It is a type of test done on an important highway construction material i.e. bitumen. Softening Point test is done to determine the consistency of bitumen. This test gives an idea of the temperature at which the bitumen attain 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 steel ball.
A brass shouldered ring
A steel ball
Ball centring guide
Brass pouring plate
Water bath and thermometers
Procedures in Softening Point Test:
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, 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 degree 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 degree Celsius per minute. It must be noted that the rise in temperature is uniform.
7. The maximum permissible variation of any 1mm period after the first 3mm shall be +0.5 degree or -0.5 degree. 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.
Observations and Calculations
|Temperature when the ball touches bottom, °C||1||2|
The softening point of bitumen/tar =………….. °C