Tuesday, March 4, 2014

Bitumen Penetration Test to Find out its Grading.


We know that penetration test is one of the important tests, which is performed to test the grade of the Bitumen. You might be looking this article to jot down the theory and procedure of the test into your laboratory/practical notebook or might be checking just to refresh your knowledge. If you have one of these reasons, reading this article surely is going to help you in fulfilling the purpose. So, here we go:


To find out the consistency/hardness of the Bitumen and thereby to find out its grade using the Bitumen penetration test.


  1. Standard Penetration test apparatus with all the accessories such as, needle, weight and timer.
  2. Heater
  3. water bath with temperature control, maintained at 25° ± 0.1 °C, containing not less than 10 litres of water.
Accessories to the Standard penetration test are:

  • Container: flat bottomed cylindrical metallic dish having 55 mm diameter and 35 mm depth.
  • Penetration Needle: A straight, highly polished cylindrical hard steel rod having a diameter of about 1 mm.
  • Time measuring device with an accuracy of 1 second.


 This test is used to check the grade of the bitumen. In other words, it is used to check the consistency or the hardness of the bitumen which is useful to find out the suitability of the bitumen to use under different climatic conditions.
Penetration value is a measure of hardness or consistency of bituminous material. It is the vertical distance traversed or penetrated by the point of a standard needle in to the bituminous material under specific conditions of load, time and temperature. 
This distance is measured in one tenths of a millimeter so, if the reading is 50 mm, that denotes a penetration of 5 mm. This test is used for evaluating consistency of bitumen. It is not regarded as suitable for use in connection with the testing of road tar because of the high surface tension exhibited by these materials.


  1. Preparation of sample: Soften the material to a pouring consistency at a temperature not more than 60°C for tars and 90°C for bitumen above the approximate softening point and stir it thoroughly until it is homogeneous and is free from air bubbles and water. Pour the melt into the container to a depth at least 10mm in excess of the expected penetration. Protect the sample from dust and allow it to cool in an atmosphere at a temperature between 15° to 30° C for one hour. Then place it along with the transfer dish in the water bath at 25° ± 0.1 °C, unless otherwise stated.
  2. Put the test cup upon the stand of the penetration apparatus.
  3. Clean the needle with benzene, dry it and load with the weight. The total moving load as per standards, must be 100 ± 0.25 gms, including the weight of the needle, carrier and super-imposed weights.
  4. Adjust the needle to make contact with the surface of the sample. This may be done by placing the needle point in contact with its image reflected by the surface of the bituminous material.
  5. Make the pointer of the dial to read zero or note the initial dial reading.
  6. Release the needle for exactly five seconds for which you can use the timer or stopwatch if timer is not provided with the apparatus.
  7. Adjust the penetration machine to measure the distance penetrated.
  8. Make at least 3 readings at points on the surface of the sample not less than 10 mm apart and not less than 10 mm from the side of the dish. 
  9. After each test return the sample and transfer dish to the water bath and wash the needle clean with benzene and dry it. In case of material of penetration greater than 225, three determinations on each of the two identical test specimens using a separate needle for each determination should be made, leaving the needle in the sample on completion of each determination to avoid disturbance of the specimen.


  • Remember that sample must be tested at 25 degrees Celsius so, sample must be prepared with the standard procedure listed above.
  • There should be no movement of the container while needle penetrates into sample.
  • The needle should be cleaned with benzene and dried before penetration.

Actual test temperature = °C
 Penetration dial readingTest 1Test 2Test 3
Penetration Value=
Mean = 
Mean Penetration Value =
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