since i was already using BioIndustries mod, which uses crushed-stone in some recipes, i chanced the basic recipe for asphalt to be 8 Crushed stone + 1 heavy oil + 1 Crude Oil. I think this is more realistic (asphalt is made 90% with crushed stone), so maybe u could implement it for players using this mod.
Overall, simple and well done, nice job and thx for your work.
Good idea, this aplies not only to BioIndustries but to all big mods. If one of these mods is present, certain parts of the recipe might be replaced by items provided by them.