Penetration test of Bitumen determines the hardness or softness of bitumen by measuring the depth in millimeter to which a standard loaded needle will penetrate vertically in five seconds while the temperature of the bitumen sample is maintained at 25 0C.
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.
Equipment for Penetration test
A penetrometer consisting of a needle assembly with a total weight of 100 gram and device for releasing and locking needle 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.
Procedure for Penetration Test of Bitumen
- The bitumen is softened to a pouring consistency, stirred well and poured into the test containers. The depth of bitumen in container is kept at least 15mm more than the expected penetration. (I.S. 1203-1958).
- Now the sample containers are placed in a temperature controlled water bath at a temperature of 25 c for one hour.
- Then at the end of one hour, the sample is taken out of water bath and the needle is brought in contact with the surface of bitumen sample at that time reading of dial is set at zero or the reading of dial noted, when the needle is in contact with the surface of the sample.
- After that the needle is released and the needle is allowed to penetrate for 5 seconds and the final reading is recorded. On that sample at least three penetration observations 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.
- The main value of three measurements is reported is the penetration test.
- The accuracy of the test depends upon pouring temperature, size of needle, weight placed on the needle, and test temperature.
- Te 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.
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.
Precautions during Penetration Test
- The container should not be moved while needle penetrates into 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 test on these materials cannot be carried out.
Penetration value of different types of bitumen used in road construction range between 20 to 225 . However 30/40 and 80/100 grade bitumen are 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 effects the use of the bitumen. Lower penetration grade is used in warm climate condition to avoid softening and high penetration grade range of 180/210 are used in cold climate condition to prevent it from excessive brittleness.
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