What is the Bitumen Penetration Test?

Penetration Test (bitumen)

Definition

The penetration test is a laboratory test that measures how deep a standard needle sinks into bitumen under a set load, time and temperature.

ASTM D5/D5M covers the test for semi-solid and solid bituminous materials. It measures consistency. A higher value means a softer material. AASHTO T 49 is the same test. It is identical to ASTM D5/D5M-13 except for a few provisions.

The asphalt cement page covers the binder and its three grading systems. This page covers the test itself.

The standard conditions

The test has three conditions: temperature, load on the needle and time. The standard fixes them, so that results are comparable.

FHWA protocol P22 states 25 °C, 100 g and 5 s as its first set of conditions. The New York State DOT specification states the same set in its asphalt cement tables. Both follow AASHTO T 49.

The result and its unit

The result is the depth of the needle. One penetration unit is 0.1 mm. A reading of 18 means that the needle sank 1.8 mm. The FAA writes the unit as dmm, for example 2 to 12 dmm.

P22 asks for the average of at least three penetrations on the same sample. AASHTO T 49 gives precision estimates in Table X for tests at 4 °C and 25 °C. They cover original binder and RTFO residue.

Penetration grades

A penetration grade is a range of penetration values at 25 °C. A specification states a minimum and a maximum. The New York State DOT grade 18-60 requires a penetration of at least 18 and at most 60. The same table sets other limits for the binder, such as flash point, softening point, loss on heating and ductility. The grade is one of several requirements.

ASTM D946 is the specification for penetration-graded asphalt cement. FAA AC 150/5370-10H lists it in its references.

What the FAA uses today

FAA AC 150/5370-10H item P-401 requires the asphalt binder of an asphalt mix surface to follow ASTM D6373, which grades binder by performance. It does not ask for a penetration grade.

The circular still uses the penetration test on the residue of seal coat materials:

• Item P-608, emulsified asphalt seal coat. The residue of the asphalt emulsion has a penetration of 50 dmm at most (608-2.2).
• Item P-608-R, rapid cure seal coat. The residue has a penetration of 2 to 12 dmm at 77 °F (25 °C) (608-R-2.2).

Both lines name ASTM D5 as the test.

Other penetration tests

The name “penetration test” belongs to several tests. FAA AC 150/5320-6G describes three that test soil and pavement layers, and not binder:

• California bearing ratio (CBR). This test measures the force that gives a set penetration of the material and compares it with the force for a standard crushed limestone. See California bearing ratio .
• Dynamic cone penetrometer. This tool measures the penetration rate of a cone in compacted materials and subgrade soils. See dynamic cone penetrometer .
• Standard penetration test. ASTM D1586 covers this soil test.

What the test does not show

The test takes a binder sample to a laboratory. The FHWA long-term pavement performance program runs it on asphalt cement that technicians extract from pavement cores. The value describes the binder at one temperature. It does not describe the mix, the pavement or its condition.

A pavement survey records the surface. Raveling, weathering, stripping and bleeding relate to the binder, but the survey does not give a penetration value. The binder grade comes from the specification and the certificate for the mix. TarmacView’s pavement condition assessment images the surface and does not test the binder.