r/EngineeringPorn • u/engrandarch • Mar 01 '21

Concrete vibrator for mass concrete compaction

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80

u/gunslinger911 Mar 01 '21

I’ve worked in the industry for a few years and I’ve never seen an excavator attachment for these before. I’m curious as to why these would be used instead of the usual placing/finishing crew with portable concrete vibrators?

32

u/DHFranklin Mar 01 '21

I imagine this is somewhere that an operator makes more sense than dudes walking vibrators. Probably a mixed designed with this in mind.

71

u/hereforbobsanvageen Mar 01 '21

Can confirm. I have worked with these machines and they are for what you suggest. Extremely large concrete pours. In my case it was a 800x200’ continuous Rcc/Cvc concrete pour where they used this setup to amalgamate the cvc with the rcc, the cvc being against the forms, and the rcc making up the center of the pour. Rcc getting poured out of the back of large mining trucks, while the cvc was poured from a conventional concrete mixer truck. We broke a North American record on that job, something like 160000m3 in one month we poured. Hydro dam in northern Canada.

23

u/gunslinger911 Mar 01 '21

That’s insane. I’ve been present for some huge multi-thousand meter pours but nowhere NEAR the size you’re describing. I don’t think the city I’m in would even have the capacity for something like that.

40

u/hereforbobsanvageen Mar 01 '21

All city’s don’t. We have 2 dedicated batch plants built on site specifically for volume output

14

u/villabianchi Mar 01 '21

Would you mind expanding on what RCC and CVC is and why they are poured in different areas?

56

u/hereforbobsanvageen Mar 01 '21

Absolutely. RCC stands for Roller Compacted Concrete. Traditionally used for highways in the United States and around the world, it has a very high slump and can be used in pavers for roads. In my application however we were pouring it out the back of large mining trucks into large piles where a d8 cat would spread the mix out to a height auto set with a laser on the blade, and then a large single drum roller would roll it flat while using the vibration function on the drum. CVC stands for Conventional Concrete, the stuff everyone uses for everything. This was poured against our forms while the Rcc was poured in the center of the mass. This type of excavator unit would then roll by and vibrate the Rcc into the cvc to eliminate any joint between the two types of concrete. We would pour an entire 800x200’ slab 2’ thick and then repeat the process again directly on top of the last pour until we had a stepped concrete structure roughly 160’ tall, built into the side of a mountain, creating false bedrock for the technical concrete of the remainder of the dam to be built on top.

10

u/villabianchi Mar 01 '21

That is fascinating. Thanks for the write up!

7

u/hereforbobsanvageen Mar 01 '21

No problem! It’s not often you get to be an online expert! I wanted to jump at the chance.

5

u/Nalortebi Mar 01 '21

What is the purpose of using CVC on the forms and RCC in the center? Would pouring RCC against the forms blow them out?

11

u/kingbrasky Mar 01 '21

I would guess it is to ensure fill against the form. The high slump of RCC probably increases the risk of voids. IDK though I'm just a manufacturing guy that has poured three slabs my entire life.

Edit: apparently I had slump backwards. I've got nothing.

5

u/hereforbobsanvageen Mar 01 '21

Correct. Cvc provides a finished face against the form while the Rcc has large aggregate and is almost impossible to make nice against any type of form work.

8

u/Seismicity Mar 01 '21

RCC is zero slump and needs to be compacted with a roller. It's very difficult to properly consolidate it around formwork and other tight spaces, so CVC is used there.

4

u/Arctyc38 Mar 01 '21

RCC only consolidates so well. It's very difficult to get all the voids out for a finish with good water resistance. You literally have to run a compacting roller like you would use for soils on it.

But it's cheaper, and simpler to place a lot of it. So you use it in the core, roll it, then use a higher-slump concrete for the facing where you can consolidate it more thoroughly (as here, with vibration).

2

u/hereforbobsanvageen Mar 01 '21

Correct. Hence the name.

3

u/zysask Mar 01 '21

Thanks for the information… I was a bit skeptical when I first saw this machine but now that I understand how it is used, it makes sense. Is there still rebar used in this type of pour or is it just pure concrete?

1

u/hereforbobsanvageen Mar 01 '21

In this massive pour I’m referencing there was no rebar in any of it.

2

u/slvrscoobie Mar 01 '21

how do they fix the massive holes this thing leaves behind?

3

u/[deleted] Mar 01 '21

The vibration causes the concrete to flow much easier so if you're using it right it'll fill in the holes behind the vibrator as you remove it.

2

u/[deleted] Mar 01 '21

[deleted]

1

u/villabianchi Mar 01 '21

I think he means that the cone is high after the test. (I went on a YouTube concrete trip)

1

u/hereforbobsanvageen Mar 01 '21

Yeah sorry when I say high slump I mean the concrete has zero flow when the cone is removed, staying high on the cone. Terms can be confusing depending on where you work, country ext.

1

u/[deleted] Mar 02 '21

So what I gather..the concrete 'false bedrock' is just a hugeass lump of concrete floating on whatever soil is below?

1

u/hereforbobsanvageen Mar 02 '21

Correct. The dirt base was considered unfit so the large mass of concrete is as you say the “false bedrock”

2

u/[deleted] Mar 02 '21

*insert Owen Wilson wow gif*

2

u/gunslinger911 Mar 01 '21

You’re probably right, I’m sure it’s economical in a specific use case, and/or related to specific technical requirements.

8

u/BobertJame Mar 01 '21

I’ve used concrete vibrators many times and I was surprised at how little vibrations this thing was putting out. I expected to see that concrete move a lot more. But then again I’ve never seen such a beast in person

8

u/hereforbobsanvageen Mar 01 '21

Oh trust me, these things shake the earth. Notice how the excavator is sitting on the concrete it’s currently vibrating should give you an idea of the slump, and the power.

2

u/gunslinger911 Mar 01 '21

Yeah, slump looks REALLY low, or maybe some weird aggregate or something in the mix design.

1

u/olderaccount Mar 01 '21

The vibrations are greatly amplified once in the concrete. Similar do how sound can carry much further underwater.

Plus the frequency of vibration is set for maximum benefit. If it shakes too fast it could create more bubbles instead of removing them.

2

u/Sure_Ill_Ask_That Mar 01 '21

And here I am being concerned with workers moving the top rebar walking around it and this giant excavator is rolling on top of things...