... make the hard to afford, easier to afford.

    It should serve as long as y'all are around to give a damn.

    Ultimately, that's all that really matters.


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    The fiberglass has some sand coating most of 1/32 thick, I imagine it is epoxy keeping it on, it don't scrape off. I don't know if it is as good as steel but it is available where the steel isn't, right here, right now.
    As mentioned above it will be in place longer than I need it baring a deep freeze or earthquake in the next few weeks.

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    Quote Originally Posted by thermite View Post
    Can't argue that.

    Moisture and rust from the soil yah pushed those into - or used moisture-carrying, then also rotting - wooden supports - follows Iron-bearing re-bar INTO the 'crete.

    Iron rust expands to as much as 14:1 vs pure Iron and has essentially zero strength in shear, tension, or cohesion.

    Ergo.. "crete done that way ultimately fails.... starting right along the line of the re-bar or wooden "pegs".

    Not complicated.

    Just inexorable.

    More thought went into those plastic gadgets than first appears.

    Hm?
    Is that real?
    I can follow that thought I guess.

    But then the question is of all the poured basements that have the small steel sticks poking out the sides of them?


    -----------------

    Think Snow Eh!
    Ox

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    Yes it’s real. There must be some old poured concrete buildings around you. Lots of them here, at least there used to be. Concrete is not a hermetically sealed product. Look at how those old buildings fail. Water gets to the reinforcement and causes rust then chunks of concrete spall off. Once the roof fails it doesn’t take all that long.


    Sent from my iPhone using Tapatalk

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    A lot of the old brick buildings in Salmon look like they need the bottom 3 feet replaced, quite a trick without a sky hook. We're in our mid 50's, it would have to be pretty bad not to out last us. Look at all the concrete the Romans left behind, those folks knew their shit

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    Chaplain towers south - cement high rise - fell down suddenly, many killed, others destitute.

    This bloke on youtube (one of the best 2 or 3 on this) does a nice series. Start a couple months back and move forward.
    Building Integrity - YouTube

    The long and short - if you let water, especially salt water (not so much an issue in Idaho) get at the rebar, the 14:1 expansion thermite talks about will happen, concrete will crack and fall off "spalling" and great trouble follows.

    It's slow. It's a little bit random.

    And of course, the structure needed the rebar to be stable in the first place - rebar is put in concrete for engineering reasons. (Maybe not always correct....)

    Most cement foundations I see the outside is painted with a black goo, surely meant to keep water out. I think modern rebar is coated as well? Drainage matters...

    We think of concrete as waterproof and fireproof. Well in relative terms it is. But as anybody who has used a plasma torch too close to the floor has noticed, it's not *totally* heat proof. Oh, and anti-ice salts will crack it too....

    You need the little rebar towers. Just like you need your seat belt...

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    What I want to know is where did we go wrong with our "modern" concrete vs concrete they poured long ago?

    One of the first shops I worked in was 70+ year old. Even then I was impressed at how FEW cracks were in the concrete floor.

    Today I am MORE impressed, my shop is less than 5 years old, and I already have several cracks.

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    Quote Originally Posted by Fal Grunt View Post
    What I want to know is where did we go wrong with our "modern" concrete vs concrete they poured long ago?
    Shiddy subgrade prep aside, two things:

    #1: Poor control of aggregate:

    - Good 'crete wants a continuous gradation of sharp aggregate. Closer to "perfect", the gradation from major-sized aggregate down to mineral fines, the better the interlock, the fewer the voids, the less room for "cement" and the less shrinkage possible.

    Cement is a GLUE. Not a filler. It has no strength to it as a filler.

    See "waterbound macadam". Re-discovery of what early man copied.. from NATURE, BTW. Same as Roman copied what volcanoes had left..

    They didn't understand the chemistry. They did not HAVE to "understand" the molecular chemistry of it. They only had to know enough to replicate "whatever it was" that nature had demonstrated to WORK.

    Roman engineers and "Acquarians" had more than a dozen different materials and formulae for different tasking. They could patch an aqueduct and turn water into it same HOUR, knowing their 'crete would hold and gain strength. Or build a road or elevated viaduct that would grow stronger for hundreds of years, not weaker.

    Some of their concrete harbour-works persist to the present day, partially immersed in seawater, every year of their service life.

    #2: Unfavourable water-cement RATIO.

    The best concrete is placed "water starved". It has to be rammed or at least vibrated into place. PITA to emplace, but that's how I do mine.

    It will then continue to ABSORB water from its environment - air included, thereafter.

    How long?

    Roman works have been confirmed by chemical analysis to still be gaining strength fully 2,000 years after original placement.

    "Modern" concrete folk pour a f****g 'soup' instead to make it fast, cheap, and easy, even "pump-able".

    It WILL shrinkage-crack and micro-crack sure as sunrise of a morning.

    "Long-range" planning isn't a thousand years.
    It's when the check clears.


    One of the first shops I worked in was 70+ year old. Even then I was impressed at how FEW cracks were in the concrete floor.
    Greenwich Park, London, England.

    Climb the hill toward Blackheath. Find a railed enclosure.

    Whatzat? The concrete and mosaic tile floor, just like the year it was emplaced. Placed water-starved. Rammed and hammered with mallets, not "poured". . of an old building.

    One built during the Roman occupation of Britain.

    Helluva lot more than "70" years ago!


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    Quote Originally Posted by Ox View Post
    Hm?
    Is that real?
    I can follow that thought I guess.

    But then the question is of all the poured basements that have the small steel sticks poking out the sides of them?


    -----------------

    Think Snow Eh!
    Ox
    It's all about your sense of how LONG such things are expected to serve.

    Distant relatives sold our G'GDad's home in East Bridgford, Nottinghamshire, England about ten years ago.

    New owners now occupy it.

    First time it left family ownership since John Hacker ('the younger'), retired a well-off silk-manufacturer - out of Yeovil - and purchased it from a minor noble as an existing manor house.

    Greatly expanded. Rebuilt twice, if I recall the history.

    Since 1598 AD.

    And that isn't at all "old" ... for UK or Europe.


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    Pop's Quonset hut was too close to a forest fire in 2015, when I opened the door to get a tow chain, always just inside the door, there was no such chain but a bunch of loose gravel instead. The chain was 6" below the surface, there were holes in the steel roof 30' up you could throw a cat through, some days later I found the concrete that made the holes over 100' away, there wasn't a piece of concrete bigger than a football left of the whole 60 x 150 slab, it was over 50 years old.
    img_1256.jpg

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    Quote Originally Posted by kustomizer View Post
    Pop's Quonset hut was too close to a forest fire in 2015, when I opened the door to get a tow chain, always just inside the door, there was no such chain but a bunch of loose gravel instead. The chain was 6" below the surface, there were holes in the steel roof 30' up you could throw a cat through, some days later I found the concrete that made the holes over 100' away, there wasn't a piece of concrete bigger than a football left of the whole 60 x 150 slab, it was over 50 years old.
    img_1256.jpg
    2 buildings that survived the atomic bomb in Hiroshima to be demolished - TheCivilEngineer.org

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    Selection Bias and Economics.

    Selection Bias: apparently a fair number of ancient and medevial structures fell down, were knocked down, or destroyed by fire. if you look for videos of Castles in the UK today you'll see some in ruins, that were clearly very stoutly built, and at least partly standing, but also partly collapsed. did the romans build things still standing? yes they did. but they also built things that collapsed? yes.

    Economics: "this old machine is still useful 100 years later! they don't build them like that anymore!" That's because they aren't that stupid anymore. The builders of that machine overbuilt it, didn't get paid for that, and neither their first buyers, nor the reasonably expected resale buyers, benefit from a current user being able to employ it. Would you really care to pay 5x more for a milling machine so somebody 100 years for now can get value out of it for basically free? No? Me neither...

    Do you want to pay 10x as much for your house to be standing in 300 years? Again, no...

    And, from everything I've read, heard, etc., (I'm not cement engineer either) Thermite's list - aggregate, foundation, water - is correct.

    Oh, and by the way, concrete likes to be watered externally after it's poured. I did that for various slabs, and oddly they've not cracked... This isn't secret - right on the bag of "repair mix" I used on a bulkhead it says "you MUST water the completed mix for at least 1 hour when done, 1 day is prefered" - I did this, we'll see how well it holds up...


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