Plate-compacted concrete - is it a thing?

[Donkmeister]

In civil engineering, roller-compacted concrete is a thing. I understand that this involves laying a dry mix and then running over it with heavy machinery, rather than pouring a wet mix into a form and screeding it off the top. Not sure if water is added or if it is simply absorbed from the air over time, though.

Question is; can that (or something similar) be achieved with a whacker plate and readily available materials, whilst curing hard in a reasonable time (a month, say?) and to the sort of hardness required to build a shed on it (i.e. not crumbling when drilled to put a dog or plug in). The goal is a slab to build a wood-framed workshop and I want a slab floor (a wooden floor isn't an option).

Years ago I built something similar by arranging for a mix-on-site truck and some friends to help me shuttle barrows of concrete back to the slab location. This time that's not going to work as TBH I don't think I'm fit enough, and nor are my mates.

It's too far to chute the concrete, and a pump simply isn't economically viable. Using a mixer is one option but if I can simply pile the dry mix up in the form, whack it then give it a sprinkle with the hose a few times a day until it's gone-off then that seems like less work than lifting several tonnes of materials into the air and doing many, many batches over several days.

Any thoughts?

 

[^woody^]

In civil engineering, roller-compacted concrete is a thing.

Is it really? Not an Instagram thing, but a proven method with standards?

 

[Deleted member 292770]

.

 

[Donkmeister]

Is it really? Not an Instagram thing, but a proven method with standards?

Has the insta-bug reached civil engineering yet? I suppose stranger things have happened

I first heard about it when they were rebuilding the Oroville dam spillway - that was a pretty substantial project - also when I googled it Tarmac and Cemex both offer RCC. However... what I'm unable to find any information on is if (and how) the basic premise can be extended down to the very small scale civil engineering that is a shed slab. Possibly it's not used because builders don't want to wait weeks for a slab to slowly go off before they build on it, but it could be that it simply doesn't work without large plant or in small quantities.

 

[Donkmeister]

pay young people.

Great in theory and I've no issue with paying someone a decent wage, but there's no shortage of building sites (hence work) round here, so a bit of a challenge to find people willing to take on a single day of work when they can guarantee an ongoing income down the road.

Then there's the fun if you find someone and they don't show; annoying when it's not time-critical but if a load of concrete arrives and your paid help hasn't, it becomes a big problem!

 

[^woody^]

I tried something similar many many years ago on a slabbing job. We infilled with dry concrete mix in certain areas and misted the surface and trowelled it.

We later found that the surface was rock hard, but the concrete under it was hard, but crumbly and the areas needed to be replaced, which we did the normal wet mix way.

Thinking about it subsequently, I put it down to cement reaction and concrete strength being determined by the initial amount of water that starts the reaction. So it makes no difference how wet the concrete gets after the reaction has started. I don't know if that's correct though.

I wonder if the method you'r refer to uses different cement to ordinary Portland or requires additives?

 

[Donkmeister]

I suppose if the outer concrete forms a hard shell from the misting, any subsequent water won't penetrate to the insides (at least, not in a useful timescale), which might be another explanation for the rock hard/crumbly nature you encountered. Whacking it might just make that issue worse.

 

[^woody^]

Unless water is mixed in, the only way it can move through a material later is via voids, and if you compact dry mix, the voids are reduced.

This it's why fine aggregate mixes, well compacted, are more water resistant.

 

[SFK]

rebuilding the Oroville dam spillway

I watched the Oroville dam re-bulit with interest (amazed at the scale and at the use of RCC).
The RCC being put down is at 12m30sec into this video.

In answer to the OPP, no simple RCC solution for home use.
Normal slab concete is relatively easy and so the norm.

SFK

 

[Donkmeister]

I watched the Oroville dam re-bulit with interest (amazed at the scale and at the use of RCC).
The RCC being put down is at 12m30sec into this video.

In answer to the OPP, no simple RCC solution for home use.
Normal slab concete is relatively easy and so the norm.

SFK

Thanks for that, I'd only read about it so was interesting to see it being laid - you can see when the excavator-mounted whacker is being used there's still some definite wetness and "squidginess" to the mix, so it's nothing like what I was thinking (dry mix down, whacker, water).

Seems like I'll be doing normal wet-form concrete then.

 

[cdbe]

Don't you have barrow mix where you live? All you need is a rake, a tamp and pair of wellies.

 

[mrrusty]

Don't you have barrow mix where you live? All you need is a rake, a tamp and pair of wellies.

You don't even need that, or at least round our way. I've used three different barrow mix companies in the last 3 years and every one has tamped and levelled for an additional £40-50. I just stand around and watch.