The bitumen softening Point Test is done to determine the consistency of bitumen. Bitumen is a viscoelastic material, which means it behaves like both a liquid and a solid state. It does not have a specific melting point. As the temperature increases, the bitumen becomes softer and the viscosity of the bitumen decreases. One of the common parameters for classifying bitumen is the softening point of the bitumen. This property shows at what temperature the bitumen softens. 

Bitumen Softening Point Test

Bitumen softening point is measured in different ways such as:

• Ring and Ball Method (R&B)
• Krämer-Sarnow Method (KS)
• Mettler Softening Point Method
• Capillary Method
• Flow Point Method
• Drop Point Method

The ring and Ball method is the most frequently used to determine the softening point of bitumen.

Why Is The Bitumen Softening Point Important?

To pave the roads and aeroplane runways, it is necessary to use a type of bitumen that has a specific degree of softness. Choosing a suitable bitumen with a good softening point depends on the weather condition and traffic loads.

For example, if the average temperature in a region is high during a year, bitumen with a    higher softening point should be used to make asphalt pavement. If during the year, the number of vehicles crossing this road is high and they put a  lot of pressure on the road surface, more bitumen should be used in the asphalt. This work increases the strength of the asphalt.

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International Standard Methods of softening point test

The softening point  test  of  bitumen  is  in  the  accordance   with  the following standards:

• ASTM D36

• ASTM E28-67/E28-99
• ASTM D6493 – 11
• IS 1205
• EN 1427
• IP 58
• ISO 4625
• JIS K 6863

The most common standard method for determining the softening point of bitumen is ASTM D36, which we will discuss further. You can see the steps of the Ring and ball method through the Video produced by the Infinity Galaxy team.

Softening point test of bitumen – Ring and ball method (Video)

Softening Point Test Procedure

The ring and ball method is widely used to determine the softening point of bitumen. In  the  infographic  below, you  can  see  a  summary  of  the  bitumen softening point test:

The required equipment to do the bitumen softening point test are:

• Two steel balls
• Two brass rings
• Beaker
• Thermometer
• Heater
• Knife
• A glass surface 
• Bitumen
• The bases holding the rings

Bitumen Softening Point Test Steps:

• In the first step, it is necessary to prepare the test sample. Heat the bitumen to a   temperature between  75  and 100 °C. Stir the bitumen well until it becomes completely liquid and free of air and water bubbles. Heat the rings to the approximate temperature of the bitumen. Prepare a mixture of glycerin and dextrin in equal proportions.
• Cover the surface of the metal or glass plate with it. Pour the heated bitumen into the rings to fill them. After cooling in the air, it is necessary to draw the extra bitumen with a heated knife at an angle of 45 degrees on the surface of the rings. So far you have understood how to prepare the sample.  In the following, we will explain the process of conducting this test.
• Place the rings filled with bitumen on the bases and place them in a water bath with a temperature of 5 °C for 15 minutes. Cool the steel balls to a temperature of 5 °C. Put them in the beaker and fill them with distilled water up to about 50 mm above the rings. Now place the steel ball in the centre of the ring and tangent to the bitumen and heat it until the temperature rises 5±0.5 °C/min.

Ring and ball method – Results

• As the temperature increases, the bituminous material softens and the balls sink through the rings. Continue heating until the balls on the bitumen reach the surface of the metal blade under the rings and note the temperature when each of the balls contacts the bottom of the plate. Consider the average of the two temperatures obtained as the bitumen softening point.
• An important point in this experiment is the process of heating the beaker and its contents, i.e. bitumen.   Since this test is very sensitive to heat, it is necessary to use the same heating rate throughout the test. It should be noted that if the bitumen is blown and hard, glycerin liquid is used instead of water.