The bitumen penetration test classifies the hardness, or consistency, of bituminous binders and is the basis of the traditional penetration-grade system (e.g. 60/70, 80/100).
What the Test Measures
Penetration is the depth, in tenths of a millimetre, that a standard needle penetrates a bitumen sample under a load of 100 g for 5 seconds at 25°C. A higher penetration means a softer binder.
Apparatus Required
- Penetrometer with standard needle and 100 g load assembly
- Sample containers and a controlled water bath at 25°C
- Timer (or automatic timing) and transfer dish
- Thermometer for bath control
NL Scientific manufactures the Advance Digital Penetrometer and the full bitumen & asphalt testing range, built to ASTM, EN, BS and AASHTO requirements with ISO/IEC 17025 accredited calibration.
Test Procedure
- Heat and pour the bitumen into the container and allow it to cool to 25°C.
- Condition the sample in the 25°C water bath.
- Position the needle to just touch the surface and zero the dial.
- Release the needle for exactly 5 seconds under the 100 g load.
- Record the penetration and repeat at three points at least 10 mm apart.
Calculation & Reporting
Report the penetration as the mean of three readings in units of 0.1 mm. The value defines the penetration grade of the binder.
Acceptance Criteria
The result must fall within the range for the specified grade (for example 60–70 for a 60/70 binder). Out-of-range values indicate the wrong grade or an aged/contaminated sample.
Frequently Asked Questions
Why are the conditions fixed at 100 g, 5 s, 25°C?
Penetration is highly temperature- and load-sensitive, so the standard fixes these conditions to make results comparable worldwide.
How does penetration relate to softening point?
Together with the ring-and-ball softening point, penetration defines a binder’s temperature susceptibility (penetration index). Both are routine binder QC tests.
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