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Need a Design Math Check. Length of Helix.

11/11/2016 8:31 PM

Okay, way too long since I had to calculate something like this so I need a basic math check.

I'm designing a large tub mixer for doing 2 - 2.5 cubic yard batches of concrete and for the tub mixer paddles I am going with a simple single turn helix of 3" x .625" steel bar stock. Being it has to both mix and push the wet mix to one end to unload it needs to have a helical shape to it.

So here's the dimensions.

The tub is ~38" dia by 66" long and I need the single bar to make a 360 degree arc in that 66" distance.

My rusty off the top of my head math says that the bar stock to make that helix paddle needs to be ~ 132" long and the online calculators agree but I feel like I am missing something in the equation relating to the bar dimensions affecting the clearances which I need to be about .5" on each side and end that the basic online calculators don't include.

Oh yea and if anyone wants to nerd out the rough math on torque to spin such a pair of them 180 degrees apart though dry 3:2:1 base concrete mix I would be curious to see what you get for theoretical worst case scenarios so I know what sort of power I am going to have to shoot for based on a ~30 RPM mixing speed.

I'm guessing 3000 foot pounds minimum but I may be way short at that in realistic operating terms.

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#1

Re: Need a design math check. Length of helix.

11/11/2016 9:27 PM

I'm certainly not going to offer any help with the math.. But i enjoy fabricating and have mixed and poured quite a few yards of concrete.. With various machines. And sometimes manually. So i can appreciate the task. That's quite a lot to mix per batch.

What shape is the tub?

Will it tip?

Will this be a cylinder with or without a taper?

How many or how frequently will it be cycled?

As for the helical shape.. Please make a great template out of cardboard first so as to rest easy with thr math.

Tub or drum?

I don't understand how a helix would unload a tub.

More info please

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#3
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Re: Need a design math check. Length of helix.

11/11/2016 9:47 PM

It's basically a 38" wide by 66" box 48" high with a half round bottom that will be mounted on a trailer.

The helix will work as a auger of sorts that will push the mix towards one end that will have a port on the bottom.

I'm to the point now with several of my larger home projects where I need to do concrete in fair sized batches that are way too big to do with a 4 cu foot drum mixer. Between the new house project and wanting to concrete the shop floor plus have a good sized pad in front and other projects my family have I need something that can do up to a 20 + yard job in a day.

Also given we have at least 120 yards of pours to do and truck delivered is pushing $130+ a yard and we can make it ourselves for around $40 it doesn't take much to see where having our own machine that can do a fair sized batch at a time is worth building.

Actually after rethinking the dimensions I have already changed things to be a 78" by 40 inch high design to make it longer and lower so loading it with the tractor will be easier.

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#4
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Re: Need a design math check. Length of helix.

11/11/2016 10:30 PM

Hmmmmm . . . . 120 cu. yds, if you were doing six inch slabs, that would be about 720 sq. yds . . . Holy aggregate Batman, that's a little larger than a flippin' football field!

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#10
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Re: Need a design math check. Length of helix.

11/12/2016 5:03 AM

Yea but it's not in a single continuous pour. More like a dozen or more smaller ones spread out over some time span.

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#2

Re: Need a design math check. Length of helix.

11/11/2016 9:41 PM

Just unwrap your helix and it is a diagonal on a rectangle, the height of the rectangle is the tub length and the width the is circumference (2 pi x radius of helix). The length, of course, is the length of the diagonal.

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#5

Re: Need a design math check. Length of helix.

11/11/2016 11:19 PM
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#6
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Re: Need a design math check. Length of helix.

11/11/2016 11:41 PM

2 yds...mounted on truck....

http://www.minimaxconcrete.com/

The above is a 3 yard concrete mixer custom made for a company working on the Panama Canal. It is run off a 27 HP Koehler Diesel engine.

http://www.minimaxconcrete.com/Currentprojects.html

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#12
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Re: Need a design math check. Length of helix.

11/12/2016 5:29 AM

I had thought about that but those designs are not easily loaded on site with common small to mid sized tractor or skidsteer loaders hence the open top tub concept.

A 38" x 78" x 20" tub mixer with 48" x 90" x 20" hopper top is easy to load with anything. Plus it's just one rolled 5' x 78" steel sheet and the rest is all flat sheet of which I all have on hand already. Same with the steel channel iron and axles for the trailer frame. No cost to me other than time and welding materials of which I have lots of that too!

That and with this design it's easily towed empty with a 1/2 ton pickup or loaded with a 3/4 ton so when I am not using it I can rent it out for $100 a day to whoever wants to do small jobs that don't justify having a full sized mix truck, plus it's partial load delivery fees, show up.

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#16
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Re: Need a design math check. Length of helix.

11/12/2016 8:53 AM

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#7

Re: Need a design math check. Length of helix.

11/11/2016 11:50 PM

Ahh.. yes. A ribbon blender.. totally tubular man.

with a gate valve. ..nice

below is a picture of what I think you have in mind.

..except that it's a side dumping double helixy style.

I'm guessing your doing a single spiral?

either way. one idea to think about.

cut roughly 38" diameter "O's" out of steel and then slit the O at some point effectively making it a large C's, but it would still look like an O since the slit would be as narrow a kerf as your cutting tool. (blade, grinder, torch, plasma, waterjet, laser)

...moving on. pull up on one end of each "C" until it's the cut ends are now permanently bent a foot or more apart.

Make enough of the same dimension to span the length of the drum and lap weld them to each other (and the radial support arms) until it looks like a roughly 74" long spring inside the drum portion. With a little finesse you could make a nice mixing/unloading blade that can be whatever height say.. 2" to 6"? and oriented at 90 degrees to the drum.

... anyhow.. those are my first thoughts. if that makes enough sense? it's late here.

What type of reduction are you thinking? pulley? gear? HP?

.. a pivot point that you could engage when almost empty (and therefore much lighter) that would allow the entire tub to tilt just a few inches towards the gate might be useful for unloading nice dry batches?. ...if you have the clearance

..and ..a wheelbarrow dump height is alway useful. huh?

..zzzzz

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#9
In reply to #7

Re: Need a design math check. Length of helix.

11/12/2016 4:07 AM

Those ribbons looks a little light weight for cement.

that actually looks to be some type of ingredients mixer for food stuffs and the like.

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#15
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Re: Need a design math check. Length of helix.

11/12/2016 7:45 AM

..That's because it is a lightweight industrial food stuff mixer. I was only using the pic for reference.

That said. The more surface area on the helical ribbon. The more power required to crank the drier stuff.

Id stick with a narrower ribbon and add a few short cross pieces on my ralial supports to break up the mix as well.

..where's my coffee?

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#21
In reply to #15

Re: Need a design math check. Length of helix.

11/12/2016 10:01 AM

I was actually holding off on my criticism. I had design 1000# cheese blenders, and not only the ribbon itself, the weakest point is the rods supporting the ribbon. They'd snap like toothpicks.

But your picture reminded me of my nieces husband and his cement experience.

smart guy, an ME, but he does stupid things. He was building a storage building 40' x 100' building about 8 years ago. For what he says to store his kids stuff? When I asked him, stuff? For a 40'x100' building, That's a lot of stuff. He said yeah bikes and 4 wheelers??

i told him if you gonna to build a building for yourself, just say it.

Anyways, he had family (in-laws, my nephews, his brother) and employees that worked at his dads company help.

but him and my two nephews poured the concrete slab. He was the general contractor. It was rough, and after the pour, a few days later it rained, and there was irregular slope on it. And puddles everywhere, some 2-4 inches deep.

i asked, where he learned to pour, Google U. Before he could answer, His wife, my niece laugh... as said yes... I think he had a talk with her later about speaking up like that.

I talked him, that learning off of Google is ok, but it only goes so far. What Google U. (That's just Google) as a hard way of to explain is experience.

When you pour cement, you try to have the cement truck spread the cement out, if you say about 3-1/2" thick, most the drivers are pretty good and can do that. Because it hard to pull cement, when he soon found out through the School of hard knocks.

well, turns out, he just had them dump it, in piles. And he soon realized his mistake. But he should have had someone with a little experience that worked cement before.

Because he ordered the trucks at 20-30 minute intervals. When a truck unloaded, another was right behind him. And he was not had his forms or markers set up.

because he was my nieces (who was like a little sister to me) husband. I refrain from saying, "for some people, the best tool in their tool box, should only be a checkbook."

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#25
In reply to #21

Re: Need a design math check. Length of helix.

11/12/2016 10:23 AM

That having t deal with fully loaded trucks showing up at timed intervals when you really don't need them at that rate is one of the best reasons for a small DIY crew to do on site as needed batch mixing.

If you don't have enough experience and guys to handle 10 yards of wet concrete at a time it's a miserable job that can go bad very fast.

The last slab I did was for my workshed last year and that was a ~3.5 yard pour for a 14' x20' and all I had for a crew was me and my wife (90% me 10% her) to work it at the time and boy was I worn out after that.

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#29
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Re: Need a design math check. Length of helix.

11/12/2016 12:00 PM

Understandable

That having t deal with fully loaded trucks showing up at timed intervals when you really don't need them

What's worse is having the trucks late also...

If you know what your doing, have a strong back and in shape... it works.... well, you work.

flat work is ok, not my choice of careers, I do care for doing walls though. When we build a barn, I was about 20, I helped the contractor set the plywood forms, and remove them. They were heavy. Now they have fiber glass.

It was hard work,p, I was 6-3" and 180 lbs., what made it worse the contractors son who was huge. 6-4 or 5. And looked like he could really work, I and his dad constantly had to ask him to move out of the way. His dad was pissed.

but I learned a lot.... not only to do the buildings and slabs we built on our own, but most important. not to work with cement as a career. I'd rather bale hay.

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#51
In reply to #25

Re: Need a design math check. Length of helix.

04/18/2017 12:27 PM

Minimum # of guys we need for a 10 yd pour is 4, preferably 5, . Depends if it is hardrock chute pour or pumped 1/4" pea gravel. Pump pours are much easier and the hose is dragged by 2 guys and the concrete is extracted pretty close to final spot. One guy is on the shovel behind the pump nozzle, evening things out, and a rough screed guy behind him. Realize that we set up screed guides not more than 10' apart. Middle elevation of slab is always set no less than 1/2' high for each 12 lineal feet, to allow for slab settlement while screeding. Pump pours are always weaker, and not recommended for loading facilities..OK for light duty driveways, sidewalks, sheds , garages etc, but hard rock is always preferable. I could go on, but I would be letting my beer get warm..

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#52
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Re: Need a design math check. Length of helix.

04/18/2017 12:37 PM

And that depends on if the guy in the RediMix truck knows what he's doing.

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#26
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Re: Need a design math check. Length of helix.

11/12/2016 10:27 AM

For the record. I wouldn't use hardware or design features that would snap or fail. I"ve left out critical dimensions and stayed true to the op design.

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#27
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Re: Need a design math check. Length of helix.

11/12/2016 10:38 AM

I'm open to other suggestions and what is their advantages or disadvantages.

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#38
In reply to #27

Re: Need a design math check. Length of helix.

11/12/2016 6:01 PM

four card stock rings laser cut and "lap welded" with a glue stick.

..advantage. diy..among others

very easy. ..and what I was trying to describe in 1st post

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#39
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Re: Need a design math check. Length of helix.

11/12/2016 6:07 PM

Through work, I was pricing out the continuous helix for a centerless screw conveyor.

28" od

6" flight face

1/4" flight thickness

The only coumpany that could do it was located in china was the only, and the only one that would do it. And this came in low (a fraction) as to compared to a welded sectional flighting made in USA or Canada.

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#41
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Re: Need a design math check. Length of helix.

11/12/2016 6:13 PM

nobody asked me to do it.

I'd have it done for about 3X the material cost.

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#44
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Re: Need a design math check. Length of helix.

11/12/2016 8:01 PM

Wow, we're looking for one, I'll supply the specs. If you would like to,quote it message me and I'll message you the drawings.

but the The China quote,

Material: 310 SS

flight as dimension earlier.

total: length 260" (they needed to make in in 2 sections)

price: $5,250.00 for both fob China.

remember no section welding, all rolled except at the the two sections together. But I'm flexible with the quote, if I can get it domestically.

Btw, sorry tcmtech,...

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#45
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Re: Need a design math check. Length of helix.

11/12/2016 8:26 PM

Seeing the spec. I'd have to say I'd be out of my comfort zone on that one. I'd end up farming it out to waukegan steel.

They are my go to guys for material and fabrication that I need and won't do.

Not that I wouldn't try. Thanks anyhow!

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#46
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Re: Need a design math check. Length of helix.

11/13/2016 10:57 AM

That is for the contact.

I appreciate it.

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#42
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Re: Need a design math check. Length of helix.

11/12/2016 6:26 PM

Interesting. I may have to do a bit of sacrificial testing with some thinner steel sheet and see what it looks like once assembled and pulled into the correct shape.

If the as calculated dimensions of starting with a 40" dia ring and stretching it out gives me a reasonable 37" x 78" helical piece I will call it good!

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#30
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Re: Need a design math check. Length of helix.

11/12/2016 12:04 PM

Noted...

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#8

Re: Need a design math check. Length of helix.

11/12/2016 2:29 AM

When viewed in projection from the end, your helical strip has an i.d. of 31", an o.d. of 37", and a neutral-axis diameter of 34". The neutral-axis circumference is 106.8". Applying Pythagorean Theorem to that and the 66" axial length gives 125.6" strip length. (You may have been computing on o.d.)

125.6/pi ≈ 39.96", call it 40" neutral-axis diameter. You could roll a flat bar to that the "hard way", or make it out of circular arc pieces totaling 360 x 125.6/106.8 ≈ 423.4º of total arc. Weld it all up and stretch/twist it into the finished helix.

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#13
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Re: Need a design math check. Length of helix.

11/12/2016 6:52 AM

I've always done my math for circles based on OD values being that's where the go/no go clearance issues seemed to always come in the as made designs but its been years since I had to make a helical shaped piece like this.

As for rolling the 5/8" x 3" bar stock I will have a local fab shop do it being I dont have the equipment for such work.

They rolled my 5' x 10' x 3/16" steel sheet into the 38" half pipe for $90 so I plan to have them roll my helix bars next but I want to have my math done ahead of time to make sure they do it right.

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#43
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Re: Need a design math check. Length of helix.

11/12/2016 7:17 PM

That won't quite work in this instance, but it won't hurt much. Your resulting piece will be a bit longer than needed. You can cut off the excess, or just ignore it, in which case the finished helix will be slightly larger in o.d. than intended.

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#11

Re: Need a design math check. Length of helix.

11/12/2016 5:18 AM

The design will be a towable and easy to maneuver 6' x 12' trailer rig that can be easily loaded with most any common loader tractor or skidsteer from the sides.

As for cost I doubt it will be much over a $1000 being I have all the steel plus drives, engines, axles and other components already on hand. I just need to nail down the numbers to figure out what needs to be cut to what lengths for the helix auger and how much power it's going to take.

Drive wise, is it's not too much I will go hydrostatic with a large chain drive reduction on the tub but if the power levels are too high to be practical with the hydrostatic drive and chain reduction I have I have an old combine that has a pair of beefy gear reduction units on its drive wheels that are more than enough to go direct drive off one of those.

Same with the engine. I have anywhere from 16 - 30 HP gas or 20 - 45 HP diesel on hand to use.

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#14

Re: Need a design math check. Length of helix.

11/12/2016 6:59 AM

A helix is just a rolled-up triangle (think, 'toilet-paper tube'). I.e., if you unroll your helix, you'll get a triangle.

Simply apply Pythagorean's formula, A2 + B2 = C2, and solve for C. C will be the length of the helix.

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#17
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Re: Need a design math check. Length of helix.

11/12/2016 9:07 AM

Really?

In all my years of math classes not once was a helix ever explained so simply.

All the calculations I saw behind finding the length of helix makes your example seem too simple to be correct.

That's why I felt the need to double check things here.

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#50
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Re: Need a design math check. Length of helix.

04/16/2017 1:27 PM

You learn that one quickly when estimating how much wire you'll need to wind a cylindrical coil. With multi-layer coils you treat each layer similarly, increasing the diameter slightly with the wire typically nested in the grooves of the previous layer - unless you're using square-cross-section wire (which I use occasionally), and then you simply increment the layer diameter by the thickness of the wire. With round wire you increment the layer diameter by √3/2 * wire diameter.

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#18
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Re: Need a design math check. Length of helix.

11/12/2016 9:13 AM
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#23
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Re: Need a design math check. Length of helix.

11/12/2016 10:12 AM

Excellent. Ga

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#22
In reply to #14

Re: Need a design math check. Length of helix.

11/12/2016 10:10 AM

But Your slope and rise is skewed. There needs to be a circumference variable

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#19

Re: Need a design math check. Length of helix.

11/12/2016 9:42 AM

A rolled helix will not be at a 90 to the drum. It will not mix or unload like the flattened spirals of my suggest. Think about it. Imo

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#20
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Re: Need a design math check. Length of helix.

11/12/2016 9:46 AM

The concrete needs to be completely emptied after each batch and the tank/mixer flushed out....you can't have any curing cement mixed in a fresh batch, it will produce crumbling product....

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#24
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Re: Need a design math check. Length of helix.

11/12/2016 10:13 AM

That's sort of true but time between batches has a huge effect on that.

Concrete takes some time to cure whereas very thin residual material often dries out before the chemical reaction takes place nullifying its curing so if batches are being done in reasonable intervals cleaning things out is not needed. The leftover bit from the last batch will just get worked with the next.

That drying out before curing and having the mix revert back to it's dry inert state is one of the biggest issues to deal with when pouring concrete on a hot dry windy day. The surface will dry out and turn to flakey crust before the bulk of it has had time to set up properly.

My brother proved that a few days ago with a smaller 10' x 10' pour he did. It was getting cold out and the pour was in a new addition to his work shed where he has in floor heat so he figures to keep the concrete warm enough to cure overnight he hooked up his hot water lines and let it rip. His hot wet concrete had its surface dry out before it cured so it looked like frosted flakes the next morning.

Fortunately the underlying bulk had not cured all the way when he found it so a good wetting down and surface rework got it to rehydrate well enough to be able to refloat and smooth out with the hope it took a bond to the partially cured underlayer.

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#28
In reply to #24

Re: Need a design math check. Length of helix.

11/12/2016 11:58 AM

I always cover the slab with plastic and allow it to dry slowly...but it depends on the mix type, some concrete nowadays cures rather quickly....I was always taught the slower it drys the harder the concrete...so the formula of the concrete mix and what additives you have, make a difference...Generally speaking the concrete batches if mixed and poured back to back don't require complete rinse out, but care should be taken to empty the mixer completely....my experience is that the concrete is workable for about 20 min, so everything must be timed around that....allowing the concrete to set in the mixer is a nightmare that can sneak up on you before you realize it....working by yourself, or with just 1 helper, you need to plan breaks, and one batch of 2.5 sq yds at a time is plenty....I have done 10yds with 3 people, but the concrete started setting before the edges were finished....It's nice to have somebody to just rinse out the mixer while you concentrate on working the concrete into place....Forms and screeds are necessary for proper thickness and level surface...$.02

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#31
In reply to #28

Re: Need a design math check. Length of helix.

11/12/2016 12:09 PM

Yes, and for faster cure time, they can add chlorine (I believe) but you cement loses it durability.

the cement work on the Hoover dam is still curing, and will be for a while.

anyways a little off-topic, the curing is a exothermic reaction. In the Hoover dam, they have water cooling pipes to make sure the curing cures evenly.

but, that's not needed here... unless he wants it.

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#32
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Re: Need a design math check. Length of helix.

11/12/2016 12:23 PM
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#33
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Re: Need a design math check. Length of helix.

11/12/2016 1:13 PM

The number of times I've heard that line about the hoover dam in incalculable.

So when do you expect the dam will cure?

It makes me think the roman coliseum might still be curing?

How many decades can the exothermic curing process last?

is the water in the cooling pipes sill exiting at an elevated temp do to this?

..

i always pour a dry mix (compared with the soup I've seen) followed by a vibratory tool to remove air pockets and bubbles, screed , and then cover with visqueen until cured.

rock solid always.

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#35
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Re: Need a design math check. Length of helix.

11/12/2016 2:47 PM

Yes, and I think the park service as some blame to it. I think it was some embellishment with the guides.

but I even saw it within the past 5 years on a documentary, as well when I took a tour there 30 years ago. The reason they put the pipes is so it wouldn't crack due to the heat couldn't escape. I was quite surprised. But when I looked into the website, it was stated that since then, they had blocked the pipes off and grouted them shut. technically the curing stopped.

i wouldnt say that about the coliseum, understandable base on my earlier post. because the Hoover dam cement is quite a bit thicker.

A professor at the university of Wisconsin-Madison started what was a 50 year study of cement at the turn of the century. But this professor made so many samples, it became a 100 year study. Which I believe is over now. (With still samples left over.)

About the dry mix, yes my neighbor used that dry mix when he put in a fence.

when cement cures, it's not that it drys out, curing is the chemical reaction happening.

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#40
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Re: Need a design math check. Length of helix.

11/12/2016 6:10 PM

..I'm being mistook again.. I don't use dry concrete mix. just low enough moisture that it will still flow well and be like a thick chunky soup.. mmm

-reason?

"When there is too much water in the concrete, there is greater shrinkage with the possibility for more cracks and reduced compressive strength. As a general rule, every additional inch of slump decreases strength by approximately 500 psi. So for example, if you ordered 5-inch slump concrete and received 7½ inches, a mix designed to be 4000 psi would end up being 2500 psi. This represents a serious loss in strength, especially if you were placing exterior concrete in a freeze/thaw climate where the standard requirement is 4000 psi for proper durability."

(from Joe Nasvik - concrete construction)

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#34
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Re: Need a design math check. Length of helix.

11/12/2016 2:37 PM

Over the last few years my brother and I have picked up all the major tools and power equipment needed for doing our own concrete work. That big piece for our puzzle is a mixer that can do the size of batches I am designing this one for.

It's not that we wanted to but given that most of the concrete contractors around town are real crooks we figured that for what hey charge we could buy good used and in some cases brand new equipment and learn to do it yourself.

The last time any of us checked around on having larger jobs done for us was when I started playing out the new house project and the lowest bid was ~$25,000 just for the labor for a slab and walls for a 27' x 56 x 8' basement and I had to dig the hole, and supply the concrete and the guys who bid it flat out told me ti was an easy job that just two of them could do in a week.

Based on that I figured they work six 10 hour days for $25,000 that's over $200 an hour per person for menial labor.

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#47
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Re: Need a design math check. Length of helix.

11/13/2016 12:24 PM

Ha,, all work is menial after you've done it a few hundred times.... then skills only come into play when something goes wrong....I used to tell my customers I don't get paid so much for what I do, but for what I know...The difference between creating art and a nightmare...haha

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#48
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Re: Need a design math check. Length of helix.

11/13/2016 12:32 PM

Until you really do it, the skill to this so called menial task is knowing how to do this.

your comment of,

I don't get paid so much for what I do, but for what I know

also applies for skilled labor on knowing how to do it, hence the work skilled

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#49
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Re: Need a design math check. Length of helix.

11/13/2016 1:57 PM

I disagree. I don't charge much for things I am familiar l with and good at because for me they are familiar and easy and thusly not much effort for me to accomplish.

As for concrete work I have done enough of it over my lifetime to know it isn't worth $200 an hour per person for labor either. Especially so if you're working with 50+ year old slow outdated processes.

I have no problem with a skilled person who is working with all modern equipment getting paid well because he can get a lot done fast but I have a huge problem with two hillbillies using slow antiquated equipment and processes expecting $200+ an hour.

At this point for us a ~27' x 56' x 5" pour done to a +- 1/4" plane tolerance is one long day with three decent guys. We have the power screed machine, power trowel, laser levels and all the other misc tooling to do that sort of work now.

We came a long way in the last 2 - 3 years and it didn't cost anywhere near what the typical contractor claims getting set up for this sort of work claims it does either.

I did that pad 90% by myself and set that building that's behind and to the left of it on my own last year.

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#36

Re: Need a design math check. Length of helix.

11/12/2016 5:27 PM

Duh, an assumption at worst case scenario is like rotating the whole cylindrical volume of concrete.

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#37
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Re: Need a design math check. Length of helix.

11/12/2016 6:01 PM

Not what he really asked

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