Bruce wrote:
Tim S wrote:

Bruce coughed up some electrons that declared:

Tim S wrote:

Bruce coughed up some electrons that declared:

Tim S wrote:

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.
On a tangential, but related note, which type of hardcore is best under a
concrete house floor (just floor, not structural raft, though it might
carry the weight of some brick internal walls, non load bearing)?

MOT Type 1.

It cannot be beaten, because apart from spreading the loads into the
ground like other granular materials, it has significant strength of
its own.
Cheers Bruce. that's the answer in advance to another bit of work...


You're welcome.

I have long been a "fan" of unbound macadams, which are granular
materials that exhibit a surprisingly high strength when compacted,
simply because of the careful grading of the various sizes of material
used. In contrast, bound materials gain their strength mainly from
being held together with a binder such as cement (as in concrete) or
bitumen (as in bitumen macadam), although some of their strength still
comes from the interlocking of the aggregate.

It comes from the 1970s when I wrote specifications for civil
engineering projects such as airports and roads. I did an extensive
literature survey of a vast range of bound and unbound materials, and
developed a library of standard specifications which could be
incorporated into the contract documents for each specific project.
Coupled with extensive site experience on road and airport projects, I
became a specialist in construction materials, something which I
thoroughly enjoyed, and which paid my mortgage for 30+ years.

And its nice that you can share that.

However in the context of using random hardcore to make a subfloor base,
I think the relevant issues are that almost any stuff will do, provided
its graded right..i.e. big lumps with concrete poured over are not as
good as smashed up stuff with a good amount of particle size variation,
with added sand and ballast to fill in the sizes that smashing wont deliver.

Plus the fact that if you have e.g. old footings and bricks lying about,
its cheaper to use them - mixed with MOT or some other substance, and
well whacked with a sledge hammer - than paying to bring in new MOT and
paying to take away the scrap.

And if a load bearaing wall is to be inserted, its advisable to use a
proper strip foundation under it as well. i.e a proper possibly
reinforced, cocrete filled trench of at least 600mm deep, and maybe a
lot more in tree root filled soil.