Bitumen is a general term for the group of oil and tar products used to make roads and pavements. Most bitumen is now obtained by refining crude oil obtained from oil wells. Bitumen also occurs in nature as asphalt 'lakes' (eg the Trinidad Lake) and 'tar sands'. In Ancient Mesopotamia (modern Iraq) bitumen was used to bind mud bricks in architecture and construction. Bitumen is still used this way as a jointing compound for sea defenses.
Chemically, a bitumen is a compound of hydrogen, oxygen and carbon. The lightest bitumens are gasses and the heaviest bitumens are solids, the weight of the compound depending on the length of the molecular chain. Methane (CH4) and Ethane (C2H6) are gases. The molecular chains up to C18H32 or are liquids at room temperature. The chains above C19 are solids at room temperature: paraffin wax, tar and the asphaltic bitumen used to make roads. Highway engineers describe the longest-chain densest hardest bitumens as 'asphalt'.
Should bitumen bound paving be used in gardens and parks? As with concrete, the simplest answer is: only if it is out of sight (eg as the foundation of a drive surfaced with gravel, possibly resin bound). Though bitumen-bound paving is cheap and durable, it symbolises PUBLIC ROAD in the eyes of the modern world. There is also a durability issue: if oil or petrol drip onto bitumen (eg from a standing vehicle) it will dissolve the binder and produce a black sticky mess which adheres to footware - and then carpets.
Bitumen paving at its best