Comparison of fatigue analysis approaches for hot-mix asphalt to ensure a state of good repair.
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2013-10-01
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Abstract:Fatigue cracking is a primary form of distress in hot-mix asphalt. The long-term nature of fatigue due to repeated
loading and aging and its required tie to pavement structure present challenges in terms of evaluating mixture
resistance. This project focused on comparing stiffness and fatigue life output from two recently developed
approaches that use repeated direct tension tests: the Modified Calibrated Mechanistic with Surface Energy
(CMSE*) approach and the Push-Pull Viscoelastic Continuum Damage (PP-VECD) approach.
The CMSE* and the PP-VECD approaches were applied to both laboratory and field specimens for two mixtures,
one from SH 24 in the Paris (PAR) District and one from US 277 in the Laredo (LRD) District of the Texas
Department of Transportation, and the results were compared. Both approaches can be used to characterize mixture
fatigue resistance with relatively low variability. Based on stiffness, both approaches predict better resistance (lower
stiffness) for the PAR mixture based on laboratory results but that the mixtures would have equivalent resistance
based on field results for the CMSE* approach. There was also good agreement between laboratory and field
specimens for the LRD mixture.
The two approaches define fatigue failure in different ways, and thus the rankings of mixture resistance may be
different. For the CMSE* approach, the stiffer LRD mixture based on laboratory specimens results in a longer
fatigue life, while for the PP-VECD approach, this mixture results in a shorter fatigue life. In addition, the PP-VECD
approach outputs significantly lower fatigue lives than the CMSE* approach does due to differences in the analysis
including critical strain values and accumulation of damage.
The CMSE* approach only requires a single test sequence, and thus fewer resources in terms of specimens and time
are needed. However, the PP-VECD approach is more user friendly in terms of the analysis, and some of the
required inputs (E*) can be used to evaluate mixture resistance to other distresses. Field specimens can be tested and
analyzed using both approaches. Ultimately, the laboratory approach used should tie to field performance.
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