Re: re-use old concrete as an aggregate ?

[PoP]

hi, do any of you builders/DIYers out there know if i could use the

>old concrete which i just dug up from the floor inside my house, >as an aggregate for the new concrete i'm going to mix up ? >i need about 1/3 (one third) of a cu m. to fill it in again (after >burying CH pipes), so obviously, as i still have all the old stuff, >i could save some money by re-using it, otherwise i'll have to >buy about 400Kg of aggregate on top of the 200Kg sand and >100Kg of cement (have i got these quantities right by the way ?)

Can't answer your question, but my concern is about you "burying the CH pipes".

That might be a good idea, and it might not. Are you sure you want to deny access to the CH pipes for all time?

PoP

[robgraham]

Yes, you can re use concrete as aggregate. In fact it's often sold crushed for this purpose. I'd also query your idea of burying CH pipes. Talk to my next door neighbour!

Rob Graham

[David W.E. Roberts]

Aggregate? See

am now questioning if I understand what aggregate is :-) I have always thought that aggregate was the lumpy material (usually about

20mm stone) which was mixed with sand and cement to form concrete. I can understand how used concrete could be crushed to give 20mm lumps to give strength to the concrete mix, but this seems a little beyond the average DIYer. When I first read this I assumed that the OP was confusing aggregate (which goes into the concrete mixer) with hardcore which is generally used as a base for poured concrete. Now I am wondering if I have missed something?

Cheers Dave R

[cuckoo flower]

sorry, perhaps i should have explained better, the CH pipes i'm 'burying' are actually run through black hepworth conduit, along with junction boxes for any T's and elbows (including the elbows at the radiator exits), so all the pipework & fittings can be removed/replaced if necessary in the future.

anyway, thanks for your help, it's much appreciated

[The Natural Philosopher]

Mmm. Aggregate possibly not the ideal word.

Concrete is just stones, held together by sand held together by cement.

Its not as strong as the stones, but its stronger than the cement, so adding bits of mashed up concrete, old bricks, paving slabs and other assorted 'hard core' won't give you as good stregnth into the new mix as fresh aggregate will, but heck, sometimes its a question of volume, not strength.

If e.g. I am building a brick pillar that might otherwise be hollow (bad idea traps water, frezes exapnds splits etc) then I will fill it up with any old bits of rubbish and slop partially gone off mortar in it to fll the gaps. Brickalyers caught short up a scaffold fill voids with worse things than that, as well.

all adds to the bulk as they say.

[David W.E. Roberts]

To go back to the original post:

"otherwise i'll have to buy about 400Kg of aggregate on top of the 200Kg sand and 100Kg of cement (have i got these quantities right by the way ?)"

This looks like a fairly standard* 4:2:1 mix for concrete using aggregate and sand instead of pre-mixed sand and aggregate (ballast).

My Collins DIY defines coarse aggregate as gravel or crushed stone between

5mm and 20mm.

*On further reference to my Collins, I note that the standard mix for concrete uses 3 of aggregate to 2 of sand. Rations of sand to aggregate given are: General purpose 1.0 : 1.5 Foundation 1.1 : 1.5 Paving 0.9 : 1.5

So I conclude: (1) The OP was probably not talking about reusing concrete as aggregate (5-20mm) (2) To properly re-use old concrete as aggregate it will need grinding down to 5-20mm particles which is not normal DIY! (3) The OP was probably talking about using the old concrete as hard core to reduce the amount of new concrete to be poured. (4) The proposed new mix probably has too much aggregate in it :-)

So to restate the question (please correct me if I am wrong):

How much of the old concrete can be broken up and re-used as hardcore when laying the new 1/3 cu m floor?

Cheers Dave R