Friday, September 11, 2020

Softening point of bitumen

Determination of softening point of a bitumen sample.

 Softening point of Bitumen

The Softening Point of bitumen or tar is the temperature at which the substance attains particular degree of softening. As per IS: 334-1982, it is the temperature in ºC at which a standard ball passes through a sample of bitumen in a mould and The ball falls through a specific height of 2.5 cm at a specified condition, when heated under water or glycerine. The binder which is used in construction of road,  must have sufficient fluidity at the time of road construction. The main reason to determine the softening point of bitumen, the maximum permissible  temperature can be heated to a bituminous binder for various road use applications.

Softening point title image


  • Ring and Ball apparatus

  • Water bath with stirrer

  • Thermometer

  • Glycerin

  • Steel balls each of 9.5mm and weight of 2.5 ± 0.08gm.


  1. Firstly heat the bitumen sample to a temperature between 75 ̊ – 100 ̊ C  and stir by a glass rod until, the bitumen changes its state to liquid and free from air bubbles and water. If necessary it can be filtered through IS sieve 30 mm. Previously heated Rings are placed to a temperature approximating to that of the molten material On a metal plate. The metal plate used   in softening point of bitumen should be coated with a mixture of equal parts of glycerin and dextrin. Leave it in open atmosphere 30 minutes for cooling, removing the excess with a warmed, sharp knife to level the material in the ring.
  2. Assemble the Softening point apparatus with the rings, thermometer and ball guides in prescribed position.
  3. Filling the water bath with the distilled water to a height of 50mm above the upper surface of the ring to a temperature of 5 ̊ C.
  4. Now gradually heated to the bath and stir the liquid so that the temperature rises at a uniform rate of 5± 0.5 ̊ C per minute for the test of softening point of bitumen.
  5. The temperature is the softening point of bitumen when any of the steel ball with bituminous coating touches the bottom plate, Carefully note down the temperature.


Softening point table image


The Softening value of given bitumen is ________________ .


  1. Should be careful the entire softening point experiment, and especially at the time of the heating of bitumen.
  2. Temperature should well controlled to the water bath.
  3. Should be taken care at the time of coating the metal plate.
  4. There shall be no smoking or the presence of other ignition sources in close proximity of test set-up.
  5. Distilled water should be used as the heating medium.
  6. During the conduct of test the apparatus should not be subject to vibration.
  7. The bulb of the thermometer should be at the same level as the rings.

Information Civil

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