"The Natural Philosopher" wrote in message
...
David W.E. Roberts wrote:

"robgraham" wrote in message
...

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


Aggregate?
See http://www.feis.herts.ac.uk/Research...sp?groupid=114
I 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?



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.

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 a
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