I've been looking at various options for what to use in a rubble trench foundation. One thing available locally at a fairly low price is asphalt millings. Now I really don't know much of anything about asphalt millings, so I'm wondering if anyone can fill me in....any chance of using this for a rubble trench foundation?
A primary function of a rubble trench foundation is it's ability to act a drain for any water. Without knowing exactly what asphalt millings are like, but knowing what asphalt is like, I would be concerned that the material would not remain "loose" enough to function as a drain. Over time would it compact into one large wad of asphalt? It seems with rubble trench, the key is have large enough material to promote fast drainage, but small enough to compact effectively, eliminating settling. I have only done one rubble trench, so I am by no means an expert.
I would steer clear of the asphalt trimmings. They seem to be most useful for driveways due to their ability to fuse together, harden and compact in hot conditions. I doubt without direct sun exposure they would ever do this, but the compacting might lead to a rubble trench that won't drain properly. It might be a good resource to mix with gravel if you are hard pressed and you can really get it that cheap. It is supposed to be more freeze resistant than gravel which is a plus.
It is soft, a primary use of the trench is to distribute the loads in the structure to the ground, so if you use a material that is soft it will not do that well. You need an engineering type answer, as some footings are placed over foam, and others over rock, depending on the loads it may be OK either way. I don't like the idea of asphalt because it is sorta yucky chemical stew.