What Is Asphalt Binder Aging?

 

Asphalt binder is exposed to heat, air and environmental conditions during asphalt production, construction and pavement service. Over time, these factors cause changes in its physical and rheological properties, which may affect pavement performance.

 

In laboratory testing, asphalt binder aging is commonly evaluated through two procedures:

 

Short-term aging: Simulates the aging that occurs during asphalt mixing and paving.

Long-term aging: Simulates further oxidative aging during pavement service.

 

The Rolling Thin Film Oven Test (RTFO) and Pressure Aging Vessel (PAV) test are widely used to simulate these two stages of aging.

 

After PAV aging, vacuum degassing may be performed when required by the subsequent testing procedure to remove entrapped air from the binder.

 

Understanding the differences between these processes helps laboratories select the appropriate testing methods and equipment.

 

1. What Is the RTFO Test?

 

The Rolling Thin Film Oven (RTFO) test is used to simulate the short-term aging of asphalt binder during mixing and paving.

 

During asphalt production, binder is exposed to elevated temperatures and air. This exposure causes oxidation and changes in its properties. The RTFO test reproduces these conditions in the laboratory by heating asphalt binder in rotating glass bottles while supplying controlled airflow.

 

A commonly used test temperature is 163°C, with a typical testing duration of 85 minutes, depending on the applicable standard and procedure.

 

What Does the RTFO Test Measure?

 

The RTFO test is commonly used to determine the mass change of asphalt binder after heating.

 

The aged binder residue can also be collected for further physical property testing, including:

 

Penetration

Viscosity

Ductility

Other relevant binder properties

 

These follow-up tests help evaluate the effects of short-term aging. They are not measurements automatically provided by the RTFO oven itself.

 

RTFO Testing Procedure

 

The general RTFO testing procedure includes:

 

1. Prepare the required asphalt binder specimens.

2. Pour the binder into the specified glass bottles.

3. Place the bottles in the rotating rack inside the RTFO chamber.

4. Set the required temperature and airflow.

5. Run the test for the specified duration.

6. Remove the aged binder residue for mass change determination and further testing.

 

RTFO Testing Equipment

 

An RTFO oven provides controlled heating, rotation and airflow to simulate short-term asphalt binder aging.

 

When selecting an RTFO oven, laboratories should consider temperature stability, airflow control, rotating speed, ease of operation and the requirements of the applicable testing standard.

 

The TBT-0610W Rolling Thin Film Oven is designed for asphalt binder short-term aging tests. It can be used to determine mass change after heating and prepare aged binder residue for subsequent physical property evaluation.

 

The equipment is referenced for testing methods including ASTM D2872, AASHTO T240, EN 12607-1 and GOST 33140-2014.

 

2. What Is the PAV Test?

 

The Pressure Aging Vessel (PAV) test is used to simulate the long-term oxidative aging of asphalt binder during pavement service.

 

While RTFO simulates short-term aging during production and construction, PAV accelerates further aging by exposing previously aged asphalt binder to elevated temperature and pressurized air for an extended period.

 

This process allows laboratories to evaluate changes in binder properties after simulated long-term aging.

 

Commonly referenced PAV standards include:

ASTM D6521

AASHTO R28

EN 14769

GOST R 58400.5

 

The applicable standard and test conditions should be selected according to the testing requirements.

 

How Does a Pressure Aging Vessel Work?

 

A PAV uses controlled temperature and compressed air pressure to accelerate the oxidative aging of asphalt binder.

 

The general procedure is as follows:

 

1. Prepare short-term aged asphalt binder using the RTFO test.

2. Place the RTFO-aged binder into stainless steel aging pans.

3. Arrange the pans inside the pressure aging vessel.

4. Set the required temperature, pressure and aging duration.

5. Apply compressed air pressure to accelerate oxidative aging.

6. After aging, remove the samples for subsequent sample preparation and performance testing.

 

A commonly used PAV aging duration is 20 hours. Some testing procedures may specify different durations, such as 65 hours. Actual conditions depend on the applicable standard and testing procedure.

 

PAV Testing Equipment

 

A Pressure Aging Vessel is designed to simulate long-term oxidative aging under controlled temperature and pressure conditions.

 

When selecting a PAV, laboratories should consider temperature and pressure control, sample capacity, operating stability and the requirements of the applicable testing method.

 

The TBT TBTPAV-I Pressure Aging Vessel is designed for accelerated long-term asphalt binder aging in laboratory applications.

 

It forms part of the TBT pressure aging and vacuum degassing system, which also includes the TBTPAV-II Vacuum Degassing Oven.

 

3. What Is Vacuum Degassing After PAV Aging?

 

After PAV aging, air bubbles may remain in the asphalt binder. Depending on the subsequent testing method, these bubbles may need to be removed before further sample preparation and testing.

 

Vacuum degassing is a sample preparation process that uses reduced pressure and controlled heating to remove entrapped air from aged asphalt binder.

 

An important point: Vacuum degassing is not a separate aging test, and it is not necessarily required after every PAV procedure. Whether it is needed depends on the applicable testing method and the requirements of the subsequent test.

 

How Does Vacuum Degassing Work?

 

The general procedure includes:

 

1. Transfer the PAV-aged binder into the appropriate containers.

2. Place the samples inside the vacuum degassing oven.

3. Set the required temperature and vacuum conditions.

4. Apply vacuum for the specified duration.

5. Remove the samples after degassing is complete.

 

The commonly referenced degassing duration is around 30 minutes, although the actual conditions should follow the applicable testing procedure.

 

Vacuum Degassing Equipment

 

A Vacuum Degassing Oven is used for post-aging sample preparation when vacuum treatment is required.

 

The TBT TBTPAV-II Vacuum Degassing Oven is designed to remove entrapped air from PAV-aged asphalt binder through controlled heating and vacuum operation.

 

It works together with the TBTPAV-I Pressure Aging Vessel as part of TBT's asphalt binder aging equipment system.

 

4. RTFO vs. PAV: What Is the Difference?

 

RTFO and PAV are complementary asphalt binder aging procedures, but they simulate different stages of the aging process.

 

Comparison	RTFO Test	PAV Test
Full name	Rolling Thin Film Oven	Pressure Aging Vessel
Aging stage	Short-term aging	Long-term aging
Simulates	Mixing and paving	Pavement service
Main conditions	Heat and airflow	Heat and pressurized air
Common temperature	163°C	Depends on binder grade and procedure
Typical duration	85 minutes	Commonly 20 hours; some procedures use longer durations
Main purpose	Evaluate short-term aging effects	Evaluate long-term oxidative aging effects

 

In simple terms, RTFO simulates the aging of asphalt binder during production and construction, while PAV simulates further oxidative aging during pavement service.

 

For long-term aging evaluation, PAV specimens are generally prepared from RTFO-aged binder rather than unaged binder.

 

Vacuum degassing is a separate sample preparation step that may follow PAV aging when required by the subsequent testing method.

 

5. What Tests Are Performed After Asphalt Binder Aging?

After RTFO and PAV aging, asphalt binder specimens can undergo further testing to evaluate changes in their physical and rheological properties.

 

Common follow-up tests include:

 

Penetration Test

The penetration test measures the consistency of asphalt binder by determining how far a standard needle penetrates the sample under specified conditions.

 

Viscosity Test

The viscosity test evaluates the flow resistance of asphalt binder at a specified temperature.

 

Ductility Test

The ductility test measures the ability of asphalt binder to stretch before breaking under specified conditions.

 

Dynamic Shear Rheometer (DSR) Test

DSR testing evaluates the rheological properties of asphalt binder, including its response to shear deformation. It is commonly used to assess high- and intermediate-temperature performance.

 

Bending Beam Rheometer (BBR) Test

BBR testing evaluates the low-temperature stiffness and stress relaxation properties of asphalt binder.

 

Direct Tension Test (DTT)

The Direct Tension Test evaluates the tensile properties of asphalt binder at low temperatures. Sample preparation and vacuum degassing requirements should follow the applicable test method.

 

These tests provide additional information about how aging affects binder performance. The selection of tests depends on the relevant specifications and research objectives.

 

Conclusion

RTFO and PAV are two important procedures for evaluating asphalt binder aging.

 

RTFO simulates short-term aging during asphalt production and paving, while PAV accelerates long-term oxidative aging under elevated temperature and pressure.

 

After PAV aging, vacuum degassing may be used to remove entrapped air from the binder when required by the subsequent testing method.

 

Together, these procedures and follow-up performance tests help laboratories evaluate changes in asphalt binder properties and understand its behavior under different aging conditions.

 

TBT SCIETECH provides asphalt binder aging equipment, including the TBT-0610W Rolling Thin Film Oven, TBTPAV-I Pressure Aging Vessel and TBTPAV-II Vacuum Degassing Oven.

 

Contact our team to discuss your testing standards and equipment requirements.

 

 

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Frequently Asked Questions (FAQ)

 

1. What is the purpose of the RTFO test?

The RTFO test simulates short-term asphalt binder aging during mixing and paving. It is commonly used to determine mass change after heating and prepare aged binder residue for further physical property testing.

 

2. What is the purpose of the PAV test?

The PAV test simulates long-term oxidative aging of asphalt binder during pavement service by exposing previously aged binder to elevated temperature and pressurized air.

 

3. What is the difference between RTFO and PAV?

RTFO simulates short-term aging during asphalt production and construction, while PAV simulates long-term aging during pavement service. RTFO-aged binder is generally used as the starting material for PAV testing.

 

4. Is vacuum degassing always required after PAV testing?

No. Vacuum degassing is a sample preparation step that may be required by certain subsequent testing methods. Laboratories should follow the applicable standard and test procedure.

 

5. How long does a PAV test take?

A commonly used PAV aging duration is 20 hours. However, some procedures may specify longer durations, such as 65 hours. The required duration depends on the applicable standard and test conditions.

 

6. Which standards are used for RTFO testing?

Commonly referenced RTFO standards include ASTM D2872, AASHTO T240, EN 12607-1 and GOST 33140-2014.

 

7. Which standards are used for PAV testing?

Commonly referenced PAV standards include ASTM D6521, AASHTO R28, EN 14769 and GOST R 58400.5.