If you want to know how your asphalt will look in the future, you don’t need a crystal ball! This blog post will map out the background, advantages and procedure associated with the Pressure Aging Vessel (PAV) for physical property testing of aged asphalt.
Oxidative aging of asphalt binder has a significant impact on long-term performance of pavements, often resulting in deterioration and cracking. A method to simulate long-term aging of the binder is important for predicting this type of damage. The Pressure Aging Vessel uses heat and pressure to reproduce the effects of in-service aging over a 7-10 year period on asphalt binder.
As we covered in our previous post, the Rolling Thin Film Oven simulates asphalt aging during mixing and placement, while the PAV replicates aging during in-service life. In the laboratory, the (RTFO) simulates this short-term aging process on a binder sample. PAV samples typically are obtained from binder residue previously aged in the RTFO and subjected to the accelerated aging methods described in ASTM D6521 This process is most often used in preparing for further tests of properties for characterization as performance graded asphalt binder in ASTM D6373 and AASHTO M 320.
The full procedure is described in ASTM D6521.
- The short-term aged binder is collected from the RTFO bottles into a single container and mixed to ensure homogeneity. The PAV is preheated to a temperature between 90°C and 110°C based on asphalt binder grading as well as the climate for which it will be used. (Values are specified in ASTM D6373 or AASHTO M320).
- 50 grams of the asphalt binder mixture is poured into each sample pan, filling the pan to an approximate film thickness of 3.2 mm. The pans are loaded into the sample pan holder and placed inside the PAV chamber. The chamber is closed and its bolts are tightened in proper sequence with a torque wrench to the manufacturer’s specifications.
- When the chamber temperature reaches the specified set-point, 305psi pressure is applied and the sample is subjected to this constant temperature and pressure for a period of 20 hours.
- At the conclusion of the 20 hours, the PAV sample chamber is brought back to atmospheric pressure slowly to avoid bubbling and foaming of the samples, which can occur if there is a rapid pressure change. Once the pressure has been equalized, the sample chamber is opened and the sample pans are transferred to a separate warming oven for 15 minutes. Entrapped bubbles in the binder residue may remain that can affect post-aging tests if not removed. The test method requires that the specimens be degassed in a vacuum oven such. The Vacuum Degassing Oven (VDO) is purpose-built for this application to remove remaining entrapped air in the sample.
- While the Vacuum Degassing oven is preheating to 170°C, remove the sample pans from the warming oven and scrape the binder residue into a container of suitable size. Place each container with recovered sample back in the warming oven until all separate containers are ready.
- Once the containers are loaded into the VDO chamber, the lid is closed tightly, and the samples are heated at 170°C for 10 minutes, then a vacuum of 15 ± 2.5 kPa absolute is applied for a period of 30 minutes. The vacuum is released and the sample containers are removed. There may still be surface bubbles on the samples, which can be removed using a torch or hot knife.
- Provides an optimal solution for simulating long-term oxidative aging of asphalt binders
- Prepares specimens for characterization under ASTM D6373 and AASHTO M 320 specifications for Performance Graded Asphalt Binder
- Complies with ASTM, AASHTO and EN 14769 specifications
- Minimizes volatile loss
- Accomplishes aging without high temperatures
- Accommodates large sample sizes
We recommend the HM-74 Pressure Aging Vessel to simulate long-term oxidative aging of your asphalt binder samples. This unit:
- Includes a platinum RTD device for accurate temperature uniformity
- Offers safety features such as a pressure relief valve and high-temperature shut-down
- Has a USB port for seamless data storage
- Has remote operation capability, offering control via most smart phones and tablets
- Features an innovative touch-screen controller for complete control and test monitoring
- Completes testing in three easy steps