Comparison of Laboratory Cracking Test Results and Field Performance

In order to evaluate the fatigue cracking resistance of asphalt mixtures, several tests have been developed over the years. The four-point bending beam fatigue test (BBFT) and overlay test (OT) are two of these tests. In order to determine the fatigue cracking resistance of asphalt mixtures, the BBFT has been used. Originally developed to evaluate the resistance of asphalt overlays to reflective cracking, the OT was further refined and evaluated for determining the fatigue cracking resistance of asphalt mixtures. Evaluation of the two laboratory tests based on the field performance of the base-layer mixtures used in five structural sections as part of the fourth (2009) research cycle of the NCAT Pavement Test Track was the objective of this study. For comparison sake, the BBFT and OT results were first used to rank the five asphalt mixtures. A transfer function was then fitted to the test results, for each test, to determine the number of cycles to failure at the temperature-corrected strain measured in the field. Finally, the five mixtures were re-ranked for comparison with the field performance at the NCAT Pavement Test Track by using the number of cycles to failure determined at the temperature-corrected field strain. The rankings of the five mixtures based on the OT results at each maximum opening displacement (0.381, 0.318, or 0.254 mm) were similar to those by the BBFT results at 800 and 400 microstrain, but different from those at 200 microstrain, as shown by the results for this study. The rankings based on the OT results, but different from those based on the BBFT results, was the same as the rankings of the five mixtures based on the number of ESALs applied until the first crack was observed on the surface, and both were determined at the temperature-corrected strain measured in the field. It is indicated by these findings that the characterization of the relative fatigue cracking resistance of asphalt mixtures is a potential use of the OT. In order to validate these findings, further evaluation using different pavement structures and mixtures is necessary.