crushed concrete for drainage?

[meaning]

Hi all - I am a newbie so I hope this isn't too off-topic:

We're in the process of preparing to pave a back patio. For this we've had to remove existing broken concrete and do a lot of digging, including a drainage trench. Yesterday I looked at the size of the area and the amount of broken concrete we have to get rid of, and a hopeful lightbulb appeared above my head. Are there any issues with using crushed concrete in a drainage trench or as a paving base?

cheers
Meaning

[Bob Willson]

Hi meaning, welcome to the board.

How can it be off topic? You just started the thread yourself.

Chunks of concrete or of anything solid like that would make an excellent sub strata for a patio. For the drainage trench it would be better if there was a lot more space between the particles such as with large gravel etc.
Is the concrete really crushed or just broken up into smallish lumps?

[meaning]

Hi Bob - thanks for the quick reply!

Sound like good news

The concrete is still in largeish chunks that I was thinking of breaking down further if it's appropriate...

cheers,
Meaning

[jackiew]

and if there is too much concrete for your patio base you may well be able to offload the surplus to someone local who is doing a similar job who didn't have concrete to destroy first. In UK in my experience people put postcards in the newsagents windows or stick signs in their front gardens offering free clean hardcore ( clean meaning that it doesn't come mixed in with a load of garden soil/weeds etc )

[Bob Willson]

I wouldn't break it down for the patio, only for the drainage trench.

[Rocker]

Bob,
20 - 25 mm is the ideal size for gravel in a drainage trench. It should not be any smaller than that. I used plastic that is used for damp-proof courses to cover the gravel in my drainage trenches, to stop the dirt percolating down into the gravel.

Rocker

[Dion N]

Bob,
20 - 25 mm is the ideal size for gravel in a drainage trench. It should not be any smaller than that. I used plastic that is used for damp-proof courses to cover the gravel in my drainage trenches, to stop the dirt percolating down into the gravel.

Rocker

In engineer techo-speak, such a drain would be known as a "blind" or "rubble" drain. It's effective, but only until the spaces between the rubble fill up with dirt that is washed down. Hence the use of the plastic to cover it. In a civil engineering application, a geo-textile or geo-fabric would be used, but that's very expensive and I reckon damp-course plastic would work fine...Ideally, you would lay the plastic in the trench and wrap the rubble in the plastic, rather than just laying it over the top, leaving a few holes at the spot where you want to collect the water from...

When it comes using the concrete as a base, you need a mix of different sized materiel so that the bigger stuff (concrete chunks etc) provides the bulk of the strength and the smaller stuff (could be sand or similar) fills in the gaps and provides so cohesive strength

[meaning]

I wouldn't break it down for the patio, only for the drainage trench.

Hi Bob

Did you mean that my existing large chunks would suffice for under the paving, or that I would need to break it up too small for that?

cheers everyone for your replies!
Meaning

[Bob Willson]

I mean that your existing chunks would be fine under the patio.