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Penetration Test of Bitumen-Procedure, Apparatus, and Uses for Road Construction

Penetration test of Bitumen determines the hardness or softness of bitumen by measuring the depth in millimeters to which a standard loaded needle will penetrate vertically in five seconds while the temperature of the bitumen sample is maintained at 25 0C.

Interested One: What is Shoring? Types and Uses

Also, the Penetration test of bitumen is used to measure the consistency of bitumen. This test is applied almost exclusively to bitumen. For Tars, cutbacks, and emulsions other consistency tests are used.

Penetration test of bitumen
Fig1. Penetration test of bitumen


Equipment for Penetration test

penetrometer consisting of a needle assembly with a total weight of 100 grams and a device for releasing and locking needles in any position.

To read the penetration value, a graduated dial is attached as shown in Fig. 1. Penetration value can be read with this dial up to 0.1 mm.

 Penetartion test – Penetrometer
Fig2. Penetartion test –Penetrometer


Procedure  for Penetration Test of Bitumen

  1. The bitumen is softened to a pouring consistency, stirred well, and poured into the test containers. The depth of bitumen in the container is kept at least 15mm more than the expected penetration. (I.S. 1203-1958). Related:- California Bearing Ratio(CBR Test) of Subgrade Soil -Procedure, apparatus, and use for pavement Design
  2. Now the sample containers are placed in a temperature-controlled water bath at a temperature of 25 c for one hour.
  3. Then at the end of one hour, the sample is taken out of the water bath and the needle is brought in contact with the surface of the bitumen sample at that time reading of the dial is set at zero or the reading of the dial is noted when the needle is in contact with the surface of the sample.
  4. After that, the needle is released, allowed to penetrate for 5 seconds, and the final reading is recorded. At least three penetration observations on that sample should be taken at distances at least 10 mm apart.  After each test, the needle should be disengaged, wiped with benzene, and dried. The amount of penetration is recorded as shown in Fig. 2.
  5. The main value of the three measurements reported is the penetration test.
  6. The accuracy of the test depends upon the pouring temperature, the size of the needle, the weight placed on the needle, and the test temperature.
  7. The grade of bitumen is specified in terms of penetration value. For example, 30/40 grade bitumen indicates the penetration value of the bitumen in the range of 30 to 40 at standard test conditions.
concept of Penetration Test
Fig3. concept of Penetration Test

Readings are taken as units of penetration

Where, 1 unit =  (1/10) mm

i.e.   If penetration value is N,

Distance penetrated = (N/10) mm.

Also Read: Field Density Test of Soil by Core cutter method for soil compaction

Precautions during Penetration Test

  • The container should not be moved while the needle penetrates the sample.
  • The sample should be free from any external materials.
  • Benzene is used to clean up the needle and dried before penetration.

Penetration test of bitumen is applied exclusively to bitumen. Tars being soft, penetration tests on these materials cannot be carried out.

Penetration value of different types of bitumen used in road construction ranges between  20 to 225. However, 30/40 and 80/100 grade bitumen is more common for road construction depending upon the type of construction and climate conditions. In hot 30/40  bitumen is preferred.

The value of temperature affects the use of the bitumen. A lower penetration grade is used in warm climate conditions to avoid softening and a high penetration grade range of 180/210 is used in cold climate conditions to prevent it from excessive brittleness.

In the last word, the Penetration test of Bitumen is used for the Garde of bitumen material in terms of its hardness. A 70/100 grade bitumen shows that its penetration value lies between 70 & 100.

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  11. Bitumen 60/70 is a semi-hard penetration grade bitumen commonly used in road construction and repair. It is suitable for producing asphalt pavements and is characterized by its specific technical specifications. This grade of bitumen is primarily utilized in the production of hot mix asphalt for base and wearing courses. It is the most commonly used grade and serves as a fundamental material for various other bituminous products.

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