Softening point of bitumen according to ring and ball apparatus may be defined as:
Softening point of bitumen
Softening point of bitumen is taken as the temperature at which the sample soft enough to allow the ball, enveloped in the sample material, to fall a distance of 1 inch (25.4 mm).
Importance of softening point of bitumen
Asphalt (bitumen) and tar, including tar pitches, do not change from solid to liquid at any definite temperature. They gradually become softer and less viscous as the temperature rises. For this reason, the determination of softening point must be made by fixed, arbitrary, and closely defined method if the results obtained are to be comparable.
Softening point is useful in the classification of certain asphalts and tars, including tar pitches. It is indicative of the tendency of the material to flow at elevated temperatures encountered in service.
- A steel ball of specified weight is placed upon a disk of sample contained within a horizontal, shouldered, metal ring of specified dimensions.
- This assembly is heated in ethylene glycol bath at a uniform rate. Maintain the bath temperature at 3-5 degree Celsius for 15 minutes. Using forceps, place a ball previously cooled to a bath temperature in ball guide.
- Heat the bath from below so that the temperature rises at a uniform rate of 5 degree Celsius per minute.
- Softening point of bitumen taken as the temperature at which sample soft enough to allow the ball to fall a distance of 1 inch.
Results obtained by this method differ from those obtained by ASTM method D 36.