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Evaluation of Asphalt Mixture Cracking Performance Using Monotonic Direct Tension Test in the AMPT

Xinjun Li, Nelson Gibson, Jack Youtcheff

Abstract


This study investigated the feasibility of using a monotonic direct tension test in the AMPT with small scale specimens to evaluate the crack properties of the asphalt materials. Ten loose asphalt mixtures collected from the FHWA’s Accelerated Loading Facility (ALF) test lanes combining various recycled asphalt pavement (RAP) and recycled asphalt shingles (RAS) percentages and warm mix (WMA) technologies were tested at three loading rates and two aging conditions. Various mechanical parameters and indexes were developed to analyze the experimental data. The laboratory monotonic testing results were compared to and statistically correlated to the ALF field cracking performance. The coefficients of variation from the experimental results indicated that the monotonic test has satisfactory repeatability. Test loading rates were found to have significant impact on the behavior of the test materials, and an actuator rate of 10mm/min is considered to be ideal for all tested materials, including both short-term oven aging (STOA) and long-term oven aging (LTOA) conditions. Aging conditions were also found to dramatically influence the monotonic testing results. The experimental results illustrated that the components (percentages of RAP/RAS and binder PG) of the asphalt mixtures and the warm mix technologies have clear effects on the monotonic testing, indicating the test is capable of differentiating such asphalt mixtures. The parameters of the total fracture energy and the total energy divided by the inflection point slope from the laboratory monotonic test were found to have very strong correlations with the field performance. As a general conclusion, this study shows that the monotonic direct tension test in the AMPT is a very promising tool to evaluate the crack properties of asphalt mixtures due to the ease in the sample preparation, compatibility with the AMPT, strong correlation with field performance and feasibility for testing field specimens.

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