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This paper presents the philosophy of the asphalt-aggregate mixture analysis system (AAMAS) concept and provides a brief discussion on those factors that must be included in the design of optimum paving mixtures based on performance-related criteria. Typically, the structural design of asphalt concrete pavements is based on assumed material properties (layer stiffness coefficients, resilient modulus, and fatigue or permanent deformation constants or both). After the structural design has been completed, materials are submitted and a mixture design is completed. The question then becomes: Does the as-placed material meet the assumptions used in structural design?
Certainly, asphalt concrete mixture design and analyses need to be related to those factors that affect pavement performance. The AAMAS objective is to predict in-place properties of the asphalt concrete in the laboratory during the mixture design stage to evaluate mixture behavior and performance under traffic and environmental loads. Thus, the focus for the development of AAMAS was to develop new laboratory mixture design procedures or modify existing procedures based on engineering properties, structural behavior and pavement performance, rather than on empirical numbers such as Marshall or Hveem stability.
Specific items addressed in the paper include compaction of laboratory mixtures to simulate the characteristics of mixtures placed in the field, preparation and mixing of materials in the laboratory to simulate the asphalt concrete plant production process, simulation of the long-term effects of traffic and the environment (this includes accelerated aging and densifi-cation of the mixes caused by traffic), and the conditioning of laboratory samples to simulate the effects of moisture-induced damage and hardening of the asphalt.
The AAMAS concept is applicable to hot-mixed asphalt concrete and includes mixture variables such as binders, aggregates, and fillers used in the construction of asphalt concrete pavements. The AAMAS currently excludes such materials or layers as open-graded friction courses and drainage layers.
mix design, asphalt concrete, asphalt specifications, paving mixtures, performance-related specifications
Von Quintus, HL
President, Brent Rauhut Engineering, Inc., Austin, TX
Consulting engineer, Cincinnati, OH
Virginia Transportation Research Council, Charlottesville, VA