Tim S wrote:

sm_jamieson coughed up some electrons that declared:

Just putting in the hardcore (MOT 1) for my floor slab. 100mm required
(BCO agreed).
First floor slab I've done.
To what depth should I rake it out before compaction to end up with
100mm ?
In other words, how much should I expect it to compact ?
Thanks,
Simon.

I don't know about MOT 1, but I can tell you for a fact that reclaimed
washed railway ballast compacts from 8" as shovelled and raked out to 6" of
solid mass under several runs with a standard single-person vibroplate
compacting machine. I learnt this little fact after 3 of us busted a gut
moving the damn stuff to help a mate make his new crossover and drive.

Said ballast consisted of rock lumps typically about 1.5" across, no fines
and not much below 1". If that's similar to type 1 MOT, then I would expect
similar compaction ratios.


The two materials couldn't be more different.

Railway ballast is a single size material, typically 2" to 1" - the
maximum size being no more than twice the minimum size is what defines
a single size material. It is usually made of granite but can be made
of other strong rocks.

MOT Type 1 is a fully graded material, with everything from 3" (75mm)
down to dust, and all intermediate sizes present. It must be made of
crushed limestone.

With MOT Type 1, the small particles fill the gaps between the larger
particles, reducing the overall void ratio (the ratio of empty spaces,
or voids, to the total volume) to 20% or less. Railway ballast has
about twice the percentage of voids.