Should hardcore be angular?

[Brigadier]

Reason I ask, I have a load of pebbles and cobbles, and will use them, if suitable.
It's only for the edging stones of a patio, so won't have to bear anything more than foot traffic.

Thanks in anticipation.

 

[noseall]

As long as they are retained and compacted then crack on. Pea gravel runs all over the place when unrestrained but is a good as anything when retained.

 

[bernardgreen]

Hard core is best when angular

for what it is worth. An extract about railway track ballast ( a by product from research into something else )

Generally, angular stones should be used ahead of rounded stones simply because they interlock with each other which can help to reduce track movement. Granite, such as Cloburn Red, is one of the best materials for the job as it will not degrade under load when wet. Few rock types meet the stringent criteria for modern high speed railway lines and Cloburn sets the standard for all the rest.

 

[noseall]

Railway tracks and sleepers are open at the top i.e. not full restrained so yes, I'd agree that a more spherical granular material in this case would be worse than angular stuff.
I've seen road (highway trenches) filled with pea gravel.

 

[Brigadier]

Begs a wider question then, Gents....

...as concrete is hard as, what purpose does hardcore serve at all?

 

[stuart45]

Begs a wider question then, Gents....

...as concrete is hard as, what purpose does hardcore serve at all?

Hardcore is a cheaper filler. If you have to take out a ft of topsoil but only need 4 inches of concrete it's cheaper but not stronger to use 8 in of hardcore than 12 in of concrete. There is a limit to the depth of hardcore you can use under a slab as it will settle, even when well compacted.
Some people think that using hardcore under foundation concrete makes a better job, but this is incorrect.