Evaluation of asphalt mixture cracking performance using the monotonic direct tension test in the AMPT

Abstract

This study investigated the feasibility of using a monotonic direct tension test in the Asphalt Mixture Performance Tester (AMPT) with small-scale specimens to evaluate the crack properties of the asphalt materials. Ten loose asphalt mixtures collected from the Federal Highway Administration’s accelerated loading facility (ALF) test lanes combining various reclaimed asphalt pavement (RAP) and recycled asphalt shingles (RAS) percentages and warm mix asphalt technologies were tested at three loading rates and two ageing conditions. Various mechanical parameters and indexes were developed to analyse the experimental data. The laboratory monotonic testing results were compared with and statistically correlated with 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 a significant impact on the behaviour of the test materials, and an actuator rate of 10 mm/min is considered to be ideal for all tested materials, including both short-term oven ageing and long-term oven ageing conditions. Ageing conditions were also found to dramatically influence the monotonic testing results. The experimental results illustrated that the components (percentage of RAP/RAS and binder performance grade) of the asphalt mixtures and the warm technologies have a clear effect on the monotonic testing, indicating that 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 correlation 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 the asphalt mixture due to the ease in the sample preparation, compatibility with the AMPT, strong correlation with field performance and feasibility for testing the field specimens.

Keywords:

• asphalt mixture
• cracking
• monotonic test
• small scale
• Asphalt Mixture Performance Tester
• loading rate
• ageing

Acknowledgements

The authors want to thank Scott Parobeck and Frank Davis in the Bituminous Mixtures Laboratory and Regis Carvalho and Mario Tinio in the Accelerated Load Facility at the FHWA Turner-Fairbank Highway Research Center for providing their skilled care in the performance data collection, specimen preparation and running the laboratory tests.

Disclosure statement

No potential conflict of interest was reported by the authors.