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February 2012 NATIONAL COOPERATIVE HIGHWAY RESEARCH PROGRAM Responsible Senior Program Officer: E. T. Harrigan Research Results Digest 369 AASHTO T 209: EFFECT OF AGITATION EQUIPMENT TYPE ON THEORETICAL MAXIMUM SPECIFIC GRAVITY VALUES This digest summarizes key findings of research conducted in NCHRP Project 10-87(01), "Precision Statements for AASHTO Standard Methods of Test," by the AASHTO Asphalt Materials Reference Laboratory (AMRL) under the direction of the principal investigator, Dr. Haleh Azari. The digest is an abridgement of the full final report, which is available for download at BACKGROUND or mechanical agitation, removes entrapped air in order to accurately determine the Gmm. AASHTO T 209, Theoretical Maximum The Gmm is then used to determine both the Specific Gravity and Density of Bituminous air void content and the in-place density of Paving Mixtures, describes a test method the HMA. In-place density is commonly for determination of the theoretical maxi- used in the acceptance and pay-factor de- mum specific gravity (Gmm) and density of termination of HMA. uncompacted hot mix asphalt (HMA).1 The Analysis of the AMRL Proficiency Gmm and the density of HMA are fundamen- Sample Program data has demonstrated that tal properties whose values are influenced mechanical agitation provides less variation by the composition of the HMA mixtures in test results when compared to manual ag- in terms of types and amounts of aggre- itation. However, several types of mechan- gates and asphalt materials. Gmm is used ical vibratory shakers are commonly used to to calculate percent air voids in compacted apply agitation. It was not known if these HMA and to provide target values for the different devices provide significantly dif- compaction of HMA. Gmm also is essen- ferent results when compared to one another. tial when calculating the amount of asphalt In addition, the effects on Gmm values of binder absorbed by the internal porosity of changes in vibration intensity from various the individual aggregate particles in HMA. settings of the vibrating devices had not AASHTO T 209 requires application been explored. of a vacuum to a sample of HMA loose mix. The vacuum, combined with either manual C O N T E N T S OBJECTIVES AND SCOPE Background, 1 The goal of this research was to eval- 1AASHTO T 209-10, Theoretical Maximum Spe- Objectives and Scope, 1 cific Gravity and Density of Hot Mix Asphalt uate the effect of using various devices Survey of State DOT (HMA). In Standard Specifications for Transpor- and methods on measured values of Gmm. Laboratories, 2 tation Materials and Methods of Sampling and The specific objectives were to (1) compare Experiment Design, 2 the Gmm between manual and mechanical Testing, 30th ed. American Association of State Results and Analysis, 7 Highway and Transportation Officials, Washington, agitation; (2) investigate the relationship Findings and Conclusions, 23 D.C., 2010. between the measured Gmm and the vibratory