Garden gravel as hardcore substitute?

[YodhrinForge]

Just wondering if it's allowed/sensible. I have a garden absolutely rammed with that heinous red gravel that was big in the 80's and early 90's and want to replace it, but paying to have it lifted or just posting on FB inviting randoms to come and shlep about my garden with shovels doesn't hugely appeal, so given I'm going to need a bunch of hardcore for the foundations of my new extension, my planned garden room, and as a subbase for a couple of new concrete floors putting it to productive use and saving myself the costs would gladden my tightfisted little heart. Maybe by mixing some sand into it to make up for the lack of fines? 

[Temp]

I can't think of a reason why not. Provided it looks like crushed rock rather than rounded river pebbles. Probably safer to use it under concrete floors rather  than in the bottom of foundation trenches? I'm not an architect or structural engineer though.

[YodhrinForge]

Aye it's this stuff: 

 

Seems to be granite from what I've read online? Thinking about it, I could somewhat over-order my concrete ballast and mix that in, end result should be fairly type 1-esque just lacking the few bigger ~40mm chunks.

Edited September 27 by YodhrinForge