softening point test

Softening Point Test of Bitumen


Softening point test of bitumen is done to determine the consistency of bitumen. This test gives an idea of the temperature at which the bitumen attains certain viscosity.

Softening point is defined as the temperature at which bitumen softens beyond some arbitrary softness i.e. bitumen softens and sags down about 25mm below the weight of a steel ball.



  1. Apparatus Required  

a. A brass shouldered ring

b. A steel ball

c. Ball centring guide

d. Ring holder

e. Brass pouring plate

f. Water bath and thermometers



  2. Procedures in Softening Point Test of Bitumen  

1. The sample is first heated with continuous stirring until it becomes sufficiently fluid to pour.

2. A slight excess of the heated sample is poured into two rings that have already been preheated to approximately the pouring temperature.

3. The apparatus is then assembled with the rings, thermometer, and ball centring guide, and filled with boiled water up to a depth not less than 102mm and not more than 108mm.

4. The water bath temperature is then maintained at about 15 degrees celsius for about 15 minutes.

5. Then, balls previously adjusted to the temperature are placed on the ball centring guide.

6. The arrangement is heated at the rate of 5 degrees Celsius per minute. It must be noted that the temperature rise is uniform.

7. The maximum permissible variation of any 1mm period after the first 3mm shall be +0.5 degrees or -0.5 degrees. All the tests in which the rate of rising doesn’t fall within these limits are rejected.

8. For each ring and ball, the thermometer reading is noted at the instant when the specimen surrounding the ball touches the base plate.

softening point test



  3. Observations and Calculations  

The temperature when the ball touches the bottom, °C12




  4. Results  

The softening point of bitumen/tar =………….. °C



  5. Precautions in Softening Point Test of Bitumen  

a. For accurate readings; distilled water should be used.

b. Bitumen stained in the container should be removed using glycerin.

c. Equipment used in testing should be cleaned thoroughly.

d. At first, switch off the hotplate and remove it by wearing hand gloves and an apron.


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