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4.6.2 Multigrade Bitumen

Multigrade bitumen is manufactured from the same sources as conventional bitumen but requires processing to reduce temperature susceptibility. This provides some of the advantages of increased binder stiffness at higher temperatures while retaining satisfactory low-temperature characteristics. Although initially introduced for use in asphalt, a multigrade binder has been developed for sprayed seal work (designated as M500) to provide an improvement in aggregate retention at higher pavement temperatures. The properties of multigrade bitumen are specified in AS 2008.

Multigrade bitumen is treated as a conventional bitumen (Class 170 or Class 320) in the design procedures.

Multigrade may be used for high-stress seals and in place of conventional bitumens in high‑temperature areas.