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Softening Point

Last updated: September 25, 2018

What Does Softening Point Mean?

The softening point of a bituminous material can be defined as the temperature at which this bituminous material further softens after its arbitrary softness point is reached. There are various methods that are helpful in determining the softening point of a bituminous material. They are as follows:

  • Vicat method as per ASTM D1525 or ISO 306
  • Heat deflection test method as per ASTM D648
  • Ring and ball method as per ASTM E28-67 or ASTM E28-99 or ASTM D36 or ASTM D6493-11 or ISO 4625

Corrosionpedia Explains Softening Point

The ring and ball method is widely used for determining the softening point of bituminous material. The purpose behind performing the ring and ball test is to determine the temperature at which a given material will soften. The apparatus needed for this test is ring and ball apparatus. It consists of:

  • Two steel balls
  • Two brass rings
  • Ball guides
  • Support to hold rings in position
  • Thermometer
  • Stirrer

The ring and ball test procedure involves:

  • The material being tested is heated to 167-212 °F (75-100 °C), above its softening point and stirred until it becomes liquid.
  • The brass rings are heated near to the temperature equivalent to molten brass and placed on a metal plate coated with dextrin and glycerin.
  • The test material is placed on the ring and allowed to cool for 30 minutes. Excess material is then removed with the help of a knife.
  • The thermometers in the apparatus are assembled.
  • The bath is now filled to a height of 2 inches (50 mm) with water until the upper surface of the rings. The starting temperature should read 41 °F (5 °C).
  • The bath is heated and stirred, ensuring that temperature increases at a uniform rate.
  • With the increase in the temperature of the bath, the bitumen material softens up and the steel balls start to sink and carry a portion of material with it.
  • The temperature is noted down when any of the steel balls touches the bottom plate. Temperature is noted again when the second steel ball touches the bottom plate. Average temperature is calculated based on two readings, providing the softening point temperature of the bituminous material.

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