"Consists of: An aggregate produced by a cold milling machine. The machine is used to remove the surface layer of a tarmaced area such as a highway or footpath. The resulting waste is loaded into a lorry and is officially known as Road Planings although many refer to them as Road Scalpings or Road Scrapings."
"Road Planings are not suitable as backfill for drainage trenches due to the high fines content and care must be taken when sourcing them as older tarmac surfaces which have been deep planed may contain tars. The use of Road Planings is generally considered environmentally sound as Bitumen is a natural substance. Using them also reduces pressure on quarried aggregate stocks.
Unfortunately the days of being to obtain Road Scalpings for free have gone as the pressure of the recession on local authorites has resulted in very little resurfacing work be carried out and thus Road Planings are not as abundant as they once were."
That is not something that I would put in the garden anyway. Road waste, what about heavy metals and oils and other nasty mechanical stuff? Neither the texture high fines , (too high for drainage ditch) nor the chemical content sounds like something the soil would like.