Bitumen penetration test

 

Grading bitumen based on physical properties is essential to get the best performance for construction and other uses. The penetration grading system was developed in the early twentieth century. Bitumen penetration grade is classified using its penetration property. Penetration property is obtained using penetration tests

What is Penetration test?

Penetration test measures the consistency and stability of pure bitumen and oxidized bitumen (Blown bitumen). For very soft materials with low viscosity such as tars, penetration tests cannot be carried out.

This test classifies bitumen according to its adhesion and hardness. To classify emulsion bitumen, a softening point test is used in addition to the penetration test.

Penetration value is measured by applying the needle with a load of 100 grams that vertically penetrates into the bitumen for 5 seconds at 25 degrees celsius. The amount of needle movement is determined in tenths of a millimeter unit (decimillimeter 0.1 mm). The higher the penetration of the needle in the bitumen, the higher the bitumen grade.

Why do we use bitumen penetration test?

We use this test to classify bitumen based on penetration value. This helps to choose the proper bitumen in the desired weather conditions for safe road construction.

The soft bitumen (higher penetration) is used in cold weather to avoid cracking. In hot weather, the hard bitumen (lower penetration) is used since it doesn’t get soft due to the heat. 

Different penetration grade and their applications

The bitumen penetration value is measured from 10 to 450 but the most commonly used range for road is 25 to 200. 
Following is a table describing the properties and applications of different penetration grade bitumens:

 Penetration gradePenetration valueSoftening pointApplication
140-5040-5052-60 ° C

Tropical areas

Mean T > 24° C

260-7060-7049-56 ° C

Mild climate region

7° C < Mean T < 24° C

385-10085-10045-52 ° C

Cold climate

Mean T < 7° C

4100-120100-12042-49 ° CUsed for road repairs in cold regions

 

Bitumen penetration Grade Standards

In different regions and countries, different Standards and Grading systems are used for determining the quality of petroleum bituminous Binders. Recognized standards for bitumen that commonly used are listed below:


    1. European Committee for Standardization (CEN)
        • Deutsche Industrie Norm (DIN EN)
        • Association Française de Normalisation (AFNOR – NF EN)
        • BSI Standards – the UK’s National Standards Body (NSB – BS EN)


    2. American Society for Testing and Materials (ASTM) 
    3. American Association of State Highway and Transportation Officials (AASHTO)
    4. South African Standard Organization (SABS)
    5. Standards Australia (AS)


The most usual methods used by the above standards for bitumen penetration testing are:

  • ASTM D 946 and AASHTO M 20 (Penetration @ 25°C)
  •  EN 12591 (Penetration @ 25°C) → NF EN; BS EN; DIN EN; etc.
  • SABS 307 (Penetration @ 25°C; Viscosity @ 60°C after RTFOT)



The component of the apparatus and test steps are given below:

  1. Components for the penetration test




    • Water bath: it contains at least 10 liters of water at a temperature of 25 °C. The sample is immersed in a depth of more than 100 mm from the top. Moreover, the supported perforated shelf which is the sample being placed on it should be above 50mm from the bottom of the bath.
    • Sample container: a small cylindrical dish with a flat bottom, which its material is metal or glass. 
    • Transfer dish or Tray: It helps in keeping the container immersed in the water bath.
    • Penetration needle: stainless steel needle which is cylindrical and high polished
    • Stopwatch: an automatic timer with an accuracy of 1/10 seconds.
    • Thermometer: it shows the temperature in the range of 0-44 °C.
    • Penetrometer: the device contains a needle. It is used to release and lock the needle in any position and allows measuring the penetration by applying a load of 100 grams with the least friction. It is important to calibrate accurately
  1. Procedure of bitumen penetration test
  •  Bitumen preparing

Heat the specimen up to 90 °C and stir the melted sample until achieving consistency and the sample doesn’t have air bubble or water. Pour it into a container and let the sample cool at atmosphere temperature. Place the above assembly in a water bath at a constant temperature of 25 °C.

 

  •  Testing of bitumen penetration

Fill the transfer dish with water from the water bath. Place the sample in the transfer dish and place the whole assembly under the stand of the penetration apparatus. Release the needle on the surface of the sample with a load of 100 gr for only 5 seconds. For each sample at least three determination are taken. It is important to use a clean needle for each determination. When measuring, the needle tip must be 10mm away from the  container side. Moreover, the location of the needle in each repeat must be 10 mm apart.

It is essential that the penetration test method be performed accurately because even a small deviation can make a big difference in the results. The most common errors are as follows:


  • Poor sampling and poor sample preparation
  •  Poor maintenance of laboratory equipment and needles
  •  Incorrect temperature and time



In repeated measurements for each sample, the maximum difference between the highest and lowest readings shall be:

Penetration (d-mm)0-4950-149150-249250-500
Maximum difference241220