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51.1 Background The Standard Specification for Performance-Graded Asphalt Binder, AASHTO M320, includes short- and long-term lab- oratory conditioning procedures to address the aging that occurs in asphalt binders during construction and over the service life of the pavement. The conditioning procedures used in AASHTO M320 are (1) the Rolling Thin Film Oven Test (RTFOT, AASHTO T240) for short-term aging and (2) the Pressure Aging Vessel (PAV, AASHTO R28) for long-term aging. These procedures were selected during the Strategic Highway Research Program (SHRP) based on previous expe- rience and limited validation studies using neat asphalt binders recovered from in-service pavements. The resources available to the SHRP asphalt research program did not allow an exten- sive validation of either short- or long-term binder laboratory conditioning procedures. Experience with AASHTO M320 has shown that the RTFOT, although satisfactory for neat binders, may not be an appropriate aging procedure for modified binders. During the procedure, some users have reported that modified asphalt binder films often do not flow within the rotating bottle, violating the basic premise of the test method (i.e., that the binder is exposed to heated air in a continuously moving thin film). Users also have reported that the binder can climb out of the bottle and recovery of stiff modified binders is difficult. These problems were evaluated in NCHRP Project 9-10, Superpave Protocols for Modified Asphalt Binders. Research completed in Project 9-10 concluded that the present RTFOT does not adequately simulate the aging of modified asphalt binders that occurs during construction. Although NCHRP Project 9-10 proposed modifications to the RTFOT in an effort to improve it, the general consensus in the industry is that the test should be replaced with one that is equally appli- cable to neat and modified binders. The PAV test was refined during the SHRP asphalt research program and adopted as the accelerated laboratory procedure for simulating the aging that occurs during the service life of a pavement. Elevated temperature and pressure and a single conditioning period are used in the PAV to accelerate aging. This methodology has been questioned by several researchers. It is well known that the kinetics of the binder aging process are binder specific. Thus, the degree of aging that occurs in the PAV may simulate 5 years of life in service for one binder and 10 or more years for a different binder. To improve AASHTO M320, new procedures to simulate short-term and long-term aging that are suitable for routine specification use should be developed. In these procedures, a single apparatus, but with different operating conditions, should be considered for the replacement of both the RTFOT and PAV procedures. NCHRP Project 9-36, Improved Proce- dure for Laboratory Aging of Asphalt Binders in Pavements, is the first in an anticipated series of projects to address the development and validation of new procedures for short-term and long-term aging that can be included in future revisions of AASHTO M320. 1.2 Objective and Scope The objective of NCHRP Project 9-36 was to select, refine, and validate an improved procedure for the short-term labo- ratory aging of asphalt binders for use in a purchase specifi- cation such as AASHTO M320. The following were consid- ered throughout NCHRP Project 9-36: 1. The short-term conditioning procedure should be equally applicable to neat and modified materials. 2. It should mimic the physical changes that occur in hot mix asphalt (HMA) mixes conditioned in accordance with AASHTO R30. 3. It should include a method to quantify binder volatility. 4. If possible, it should be extendible to long-term aging. This report documents the research completed in NCHRP Project 9-36. C H A P T E R 1 Introduction