Dry Poured Concrete

[port125]

Something I have never seen before.

My you tube recommended me a video on a method to dry-pour concrete.
Basically screed off bagged concrete and water with a garden-hose.

One video is for a slab for a chicken coop - OK no load I get it.
But searching similar videos start they escalate up until they are putting structures on these slabs. That makes me nervous

Similar videos Tens of millions of views.

Promoting this seems reckless. I would think the best case is it holds up a couple/few years and needs replaced.

How would this hold up? Would it hold up? Has anyone actually specified or allowed this technique?

.

 

[jerseyshore]

That's good for fence posts, but not much else I would think.

 

[phamENG]

That's a "it gets just as hard as if you mix it, so it's just common sense to do it this way" sort of argument. It's no good for anything you want to last. I guess you might be able to call it a bastardized form of controlled low strength material, but even that's a stretch. Yes, I've done it for fence posts...supports a 14' farm gate well enough with a 4' embedment on the post...but anything else and it's not going to work.

 

[jerseyshore]

YouTube is littered with these types of homemade construction techniques that people think are revolutionary.

Just last week when there was that thread about truss repairs, I got a recommendation on YT for some guy in his attic repairing dozens of trusses. It was all wrong, but it had a ton of views. I guess this quality of work keeps us busy.

 

[Ussuri]

Is that even concrete? From the picture above I can't really see any aggregate

 

[port125]

Jerseyshore, You're spot on. Maybe this post should have been titled "Stupid stuff they do on YouTube."

Ussuri, Earlier in the video they show them pouring premix bags, they go to some trouble to push the aggregate down to get a nice finish.

I'm am putting it on my list to pour a sample of one of these as and core it out, for Science.

 

[jerseyshore]

Push the aggregate down for a nice finish, that's genius. Why doesn't everyone do that? I hate seeing those pesky rocks in my concrete too.

Reminds me of my first concrete design class in college; it was our first time mixing concrete and testing cylinders & a beam. Little competition to see who could make the best concrete. A few friends in a different group didn't realize that they tared the scale with the water in the bucket. So they went along their business and added the weight of water that they calculated was needed.

Let me tell you that was the most beautiful mix of concrete I've ever seen. The finish was so smooth it looked like clay. Well it also performed like clay too. When they took out the cylinder for the 3 day test, it slumped on its own. By 7 days, still mush. 28 days for the beam test, it deflected just under its own weight. But man did it look pretty.

That's how I picture this mix to perform.

 

[dauwerda]

Push the aggregate down for a nice finish, that's genius. Why doesn't everyone do that?

Well, this is actually a thing, typically only required for low slump concrete (super p has pretty much done away with the process, or if you are in the residential, just adding water ). I have always heard them referred to as jitterbugs.

https://www.concretenetwork.com/concrete/concrete_tools/tampers.htm

*edit* vibratory screeds have also eliminated the need as they do the same thing (push some of the course aggregate down and cause cream to rise to the top for finishing).

 

[EdStainless]

On the farm we used to build small retaining walls by stacking bags of mix, driving rebar stakes through them, and then walking away.


= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy, consulting work welcomed

 

[Aesur]

On the farm we used to build small retaining walls by stacking bags of mix, driving rebar stakes through them, and then walking away.

You should have used sandbags with barbwire between them, probably cheaper.

 

[phamENG]

I see the dry stacked bags of concrete around here for driveways over culverts all the time. If the driveway is wide enough that they're never loaded and you never touch them they're fine. But any sort of actual load on them and they fall apart pretty quickly. I think one of my neighbors has done it twice since I moved out here 8 years ago...

 

[jittles]

Better or worse than over-addition of water for a nice easy pourable "mix"?

I'd probably vote worse still, at least with too much water you're still actually mixing it thoroughly (presumably). But it might be closer than you'd think...

 

[JStephen]

"On the farm we used to build small retaining walls by stacking bags of mix, driving rebar stakes through them, and then walking away."

That's not just a farm thing, I've seen that done for hiking trail construction, also similar methods used to contain concrete for concrete encasement of pipe.

 

[Brad805]

Another method is called soil cement. Sprinkle cement on the ground and then rototill the area.

People will be people. Cheap and doing things twice is the way of the world.

 

[MotorCity]

You mean everything I learned about engineering by watching YouTube is wrong??? Say it ain't so.

 

[canwesteng]

I don't understand the stacking bags of premixed concrete concept - is it just an expensive sandbag?

 

[phamENG]

It's an expensive sandbag that gets hard.

 

[wrantler]

I kinda view youtube as a form of job security. The more things ppl mess up by DIY the more ppl call me up for a fix!

 

[JLNJ]

I made some similar "dirtcrete" for my fenceposts (as jerseyshore noted). Dry mix some portland cement with whatever came out of the hole, backfill around the posts and wet it down.

 

[hokie66]

Soil cement is established technology. Mixing cement with soil is used for stabilizing the subgrade and base courses in pavements. About 3 to 5% Portland cement by weight, I think.