All of you are aware that the bitumen is a by-product material of petroleum which is mainly used for road construction work & other miscellaneous work.

We are going to discuss the test, which is useful to grade the bitumen-based on its consistency.

What is the penetration test of bitumen?

Bitumen penetrated in a semi-solid state at the temperature of 25°C by a steel needle carrying 100gm load for 5 seconds to measure the consistency & hardness of the bitumen is known as a penetration test of bitumen.

The value of penetration is measured in 1/10 mm.

Why is the penetration test of bitumen done? (Importance)?

  • To differentiate the bitumen grade.Bitumen
  • To measure the hardness, softness, and consistency of the bitumen.
  • Ensure the grade of bitumen, whether it is safe to use in construction work.
  • It helps to access the sustainability of bitumen in different weather conditions.
  • Based on the bitumen grade, it can be used in related temperature conditions to make the road.

The different grades of bitumen have been listed below & the measured penetration value can be correlated to those values.

Bitumen Grade Penetration Value
S-35 30 to 40
S-45 40 to 50
S-55 50 to 60
S-65 60 to 70
S-90 80 to 100
S-200 175 to 225

Bitumen grade 80/100 meaning

The grade 80/100 represents the penetration value of bitumen that lies between 80 to 100, which is arrived from the penetration test. The grade 80/100 mostly used in India because of hot weather conditions. 

Lower Penetration is preferred in hot climatic conditions so that it doesn’t get soft due to the heat. On the other hand, higher penetration value is preferred in cold conditions to avoid brittleness.

The penetration test of bitumen has been conducted as per IS code 1203.

Bitumen Penetration Test

Apparatus Required Penetration of Bitumen Test Apparatus

  • Penetrometer – Contains 100gm penetration carrier & graduated scale (1 in 10mm) & a knob to release the weight carrier. A spirit level at the base to maintain the even surface.
  • Penetration needle – Stainless Steel needle (SS316)
  • Sample container – 55mm dia & 35mm Depth
  • Water bath – It should contain 10 litres of water & maintain at 25°C.
  • Stopwatch – 1/10 seconds or Automatic penetrometer timer
  • Transfer tray – To immerse the sample container into the water.
  • Thermometer – 0 to 44°C

Specimen Preparation

The sample bitumen has to be melted at 90°C which must be in uniformity & without bubbles. Ensure the specimen does it free from moisture & dust.


Bitumen Penetration Test

  • Allow the bitumen to reach the sufficient melting point then pour that into the container & allow it to cool in the natural atmosphere up to 1 hour.
  • Now switch on the water bath & set the temperature 25°C & fill the water in the transfer tray.
  • Then immerse the sample container in the transfer tray & place that into the water bath up to 1 to 2 hours.
  • Now place the container over the base of the penetrometer. After that, the steel needle has to be cleaned by the benzene & fix to the weight carrier.
  • Before starting the penetration, the needle should touch the top surface of the bitumen. The adjustment screw of the penetrometer can do it.
  • Take an initial reading as G1 from the graduated scale.
  • Switch on the automatic timer for 5seconds now the needle penetrates slowly to the bitumen & automatically stops the penetration after 5 seconds.
  • Now take the final reading from the graduated scale as G2.

Penetration value of bitumen test

The Penetration value = G2- G1

A minimum of 3 tests has to be done for the same sample at different points. Each test point should be conducted at 10mm away from the previous test point. It should also be 10mm inside of the container, as shown in the below picture.

Penetration reading Point 1 Point 2 Point 3
Initial reading G1
Final Reading G2
Average Penetration value

The average value of the 3 test points is the Penetration value of the bitumen. The penetrate value difference between those test points should be in the limit as given below.

Penetration Difference
0 to 49 2
50 to 149 4
150 to 249 6
250 and above 8

Precautions to be taken

  • Ensure the sample is free from dust & other impurities.
  • Ensure the sample has no water mixed while immersing in a water bath.
  • Ensure that there is no oscillation happening while the needle penetrates the bitumen.
  • Must wear a hand glove while heating the bitumen.
  • Take reading more accurately to avoid errors in this test.

Video Illustration

Video Courtesy – NCTEL

Happy Learning 🙂


Bala is a Planning Engineer & he is the author and editor of Civil Planets.

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