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5 CHAPTER 1 Introduction 1.1 Background a pavement. Elevated temperature and pressure and a single conditioning period are used in the PAV to accelerate aging. The Standard Specification for Performance-Graded Asphalt This methodology has been questioned by several researchers. Binder, AASHTO M320, includes short- and long-term lab- It is well known that the kinetics of the binder aging process oratory conditioning procedures to address the aging that are binder specific. Thus, the degree of aging that occurs in occurs in asphalt binders during construction and over the the PAV may simulate 5 years of life in service for one binder service life of the pavement. The conditioning procedures used and 10 or more years for a different binder. in AASHTO M320 are (1) the Rolling Thin Film Oven Test To improve AASHTO M320, new procedures to simulate (RTFOT, AASHTO T240) for short-term aging and (2) the short-term and long-term aging that are suitable for routine Pressure Aging Vessel (PAV, AASHTO R28) for long-term specification use should be developed. In these procedures, aging. These procedures were selected during the Strategic a single apparatus, but with different operating conditions, Highway Research Program (SHRP) based on previous expe- should be considered for the replacement of both the RTFOT rience and limited validation studies using neat asphalt binders and PAV procedures. NCHRP Project 9-36, Improved Proce- recovered from in-service pavements. The resources available dure for Laboratory Aging of Asphalt Binders in Pavements, to the SHRP asphalt research program did not allow an exten- is the first in an anticipated series of projects to address the sive validation of either short- or long-term binder laboratory development and validation of new procedures for short-term conditioning procedures. and long-term aging that can be included in future revisions Experience with AASHTO M320 has shown that the of AASHTO M320. 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 1.2 Objective and Scope binder films often do not flow within the rotating bottle, violating the basic premise of the test method (i.e., that the The objective of NCHRP Project 9-36 was to select, refine, binder is exposed to heated air in a continuously moving thin and validate an improved procedure for the short-term labo- film). Users also have reported that the binder can climb out ratory aging of asphalt binders for use in a purchase specifi- of the bottle and recovery of stiff modified binders is difficult. cation such as AASHTO M320. The following were consid- These problems were evaluated in NCHRP Project 9-10, ered throughout NCHRP Project 9-36: Superpave Protocols for Modified Asphalt Binders. Research completed in Project 9-10 concluded that the present RTFOT 1. The short-term conditioning procedure should be equally does not adequately simulate the aging of modified asphalt applicable to neat and modified materials. binders that occurs during construction. Although NCHRP 2. It should mimic the physical changes that occur in hot mix Project 9-10 proposed modifications to the RTFOT in an asphalt (HMA) mixes conditioned in accordance with effort to improve it, the general consensus in the industry is AASHTO R30. that the test should be replaced with one that is equally appli- 3. It should include a method to quantify binder volatility. cable to neat and modified binders. 4. If possible, it should be extendible to long-term aging. The PAV test was refined during the SHRP asphalt research program and adopted as the accelerated laboratory procedure This report documents the research completed in NCHRP for simulating the aging that occurs during the service life of Project 9-36.