Desirable properties of bitumen

A bituminous binder for roads should have the following properties.

1. Adequate consistency - suitable viscosity and penetration for the climate and traffic: sufficiently fluid at the mixing and spraying temperatures (to coat aggregate) and stiff enough at service temperature to avoid bleeding and rutting.
2. Low temperature susceptibility - its properties should change little with temperature (high penetration index), so it neither softens in summer nor cracks in winter.
3. Good adhesion and cohesion - strong bond with aggregate (resists stripping when wet) and good internal cohesion (adequate ductility).
4. Ductility and flexibility - ability to deform without cracking under traffic and settlement.
5. Durability / resistance to ageing - low loss on heating, resists oxidation, hardening and weathering.
6. Water resistance - impermeable and not damaged by water; low water content.
7. Safety - high flash and fire point to allow safe heating; no foaming when heated.
8. Purity - solubility in trichloroethylene of at least 99%, free of water, wax and impurities.
9. Workability - easy handling, mixing and spreading.
10. Economy and availability.