Definition : Bitumen whose rheological properties have been modified during manufacture by the use of a chemical agent such as crumb rubber powder, synthetic polymers, sulphur, and certain organometallic compounds.
1. Oxygen and oxidation ''catalysts'' as well as fibres and inorganic powders are not considered to be bitumen modifiers.
2. Modified bitumens may be employed directly or in the form of cutbacks or emulsions or blended with (e.g.) lake asphalt [CEN].