United States Department of Transportation
i
Characterization of Louisiana asphalt mixtures using simple performance tests and MEPDG.
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2014-04-01
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Abstract:The National Cooperative Highway Research Program (NCHRP) Project 9-19, Superpave Support and Performance
Models Management, recommended three Simple Performance Tests (SPTs) to complement the Superpave volumetric
mixture design method. These are the dynamic modulus, flow time, and flow number tests. In addition, the Mechanistic
Empirical Pavement Design Guide (MEPDG) developed under NCHRP project 1-37A uses dynamic modulus to characterize
Hot Mix Asphalt mixtures for pavement structural design. The objectives of this study were to (1) characterize common
Louisiana asphalt mixtures using SPT protocols, (2) develop a catalog of dynamic modulus values for input into the MEPDG
software, (3) evaluate the sensitivity of rut prediction of the MEPDG program, (4) assess the prediction of dynamic modulus
values using Witczak and Hirsch models, and (5) compare dynamic modulus data obtained from axial and Indirect Tensile
(IDT) modes of testing. Fourteen rehabilitation projects across Louisiana were selected to provide a total of 28 asphalt
mixtures for this study. Laboratory mechanistic tests were performed to characterize the asphalt mixtures including the
dynamic modulus in axial and IDT modes, flow time, flow number, and Hamburg type loaded wheel tracking tests. A catalog
of dynamic modulus values was developed and grouped by design traffic level. Test results indicated that dynamic modulus
was sensitive to the design traffic level, nominal maximum aggregate size, and the high temperature performance grade of
the binder. Mixtures designed for higher traffic levels, with larger aggregate, and higher grade binder tended to have higher
dynamic modulus values at high temperature. The MEPDG simulations carried out using the “nationally calibrated” default
calibration factors overestimated the rut predictions by a significant amount. To address this problem, a local calibration of
the MEPDG rut prediction model was performed and preliminary ranges of local calibration factors were developed. Both the
Witczak and Hirsch models predicted dynamic modulus with reasonable accuracy. Dynamic modulus test results obtained
from axial and IDT modes showed no statistical differences for the majority of the mixtures tested.
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