I believe that a bitumen surface is applying a mix of small gravel and
bitumen, an asphalt surface is bitumen mixed with a wide range of
particle sizes( like a concrete mix). Asphalt is ideally applied as a
much thicker layer, with a much heavier roller as it is a less flexible
mix, but takes greater loadings. IME, both are poor surfaces compared
with concrete. Asphalt in particular suffers from surface "heave" if the
subsoil/base is not stable.

Regards
Capitol