Explain the procedure for determining softening point of bitumen.
1 Answer

Procedure for determining softening point of bitumen:-

1) Sample material is heated to a temperature between 750$^\circ$C to 1000$^\circ$ C above the approximate point until it is completely fluid and is poured in heated rings placed on metal plate.

2) To avoid sticking of the bitumen to metal plate, coating is done to this with a solution of glycerin and dextrin.

3) After cooling the rings in air for 30 minutes, the excess bitumen is trimmed and rings are placed in the support.

4) At this time, the temperature of distilled water is kept at 500$^\circ$C. This temperature is maintained for 15 minute after which the balls are placed in position.

5) The temperature of water is raised at a uniform rate of 50$^\circ$C per minute with a controlled bottom plate by sinking of balls. At least two observations are made.

6) For material whose softening point is above 800$^\circ$C, glycerin is used in heating medium and the starting temperature is 350$^\circ$C instead of 50$^\circ$C.

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