Publication Number: FHWA-SA-96-014
Date: March 1996

States Receive Next Item in Pooled-Fund Purchase

All 50 States have now received a pressure aging vessel (PAV), as part of the pooled-fund purchase of Superpave equipment. The purchase was arranged by the Federal Highway Administration (FHWA), using funds provided by the States.

To simulate real-world aging conditions of the asphalt binder, the PAV exposes the binder to high pressures and temperatures that would occur naturally during a pavement's life.

The binder samples are first aged in a rolling thin film oven, which simulates the aging that occurs during mix production and pavement construction. The samples are then arranged in PAV pans and placed on a sample rack. The PAV is preheated to the desired temperature, and the sample rack is placed in the hot vessel.

The aging process is conducted at varying temperatures, depending on the climate in which the pavement will be placed. When the vessel temperature is within 2 °C of the required temperature, pressure is applied and the timing for the aging period begins. After 20 hours, the pressure is slowly released, and the samples are removed for further testing.

The original SHRP design for the PAV consisted of a heavy pressure aging vessel and a forced draft oven. The hot, heavy steel vessel had to be lifted in and out of the convection oven, posing a hazard for technicians.

The redesigned PAV, which has been supplied to the States by Applied Test Systems, Butler, Pennsylvania, is safer and less cumbersome to operate, no longer requiring that the heavy vessel be lifted out of the oven. Another advantage of the new design is that it is automated. The original device was operated manually; a technician had to time the process, shut off the device, release the pressure, and remove the samples. The new PAV automatically turns itself off and depressurizes the vessel after the test is completed.

"The new vessel is much easier to use and a lot less labor intensive," says John D'Angelo, FHWA's manager for the project. "Not only is the device easier for technicians to work with, but now they can set up the test and leave it overnight to run itself."

States have now received almost all of the Superpave binder test equipment. The last item remaining to be purchased is the direct tension tester, which is scheduled for delivery in early 1997. The full set of the Superpave asphalt binder test equipment includes the dynamic shear rheometer, the rotational viscometer, the bending beam rheometer, the rolling thin film oven, the PAV, and the direct tension tester.

For more information contact John D'Angelo at FHWA at 202-366-0121 (fax: 202-366-7909).