The penetration value test on bitumen serves as a crucial measure of its hardness and consistency. Specifically, a bitumen grade like 80/100 signifies that its penetration value falls within the range of 80 to 100. This value is determined by the vertical distance penetrated by a standard needle into the bituminous material under specific conditions of load, time, and temperature, measured in tenths of a millimeter.
Significance of Penetration Test
The penetration test is primarily utilized to evaluate the consistency of bituminous materials. However, it's worth noting that it isn't deemed suitable for testing road tar due to the high surface tension exhibited by such materials. The key objectives of conducting penetration tests on bitumen include:
Assessment of Consistency
Determining the consistency of bituminous material, which is crucial for various construction applications.
Evaluation of Suitability
Assessing the suitability of bitumen for use under diverse climatic conditions and in different types of construction projects.
Determination of Penetration Value of Bitumen
Apparatus for Penetration Test
Container
A flat-bottomed cylindrical metallic dish, typically 55 mm in diameter and 35 mm in depth. For penetration values exceeding 225, a larger dish of 70 mm diameter and 45 mm depth is necessary.
Needle
A straight, highly polished, cylindrical hard steel rod.
Water bath
Maintained at 25°C ± 0.1°C, containing at least 10 liters of water, with the sample immersed to a depth not less than 100 mm from the top and supported on a perforated shelf not less than 50 mm from the bottom of the bath.
Transfer dish or tray
Provides support to the container without rocking it, ensuring complete immersion during the test.
Penetration apparatus
Facilitates needle penetration with minimal friction and precise calibration to deliver results in tenths of a millimeter.
Thermometer
Range of 0-44°C with readability up to 0.2°C.
Time measuring device
With an accuracy of one second.
Procedure for Bitumen Penetration Test
- Preparation of Test Specimen: Soften the material to a pouring consistency at specified temperatures, stir thoroughly to remove air bubbles and water, and allow it to cool under controlled conditions.
- Testing Process: Fill the transfer dish with water, place the sample, clean and load the needle with the required weight, adjust the needle, release it for five seconds, and measure the penetration distance.
- Multiple Readings: Conduct at least three readings at points on the sample's surface, ensuring adequate spacing and distance from the dish's side.
Precautions during Penetration Test
- Ensure no movement of the container during needle penetration.
- Verify that the sample is free from any extraneous matter.
- Clean the needle with benzene and dry it before each penetration.
Observations for Penetration Test
Actual test temperature = °C
| Penetration dial reading | Test 1 | Test 2 | Test 3 |
| (a) Initial | Â | Â | Â |
| (b) Final | Â | Â | Â |
| Penetration Value | Â | Â | Â |
Result of Test
Mean Penetration Value =
Recommended Penetration Value of Bitumen
The penetration test serves as a commonly adopted method to grade bitumen based on its hardness. Different grades are recommended for various climatic conditions and construction types. For instance, the Indian Road Congress (IRC) suggests bitumen grades such as 30/40, 60/70, and 80/100 for bituminous macadam and penetration macadam applications. In warmer regions, lower penetration grades are preferred to prevent softening, while higher penetration grades like 180/200 are utilized in colder regions to avoid excessive brittleness. Additionally, high penetration grade bitumen finds applications in spray application works.
Read More:
Types of Bitumen Mixes for Pavement Construction and their Applications
Bituminous Materials - Types, Properties and Uses in Construction
Viscosity of Bituminous Materials - Measurements and Factors