The softening point is defined as the mean of the temperatures at which the bitumen disks soften and sag downwards a distance of 25 mm under the weight of a steel ball.
Equipment & Apparatus Required:-
- Ring and Ball apparatus,
- Steel balls
- Brass rings
- Ball guide
- Bath with stirrer
Scope & Significance:-
- This method is useful in determining the consistency of bitumen as one element in establishing the uniformity of shipments or sources of supply.
- Softening point is the temperature at which the bituminous binders have an equal viscosity (i.e. the consistency of all the grades will be same at the softening point e.g. if two samples have softening points of 40 °C and 80 °C respectively, both will have the same consistency at their softening point.).
- The test gives an idea of the temperature at which the bituminous materials attain a certain viscosity.
- Bitumen with higher softening point may be preferred in warmer places.
- The softening point should be higher than the hottest day temperature, which is anticipated in that
area otherwise bitumen may sufficiently soften and result in bleeding and development of ruts.
- The sample material is heated to a temperature between 75° and 100°C above the approximate softening point until it is completely fluid and is poured in heated rings placed on the metal plate.
- To avoid sticking of the bitumen to the metal plate, A coating is done to this with a solution of glycerin and dextrin.
- After cooling the rings in the air for 30 minutes, the excess bitumen is trimmed and rings are placed in the support.
- At this time the temperature of distilled water is kept at 5°C. This temperature IS maintained for 15 minutes after which the balls are placed in position.
- Then the temperature of the water is raised at a uniform rate of 5°C per minute with a controlled heating unit until the bitumen softens and touches the bottom plate by the sinking of balls. At least two observations are made. For material whose softening point is above 80°C, glycerin is used for heating
medium and the starting temperature is 35°C instead of 5°C.
Temperature when the ball touches bottom, °C
Ball – 1
Ball – 2
Average Temperature =
The experiment has been performed successfully and the softening point came out to be ……….°C
- Use hand gloves, apron while removing containers from hot plate after switching off the hotplate.
- Use glycerin for remove of bitumen from the container.
- Use distilled water in the test for an accurate result.
- Use safety shoes & Apron at the time of the test.
- Equipment should be cleaned thoroughly before testing & after testing.
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