It's all about geometry, a really well balanced mix of rock sizes will allow you to minimize the gaps that need to be filled with liquid asphalt. So they need to make some of each size of rock not just the sand. It might be hard to visualize, but a bucket full baseballs and a bucket full of marbles have the same amount of void space in between, but a mixture of the two has less space.
America call it asphalt the rest of the world call it tar. Its like " to be different from everybody I will make my own words for stuff that already has a name".
Tar is not asphalt. Asphalt: a mixture of dark bituminous pitch with sand or gravel, used for surfacing roads, flooring, roofing, etc. Tar: a dark, thick, flammable liquid distilled from wood or coal, consisting of a mixture of hydrocarbons, resins, alcohols, and other compounds. It is used in roadmaking and for coating and preserving timber. Macadam: broken stone of even size used in successively compacted layers for surfacing roads and paths, and typically bound with tar or bitumen.
