R&B

The Softening Point determines at what temperature the bitumen weakens under a certain stress and is thus also indicative for the resistance against permanent deformation. Modification can increase the softening point considerably. However, it is not a good indicator of resistance to permanent deformation, since it, for instance, does not take the elastic recovery into account.

A sample of binder is poured into a ring. The ring is placed on another ring in a water (or glycerol) bath. The temperature of the bath is increased while a steel sphere is lying on the sample. When the binder weakens the sphere will slowly sink through the sample and deform it to break the light beam. The temperature at which the light beam is broken is the Softening Point.